Improved time representation model for the simultaneous energy supply and demand management in microgrids

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South African Journal of Botany 2002, 68: 191–198 Printed in South Africa — All rights reserved

SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254–6299

Diversity and distribution of seagrasses around Inhaca Island, southern Mozambique SO Bandeira Department of Marine Botany, Göteborg University, PO Box 461, SE 405 30 Göteborg, Sweden Present address: Department of Biological Sciences, Universidade Eduardo Mondlane, PO Box 257, Maputo, Mozambique e-mail: [email protected] Received 21 September 2000, accepted in revised form 15 August 2001

Nine seagrass species were identified around Inhaca as well as a more narrow form of Thalassodendron ciliatum (Forsk.) den Hartog occurring in rocky pools at the north east coast. Seagrasses were mapped and grouped in seven distinct community types (in order of areas covered): Thalassia hemprichii/Halodule wrightii, Zostera capensis, Thalassodendron ciliatum/Cymodocea serrulata, Thalassodendron ciliatum/seaweeds, Cymodocea rotundata/Halodule wrightii, Cymodocea serrulata and Halophila ovalis /Halodule wrightii; with the ninth species Syringodium isoetifolium occurring in three of these communities. A dichotomous identifica-

tion key is presented. Seagrasses covered half of the whole intertidal area around Inhaca Island and diversity was also high at community level. Transects at macro and micro scales showed zonation of species which may be due to tidal gradients or topographic variation. Cluster analysis indicated ecological dissimilarities between co-dominant species. A decline of Zostera capensis has recently been seen outside the local village. Baseline studies like this are important for coastal zone management in developing countries, where large future changes in seagrass cover can be expected.

Introduction Although diversity and occurrence of seagrasses are generally known on a global scale (Den Hartog 1970, Phillips and Menez 1988, Kuo and McComb 1989), very few studies have been published from the east African region and Mozambique. In coastal areas of developing countries, one can expect large future changes as tourism, modern fishing techniques, aquaculture, shipping and industrialisation increase. Thus, baseline studies such as the present one are needed to document the original pristine and natural distribution of dominant species and communities before anthropogenic impact and changes in water quality have grown too large. Results of such studies should then be taken into consideration for coastal zone management and the protection of biodiversity. In Mozambique, the first publications of seagrasses were by Moss (1937) and Cohen (1939); they were followed later by a number of studies performed by scientists based in South Africa (Kalk 1959, Macnae and Kalk 1962, Macnae 1969, Munday and Forbes 1979) dealing mostly with seagrasses of Inhaca Island but including also other areas of the country. Later, marine botanical work covering southern Mozambique and a taxonomical compilation on seagrasses in the western Indian Ocean was published (Bandeira 1995, 1997). Martins (1997) produced a first account on Zostera capensis of Inhaca Island and the Maputo area covering

both distribution and other ecological performances. Recently, De Boer (2000) emphasised the importance of seagrasses as a nutrient source in the southern bay at Inhaca. Distribution and factors influencing their zonation patterns in other areas of the western Indian Ocean were mostly carried out in Kenya and Tanzania (Isaac 1968, Uku et al. 1996, Björk et al. 1997, 1999). Despite all this, and the importance those communities have as nursery and foraging areas for the fauna, including many commercial fishes (Larkum et al. 1989), there is still little research focussed on the distribution of seagrass communities and their zonation in the region. This paper updates and revises earlier research, emphasising the distribution and zonation of the seagrass communities around Inhaca Island. Methods Inhaca island is situated north east of Maputo Bay between latitudes 25°58’S and 26°05’S and longitudes 32°55’ and 33°00’E. The intertidal zones around this island have two contrasting features. The east side is exposed to the open sea, to the dominant south east wind (Kalk 1995), and to an abrupt depth increase at the beach line. The west side, facing Maputo bay, is relatively protected having a gentle topographic slope reaching in some areas a distance of 1km

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between the coast and the low spring tide level. The tidal amplitude vary between 0.1m and 3.9m. Inshore water temperature around Inhaca island varies within the extremes of 20–39°C, and the salinity within 30–39ppt (mean 35ppt) while being constant at 35ppt at the northern end of Inhaca Island (Bandeira unpublished data). Specimens of seagrasses were collected and identified using literature (Macnae and Kalk 1969, Den Hartog 1970, Larkum et al. 1989, Simpson 1989). Identification was checked with herbarium material at Eduardo Mondlane University Herbarium (LMU). A dichotomous identification key was made based on characters from both fresh and dried material as well as from literature (Isaac 1968, Macnae and Kalk 1969, Den Hartog 1970, Phillips and Menez 1988, Larkum et al. 1989). To map the seagrass communities around Inhaca two main steps were followed. Firstly, the species composition was determined semi-quantitatively by applying a nominal scale of frequency of species occurrence: highly frequent, frequent and present. The communities were then characterised by the number of highly frequent species. Secondly, ground truthing (walking and snorkelling during spring low tide) all over the island with a map 1:10 000 was made in order to delineate the contours of the seagrass communities; a reference point on the island, for precision of mapping, was used (Kirkman 1996). Black and white aerial photographs were also used to visualise inner and outer contours of the seagrass beds. The community types were named after the most dominant species. For this, visual estimates of percentage cover based on density classes (Tomasko et al. 1993) were also used. The area of each community type was calculated by weighing paper with the traced area. Some of the seagrass communities show macro-scale and micro-scale variation in species composition, which may be derived from the tidal gradient and small scale topographic variation. Therefore, macrotransects and microtransects were performed to study the zonation patterns. Six macrotransects, 1m wide, running from the coastline to the low water spring tide level were marked and a sample collected in a 1m2 quadrat at each 10m of the transect. These macrotransects were outlined in three community types (with higher species diversity): Thalassia hemprichii/Halodule wrightii, Thalassodendron ciliatum/ Cymodocea serrulata and Zostera capensis. Two microtransects showing species diversity on a small-scale depth gradient were analysed during low tide in the T. hemprichii/H. wrightii community type located at the south bay of the island. At 1m long microtransects, presence/absence of species were recorded at each cm. The reason for choosing only the T. hemprichii/H. wrightii community for closer analysis was that this community shows a high species diversity at a small scale. Also, most of its topography has small depressions and elevations intermingled with smooth surfaces. Data on macrotransects were subjected to cluster analyses using the computer programme STATISTICA 5.5, to ascertain possible ecological affinities between seagrass species (Shepherd and Womersley 1981).

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Results Species diversity and taxonomical key Nine seagrass species distributed in three families were identified for Inhaca: Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., C. serrulata (R. Br.) Aschers. et Magnus, Halodule uninervis (Forsk.) Aschers. in Bossier, H. wrightii Aschers., Syringodium isoetifolium (Aschers.) Dandy, Thalassodendron ciliatum (Forsk.) den Hartog (Cymodoceaceae), Halophila ovalis (R.Br.) Hook. f., Thalassia hemprichii (Ehrenb.) Aschers. in Petermann (Hydrocharitaceae) and Zostera capensis Setchell (Zosteraceae). An identification key for these species is given (Appendix 1). T. ciliatum occurs in two forms: in sandy substrate with broad/wide leaves and in rock pools with narrow, shorter leaves. Different size-forms of leaf width were observed in Halophila ovalis varying from 1.5–14mm in width. Size forms and leaf tip variants were also observed in Halodule wrightii. Such morphological variations also occur in Brazilian H. wrightii. (Creed 1997). Mapping Seven seagrass community types were identified around Inhaca (listed in order of areas covers): Thalassia hemprichii/Halodule wrightii, Zostera capensis, Thalassodendron ciliatum/Cymodocea serrulata, Thalassodendron ciliatum/seaweeds, Cymodocea rotundata/Halodule wrightii, Cymodocea serrulata and Halophila ovalis /Halodule wrightii (Table 1). The boundaries of each community type were drawn and the seagrass map was then established (Figure 1). Overall, seagrasses covered around 50% of the entire intertidal area around Inhaca. The three largest community types: T. hemprichii/H. wrightii, Z. capensis and T. ciliatum/C. serrulata covers 88% of the seagrass beds around the island (Table 2). T. hemprichii/H. wrightii is the most species-rich community type, where all nine seagrass

Table 1: Species composition in each seagrass community type Community type Th/Hw Tc/Cs Cs Cr/Hw Ho/Hw Zc Tc/seaweeds

Th *** *

Tc * ***

*

Cs * *** ***

Species Hw Hu *** ** ** ** * * *** *** *** * * Cr ** *

Si * ** *

***

Cr–Cymodocea rotundata Cs–Cymodocea serrulata Hu–Halodule uninervis Hw–Halodule wrightii Si–Syringodium isoetifolium Tc–Thalassodendron ciliatum Th–Thalassia hemprichii Zc–Zostera capensis Ho–Halophila ovalis

***–highly frequent **–frequent *–present

Zc **

Ho ** **

* *** ***

South African Journal of Botany 2002, 68: 191–198

Figure 1: Map of Inhaca Island showing the seagrass communities

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Table 2: Area occupied per each community type Area(km2)

Community Type Thalassia hemprichii/Halodule wrightii Zostera capensis Thalassodendron ciliatum/ Cymodocea serrulata Thalassodendron ciliatum/seaweeds Cymbocea rotundata/Halodule wrightii Cymodocea serrulata Halophila ovalis/Halodule wrightii

20.10 10.63

Percentage of total 43.72 23.12

9.54 3.49 1.83 0.27 0.11

20.75 7.60 3.98 0.59 0.24

species listed for Inhaca are represented, closely followed by the T. ciliatum/C. serrulata community with eight species (Table 1). Z. capensis (the second largest community type, located at the south bay and at Portinho) dominates in areas with high content of organic matter and, apparently, with high quantity of ooze and mud compared with the other community types (cf. Martins 1997). This community is mostly located in an area surrounded by mangroves both at Inhaca Island and the mainland peninsula in the south. Recently, a decline of Z. capensis was observed at the Harbour area (Portinho, Figure 1, personal observation). This decline might be due to increasing density of boats, shallow water fishing, and in addition, increasing trampling of the area at low tide. The T. ciliatum/C. serrulata community occurs in an extensive area with gentle topographic slope. The real area cover of this community type is higher than what was calculated since a rather extensive area of T. ciliatum is constant-

ly subtidal, and could not be mapped, thus increasing the total cover of seagrass beds around the island. At the northernmost point of the island (Ponta Mazónduè), a community of T. ciliatum and seaweeds has established in rocky pools and creeks. This is an area of high hydrodynamics with huge surf waves and strong currents. Here, T. ciliatum and seaweeds are strongly attached to the substrate, and grow directly on rocks. The most common seaweed species observed here were: Anadyomene wrightii Harvey ex J.E. Gray, Colpomenia sinuosa (Martens ex Roth) Derbès et Solier, Chamaedoris delphinii (Hariot) Feldmann et Boergesen, Dictyota spp. Digenea simplex (Wulf.) C. Ag., Gracilaria spp., Halimeda cuneata Hering in Krauss, Hormophysa cuneiformis (J.F. Gmelin) P.C. Silva, Hypnea rosea Papenfuss, Neomeris vanbosseae M. Howe, Pseudocodium de-vriesii Weber van Bosse, Padina boryana Thivy, Sargassum spp., Valoniopsis pachynema (G. Martens) Boergesen and Valonia macrophysa Kützing. An extensive list of seaweeds occurring at Inhaca island mostly at Ponta Mazónduè is provided by Critchley et al. (1997). Zonation The species Thalassia hemprichii (Figure 2a) and Thalassodendron ciliatum (Figure 3a) tends to occupy deeper areas far from the coastline whereas, Halodule wrightii (Figure 2a) and Cymodocea serrulata (Figure 3a) tends to occupy shallow areas closer to the coastline. T. ciliatum, in the subtidal fringe, occurs in homogenic stands except in some areas where it is also accompanied by a band of Syringodium isoetifolium parallel to the coastline. The rela-

(a) Th Tc Cs Cr Hw Zc Ho 0

100

200

300

400

600 500 DISTANCE (m)

700

800

900

1 000

(b) Th Tc Ho Cs Cr Zc Hw

Figure 2: (a) Macrotransect of the Thalassia hemprichii/Halodule wrightii community type from northern bay (0m corresponds to the level of low water spring tide); (b) cluster analysis of the same transect. For species symbols see Table 1

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(a) Th Tc Cs Hw Hu Si Zc

0

100

200

300

400

500

DISTANCE (m)

(b)

Th Si Hw Hu Zc Cs Tc

Figure 3: Macrotransect of the Thalassodendron ciliatum/Cymodocea serrulata and Zostera capensis community types at Portinho area (0m corresponds to the level of low water spring tide); (b) cluster analysis of the same transect. For species symbols see Table 1

tionship between T. hemprichii and H. wrightii in the T. hemprichii/H. wrightii community type is repeated at small scale variation in the microtransect where most T. hemprichii occups depression areas and most H. wrightii was found in elevated areas (Figure 4) all observed at spring low tide, when this seagrass meadow was only covered by residual water. This microtransect also showed that Halodule uninervis has a tendency to occur in submerged areas, while Cymodocea rotundata occurs in both immersed and emersed areas (Figure 4). Those two species have broader leaves, especially if compared to H. wrightii and Zostera capensis. Cluster analysis revealed a high dissimilarity index between the co-dominant species in each community type, as the two co-dominants seem to explore different zonation patterns (Figures 2b, 3b). Discussion Nine seagrass species occur around Inhaca, making up 75% of the total number of seagrass species occurring in Mozambique and 16% of the 58 world seagrass species (Den Hartog 1970, Kuo and McComb 1989). This diversity is high for such a small area as Inhaca Island. Furthermore, all nine species could be found within only a small area of Thalassia hemprichii/Halodule wrightii community type. One of the highest species diversity observed in the world was reported by Walker et al. (1988) for Shark Bay, Western Australia, with 12 species in an area 84 times bigger than that of Inhaca island. Twelve seagrass species occur along the whole eastern African coast and 26 along western Australian waters (Isaac 1968, Kuo and McComb 1989, Bandeira 1997). Extensive areas with seagrasses were also

observed in northern Mozambique and Tanzania (Bandeira and António 1996 and personal observation). The taxonomic key presented is based on distinctive and practical features to differentiate the species. The key can be used for either fresh or dried specimens. Halophila ovalis showed large leaf variability, with broad, narrow and intermediate leaf forms; the shape of the leaf blade being obovate-ovate, oblong-elliptic up to linear. Very narrow forms were described as H. ovalis (R. Br.) Hook. f. ssp. linearis (Den Hartog) Den Hartog (Den Hartog 1970, Kuo and McComb 1989). Plasticity of H. ovalis has also been observed elsewhere (McMillan 1983) and some variability seems related to different salinities (Benjamin et al. 1999). The seagrass community types observed in this study are similar to those observed along other parts of the Mozambican coast such as the north beach of Maputo city, where Zostera capensis is the dominant species and coexists with Halodule wrightii (Martins 1997); at Bazaruto Island (21°34’S, 36°00’E) where Thalassodendron ciliatum was observed as dominant to the west coast; at Inhassoro (21°32’S, 35°12’E) where Thalassia hemprichii, coodominant with H. wrightii and T. ciliatum, occurs in subtidal areas (personal observation). At Mecúfi (northern Mozambique (13°17’S, 40°34’E), a coral limestone area), the seagrasses often occur together with seaweeds (Bandeira and António 1996). Coppejans et al. (1992) reported the existence of beds dominated by T. hemprichii, T. ciliatum and Enhalus acoroides L. (Royle) in Kenya. Hemminga et al. (1995) found that T. ciliatum was the dominant species in subtidal areas in Kenya. Stands of E. acoroides were observed by the author at Quissanga Bay and Quirimbas Archipelago (northern Mozambique, around 12°22’S, 40°35’E); Z. capen-

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Figure 4: Changes in species composition with depth along a one metre microtransect of the Thalassia hemprichii/Halodule wrightii community type

sis which forms rather pure stands in the Maputo Bay area and at Inhaca, was only observed in a mangrove area of Mecúfi (Bandeira and António 1996). In the Indo-Pacific region the seagrasses T. hemprichii, T. ciliatum and E. acoroides dominate in many areas (Brouns 1985a, b, Brouns and Heijs 1986, Miller and Sluka 1999). Cluster analysis tended to reflect ecological affinities (Shepherd and Womersley 1981, Bandeira and António 1996). Different zonation patterns between T. hemprichii and H. wrightii and between T. ciliatum and C. serrulata have also been observed elsewhere (Coppejans et al. 1992). Thalassodendron ciliatum in rocky pools, at Ponta Mazónduè, have adapted to strong waves and water-swept habitat similar to other rocky areas in southern Mozambique and eastern South African coast (Barnabas 1982, 1991, Bandeira 1995). A closer inspection of this community showed that T. ciliatum accumulates shell debris and sometimes large grained sand amongst roots and rhizomes. This may help anchorage of the plants. It also seems that in rainy seasons (October–March), when winds are stronger, some rocky pools accumulate some sand. T. ciliatum in rocky habitat seems to have adapted similarly to Phyllospadix spp., a genus occurring only on rocks on water-swept Pacific shores (Den Hartog 1970, Turner 1985, Cooper and McRoy 1988, Ramírez-García et al. 1998). North of Inhaca island, east of the small Portuguese island and between these two islands at the silted channel, new sand is often brought in (Hatton and Couto 1992) and these new areas are colonised by Cymodocea serrulata which acts as a pioneer species. C. serrulata is reported to be highly tolerant to siltation (Bach et al. 1998). Halophila ovalis ssp. linearis and Halodule wrightii have also been found as pioneers at the bare areas close to the coastline, at the west coast of Inhaca. These findings agree with those reported by Coppejans et al. (1992) who stated that H. ovalis and H. wrightii are pioneer species in Gazi Bay, Kenya. These species have been observed as pioneers also elsewhere (Gallegos et al. 1994, Bach et al. 1998). Recently, in 2000, it was observed that part of the sand bank, in the northern bay of the island, never became submerged giving rise to Sangala Island some 1 500m in length and 40m in width (Figure 2, personal observation). Flowering of seagrasses at Inhaca has been seen fre-

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quently only in Thalassodendron ciliatum (but not in the rock pools), Thalassia hemprichii and Halophila ovalis. At Mecúfi, frequent flowering of Syringodium isoetifolium has also been observed. In Kenya, apart from the above species, flowering was seen once or a few times, or only flower fragments were collected, in Cymodocea serrulata, Enhalus acoroides, Halodule uninervis, Halophila minor and Halophila stipulacea (Isaac 1968, McMillan 1980). C. serrulata, H. stipulacea, S. isoetifolium and Zostera capensis from Kenya did, however, flower under experimental environmental manipulations in Texas (USA) in controlled conditions of temperature, salinity, day/night period, nutrients with synthetic seawater (McMillan 1980). The technique for mapping seagrasses could be improved for more accuracy and possibly for better comparison with other studies carried out elsewhere. Remote sensing techniques such as photo-interpretation using digitised colour aerial photographs or videos could be used (Long et al. 1994, Chauvaud et al. 1998, Ramage and Schiel 1999). Landsat images could also be used (Kirkman 1996, Ward et al. 1997). The information collected can be loaded in a Geographical Information System (GIS) (Kirkman 1996). Such data gathered in GIS, including maps, could be useful for the study of losses and increase of seagrass beds (Lee Long et al. 1996, Garrabou 1998). A combination of different methods, involving both simple and high-tech methods, combining e.g. digitised aerial photographs, GIS and ground-truthing, would be ideal to get a better picture of seagrass mapping, diversity, zonation, as well as for understanding possible dynamics in plant distribution (Kirkman 1990, 1996, Chauvaud et al. 1998). The ecological demands of the seagrass species making up the different communities at Inhaca could not be analysed. Tidal gradient associated with species tolerance to desiccation might be among the main factors inducing zonation. Björk et al. (1999) did not find any apparent relation between zonation and desiccation in tropical seagrasses from Zanzibar, as the shallow intertidal species were, in general, more sensitive to desiccation than the deeper species. The species growing highest in the intertidal zone, e.g. Halophila ovalis and Halodule wrightii, did not seem to desiccate much in situ during low tide because their leaves lie flat on the moist sand (Björk et al. 1999). Björk et al. (1997) showed that intertidal species growing mostly at shallow depths, e.g. H. wrightii, had a higher affinity for the form of carbon (HCO3–) commonly available in desiccating environments contrarily to species occurring more in subtidal regions/waters, e.g. T. ciliatum, which showed low affinity to this inorganic carbon species. At saturating irradiances the seagrass Cymodocea serrulata, which grew in the intertidal areas of Inhaca island, showed almost twice as high net photosynthetic rate as that of T. ciliatum (Johnson et al. 1993). Nutrient competition between species as well as growth pattern may also affect the species composition and successions in seagrass beds as was shown to occur between H. wrightii and Thalassia testudinum in Florida, USA (Fourqurean et al. 1992). Acknowledgements — I thank Prof Inger Wallentinus (Department of Marine Botany, Göteborg University, Sweden) and Dr John Hatton (Department of Biological Sciences, Universidade Eduardo

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Mondlane) for their constructive comments. Almeida Guissamulo helped with the cluster analysis. My thanks are extended to Viriato Chiconela, Francisco Mapanga and Lourenço Covane. Financial support was provided by Universidade Eduardo Mondlane and SAREC (Swedish Agency for Research Cooperation with Developing Countries).

References Bach SS, Borum J, Fortes MD, Duarte CM (1998) Species composition and plant performance of mixed seagrass beds along a siltation gradient at Cape Bolinao, The Philippines. Marine Ecology Progress Series 174: 247–256 Bandeira SO (1995) Marine botanical communities in southern Mozambique: sea grasses and seaweed diversity and conservation. Ambio 24: 506–509 Bandeira SO (1997) Seagrasses. In: Richmond MD (ed) A Guide to the Seashores of Eastern Africa and the Western Indian Ocean Islands. Sida/Department for Research Cooperation, SAREC, Stockholm, Sweden, pp 64–67. ISBN 91–630–4594–X Bandeira SO, António CM (1996) The intertidal distribution of seagrasses and seaweeds at Mecúfi Bay, Northern Mozambique. In: Kuo J, Phillips RC, Walker DI, Kirkman H (eds) Seagrass Biology — Proceedings of an International Workshop, Faculty of Sciences, Univ. of Western Australia, Perth, pp 15–20. ISBN 0–86422–445–1 Barnabas AD (1982) Fine structure of the leaf epidermis of Thalassodendron ciliatum (Forsk.) den Hartog. Aquatic Botany 12: 41–55 Barnabas AD (1991) Thalassodendron ciliatum (Forsk.) den Hartog: root structure and histochemistry in relation to apoplastic transport. Aquatic Botany 40: 129–143 Benjamim KJ, Walker DI, Mccomb J, Kuo J (1999) Structural response of marine and estuarine plants of Halophila ovalis (R.Br.) Hook. f. to long-term hyposalinity. Aquatic Botany 64: 1–17 Björk M, Uku J, Weil A, Beer S (1999) Photosynthetic tolerances to desiccation of tropical intertidal seagrasses. Marine Ecology Progress Series 191: 121–126 Björk M, Weil A, Semesi S, Beer S (1997) Photosynthetic utilisation of inorganic carbon by seagrasses from Zanzibar, East Africa. Marine Biology 129: 363–366 Brouns JJWM (1985a) A comparison of the annual production and biomass in three monospecific stands of the seagrass Thalassia hemprichii (Ehrenb.) Aschers. Aquatic Botany 23: 149–175 Brouns JJWM (1985b) A preliminary study of the seagrass Thalassodendron ciliatum (Forsk.) den Hartog from Eastern Indonesia. Biological Results of the Snellius II expedition. Aquatic Botany 23: 249–260 Brouns JJWM, Heijs FML (1986) Production and biomass of the seagrass Enhalus acoroides (L.f.) Royle and its epiphytes. Aquatic Botany 25: 21–45 Chauvaud S, Bouchon C, Maniere R (1998) Remote sensing techniques adapted to high resolution mapping of tropical coastal marine ecosystems (coral reefs, seagrass and mangrove). International Journal of Remote Sensing 19: 3625–3639 Cohen E (1939) The marine angiosperms of Inhaca Island. South African Journal of Science 36: 246–256 Cooper LW, McRoy CP (1988) Anatomical adaptations to rocky substrates and surf exposure by the seagrass genus Phyllospadix. Aquatic Botany 32: 365–381 Coppejans E, Beeckman H, De Wit M (1992) The seagrass and associated macroalgal vegetation of Gazi Bay (Kenya). Hydrobiologia 247: 59–75 Creed JC (1997) Morphological variation in the seagrass Halodule wrightii near its southern distribution limit. Aquatic Botany 59:

197

163–172 Critchley AT, Aken ME, Bandeira SO, Kalk M (1997) A revised list of seaweeds from Inhaca Island, Mozambique. South African Journal of Botany 63: 426–435 De Boer F (2000) Biomass dynamics of seagrasses and the role of mangroves and seagrass vegetation as different nutrient sources for an intertidal ecosystem. Aquatic Botany 66: 225–239 Den Hartog C (1970) The seagrasses of the world. North-Holland Publ. Comp., Amsterdam, Netherlands Fourqurean JW, Zieman JC, Powell GVN (1992) Relationships between porewater nutrients and seagrasses in a subtropical carbonate environment. Marine Biology 114: 57–65 Gallegos ME, Merino M, Rodriguez A, Marbá N, Duarte CM (1994) Growth patterns and demography of pioneer Caribbean seagrasses Halodule wrightii and Syringodium filiforme. Marine Ecology Progress Series 109: 99–104 Garrabou J (1998) Applying a geographical information system (GIS) to the study of the growth of benthic clonal organisms. Marine Ecology Progress Series 173: 227–235 Hatton JC, Couto, AL (1992) The effect of coastline changes on mangrove community structure, Portuguese Island, Mozambique. Hydrobiologia 247: 49–57 Hemminga MA, Gwada P, Slim FJ, De Koeyer P, Kazungu J (1995) Leaf production and nutrient contents of the seagrass Thalassodendron ciliatum in the proximity of a mangrove forest (Gazi Bay, Kenya). Aquatic Botany 50: 159–170 Isaac FM (1968) Marine botany of the Kenya coast 4. Angiosperms. Journal of East African Natural History Society of Natural Museum 27: 28–47 Johnson JM, Choinski Jr JS, Heyes JA, Bandeira SO (1993) Factors affecting photosynthesis in the Mozambican seagrasses Cymodocea serrulata and Thalassodendron ciliatum. Photosynthetica 28: 307–312 Kalk M (1959) A general ecological survey of some shores in northern Moçambique. Revista de Biologia 2: 1–24 Kalk M (1995) A Natural History of Inhaca Island Mozambique. Witwatersrand University Press, Johannesburg, South Africa Kirkman H (1990) Seagrass distribution mapping. In: Phillips RC, McRoy CP (eds) Seagrass Research Methods. UNESCO, France, pp 19–25. ISBN 92–3–102660–7 Kirkman H (1996) Baseline and monitoring methods for seagrass meadows. Journal of Environmental Management 47: 191–201 Kuo J, McComb AJ (1989) Seagrass taxonomy, structure and development. In: Larkum AWD, McComb AJ, Shepherd SA (eds) Biology of Seagrasses. A Treatise on the Biology of Seagrasses with Special Reference to the Australian Region. Elsevier, Amsterdam, pp 6–73. ISBN 0–444–87403–8 Larkum AWD, McComb AJ, Shepherd SA (1989) Biology of Seagrasses. A Treatise on the Biology of Seagrasses with Special Reference to the Australian Region. Elsevier, Amsterdam, Netherlands Lee Long WJ, Coles RG, Mckenzie LJ (1996) Deepwater seagrasses in northeastern Australia — how deep, how meaningful? In: Larkum AWD, McComb AJ, Shepherd SA (eds) Biology of Seagrasses. A Treatise on the Biology of Seagrasses with Special Reference to the Australian Region. Elsevier, Amsterdam, Netherlands, pp 41–50. ISBN 0–444–87403–8 Long BG, Skewes TD, Poiner IR (1994) An efficient method for estimating seagrass biomass. Aquatic Botany 47: 277–291 Macnae W (1969) Sea grasses. In: Macnae W, Kalk M (eds) A Natural History of Inhaca Island, Mozambique. Witwatersrand Univ. Press, Johannesburg, South Africa, pp 28–30 Macnae W, Kalk M (1962) The fauna and flora of sand flats at Inhaca Island, Mozambique. Journal of Animal Ecology 31: 93–128

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Macnae W, Kalk M (1969) A Natural History of Inhaca Island, Mozambique. Witwatersrand Univ. Press, Johannesburg, South Africa Martins AR (1997) Distribuição, estrutura, dinâmica da erva marinha Zostera capensis e estudo de alguns parametros fisicos em duas areas da baía de Maputo. Licenciatura thesis, Eduardo Mondlane University, Maputo, Mozambique. (in Portuguese) Mcmillan C (1980) Flowering under controlled conditions by Cymodocea serrulata, Halophila stipulacea, Syringodium isoetifolium, Zostera capensis and Thalassia hemprichii from Kenya. Aquatic Botany 8: 323–336 Mcmillan C (1983) Sulphated flavonoids and leaf morphology of the Halophila ovalis – H. minor complex (Hydrocharitaceae) in the Pacific Islands and Australia. Aquatic Botany 16: 337–347 Miller MW, Sluka RD (1999) Patterns of seagrass and sediment nutrient distribution suggest anthropogenic enrichment in Laamu Atoll, Republic of Maldives. Marine Pollution Bulletin 38: 1152–1156 Moss M (1937) A preliminary account of the “seagrasses” of Delagoa Bay. South African Journal of Science 33: 234–345 Munday J, Forbes PJ (1979) A preliminary checklist of the flora of Inhaca Island, Moçambique: based on the collection of A.O.D. Mogg. Journal of South African Botany 45: 1:10 Phillips RC, Menez EG (1988) Seagrasses. Smithsonian Contributions to the Marine Sciences 34: 1–104 Ramage DL, Schiel SR (1999) Patch dynamics and response to disturbance of the seagrass Zostera novazelandica on intertidal platforms in southern New Zealand. Marine Ecology Progress Series 189: 275–288

Ramírez-García P, Lot A, Duarte CM, Terrados J, Agawin NSR (1998) Bathymetry distribution, biomass and growth dynamics of intertidal Phyllospadix scouleri and Phyllospadix torreyi in Baja California (Mexico). Marine Ecology Progress Series 173: 13–23 Shepherd SA, Womersley HBS (1981) The algal and seagrass ecology of Waterloo Bay, South Australia. Aquatic Botany 11: 305–371 Simpson D (1989) Hydrocharitaceae. In: Polhill RC, Simpson D (eds) Flora of Tropical East Africa. Royal Botanic Gardens, Kew, UK, pp 1–29. ISBN 90–6191–349–1 Tomasko DA, Dawes CJ, Fortes MD, Largo DB, Alava MNR (1993) Observations on a multi-species seagrass meadow offshore of Negros Oriental, Republic of the Philippines. Botanica Marina 36: 303–311 Turner T (1985) Stability of rocky intertidal surfgrass beds: persistence, pre-emption and recovery. Ecology 66: 83–92 Uku JN, Martens EE, Mavuti KM (1996) An ecological assessment of littoral seagrass communities in Diani and Galu coastal beaches, Kenya. In: Björk, Semesi AK, Pedersén M, Bergman B (eds) Current Trends in Marine Botanical Research in the East African Region. SIDA, Uppsala, pp 280–302. ISBN 91–630–4907–4 Walker DI, Kendrich GA, Mccomb AJ (1988) The distribution of seagrass species in Shark Bay, Western Australia, with notes on their ecology. Aquatic Botany 30: 305–317 Ward DH, Markon CJ, Douglas DC (1997) Distribution and stability of eelgrass beds at Izembek Lagoon, Alaska. Aquatic Botany 58: 229–240

Appendix 1: Identification key for the nine seagrass species occurring at Inhaca Island 1a. 1b. 2a. 2b. 3a. 3b. 4a. 4b. 5a. 5b. 6a. 6b. 7a. 7b. 8a. 8b.

Leaves petiolate ________________________________________________________________________________ Halophila ovalis Leaves never petiolate, always with a leaf blade and leaf sheath _______________________________________________________2 Leaf blade cylindric or circular in transverse section ______________________________________________ Syringodium isoetifolium Leaf blade flattened, strap-shaped or rectangular in transverse section, not cylindrical or circular as above _____________________ 3 Leaves narrow, in general less than two mm wide; leaf apex concave, convex or obtuse____________________________________4 Leaves broad, in general more than two mm (mostly more than four mm) wide; leaf apex round, often serrulate___________________6 Leaf apex obtuse or rounded; parallel and translucent transverse veins present, parallel veins more than five; shoot and rhizome yellowish _______________________________________________________________________________________ Zostera capensis Leaf apex not obtuse, always concave-bidentate or convex-tridentate; transverse veins absent, parallel veins three; shoot and rhizome not yellowish ______________________________________________________________________________________________ 5 Leaf blade usually less than 1 mm wide; apex concave or bidentate ________________________________________ Halodule wrightii Leaf blade usually more than 1 mm wide; apex convex or tridentate _____________________________________ Halodule uninervis Roots and shoots arising at each rhizome node ___________________________________________________________________ 7 Roots and shoots usually arising at each fourth or more rhizome nodes ________________________________________________ 8 Older leaf sheaths attached on stem, leaving a shaggy mass surrounding the lower shoot; leaf pale-green, with apex entire or minutely serrulate; one root per each rhizome node ____________________________________________________ Cymodocea rotundata Older leaf sheaths becoming detached leaving a naked lower stem; leaf not pale-green, apex serrulate; two roots per each rhizome node _____________________________________________________________________________________ Cymodocea serrulata Roots and shoots usually arising in more than each fourth rhizome node; older leaf sheaths persistent, leaving a shaggy mass surrounding the shoot; apex not serrulate; stem, rhizome and roots herbaceous ______________________________ Thalassia hemprichii Roots and shoots arising in each fourth rhizome node; older leaves becoming detached leaving a naked stem; apex strongly serrulate; stem, rhizome and roots semi-ligneous or ligneous (occurring in sandy and rocky habitats, the latter with narrow leaves, thinner stem and condensed rhizome) __________________________________________________________________ Thalassodendron ciliatum

Edited by RN Pienaar