Community structure and biomass distribution of seagrasses and macrofauna in the flores sea, Indonesia

197

Netherlands Journal of Sea Research 23 (2): 197-214 (1989)

COMMUNITY STRUCTURE AND BIOMASS DISTRIBUTION OF SEAGRASSES AND MACROFAUNA IN THE FLORES SEA, INDONESIA* P.H. NIENHUIS 1, J. COOSEN 2 and W. KISWARA 3 1Delta Institute for Hydrobiological Research, Vierstraat 28, 4401 EA Yerseke, The Netherlands. 2Tidal Waters Department, Ministry of Civil Works, P.O. Box 8039, 4330 EA Middelburg, The Netherlands. 3Centre for Oceanological Research and Development, Indonesian Institute of Sciences, P.O. Box 580 DAK, Ancol Timur, Jakarta, Indonesia.

ABSTRACT In several locations in the Flores Sea region the community structure and the biomass distribution of seagrasses were studied along transects perpendicular to the shoreline. The share of each species within a sample plot was estimated, divided in above- and below-ground biomass. Statistics regarding substrate coverage, shoot density and leaf-area index were sampled. A standard relation was calculated between seagrass dry weight, ash-free dry weight and organic carbon content. The biotic data were related to environmental factors: DOC and nutrients in the water, salinity, tidal amplitude, sediment composition. A relation was estimated between bottom coverage of seagrasses and standing stock. Further calculations of biomass-production ratios allow a quick and rough estimate of seagrass productivity. Maximum above-ground biomass values (500-700 g AFDW.m-2) together with qualitative data indicate resource (=space) partitioning among the component seagrasses within a community, and suggest a carrying capacity of the reefflat habitat for seagrass density and biomass. A tentative model was constructed, starting from a constant, non-disturbed multispecies vegetation in the lower intertidal and subtidal zone on sand and coral rubble, and moving into several suboptimal situations. The upper shore carries an impoverished, constrained vegetation (irregular tides, desiccation, harvesting). Sediment reworking by animals and physical displacement of sand disturbs the vegetation and favours pioneer species. Muddy habitats bordering mangroves carry monospecific stands showing extremely high biomass (e.g. below-ground Enhalus acoroides 3500 g AFDW-m-2). Thalassia hemprichfi

and Enhalus acoroides are the most constant species in all habitats mentioned. Macrofauna biomass within the seagrass beds fluctuated widely (maximum values 50-70 g AFDW.m-2 in mixed seagrass vegetations) and only a weak relation between benthic macrofauna biomass and seagrass community structure and biomass was found. 1. INTRODUCTION In Indonesian coastal waters seagrasses occupy the habitat in between the sandy beach or the silty mangal and the coral reefs proper. Seagrass beds are common ecosystems growing in the inner intertidal and upper subtidal fringe around the mainlands and the coral islands, whereas coral growth occurs in the outer subtidal fringe. In the transition area corals and seagrasses grow intermingled. There is much interaction between seagrasses and coral reef areas in terms of migration of animals and ultimately in transfer of nutrients between the two (HECK & ORTH, 1980; KIKUCHI, 1980; LiVINGSTON, 1984; ZIEMAN, 1987). Quantitative data to support these hypotheses for Indonesian seagrass beds, however, are lacking. The importance of seagrass beds is generally recognized: They provide a physical structure, a habitat, for many organisms. For infauna the bed provides sediment stability and protection from demersal and digging predators. For epifauna seagrass beds offer an increased living space and a substratum for attachment and growth of epiphytes which may serve as a major basis for the food web. Provision of habitat and shelter may be more important than their contribution to primary production. Seagrasses are believed to provide a direct, but minor source of food to herbivores (VIRNSTEIN, 1987). Finally, seagrass beds may form conspicuous catchment areas for se-

*Communication no. 396 of the Delta Institute for Hydrobiological Research, Vierstraat 28, 4401 EA The Netherlands

Yerseke,

198

P.H. NIENHUIS, J. COOSEN & W. KISWARA

diments eroded from mangrove swamps that would otherwise be lost in the deeper coastal waters (cf. ALEEM, 1984). Virtually nothing was known of the ecology of seagrasses growing in remote Indonesian waters. NONTJI (1987)in his handbook on Indonesian marine biology only briefly mentions seagrasses, although important herbivorous mammals (dugongs) live from the productivity of the beds. DEN HARTOG (1970) and KISWARA & HUTOMO (1985) published qualitative data on the distribution of seagrasses in the Banda Sea and the Flores Sea. NIENHUIS (1986) gave data on the (low) heavy metal concentrations in seagrasses from the Flores Sea. During the Indonesian-Dutch Snellius-II Expedition to eastern Indonesian waters in SeptemberNovember 1984 a research group investigated several aspects of coral reefs and adjoining seagrass fields in the Flores Sea (VAN DER LAND & SUKARNO, 1986). The aim of this paper is to give a survey of community structure and biomass distribution of seagrasses, together with some notes on biomass of macroalgae and macrofauna, related to significant environmental factors. Primary production of seagrasses and community metabolism of seagrass beds were studied by Brouns (pers. comm.) and LINDEBOOM & SANDEE (1989), respectively. Acknowledgements.--The Snellius-II Expedition in 1984 was organized by the Indonesian Institute of Sciences (LIPI) and the Netherlands Council of Oceanic Research (NRZ). Thanks are due to the following persons: Dr. J. van der Land was the chief organizer of the coral reef-seagrass research group. Captain and crew of R.V. 'Tyro' and K.M. 'Samudera' guided us safely through the Indonesian waters. Dr. J.J.W.M. Brouns was of great practical help in the field. Dr. H.J. Lindeboom provided fruitful contributions to discussions. A.J.J. Sandee offered logistical support both in t'he organization and in the execution of the expedition. J.M. Verschuure treated the samples in the DIHO laboratories. J. Nieuwenhuize and A.G.A. Merks and their collaborators did the chemical analyses. Dr. A.G. Vlasblom gave statistical advice. 2. MATERIAL AND METHODS During the period 6-31 October 1984 the research vessel 'Tyro' of the Snellius-II Expedition visited four stations (coral reefs and adjoining seagrass beds) in the Flores Sea, between Sulawesi in the north and Sumbawa-Flores in the south (Fig. 1). The stations are situated in untouched isolated areas, without industry and with no or very insignificant freshwater run-off. Spread over the four stations approximately 100 quantitative samples containing the above- and

below-ground parts of the seagrasses, macroalgae and benthic macrofauna were collected by snorkling and scuba diving, using an aluminum cylinder, height 1 m and surface area 0.1 m2, placed vertically over the sampling plots, over a depth gradient from high water level down to 7 m below average sea-level. At each of the four stations several localities were visited (see for exact localities Table 4, derived from VAN DER LAND & SUKARNO, 1986). Distribution of seagrasses along transects was studied, using land- and seamarks, measuring tape, a depthmeter and a viewbox with plexiglass bottom. The plants were thoroughly rinsed in sea-water at the sampling localities and transported in plastic bags to the laboratory on board the ship. The samples were separated into seagrass species (nomenclature according to DEN HARTOG, 1970) and the species were fractionated into leaves, shoots (lateral shoots, branches or stems often including old leaf-sheaths sensu DEN HARTOG, 1970)and rhizomes and roots. Leaves and shoots were regarded as above-ground biomass, rhizomes and roots as below-ground biomass. The separate fractions were again intensively rinsed in sea-water, epiphytes were removed by scraping and washing, thus removing the adhering calcareous material for almost 90%. The seagrass fractions were dried at 60-80 °C to constant weight (DW) and sealed in plastic bags. ;.°

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Fig. 1. Sampling stations visited during the seagrass survey, October 1984. 1 = Kepalauan (archipelago) Salager; 2=Kep. Taka Bone Rate; 3=Pulau (island) Komodo; 4 = Pulau Sumbawa, Teluk (bay) Bima and Teluk Sanggar.

SEAGRASSES AND MACROFAUNA IN THE FLORES SEA

199

Mixed vegetation (MV), Thalassia hemprichii (TH) vegetation, Enhalus acoroides (EA) vegetation, Thalassodendron ciliatum (TC) vegetation, Halodule uninervis (HU) vegetation, Halodule ph~ifolia (HP) - Syringodium isoetifoliurn (SI) vegetation, Halophila ovalis (HO) vegetation and Cymodocea serrulata (CS) vegetation. Cymodocea rotundata (CR) occurs in some vegetation units mentioned. LAI (leaf area index) refers to the surface area of the seagrass leaves within the watercolumn above 1 m2 of ground. Dry weight/leaf area conversion factors (in g DW.cm -2) are borrowed from JOHNSTONE (1981). Quantitative data were stored in an Olivetti microcomputer. Regression analysis was performed by using a best fitting curve procedure (see Figs 4 and

The benthic macrofauna (epifauna and infauna) was withdrawn from the 0.1 m2 cores by washing and sieving (3 and 1 mm) the material in the field. In the shipboard laboratory the samples were sorted in the following taxonomical groups: Polychaeta (P), Bivalvia (B), Gastropoda (G), Crustacea (C), Porifera (P) - possibly not covering the entire group of sponges - Holothuroidea (H) and Ophiuroidea (0). All animal samples were dried (DW) at 60-80 °C and sealed in plastic bags. Further treatment took place in the DIHO laboratories, Yerseke. Ash-free dry weight (AFDW) of all plant and animal material was established by combustion at 550-570 °C for 2 hours. Water samples were collected at the four stations above the seagrass beds. The samples were frozen and stored for almost one year after which analyses took place in the DIHO laboratories. Chlorinity was measured titrimetrically, ortho-phosphate (PO4-P), reactive silicate (SiO2-Si), ammonium nitrogen (NH4-N) and nitrate/nitrite nitrogen (NO3-N) were measured on a Technicon AA II Auto-analyzer, according to slightly modified techniques described by STRICKLAND & PARSONS (1972). Dissolved organic carbon (DOC) was measured colorimetrically, according to SCHREURS (1978). Particulate organic carbon (POC) was analyzed with a Coleman C-H analyzer. Total Kjeldahl-nitrogen and total phosphorus in the seagrass samples and sediment characteristics were established according to NIEUWENHUIZE et al. (1978, 1979). The 0.1 m2 quantitative seagrass samples were rearranged in vegetation units, distinguished on the dominance of component species (i.e. the species with the greatest coverage in a vegetation layer SHIMWELL, 1971) and on the frequency of occurrence of these species (refers to the chance of recording a species in any single sample; SHIMWELL, 1971):

5). 3. RESULTS 3.1. SEAGRASS HABITATS AND SEAGRASS

CHEMICAL COMPOSITION The four stations in the FIores Sea are characterized as follows (Fig. 1): (1) Salayer habitats range from a silty mangrove dominated bay (Ioc. 207), via sheltered sandy habitats on the leeside of a small island (Ioc. 157) to open coastal slightly inclining inner reef flats up to 500 m in width covered with sand and rubble (Iocs 158, 161, 215). Hundreds of hectares of dense seagrass beds fringing the islands were explored. (2) Taka Bone Rate archipelago, a large pseudo-atoll comprises a number of small coral islands surrounded by an inner reef flat of varying inclination, covered with sand and rubble. Large areas are covered with instable sand and sandbanks with only very little seagrass growth (Ioc. 146). The more constant, slightly inclining reef flats and lagoons car-

TABLE 1 Enironmental parameters measured in the water column of seagrass beds in the Flores Sea, Indonesia, October 1984. SAL = Salayer; TBR = Taka Bone Rate; KOM = Komodo; SUM = Bima Bay and Sanggar Bay, Sumbawa.

N SAL TBR KOM SUM

3 5 5 6

N SAL TBR KOM SUM

SD 19.01 18.84 18.96 19.03

0.05 0.09 0.10 0.03

NH4-N (mg.dm-3) X SD

4 9 6 9

0.022 0.017 0.022 0.026

0.007 0.014 0.017 0.012

SD 3 5 5 6

N

0.008 0.009 0.007 0.007

0.002 0.003 0.005 0.003

NO3-N (mg.dm -3) X SD

4 9 6 9

0.018 0.020 0.063 0.019

0.005 0.004 0.017 0.005

N

SD

3 5 5 6

N

0.073 0.056 0.100 0.078

0.006 0.005 0.037 0.015

DOC (mg'drrr 3) X SD

3 6 4 6

1.57 1.14 1.18 1.46

0.40 0.10 0.18 0.20

200

P.H. NIENHUIS, J. COOSEN & W. KISWARA

ry rather dense seagrass beds (Iocs 141, 225). The outer reef flat beyond the reefcrest descends abruptly to deeper water. (3) Komodo island is surrounded on the east side by a complicated archipelago of smaller islands and extensive reef flats. Seagrasses were found in habitats ranging from sheltered localities fringed by mangroves and dominated by silty to fine grained sediments with local coral heads (Iocs 88, 90, 92) to more exposed localities with sandy beaches and slightly inclining sand and rubble covered reef flats (Ioc. 255). (4) Sumbawa is one of the larger islands. In Bima Bay and Sanggar Bay on the N coast seagrass habitats range from fine grained sandy beaches (Ioc. 241) to sand covered, slightly inclining inner reefflats, approximately 300 m in width (Iocs 269, 270, 122). Off Tambora volcano (eruption in 1815) large areas with dark coloured terrigeneous sandy sediments, often considerably inclining were devoid of seagrasses. All sampling areas are characterized by clear coastal water, without dominating influences of river run off. Table 1 summarizes data on environmental parameters measured in the water column of the seagrass beds. Chlorinity varies between 18.8 and 19.3%0 CI- and indicates a slight influence of the mainland. Nutrient concentrations (PO4-P, SiO2-Si, NH4-N, NO3-N ) are low (in most cases less than 0.06 mg.dm-3), suggesting a rapid turnover of available nutrients into living biomass. DOC concentrations between 0.9-2.0 mg.dm -3 are slightly raised owing to biological processes within the inshore ecosystems. It was observed several times that within seagrass vegetations exposed at low water, the watermass coloured yellow when the tide progressed. Sediments were characterized using an arbitrary scale in the field: I = silt; II = fine sand; III = medium sand; IV = coarse sand; V = fine coral rubble; VI = coarse coral rubble; VII = massive coral (see Table 4). This scale was checked on sediment samples taken from the field, within the range of fine to

um sand; IV = coarse sand; V = fine coral rubble; VI = coarse coral rubble; VII = massive coral (see Table 4). This scale was checked on sediment samples taken from the field, within the range of fine to coarse grained sands (Table 2). Only isolated coral islands (Taka Bone Rate) show white to pale yellow, recently formed coral sands all around. The larger islands (Salayer, Komodo, Sumbawa) show darker and older terrigeneous sediments, mixed with recent coral sand (Table 2). The water temperature within the subtidal seagrass beds varied only little during the day and showed values between 25 and 29 °C. Surface irradiance showed a maximum of approximately 2300 #E.m-2.s -1 at noon (daylight from 6 AM to 6 PM) (LINDEBOOM & SANDEE, 1989). The tidal curve shows an irregular semidiurnal pattern with an average maximum amplitude of approximately 1.5 m (Fig. 2), but with local irregularities. Table 3 shows data on ash-free dry weight and elementary analyses (C expressed as Particulate Organic Carbon, total N and total P expressed as P205) of the seagrass species from the 4 localities, expressed as % of dry weight (P as %0 of dry weight). The tendencies within the data are clear. AFDW (excluding Thalassodendron ciliatum) varies between 56.2 and 83.7% of DW and has the lowest levels in leaves (56.2 - 70.0% ), intermediate levels in shoots (61.0 76.0%) and the highest levels in rhizomes and roots (71.7-83.7%). Differences between the separate species are only small. POC shows a slightly irregular concentration pattern. In some species the lowest values occur in leavese and the highest in rhizomes and roots, but the opposite was also measured. POC varies between 28.1 and 40.8% of DW. Differences between the sem

TABLE 2 Sediment characteristics of east Indonesian seagrass beds. According to the Wentworth classification phi units between 1.32 and 2.32 correspond with medium to fine sands. Most sediments contain coral rubble and sediment conglomerates. Color characteristics are taken from Munsell Soil Color Charts, 1954. w = white; y = yellow; g = grey; b = brown; p = pale; I = light; d = dark; v = very. Sediment from the Tambora eruption (Sumbawa) in 1815 is very dark grey to black.

station

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Salayer Taka Bone Rate Komodo Sumbawa _ (Sanclqar, Bima)

1.93 1.81 1.92 1.32

- 2.20 - 2.32 - 2.08 - 2.28

color py; Ig; g; dg w p Igl g Ibg; dgb; vdg

0

Time ( h )

Fig. 2. Predicted tidal amplitude at Bima Bay, Sumbawa, October 14, 1984 ( ) and October 21, 1984 (..... ). Data derived from Indonesian Tide Tables 1984.

SEAGRASSES AND MACROFAUNA IN THE FLORES SEA

201

TABLE 3 Ash-free dry weight (AFDW) and elementary analyses (C, N, P) of seagrass species from the Flores Sea, Indonesia, expressed as % (P: %o) of dry weight. Iv = leaves; sh = shoots; rh = rhizomes and roots; pl = entire plants. For abbreviations of species see Material and methods. Species TH CR CS SI EA HO HU HP TC

material Iv sh rh Iv sh rh Iv sh rh Iv sh rh Iv sh rh DI Iv sh rh I~1 )v sh rh

AFDW (%) N X SD 10 10 10 8 6 6 6 5 5 6 5 4 9 4 5 3 6 4 5

66.3 61.0 71.7 70.0 71.9 83.7 69.6 76.0 77.3 56.2 67.8 71.7 64.9 69.3 77.0 63.7 65.4 68.7 73.2

1 1 1

72.3 83.7 80.2

3.5 6.1 6.0 5.7 4.1 4.3 3.4 3.5 7.4 2.6 5.7 5.4 3.8 6.3 3.8 8.0 1.9 3.7 3.4

N 8 8 7 6 5 5 5 5 4 6 4 4 6 5 3 5 6 5 5 4 4 4 4

parate species are small, but TC forms an exception: it has the highest POC values in leaves as well as in shoots and rhizomes. N concentrations vary between 0.7 and 1.8% of DW and show only small differences between species. N has the highest values in leaves (1.0 - 1.8%), in-termediate values in shoots (0.8 - 1.2%) and lowest values in rhizomes and roots (0.7- 1.1%). P concentrations vary between 2.3 and 5.7%o of DW and show considerable differences between species (TC has the lowest concentrations viz. 2.3 3.6%o and EA the highest viz. 4.3 - 5.7%o). P shows the highest values in leaves (3.4- 5.7%0, except in CR), intermediate values in shoots (2.5- 5.1%0) and lowest values in rhizomes and roots (2.3 - 4.3%0). 3.2. SEAGRASS DISTRIBUTION ALONG TRANSECTS Fig. 3 gives a diagrammatic representation of the zonation pattern of seagrass vegetation units as distinguished in Table 4, distributed along transects perpendicular to the shoreline, tn the Flores Sea seagrass beds form the intertidal and upper subtidal fringe around the islands, whereas coral reefs proper form the outer lower subtidal fringe. In the transition area corals and seagrasses grow intermingled down to approximately 7 m (sometimes 20 m) below average sea level. A general zonation pattern can be seen throughout the research area, related to tidal amplitude, exposure, sediment type and inclination (stability) of the reefflat.

POC (%) X SD 31.4 26.2 32.5 32.1 30.8 36.0 31.9 35.1 35.2 28.1 32.0 35.5 30.6 32.9 31.0 22.3 32.0 28.8 31.9 29.5 34.3 40.7 40.8

2.3 4.5 2.1 3.1 3.9 1.6 0.7 3.6 1.8 3.3 1.2 1.3 1.1 2.1 1.6 3.9 2.1 2.1 1.5 3.6 1.8 3.5 1.2

N

N(%) X

SD

N

8 8 8 6 6 3 5 4 4 5 4 3 5 5 3 8 7 4 5 4 4 4 4

1.7 0.8 0.7 1.3 1.2 1.0 1.8 1.0 0.8 1.0 0.8 0.7 2.0 1.2 1.1 1.2 1.4 0.8 0.7 1.2 1.3 0.8 0.7

0.3 0.2 0.3 0.5 0.7 0.8 0.7 0.4 0.3 0.1 0.1 0.1 0.5 0.5 0.3 0.5 0.3 0.2 0.1 0.3 0.6 0.2 0.1

6 8 8 6 5 5 5 5 3 5 5 4 5 5 3 4 6 5 4 3 4 4 4

P205 (%o) X SD 4.0 4.0 2.4 3.9 2.5 3.6 5.3 3.3 3.0 3.4 2.9 2.6 5.7 5.1 4.3 4.8 5.3 2.4 2.4 4.8 3.6 2.7 2.3

0.4 1.4 0.5 0.8 0.3 2.6 1.2 0.7 0.5 0.5 0.6 0.4 0.6 1.5 0.2 2.0 0.5 0.3 0.3 1.1 0.6 0.5 0.5

TC vegetation (Fig. 3; Table 4) was only encountered in stable (constant) sublittoral localities (Salayer, Taka Bone Rate) among coral heads, rooting in coarse grained sediments with coral rubble or massive coral. The most important area for seagrasses is the lower intertidal and upper subtidal zone, where a complex vegetation may occur in which a blend of seven or eight species grow together. In decreasing order of frequency of occurrence these species are TH (occurs in 96%, of the samples), SI (83%), CR (83%), EA (65%), HU (65%), CS (61%), HO (35%) and HP (9%). Each of the species mentioned may dominate locally (Table 4). This mixed vegetation (MV) grows on slightly inclining or almost horizontal sand and rubble covered reefflats with high constancy in time. Above-ground coverage of the foliage is often high, and below-ground the dense mat of interwoven rhizomes and roots binds much sediment. Erosion pits in the surface soil of the mixed vegetations may be 20-50 cm deep. The MV does not occur in extremely sheltered, silty habitats near mangroves (Fig. 3, Komodo), on recently deposited sediments (Taka Bone Rate) and on steep, unstable sediment slopes (Sumbawa). The vegetation is sparse in areas with heavy bioturbation by larger invertebrates. MV is also lacking in the upper part of the intertidal zone where desiccation prevails during low water. The TH vegetation is the most widespread vegetation unit, frequently occurring as an impoverished

202

P.H. NIENHUIS, J. COOSEN & W. KISWARA

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tidal spots (Komodo; Fig. 3) or localities with heavy bioturbation where EA can survive because of its firm anchorage by its large rhizomes. HU often forms almost monospecific vegetations in disturbed open spots of the inner reefflat, or on steep sediment slopes (Taka Bone Rate; Fig. 3), ranging from silty sand to coarse grained sand, both in the intertidal zone and subtidally. HU acts as a pioneer, a ruderal sensu GRIME (1979). The intertidal zone is characterized by pioneer (colonizer) vegetations, dominated by HO, CR and HP (Fig. 3; Table 4). HO has a wide vertical range and occurs from the intertidal zone down to the lower subtidal zone (more than 20 m water depth), especially growing on recently disturbed sediments, such as mounds of burrowing invertebrates. A situation not depicted in Fig. 3 is a steeply inclining sandy bottom, sloping to deeper water, without the occurrence of an outer reefcrest. At Taka Bone Rate, e.g., HU is dominating and shifting into a CS and HO vegetation in deeper water, down to 20 m.

T H - -

Fig. 3. Diagrammatic representation of the zonation pattern of seagrass vegetation units (cL Table 4) along transects perpendicular to the shoreline, Flores Sea Indonesia, October 1984. Approximate length of transects; Salayer and Taka Bone Rate 500 m, Komodo and Sumbawa 300 m. Tidal amplitude (HW minus LW) approximately 1-1.5 m. Substrate in seagrass beds is sediment, ranging from silt (Komodo) to coarse grained sand with coral rubble. Coral = massive coral of reefflat; Taka Bone Rate shows a reefcrest descending to deeper water. Coral heads = isolated coral heads scattered over the inner reefflat. TH = Thalassia hemprichii; CS = Cymodocea serrulata; EA = Enhalus acoroides; HO = Halophila ovalis; HU = Halodule uninervis; HP = Halodule pinifolia; TC = Thalassodendron ciliatum; MV = mixed vegetation. variant of the MV under increasing disturbance (Table 4). TH may also form monospecific stands (Taka Bone Rate, Komodo). The vegetation has a large vertical range from the intertidal zone down to the lower subtidal zone where TC dominates (Fig. 3), growing as well in silty sand as in medium to coarse grained sand and coral rubble. TH does not act as a pioneer proper but as a constant species which can stand considerable stress and disturbance (sensu GRIME, 1979), thus behaving as a competitor-stress tolerator. The EA vegetation is widespread, especially in silty sediments, but it roots in medium to coarse grained sediments as well. EA is often accompanied by TH (Table 4). EA forms monospecific stands in habitats deviating from the MV habitat type, viz. silty sub-

Table 4 gives the biomass data of the component species of all the samples analyzed, for leaves (Iv), shoots (sh) as well as for rhizomes and roots (rh), and grouped according to the vegetation units distinguished. Sediment type, vertical cover of the foliage and leaf area index (LAI) are also given, together with the biomass data of accompanying macroalgae. The ratio I v : s h : r h - b i o m a s s is for TH in MV 1.0:2.6:3.8 (n=19), for TH in TH vegetation 1.0 : 2.0 : 3.6 ( n = 2 0 ) and for TH in EA vegetation 1.0 : 2.6 : 3.8 (n = 9). The ratio is rather constant, irrespective of the vegetation type. For EA in MV the ratio Iv : (sh + rh) is 1.0 : 9.5 ( n = 13), and for EA in EA vegetation Iv : sh : rh is 1.0 : 0.6 : 6.3 (n = 15). EA invests much biomass in its deeply growing thick rhizomes: below-ground biomass is 6 to 10 times larger than above-ground biomass. CR (n = 20), CS (n = 14) and HU ( n = 19), the pioneers and colonizers, have roughly a ratio Iv : sh : rh is 1 : 1 : 2, with the tendency of developing larger below-ground biomass in established, mixed vegetations than in monospecific pioneer vegetations. The restricted number of samples of TC ( n = 7 ) demonstrate I v : s h : rh of 1.0 : 1.2 : 5.6, which underestimates the belowground rhizome biomass, growing between massive coral heads, more than 50 cm deep. The constant species (TH, EA, TC) show roughly a 2 to 4 times larger investment in below-ground biomass, relative to the above-ground biomass, than the colonizers (HU, CR, CS). Fig. 4 shows a transformation of the data presented in Table 4, using regression analysis. Only (highly) significant correlations are shown. The positive

SEAGRASSES AND MACROFAUNA IN THE FLORES SEA

relation between cover and above-ground biomass of MV (integrated biomass of the component species) shows a variation of approximately 200 to 600 g AFDW-m -2 at 90% cover. The maximum value of 600 g AFDW.m-2 indicates the carrying capacity of the above-ground habitat. The positive relation between LAI, a parameter for the photosynthetic potential of the seagrass vegetation, and cover of MV indicates again a wide variation; The maximum value of LAI is 10 m2m -2. The positive relation between LAI and above-ground biomass is expected, because above-ground biomass is a function of LAI. The same statistics are presented for TH, EA and HU vegetation (Fig. 4 data from Table 4), revealing positive relations between above-ground biomass and cover, between LAI and cover and between LAI and above-ground biomass. Maximum biomass in TH vegetation is estimated at approximately 500 g AFDW.m -2 at 90% cover and LAI 10 m2m -2. TH vegetation shows, moreover, a highly significant positive correlation between above-ground biomass and below-ground biomass (B-AG : B-BG = 1 : 1.5). Maximum above-ground biomass of EA vegetation is 500 to 700 g AFDW.m -2 and LAI 8 to 13 m2.m -2 at 90% cover. Below-ground biomass is extremely high, viz. 3500 g AFDW.m -2, 5 times higher than the maximal above-ground biomass. Data for HU are restricted, but regression analysis reveals a maximum above-ground biomass of approximately 300 g AFDW.m -2 at 90% cover. B-AG shows almost the same values as B-BG, which means that the pioneer has a lower maximum biDmass than the constant (mixed) vegetations, and that HU invests in above-ground biomass, relative to below-ground biomass. Regression analyses between above-ground biomass, cover and LAI of TC vegetation and HO vegetation (cf. Table 4) did not reveal significant correlations. The numbers of shoots per surface area are species dependent. The range of the numbers of shoots is extremely large (Table 5), with EA showing the smaller numbers (average 140.m -2) and HU the larger (average 14800.m-2). The morphology of the plants (shoots) is influenced by ecological factors. EA shoots reach a length of 1.5 to 2 m in silty subtidal localities, but in intertidal localities the plants remain much smaller. The same counts for TH, showing fully developed shoots of high biomass in subtidal habitats or in intertidal depressions, and smaller, often damaged shoots in intertidal habitats exposed to desiccation. In silty subtidal habitats (mangal Komodo) it was observed that CS and HO produced much more biomass per shoot, both above- and below-ground, than in sandy intertidal habitats. In general there is no significant relation between number of shoots.m -2 and B-AG, with the exception of TH and CR and CS (Fig. 5). TH in monospecific

203

stands shows 1.5 times more shoots at the same BAG than in MV. CR and CS, species with colonizing abilities, show a relatively low above-ground biDmass relative to the high numbers of shoots (Fig. 5). In all 0.1 m 2 samples mentioned in Table 4, cover and biomass of macroalgae were established. Macroalgae are almost always present, in most cases with low cover (5-20%), sometimes higher (up to 50%). Biomass of macroalgae is extremely variable with a maximum of 251 g AFDW.m-2 (HU, Taka Bone Rate), which means that macroalgae may contribute substantially to the phytomass in seagrass vegetations. Many algae are encrusted calcareous species (Caulerpa, Hafimeda, Udotea), others are cartilaginous reds (Eucheuma, Gracilaria) (VAN DER LAND & SUKARNO, 1986). The average AFDW of the algal samples is roughly only 15% of DW. No statistical relation between seagrass biomass and algal biDmass could be established. Both groups of plants seem structurally independent components of the vegetation. 3.4. MACROFAUNA BIOMASS DISTRIBUTION Biomass data of the seven taxonomic groups distinguished, are estimated per field sample. Maximum biomass amounts to 50 g AFDW.m -2 in MV (Sumbawa 122-3), 42-68 g in TH vegetation (Taka Bone Rate 146-0 and Salayer 215-2, resp.), 56-57 g in EA vegetation (Komodo 90-4 and Salayer 161-2, resp.) and 41 g in TC vegetation (Taka Bone Rate 225-4). In many samples Porifera count for more than 50% of the total biomass (maximum biomass of sponges amounted to 38-60 g AFDW.m -2, respectively Taka Bone Rate 225-4 and Salayer 215-2). Occasionally Holothuroidea may also take a considerable share in the samples (maximum 31-55 g AFDW.m -2, Komodo 92-3 and 90-4, respectively). Muddy stations at Komodo contain only 2 g AFDW.m-2, whereas sandy coral stations have 20-30 g AFDW.m -2. Fig. 6 depicts the average biomass values of the separate taxonomic groups per vegetation unit. MV, TH and EA vegetations show a regular distribution of biomass over the taxonomical groups. All groups are almost evenly represented, except for Porifera in TH and EA vegetation and Porifera and Holothuroidea in EA vegetation. The average macrofauna biomass within the vegetation units mentioned ranges from 15.2 (MV) to 22.5 g AFDW-m -2 (EA). The sublittoral TC vegetation has an average biomass of 15.4 g AFDW.m-2, again with a relatively large share of sponges. The pioneer seagrass vegetations (HU, HO, CS, HP) show a different picture: not all animal groups are represented, and the groups available have a low biomass, ranging from 1.4 g AFDW.m -2 (HO) to 5.8 g AFDW.m -2 (CS). Obviously, established constant vegetations show

204

P.H. NIENHUIS, J. COOSEN & W. KISWARA

TABLE 4 Biomass data of seagrass and macroalgae in g AFDW.m -2 for the constituent species in the quantitative samples (0.1 m2 taken during October 1984, Flores Sea, Indonesia, arranged per vegetation unit.

MIXED VEGETATION (MX~ SAL Station 158.1 158.2 Sediment Ill-IV Ill-IV Cover 90.05 90.05 LAI 3.4 10.0 TH CR CS SI EA

Iv sh rh Iv sh rh Iv sh rh Iv sh rh Iv sh rh

mo

41.2 179.9 155.8 20.4 6.8 25.9

15.7 10.4 45.7 2.5 25,2 0.9

SAL 158.3 III- VI 90.20 3,4

SAL 158,4 III- VI 90.15 4.2

SAL 158,5 III- VI 90.10 4.3

SAL 161.4 III- VI 50.20 2.4

SAL 161.5 III- VI 40.40 1.8

SAL 161.6 III- VI 60.20 2.3

SAL 161.7 III- VI 60.05 2.9

SAL 161.8 III- VI 60.20 3.4

TBR 141.D III- V 90.05 9.3

137.0 331.4 367.0 25.2 15.0 19.8 24.0 16.2 41.4 20.4 10.2 32.4 5.4

22.2 127.2 217.2 16.7 5.8 1.3 22.2 7,8 78.0 14.3 5.2 28.2

58.4 204.6 426.9 6.0 1.8 13.2 8.4 4.8 27.0

55.8 181.8 210.2 10.2 6.6 58.8

18.7 34.3 70.8 9.9 9.0 17.5

17.8 22.6 35.9 10.5 1.8 9.4 3.0 1.6 1.9 4.9 0.9 6.9 24.7

23.6 28.0 52.8 3.2

24.4 27.6 25.2 21.9 7.5 22.8

17.6 40.0 57.5 20.1 50.0 42.8

9.3 0.5 10.8 29.2

48.1 20.0 29.6

1.2

60.6

91.6

62.8

2.1 1.4 3.1

2.4 0.8 2.8

146.6 167.3 202.5

67.6 33.1 163.1 6.4

87.2 36.4 124.4 41.6

232.4 277.3 322.4

18.0

31.2

14.9 58.5 40.8 19.2 6.4 29.6 0.9 0.8 3.0 3.7 1.4 5.0 13.0

244.2 3.0

315.6

30.7

189.6

6.8 3.3 9.1

4.8 5.4 9.2

378.9 0.2 3.7 5.3 7.0

58.5 70.4 118.2 8.7

40.8 48.7 287.1 30.8

64.6 32.2 440.2 9.8

HU HP T_,

sh rh Iv sh rh Iv sh rh

Algae

79.8 197.1 253.5 6.8

212.0 372.8 461.8 13.8

75.4 146.0 385.3 48.6

90.8 211,2 714.3 117.6

97.2 188.4 584.6 52.8

7.4

3.2 16.3 3.3 8.8 3.6 0.4 3.6 18.8

TC VEGETATION Station Sediment Cover LAI TH CR SI

Iv sh rh Iv rh Iv sh rh

Ho pv

TC

sh rh Iv sh rh Algae

SAL 215.5 IV-Vl 70.05 7.3

TBR 141, I I V- VI 60.05 2.8

TBR 225.1 III- VI 70.10 1.1

TBR 225.2 III- VI 90. 10 1.6

TBR 225.3 III- VI 70.05 2.1

TBR 225.4 III- VI 50.05 1.5

TBR 146.3 III- VI 70.20 4.8

46.4 19.9 55.4 9.6 6.8 2.4 1.2 7.2

6.4 10.8 19.6

10.4 8.4 16.0

5.0

14.4

40.0

41.6

9.2 18.0 39.2 4.0 4.8

22.8 28.8 29.6 2.4 6.4

144.6 100.4 103.8 203.0 121.5 173.2

85.6

21.9 37.5 279.4 32.3 45.9 295.4 2.0

47.0 77.0 420.0 52.0 77.0 460.0 2.0

8.3 27.2 56.9 461.4 41.6 56.9 511.3

18.8 12.7 19.4 96.1 25.9 37.4 158.9

140.9 92.0 10.8 160.5 5.2

116.9 139.3 720.9 142.1 168.1 756.9 16.6

S E A G R A S S E S AND M A C R O F A U N A IN THE F L O R E S SEA

205

TABLE 4 (continued)

MIXED VEGETATION SUM SUM 241.2 241.3 III-V I1-111 40.05 40.05 2.6 3.6 TH CR

34.9 66.5 150.8 5.7 5.5 3.3

(MV) Continued SUM SUM 269.1 269.2 III-V III-V 60.05 80.05 4.6 7.8

41.4 75.9 246.9 4.3 9.7 17.9

SI

11.5 32.1 19.4 41.7 30.9 20.5 75.7 52.5 22.8 215.6

0.7 12.5 2.9 113.2

EA HO HU

42.9 191.2 0.2 2.6 3.6 6.3

16.1 19.5 55.1

HP "K

55.7 78.5 274.3 Algae 0.3

25.9 28.9 31.0 32.5 44.9 48.3 44.8 21.3 24.9 17.2 9.7 29.3

22.3

CS

11.7 88.6 78.5 467.9

131.6 82.2 421.9 11.1

1.2 43.1 81.9 52.8 5.2 5.0 18.9 168.7 191.7 206.4 6.1

HP-SI VEGETATION SUM 269.5 III 50.05 1.8 CR CS Sl HO HU HP .Y, Algae

Iv sh rh Iv rh

SUM 269.3 III-V 70.05 2.9

SUM 269.4 III-V 70.10 5.5

22.7 46.7

26.1 16.0 4.8 12.4 82.7 41.0 90.4 79.2 34.4 1848.0

15.4 9.1 15.2

4.5 49.6 112.6 232.3

65.0 121.7 298.7 14.6

SUM 122.1 II-IV 70.05 4.3

177.9 80.2 1999.6 57.7

SUM 122.2 II-IV 50.05 2.2

4.2 12.5 98.0 31.5 98.4

41.0 20.7 64,5

18.7 14.0 18.2 18.5 46.0 71.2 135.2 91.5 187.8

5.2 25.0 50.0 75.0 70.2 70.7 157.2

2.0 FJ sh rh Iv sh rh Iv sh rh

9.8 82.1 35.7 24.4 146.0

13.2 10.3 6.6 15.9

56.8 18.9 35.8

SUM 270.2 III-VI 70.05 6.0

SUM 270.3 III-VI 80.05 5.6

SUM 122.3 II-Vl 90.05 7.3

SUM 122.4 II-VI 90.05 7.7

SUM 122.6 II-VI 90.05 6.1

16.0 21.6 48.0

10.9 81.6 103.4

13.3 8.3 7.8 11.4

12.3 12.6 11.2

31.7 97.8 105.4

51.4 34.0 52.8 22.3 t9.4 50.5 28.6

99.1 39.5 101.9 62.9 37.5 115.7

121.0 32.0 130.1 39.9 57.8 100.3

65.4 115.5 158.1 51.3 30.0 90.0

3.1 0.5 16.0

180.1 6.2 21.3 74.1 134.8

7.0

1.8

120.8 148.1 271.5 6.7

134.5 209.1 527.8 9.7

186.7 85.3 232.4 0.5

173.2 102.4 243.4 4.6

6.2 84.0 108.8 155.1 17.7 17.2 9.4 36.8

0.7 38.4 65.8 161.7

25.9 24.4 61.9

Iv sh rh

SUM 270.1 III-VI 80.00 3.4

105.5 91.3 227.3

148.4 243.3 353.5 2.5

SAL = Salayer; TBR = Taka Bone Rate; KOM = Komodo; SUM = Sumbawa. Station numbers according to the Snellius-II Expedition Progress Report, Theme 4, 1986. Sediment type: see text. Cover in % for seagrasses (left) and macroalgae (right). Percentage cover refers to the vertical projection of the foliage of the plants on the sediment. LAI = leaf area index in m2m -2, see Material and methods. TH = Thalassia hemprichii; CR = Cymodocea rotundata; CS = Cymodocea serrulata; SI = Syringodium isoetifolium; EA = Enhalus acoroides; TC = Thalassodendron ciliatum; HO = Halophila ovalis; HU = Halodule uninervis; HP = Halodule pinifolia; Iv = leaves; sh = shoots; rh = rhizomes and roots; pl = entire plants.

206

P.H. NIENHUIS, J. COOSEN & W. KISWARA

TABLE 4 (continued) HU VEGETATION SAL 207.2 f-If 40.05 1.4 TH SI HO HU HP .~,

Iv sh rh Iv rh 131 Iv sh rh ~3J

TBR 141.A III-V 90.20 4.9

TBR 141.B ttl-V 90.05 6.0

TBR 141.C III-V 90.05 4.3

SUM 122.7 It-V 15.05 0.9

SUM 122.8 II-V 15.05 1.3

58.4 172.4 179.2 8.8 12.5 43.9 47.1 193.9

19.4 27.7 59.7 3.7 5.5 7.4 107.9 144.9 164.0

94.6 127.3 136.7

19.7 5.9 38.5

111.1 219.5 385.8 250.8

131.0 172.6 236.6 1.4

94.6 127.3 136.7

19.7 5.9 38.5

29,7 8.5 58.6 3.3 29.7 8.5 61.9

SAL 215.2 III-V 70.30 5.0

SAL 215.3 III-V 85.10 5.0

SAL 215.4 III-V 70.10 9.8

TBR 141.2 III 10.05 2.0

TBR 141.3 III 20.30 2.5

TBR 141,4 III 40.10 1.8

TBR 225.0 II-IV 60.10 3,9

TBR 225.5 IIAIV 90.05 5.8

TBR 146.1 Ill-IV 90.10 7.3

74.9 135.4 402.1 15.7 4.1 15.2

89.6 288.0 668.8 9.6 9.6 50.4

150.4 68.8 166.4 22.5

37.6 32.8 82.4

45.9 120.3 73.5

24.8 30.0 104.0 10.8 33.8 113.9

56.0 169.6 256.0 4.8

91.8 217.8 558.3 23.9 37.4 133.8

119.8 240.6 330.9 24.8 19.2 73.6

35.6 63.8 217.9 15.6

60.8 169.6 267.2 10.0

115.7 255.2 692.1

144.6 259.8 404.5

7.0 32.8 43.2 32.8

sh rh

50.2

Algae TH VEGETATION SAL SAL Station 157.3 215.1 Sediment III-V III-V Cover 50.05 80.05 LAI 3.7 7.3 TH CR SI EA

Iv sh rh Iv sh rh Iv rh Iv rh

30.0 152.8

127.8 185.6 332.8

11.2

7.2 6.4 63.9 111.4

12.8 28.0

6.4 44.8

93.9

140.6 185.6 360.8 2.4

97.0 139.5 462.1 52.8

99.2 297.6 719.2 15.2

180.1 68.8 172.8 11.2

37.6 32.8 82.4

45.9 120.3 73.5 36.0

SAL 161.3 I1-111 30.40 1.5

SAL 157.4 III-V 60.05 3.9

SUM 241.1 III-VI 40,20 3,4

KOM 092.2 I1-111 70,05 3.9

KOM 092.3 III-V 70.05 3.4

KOM 092.4 III-V 90.05 4.8

KOM 090.4 III-V 80.05 12.9

1.0

52.0 61.6 31.2

10.2 31.0 27.8

39.9 103.7 178.0

39.2 144.0 316.8

52.0 155.2 112.8

16.8 9.2

61.3 15.8 384.3

49.6 16.4 444.8

10.2 2.0 10.4 67.6 64.9 481.9

101.2 119.5 562.3 3.1

88.8 160.4 761.6

HU Iv sh rh

264.2

Algae EA VEGETATION SAL Station 161.1 Sediment I1-111 Cover 20.40 LAI 1.8 TH OS SI EA HU

Alqae

Iv sh rh Iv sh rh Iv sh rh Iv sh rh rh Iv sh rh

SAL 161.2 I1-111 05.50 0.6 t .3

1.1 1.7 0.6 5.4

61.8

20.8

54.8

43.1

91.8

318.6

81.7

246.0

82.6

61.8

22.1

318.6 55.2

81.7 83.2

57.5 0.6 252.5 54.0

95.1 61.6 113.8 18.4

436.6 8.5 102.0 31.0 472.9 14.7

129.8 222.1 605.1 8.2

KOM 088.1 I 50.00 6.5

KOM 088.2 I 40,05 3,5

418.6 78.9 958.8

223.6 35.9 542.1

118.4 26.3 704.0

435.4 88.1 958.8

223.6 35.9 542.1

118.4 26.3 704.0

S E A G R A S S E S AND M A C R O F A U N A IN THE FLORES SEA

207

TABLE 4 (continued)

CS VEGETATION KOM KOM KOM 090.1 088.4 088.5 II I-II I-II 90.05 70.05 40. 05 4.8 1.6 1.6

HO VEGETATION SAL 157.1 II 60.05 0.8 TH CS HO HP Y_.

Iv sh rh Iv sh rh Iv sh rh pl Iv sh rh

SAL 157.2 II 50.05 0.3

27.2

2.7 3.8

27.2

7.9 1.1

TH VEGETATION (continued) TBR TBR Station 146.2 146.0 Sediment Ill-IV III Cover 80.20 50.50 LAI 5.4 2.7

CR St EA

Iv sh rh Iv sh rh Iv rh Iv rh

99.8 345.7 367.6

49.9 189.4 196.1

Iv sh rh

99.8 345.7 367.6 9.6

49.9 189.4 196.1 60.0

SI EA HU Y_. Algae

0.6 8.5

13,5

9.2 0.9 3.1 1.3

12.0

22.6

2.2

8.4

13.5

12.0

95.1 20.7 53.4

30.9 15.6 25.9

17.4 3.4 25.0 17.4

9.1

22.6

10.5 0.9 5.3

KOM 092.1 II 60.05 3.2

KOM 090.3 III 90.00 4.8

KOM 255.4 III- V 70.05 3.8

KOM 255.5 III- V 70.05 4.9

KOM 255.6 III- V 80.10 7.5

KOM 255.7 III- V 60.10 2.5

KOM 255.8 III- V 50.05 0.9

SUM 270.4 II 10.05 0.6

60.8 65.4 195.2

89.8 107.0 218.3

70.7 248.1 215.8

91.8 156.4 221.4

139.2 234.1 642.7

45.8 160.9 239.7

16.5 35.5 79.8

4.5 7.3 8.8 5.1 7.5 10.9

89.8 107.0 218.3

70.7 248.1 215.8 2.3

91.8 156.4 221.4

139.2 234.1 642.7 24.2

45.8 160.9 239.7 11.7

16.5 35.5 79.8

71.2 65.4 199.6 1.3

EA VEGETATION (continued) KOM KOM KOM Station 088.6 255.1 255.2 Sediment I-II III-V III-V Cover 50.05 80.05 80.05 LAI 3.6 3.9 7.0

CS

KOM 088.3 I 10.05 1.0

8.4

95.1 20.7 53.4

30.9 15.6 25.9

17.4 3.4 42.4 0.6

4.4

Algae

TH

KOM 090.2 II 10.00 0.6

10.4

Ho HU 2

TBR 141.E III 30.05 0.9

1.4

Algae

TH

SAL 207.1 I1-111 10.05 0.1

Iv sh rh Iv sh rh Iv sh rh Iv sh rh rh Iv sh rh

123.2 356.0 123,2 356.0 2.7

KOM 255.3 III-V 80.05 5.3

3.6 13.2 14.8 30.5

SAL = Salacer: TBR = Taka Bone Rate; KOM = Komodo; SUM = Sumbawa Station numbers according to the Snellius-II Expedition Progress Report, Theme 4, 1986. Sediment type: see text. Cover in % for seagrasses (left) and macroalgae (right). Percentage cover refers to the vertical projection of the foliage of the plants on the sediment. LAI = leaf area index in m2m 2, see Material and methods. TH = Thalassia hemprichii; CR = Cymodocea rotundata; CS = Cymodocea serrulata; SI = Syringodium isoetifolium; EA = Enhalus acoroides; TC = Thalassodendron ciliatum;

49.7 94.8 224.7

11.3 43.3 39.8

18.5 66.2 102.1

41.2 17.8 415.0

221.8 439,6 3462.9

150.0 109.9 2057.2

HO = Halophila ovalis; HU = Halodule uninervis; HP = Halodule pi£ifolia;

90.9 112.6 639.7 5.4

233.1 482.9 3502.7 0.6

168.5 176.1 2159.9 0.7

Iv sh rh pl

= = = =

leaves; shoots; rhizomes and roots; entire plants.

208

P.H. NIENHUIS, J. COOSEN & W. KISWARA

a greater diversity in macrofauna groups associated with them, than the colonizing vegetations. The same holds for biomass values which are higher in established seagrass vegetations. In general, a significant positive relation between seagrass percentage cover, seagrass biomass and macrofauna biomass could not be established; the variability within the data set is extremely large. Only MV and TH vegetations indicate a significant correlation between seagrass biomass and biomass of bivalves, gastropods and crustaceans. Sponges and sea cucumbers with their erratic high values did not correlate with seagrass biomass or cover in a single case, 4. DISCUSSION Seagrasses are flowering plants growing in shallow coastal waters of tropical and temperate seas. They occupy a wide range of habitats from coarse sand and coral rubble to soft muddy bottoms, and from the intertidal zone down to 20 m water depth (or more). Altogether there are 12 genera of seagrasses, seven of which inhabit tropical seas. Tropical seagrasses are concentrated in two geographical regions viz. the Western Indo-Pacific area, harbouring 7 genera, and the Caribbean-Eastern-Pacific coast of Central America, harbouring only four genera, also occurring in the Western Indo-Pacific (DEN HARTOG, 1970). Twelve species of seagrass inhabit Indonesian waters: TH, EA, SI, TC, HU, HP, CR, CS, HO, Halophila ovata, Halophila decipiens and Halophila spinulosa. Most species occur all over the Indonesian archipelago, except for TC, which seems to be distributed only in the eastern part of the country. Halophila decipiens and H. spinulosa have a limited distribution (KISWARA & HUTOMO, 1985).

This paper presents the first quantitative data on seagrass biomass distribution in the Flores Sea, sampled over a period of three and a half weeks. The restricted number of samples does not allow firm conclusions on quantitative distribution patterns and results from future research may slightly alter our points of view. Seagrass vegetations are rather simple ecological structures containing only a small number of seagrass species (maximum 12), in contrast to adjacent coral reefs with their overwhelming diversity (cf. VAN DER LAND & SUKARNO, 1986). An advantage of the relative simple community structure of seagrass beds is the fact that dominant and frequently occurring seagrass species are good candidates for quantitative ecological research. Shoot density is a parameter which is easily determined and often used as a rough estimate for standing stock (JACOBS, 1984). In most cases, however, we did not find a significant relation between shoot density and above-ground biomass. Variability in density is large, dependent on species but also on ecological circumstances. This means that number of shoots per surface area cannot be used as a good indicator for biomass in Flores Sea seagrass beds. Cover of the above-ground parts of the seagrass vegetation seems a reliable indicator for aboveground biomass. This counts for the established (constant) vegetations (MV, TH, EA). For pioneer vegetations (except for HU) the relation is not significant. Percentage cover of seagrass foliage can easily be established by snorkling or by making observations from a small boat, using a view-box with perspex bottom. Considerable areas can be explored within a few hours, resulting in a rapid indication of standing

Fig. 4. Regression analyses of quantitative biomass and cover data from Table 4. B-AG ~ above-ground biomasss (i.e. leaves and shoots); B-BG = below-ground biomass (i.e. rhizomes and roots); LAI = leaf area index.

nr.

vegetation

equation

n

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Mixed Mixed Mixed Thalassia hemprichii Thalassia hemprichfi Thalassia hemprichii Thalassia hemprichii Enhalus acoroides Enhalus acoroides Enhalus acoroides Enhalus acoroides Halodule uninervis Halodule uninervis Halodule uninervis Halodule uninervis

Iogy = 1.6381 + 0.0098x y = -0.947 + 0.079x y = 0.734 + 0.016x Iogy = 1.631 + 0.011x y = 0.018 + 0.070x y = -8.081 + 5.434 Iogx y = 8.905 + 1.211x y = -69.684 + 5.459x y = 0.329 + 0.072x Iogy = -1.117 + 0.747 Iogx Iogy = 2.288 + 0.002x Iogy = 1.203 + 0.014x Iogy = -0.141 + 0.096x y = -4.941 + 4.087 Iogx Iogy = 1.593 + 0.003x

23 23 23 21 21 21 21 15 15 15 15 6 6 6 6

r 0.789 0.620 0.891 0.814 0.733 0.741 0.764 0.745 0.631 0.940 0.802 0.965 0.977 0.978 0.981

P < < < < < < < < < < < < < < <

0.001 0.01 0.001 0.001 0.01 0.001 0.001 0.01 0.1 0.001 0.001 0.01 0.001 0.001 0.001.

SEAGRASSES AND MACROFAUNA IN THE FLORES SEA

LAI (m 2rn 2)

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P.H. NIENHUIS, J. COOSEN & W. KISWARA

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vegatation

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n

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Thalassiahemprichii in mixed vegetation Thalassiahemprichii in TH vegetation Cymodocearotundata Cymodoceaserrulata

Iogy = 1.4416 + 0.0006x y = -746.784 + 326.856 Iogx y = -80.041 + 41.135 Iogx y = 1.118 + 0.087x

20 20 25

stock. Estimation of cover percentage of seagrass foliage should be recommended as an easy and quick parameter for coastal inventories. Maximum above-ground biomass values (500-700 g AFDW.m -2) together with qualitative physiognomic data indicate resource (= space) partitioning among the component seagrasses within a mosaic community, and suggest a carrying capacity of the reef-flat habitat for seagrass density and biomass (MV, TH, EA). A tentative model may be constructed,

r

P

0.872 0.872 0.677 0.940

<0.001 < 0.001 <0.001 <0.001

starting from a constant, non-disturbed multispecies vegetation in the lower intertidal and subtidal zone on sand and coral rubble, and moving into several suboptimal situations. The upper shore carries an impoverished, constrained vegetation (irregular tides, desiccation, human disturbance). Sediment reworking by animals and physical displacement of sand disturb the vegetation and favour pioneers among the grasses. Muddy habitats bordering mangroves carry monospecific stands showing

TABLE 5 Numbers of shoots.m-2 in the sampling plots of the Flores Sea seagrass beds. All plots have a foliage coverage of more than 70% (except TC: more than 50%). For abbreviations of seagrass species names (Sp.) see: Material and methods. Sp.

MIXED MEADOWS N X SD

TH CR CS SI EA HO HU

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748 276 767 1736 86 117 5689

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811 543 58 6076 272

range

360-2542 220-1160 52-208 7887-19413 560-1100

SEAGRASSES AND MACROFAUNA IN THE FLORES SEA

211

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Fig. 6. Average macrofauna biomass values of the separate taxonomic groups per seagrass vegetation unit in g AFDW.m -2 (Flores Sea, October 1984). MV = mixed vegetation; TH = Thalassia hemprichii vegetation; EA = Enhalus acoroides vegetation; TC = Thalassodendron ciliatum vegetation; HU = Halodule univervis vegetation; HP = Halodule pinifolia vegetation; CS = Cymodocea serrulata vegetation; HO = Halophila ovalis vegetation; P = Polychaeta; B = Bivalvia; G = Gastropoda; C = Crustacea; P = Porifera; H = Holothuroidea; O = Ophiuroidea. extremely high biomass (e.g. below-ground EA 3500 g AFDW.m-2). TH and EA are the most constant species in all habitats mentioned. Established vegetations (MV, TH, EA, TC) show little variation in biomass over the year, as was demonstrated by BROUNS (1985a, 1985b, 1987a, 1987b) in a three-years study in Papua New Guinea. Growth and decomposition (including grazing) seem to be in equilibrium. Excess b i o m a s s - c o v e r 100O/oor piling up of decaying material is very seldom 5.

6

found. This is in contrast with the growth strategy of pioneers and colonizers (HU, CS, CR, HO, HP) which change their spatial position and biomass distribution in the course of the year. The relation between seagrass biomass and primary production was studied by Brouns (pers. comm.) and LINDEBOOM & SANDEE (1989). Some of their results are depicted in Fig. 7, together with data from a (sub)tropical area in the Caribbean, Central America (ZIEMAN, 1987). Although the absolute data /

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Biomass ( g DW m-2) Biomass ( g AFDW m-2) Biomass (g DW m-2) Fig. 7. Comparison of results from the literature, regarding the relation between seagrass production and Diomass. 1. Derived from LINDEBOOM& SANDEE(1989). Gross production of Thalassia hemprichfi community, using oxygen evolution method (above-ground biomass indicated), FIores Sea; 2. Derived from Brouns (pers. comm.). Net production of seagrass leaves (several species), using the leaf marking method; leaf biomass indicated, Flores Sea; 3. Derived from ZIEMAN (1987). Production (between gross and net) of above-ground Thalassia testudinum, using 14C method, Caribbean.

212

P.H. NIENHUIS, J. COOSEN & W. KISWARA

may not be compared directly, because different methods were used (including different incubation techniques), a clear conclusion may be drawn from Fig. 7: with each of the methods used a linear relation between above-ground biomass (up to 250 g AFDW.m -2) and productivity may be obtained. Combining the positive relation between seagrass cover and biomass and the relation between biomass and production, points to the fact that percentage cover may be used as an indicator for the production potential of established, full grown seagrass beds. According to LINDEBOOM & SANDEE (1989), who used the oxygen evolution method in isolated bell jars, the maximum gross production of a Flores Sea seagrass community, including epiphytes, macrophytes and fauna, is roughly 5 g C.m-2.d -1 The maximum oxygen consumption (respiration, mineralization) of the entire community underneath a bell jar is roughly 4 g C.m- 2.d- ~, which leaves a net production of 1 g C.m-2.d -1 for the seagrass community. It may be concluded from the data of LINDEBOOM & SANDEE (1989) that most energy fixed in the seagrass bed is used within the community for several consumption purposes. Obviously there is a substantial benthic oxygen consumption, both during the day and at night, by all biota underneath the bell jar, viz. seagrass plants, epiphytes, benthic algae, macro-, meio- and microfauna and bacteria. The estimated nutrient values in the water over the seagrass beds are extremely low (Table 1). This fact combined with the high community respiration indicates high decomposition and mineralization rates and a quick re-allocation of minerals into primary biomass. The seagrass system seems to be energetically self-sustaining, and only a minor part of the produced organic matter may be exported to adjacent ecosystems (i.e. coral reefs). Another indication of quick recycling of organic material is the lack of large accumulations of decomposing seagrass along the shore or on the outer reefflat. (These accumulations are a normal feature along seagrass beds in temperate areas). The net oxygen production of the entire seagrass community, converted into organic carbon, may be low, but the net production of above-ground seagrass biomass is relatively high, viz. roughly 3 g C.m-2.d -1 at a maximum (Brouns, pers. comm.). This figure is obtained with the leaf-marking technique, implying that only net leaf productivity is concerned and that epiphytes and benthic micro- and macroalgae are not included. The question to which extent the production of 3 g C.m-2"d -1 benefits grazers (herbivores) directly cannot be answered. Virtually nothing is known about grazer impact in the Flores Sea (dugong, turtles, fish, sea urchins, gastropods, etc.). How much of the produced

seagrass is exported as particulate organic carbon to neighbouring ecosystems is also completely unknown, but based on scattered observations the amount is presumably low (less than 10% of net production). Qualitative observations from the 'Tyro' revealed floating leaves of Thalassia hemprichii many miles from the shore. Dependent on direct grazing and export of seagrass biomass, the amount left in the seagrass bed is available for in situ decomposition and mineralization. The self-sustaining nature of the seagrass ecosystem does not exclude the existence of important biotic interactions with adjacent ecosystems on the second or third trophic level. The seagrass system is known as an important habitat for hundreds of animal species (NONTJI, 1987; HUTOMO & MARTOSEWOJO, 1977), but it is unknown how many of these are restricted to seagrass beds during (parts of) their life cycle either for shelter or for food. Most research on tropical seagrass beds in the Western Indo-Pacific area has been concentrated on the East African coast (ALEEM, 1984) and on the coast of Papua New Guinea. The south coast of Papua New Guinea, near Port Moresby, has been thoroughly explored by a number of researchers (JOHNSTONE, 1978a, 1978b, 1979; BROUNS & HEYS, 1986; HATTORI et al., 1985 HATTORI, 1987). There is a striking similarity between the seagrass vegetation in the Flores Sea and the vegetation of the south coast of Papua New Guinea, both concerning species distribution patterns, biomass allocation and growth rates. Both areas are situated at the same geographical latitude (5 to 10°S), but about 3000 km removed from each other. BROUNS (1985a) used the leaf marking and plastochrone interval method to estimate productivity of seagrasses from Papua New Guinea. Aboveground net production of Thalassia hemprichii in a monospecific vegetation amounted to a maximum of 5.5 g AFDW.m-2..d -1, below-ground production was maximally 0.8 g AFDW.m-2.d -1 in the same vegetation. Above-ground biomass in a dense Thalassia hemprichii bed amounted to 275 g AFDW.m -2 (leaf blades and leaf sheaths 160 g AFDW-m-2), and below-ground biomass to 680 g AFDW.m -2, which data fit the Flores Sea picture depicted in Fig. 4. BROUNS (1985a) calculated a mean turnover rate (P/B ratio) for Thalassia leaves and leaf sheaths of 0.03 -d -1. Assuming a continuous growth during the year the annual net leaf production may be calculated at 1750 g AFDW.m-2.y -1 (approximately 875 g C.m-2.y-1). BROUNS (1985b) used the same method to estimate above-ground productivity of Thalassodendron ciliatum in the Flores Sea at 4.5 g AFDW-m-2.d -1. Assuming a constant rate of leaf production throughout the year he calculated an an-

SEAGRASSES AND MACROFAUNA IN THE FLORES SEA

nual above-ground production of 1500 g AFDW.m - 2.y- 1 (approximately 750 g C. m - 2.y- 1). Above-ground biomass data mentioned by BROUNS (1985b) were roughly 200 to 400 g AFDW-m -2 and are in agreement with our data in Fig. 4. Total above- and below-ground production of Cymodocea serrulata and C. rotundata from Papua New Guinea was 4.9 and 3.0 g AFDW.m-2.d -1 respectively, of which 70% was leaf production. For Halodule uninervis total net production amounted to 6.0 and 4.0 g AFDW.m-2.d -1, at intertidal and subtidal sites, respectively. Maximum production was recorded for Syringodium isoetifolium, 9.0 g AFDW.m-2.d -1, of which 60% was contributed by the leaves. Mono-specific patches of CS as well as CR and HU showed considerable changes in aboveground biomass during the year (BROUNS, 1987a). BROUNS (1987b) also attempted production measurements for a mixed seagrass bed containing six species at Port Moresby, Papua New Guinea. Above-ground biomass amounted to 210 g AFDW.m -2 and showed only little variation throughout the year (195-246 g AFDW.m-2). Belowground biomass was estimated at 419 g AFDW.m -2. Above-ground production of the mixed vegetation was estimated at 3.9 g AFDW.m-2.d -1 (approximately 2 g C m-2.d-1). Coral reefs and adjacent seagrass beds are subject to exploitation for the fish they support and also for the corals themselves which are a valuable construction material (BROWN, 1986). There is much discussion about the importance of seagrass beds for animal life. Habitat and food functions are obvious, but little quantitative information is available (HuTOMO & MARTOSEWOJO, 1977; cf. VIRNSTEIN, 1987). Our data set on macrofauna biomass is far too restricted to draw firm conclusions and, moreover, it does not contain all animal groups present in the seagrass beds. Significantly higher macrofauna diversity and biomass in established seagrass vegetations were found than in disturbed, pioneer vegetations. A relation between seagrass biomass and faunal biomass could no'. be detected. MUKAI et al. (1987), however, found in Papua New Guinea seagrass beds a positive relation between seagrass cover and density of animals (numbers.m -2) for a number of larger invertebrates. Specific habitat functions and animal-food relations have to be looked for carefully in future research in Indonesian seagrass beds. At several localities, especially at Sumbawa, the coastal population has a considerable impact on the macrofauna. People collect adult bivalves and gastropods and sometimes sea cucumbers (trepang) from the seagrass beds at low water. The ecological effects of this superficial exploitation are of minor importance, but selective collection of animals over

213

specific areas may have local influence on the biomass relations between seagrasses and larger benthic animals. 5. REFERENCES ALEEM, A.A., 1984. Distribution and ecology of seagrass communities in the Western Indian Ocean. In: M,V. ANGEL. Marine Science of the NW Indian Ocean and adjacent waters.--Deep-Sea Res. 31 (6-8A): 919-933. BROUNS,J.J.WM., 1985a. A comparison of the annual production and biomass in three monospecific stands of the seagrass Thalassia hemprichii (Ehrenb.) Aschers.--Aquat. Bot. 23: 149-175. , 1985b. A preliminary study of the seagrass Thalassodendron ciliatum (Forssk.) Den Hartog from Eastern Indonesia.--Aquat. Bot. 23: 249-260. ----, 1987a. Aspects of production and biomass of four seagrass species (Cymodoceoideae) from Papua New Guinea.--Aquat. Bot. 27: 333-362. ----, 1987b. Quantitative and dynamic aspects of a mixed seagrass meadow in Papua New Guinea.--Aquat. Bot. 29: 33-48. BROUNS, J.J.W.M. & F.M.L. HEYS, 1986. Structural and functional aspects of seagrass communities and associated algae from the tropical West-Pacific. Ph-D thesis Nijmegen University: 1-431. BROWN, B.E., 1986. Human Induced damage to coral reefs.--Unesco Reports in marine Science 40. Unesco, Paris: 1-180. GRIME, J., 1979. Plant strategies and vegetation processes. Wiley, Chichester: 1-222. RARTOG, C. DEN, 1970. The seagrasses of the world.-Verh. K. ned. Akad. Wet., Afd. Natuurk. 2e reeks, 59 (1): 1-275. HATTORI, A., 1987. Studies on dynamics of the biological community in tropical seagrass ecosystems in Papua New Guinea: the second report. Ocean Research Institute, Univ. Tokyo: 1-121. HATTORI, A., K. AIOI, H. IIZUMI, I. KOIKE, H. MUKAI, M. NISHIHIRA,S. NOJIMA& Y. YOKOHAMA,1985. Studies on dynamics of the biological community in tropical seagrass ecosystems in Papua New Guinea. Ocean Research Institute, Univ. Tokyo: 1-49. HECK, K.L. & R.J. ORTH, 1980. Seagrass habitats: the roles of habitat complexity, competition and predation in structuring associated fish and motile macroinvertebrate assemblages. In: V.S. KENNEDY. Estuarine perspectives. Academic Press, New York: 449-464. HUTOMO, M. & S. MARTOSEWOJO,1977. The fishes of the seagrass community on the west side of Burung Island (Pari Islands, Seribu Islands) and their variations in abundance.--Mar. Res. Indonesia 17: 147-172. JACOBS,R.P.W.M., 1984. Biomass potential of eelgrass (Zostera marina L.).--CRC Critical Reviews in Plant Sciences 2: 49-80. JOHNSTONE, I.M., 1978a. The ecology and distribution of Papua New Guinea seagrasses. I. Additions to the seagrass flora of Papua New Guinea.--Aquat. Bot. 5: 229-233. , 1978b. The ecology and distribution of Papua New

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P.H. NIENHUIS, J. COOSEN & W. KISWARA

Guinea seagrasses. II. The Fly Islands and Raboin Island.--Aquat. Bot. 5: 235-243. - - - - , 1979. Papua New Guinea seagrasses and aspects of the biology and growth of Enhalus acoroides (L.f.) Royle.--Aquat. Bot. 7: 197-208. - - - - , 1981. Survey methods for the analysis of seagrass meadows with respect to their potential as dugong and turtle habitat with a field key to the seagrasses of Papua New Guinea. Univ. Papua New G u i n e a . Department of Biology. Occasional Paper 8 (unpublished report). KIKUCHi, R., 1980. Faunal relationships in temperate seagrass beds. In: R.C. PHILLIPS & C.P. MCROY. Handbook of seagrass biology: an ecosystem perspective. Garland STPM Press, New York, London: 153-172. KISWARA, W. & M. HUTOMO, 1985. Habitat dan sebaran geografik Ramun.--Oseana 10: 21-30. LAND, J. VAN DER & SUKARNO, 1986. The Snellius-II Expedition Progress Report Theme IV Coral Reefs. Part 1 R.V. 'Tyro' and K.M. 'Samudera', SeptemberNovember 1984. Royal Netherlands Academy of Arts and Sciences, Amsterdam; Indonesian Institute of Sciences, Jakarta: 1-76. LINDEBOOM, H.J. & A.J.J. SANDEE, 1989. Production and consumption of tropical seagrass fields in eastern Indonesia measured with bell jars and microelectrodes.--Proc. Snellius-II Symp., Neth. J. Sea Res 23: 181-190. LIVINGSTON, R.J., 1984. Trophic response of fishes to habitat variability in coastal seagrass s y s t e m s . Ecology 65: 1258-1275. MUKAI, H., M. NISHIHIRA & S. NOJIMA, 1987. V. Consumers and decomposers. 1. Distribution and biomass of predominant animals. In: A. HATTORI. Studies on dynamics of the biological community in tropical

seagrass communities in Papua New Guinea: the second report. Ocean Research Institute, Univ. Tokyo: 62-75. MUNSELL SOIL COLOR CHARTS, 1954. Munsell Color Company Inc. Baltimore, Maryland, USA. NiENHUiS, P.H., 1986. Background levels of heavy metals in nine tropical seagrass species in Indonesia.--Mar. Poll. Bull. 17: 508-511. NONTJI, A., 1987. Laut Nusantara. Penerbit Djambatan, Jakarta: 1-368. NIEUWENHUIZE, d., J.M. VAN LIERE & M.LP. VAN ESBROEK, 1978. De bepaling van particulaire organische koolstof door middel van de Coleman C-H analyzer.--Delta Instituut voor Hydrobiologisch Onderzoek, Rapp. Verslagen nr. 1978-5 (unpublished report). - - - - , 1979. Bodem- en gewasanalyses. Delta Instituut voor Hydrobiologisch Onderzoek. (unpublished report). SCHREURS, W., 1978. An automated colorimetric method for the determination of dissolved organic carbon in seawater by UV-destruction.--Hydrobiol. Bull. 12: 137-142. SHIMWELL, D.W., 1971. Description and classification of vegetation. Biology Series Sidgwick & Jackson, London. STRICKLAND, J.D.H. & T.R. PARSONS, 1972. A practical handbook of seawater analysis.--Bull. Fish. Res. Bd. Can. 167: 1-311. VIRNSTEIN, R.W., 1987. Seagrass-associated invertebrate communities of the Southeastern USA: a r e v i e w . Florida Mar. Res. Publ. 42: 89-116. ZiEMAN, J.C., 1987. A review of certain aspects of the hfe, death, and distribution of the seagrasses of the Southeastern United States 1960-1985.--Florida Mar. Res. Publ. 42: 53-76.