Detached chlorophytes as nursery areas for fish in Sulaibikhat Bay, Kuwait

Estuarine,

Coastal

and Shelf

Science

(1989) 28, 185-193

Detached Chlorophytes for Fish in Sulaibikhat

as Nursery Bay, Kuwait

Areas

J. M. Wright Zoology

Department,

Received

1 I May

Kuwait

University,

1988 and in revised

P.O.

form

Keywords: nursery grounds; chlorophyta; diet; seining; trawling; Arabian Gulf

Box 5969

3 October

Safat,

13060,

Kuwait

i 988

intertidal

environment;

Mugilidae;

This paper describes the role of accumulations of detached chlorophytes as temporary nursery areas for the fish assemblage of Sulaibikhat Bay, Kuwait. The chlorophytes were produced during the spring bloom in the intertidal and near sublittoral. The accumulations in the shallow near shore areas were at a peak during early March. During this time young of the year of Liza carinuta dominated the assemblage in shallow water and these fish were closely associated with the patches of detached chlorophytes, and used them as a physical refuge and as a temporary food resource. In deeper water the catches were dominated by mature Leiognathus brevirosrris, the numbers of which were related to the volume of weed at the beginning of the bloom but not toward the end of the bloom. Although L. brevirostris appeared not to use the weed as a refuge this species utilized the weed as a temporary food resource. During the study there was no evidence of weed-associated amphipods being utilized as a food resource.

Introduction Extensive growth of chlorophytes, notably of the genera Ulva, Enteromorpha, Cladophorcl and Chaetomorpha, has been related to eutrophication, particularly in semi-enclosed systems (Lenanton et al., 1984 Lenanton et al., 1985; Rosenberg, 1985). This growth is typically seasonal in temperate environments with a spring bloom that may persist into the autumn in the U.K. (Hull, 1987), whilst in the Peel-Harvey estuary of Western Australia chlorophytes are present all year round but die back in the winter (Lenanton et al., 1984). The presence of large amounts of macrophyte growth has been considered beneficial to fish populations, firstly by providing protection against piscivorous birds (Lenanton et (II., 1982; Lenanton et al., 1984; Robertson & Lenanton, 1984), and secondly by increasing food availability indirectly through the detritus food chain (Lenanton et al., 1982; Lenanton et al., 1984; Robertson & Hansen, 1982). Detrimental effects of chlorophyte blooms may occur when the algae form a mat in low wave energy environments, when macrofaunal densities may be decreased (Hull, 1987) or if decomposition of the bloom leads to an oxygen deficiency and subsequent fish kills (Lenanton et al., 1984). Sulaibikhat Bay covers an area of approximately 46 km’ with an intertidal region of up to 4 km width and a maximum depth of approximately 4 m (Al-Sdirawi, 1984). The bay is semi-enclosed and communicates with the larger and deeper Kuwait Bay (Figure 1). The ~~‘52-i714’89

0201X5+09

$03.00;0

0 1989 Academic Press Limirrd

186

J. M. Wright

Arabian

Maibikhat

Gulf

Bay

290 State

of Kuwait

0

20km 4~” Figure

1. Map

Saudi Arabia of Kuwait

showing

location

of Sulaibikhat

Bay.

annual range of sea temperatures in Kuwait waters is 15.9 C-31.6 C and the annual range of salinity is 36.5-41.2 %O (Houde et al., 1986). Kuwait Bay is an important nursery ground for members of the families Mugilidae, Engraulidae and Haemulidae whilst only Leiognathus brevirostris [(Valenciennes), (Leiognathidae)] is considered to spawn in the Bay (Dames & Moore, 1983). Sulaibikhat Bay is an important nursery ground for nine species of fish including Liza carinata (Valenciennes), (Mugilidae) and L. brevirostris (Wright, 1988a). This study is an attempt to assess the importance of the annual appearance of accumulations of detached chlorophytes in the spring to the fish assemblage of Sulaibikhat Bay. In particular to determine which species of the assemblage utilize the patches of weed as a refuge and as a dietary resource, either directly by consuming the weed or indirectly by consuming members of the detritus food chain which use the chlorophytes.

Materials

and methods

Fish were captured at the height of the spring bloom of chlorophytes between 18 February and 28 March 1988 in Sulaibikhat Bay, Kuwait (29”21’N, 47”52’E). Two methods were employed to capture fish in the intertidal zone at or just before the time of high tide. For the first method an otter trawl of 4 m mouth width made of 13 mm stretch mesh throughout and a cod end lined with 6.5 mm stretch mesh was used. The net was trawled behind a 7 m boat in a depth of 2-06 m depth at a speed of 0.5 m s-l for a period of 5 min sweeping

lktuched

cklorophytes QSnursery areasforfish

187

an area of approximately 600 m’. On each day of sampling 12 trawls were taken parallel to the shore and within a horizontal distance of 500 m of each other. For the secondmethod a beach seine of 6.15 m length and 2.10 m depth made of 6.5 mm stretch mesh throughout wasused. The seinewas set in 0.5 m of water and hauled perpendicular to and toward the beach for 20 m, sweeping an area of approximately 120 m’. On each day of sampling six hauls were taken so as to avoid patches of floating weed and up to 12 hauls were taken through patches. All hauls were taken within a horizontal distance of 200 m of each other. The entire catch for both methods was sorted in the laboratory and the volume of chlorophytes captured determined to the nearest 100 ml using a 1 000 ml measuring cylinder. The number, total lengths and weights were recorded for each species.When catcheswere large a sub-sampleof 100fish were measured. The weed volume, length and weight data were log transformed to overcome skewnessin the data and to ensure that variance was independent of the mean. The catchesof chlorophytes from a long term survey (seeWright, 1988a,b) were usedto show the progression of the spring blooms in 1987 and 1988 within Sulaibikhat Bay. In this survey twelve 5 min trawl hauls were taken within the bay each month, five from the subtidal region, in depths of between 8-4 m, and seven from the intertidal region, in the depths of between 2-0.6 m. The volume of chlorophytes in each trawl wasdetermined in the sameway asfor the present study. For both trawl and seinecatchesthe number and weight data were correlated with weed volume. Numbers, weights and mean lengths for the seinedata were alsosubjected to twoway analyses of variance (ANOVA) to determine whether these biological variables differed between date of sampling (period) and presence of absence of weed patches fpatch). One-way ANOVA was used to assesswhether one species, present in large numbers on only one day of sampling, was associatedwith patches of weed. Diet was examined using the method of weighted points (Hyslop, 1980). In this study the stomach contents were smeared between two microscope slides and each food item assigneda percentage of the total stomach contents (Hynes, 1950). These percentages were then multiplied by a stomach fullness index between O-5, where 0 corresponds to an empty stomach and 5 to a fully distended stomach(Haram &Jones, 1971).A total of 20 fish were examined for each speciesand the mean value determined.

Results

A bloom of Enteromorpha intestinalis (Linnaeus), Enteromorpha flexuosa (Wulfen ex Roth), Enteromorpha clathrata (Roth), Ulva lactuca Linnaeus, Chaetomorpha aerea (Dillwyn) Kutzing and Cladophora sericoides BDrgesen typically began to appear in January. By February or March extensive accumulations of these specieswere present and by April or May they had disappeared(Figure 2). A total of 23 713 fish, belonging to 18 speciesin 14 families, were captured during the study from a total of 36 trawl hauls and 51 seine hauls (Table 1) The trawl catches contained a total of 731 fish from 13 speciesin 12 families. The dominant species, L. brevirostris, waspresent with well developed gonads. The next most abundant species,L. carinata, was present as fish of age I+ or older. The remaining speciesconstitute three groups. Mature demersal speciesincluded Acentrogobius ornatus (Riippell), (Gobiidae), Pseudosynanceia melanostigma (Day), (Scorpaenidae), Gobius brevirostris Giinther, (Gobiidae), Sillago sihama (Forsskal), (Sillaginidae), Acanthopagrus berda ForsskBl,

188

3. M. Wright

I987 Figure 2. Mean volume of detached chlorophytes of 1987 and 1988 with 95”,, confidence limits.

1. Percentage frequency total catches (*, less than O,l”,,

TABLE

1988 in trawls during

captured

of occurrence for the two methods and ~, no data)

the springs

of capture

and for the

Trawl Species

(Family)

Liza carinata (Mugilidae) Leiognathus brevirostris (Leiognathidae) Liza subviridis (Mugilidae) Sardinella sp. (Clupeidae) Sillago sp. (Sillaginidae) Sillago sihama (Sillaginidae) Acentrogobius ornatus (Gobiidae) Pseudosynanceia melanostigma (Scorpaenidae) Thryssa hamiltonii (Engraulidae) Gobius brevirostris (Gobiidae) Sardinella longiceps (Clupeidae) Solea elongata (Soleidae) Hemiramphus marginatus (Hemiramphidae) Boleophthalmus boddarti (Gobiidae) Scartelaos viridis (Gobiidae) Aphanius dispar (Cyprinodontidae) Strongylura strongylura (Belonidae) Acanthopagrus berda (Sparidae) Z’omadasys s&dens (Haemulidae)

No.

Seine “(1

No.

“/I

63 531 0 47 0 24 22 11 7 7 7 6 4 0 0 0 0

8.6 72.6 0 6.4 0 3.3 3.0 15

22 472 0 359 98 42 1 0 0

1.0 1.0 1.0

2 0 0

0 0

0.8 05 0 0 0 0

0 0 4 2 1

0 0 * * *

1

O-l

1 0

0

1

0.1

0

0

97.8 0 1.6 0.4 0.2 * 0 0 l

l

(Sparidae) and Pomadasys stridens (Forsskil), (Haemulidae). The second group constituted mature pelagic species and included Thryssa hamiltonii (Gray), (Engraulidae), Sardinella longiceps Valenciennes, (Clupeidae) and Hemiramphus marginatus (Forrskil), (Hemiramphidae). The third group was made up of fish present only as juveniles and included Solea elongata Day, (Soleidae), and a Sardinella sp. (Clupeidae).

Detached

chlorophytes

I8 February

1588

as ntmery

areas for fish

I2 March

1988

Figure 3. Log of fish biomass in g + I and log of fish numbers + 1 against log wred volume in ml + 1 for the trawl hauls on the three days of sampling. (0 = P < 0.05, 0 0 = P-cO.01, all with 10 d.f.)

The seine hauls were dominated by the young of the year of L. carinata. The mature demersal group of fish was represented by Boleophthalmus boddarti Pallas, (Gobiidae), Scartrlaos virdis (Hamilton-Buchanan), (Gobiidae) and Aphanius dispar (Riippell), (Cyprinodontidae) with the B. boddarti normally resident in burrows. Mature pelagic species were represented by T. hamiltonii and Strongylztra strongylura (van Hasselt), (Belonidae). The remaining species were present as juveniles and included a second species of Mugilidae, Liza subviridis (Valenciennes), S. sihama, a second species of Sillaginidae, Sillago sp. (see Kuronuma & Abe, 1986) and the same Sardine&z sp. as captured in the trawls. For the trawl data a significant positive correlation was observed at the beginning of the bloom between weed and biomass, but as the bloom developed numbers and biomass became increasingly negatively correlated with weed (Figure 3). The correlations of weed volume with fish numbers and biomass for the seine hauls were not significant on any of the sampling days (Figure 4). The two-way ANOVA’s showed that there were no significant period with patch interactions (Table 2). All biological variables were significantly different between areas with patches and areas without patches. Total numbers of fish and numbers of L. carinata were significantly higher in patches than in areas without patches (P < 0.01 for both variables) as was total biomass (P< 0.01). Two-way ANOVA of length data for all Liza carinata had a significant period effect reflecting growth (P < 0.001). When year 1 + fish or older are removed from this data set there are still a significant period effect (PC 0.001). These two data sets, length of all Liza carinata and length of 0 + Liza carinata, differed significantly between patches and areas without patches, with smaller fish occurring in the patches (P < 0.01 for all Liza carinata, PC 0.001 for 0 + year Liza carinata). One-way ANOVA of the Liza sztbviridis catches on 25 March 1988 showed no significant difference between patches and no patches (F= 4.28,. ,-1, 0. 1 > P> 0.05).

190

J. M.

Wright

22 +

February

1988

8 March

5.5

‘pGG$

= 0.30,

1988

25

I5 d f, NS

March

r= -0.17,

1988 14 df,

NS

0

5.c

0% 0

5.5

O0

4.5

0043 I

4.0 4 + t 2 z 5 i;

( 0

2

8

: ,

80

CQ

3.51 ‘TliizGq

d f, NS

3

0 0

0

Ir-I

r = 0.30,15

(3

3

0 o&p””

4

IS 0 0

r=0.22,16df,l

4.5

?I 0

2

2

8

08

8

oO” 0

-ET / -L

I

2

3

:,

4

0

I I234

I

log (Weed

Figure volume

I

I

'02L:/ volume

4

+ Ii

4. Log of fish biomass in g+ 1 and log of fish numbers in ml + 1 for the seine hauls on the three days of sampling.

+ 1 against

log weed

TABLE 2. F-values and levels of signficance for the two-way ANOVA’s of numbers (N), biomass (B), number of Liza carinata (N, Liza) total length of L. carinata (TL, Liza ) and total length of young of the year L. carinatu (TL, Of Liza). l *P
Source of variation

d.f.

Period Patch Period patch Residuals

2 1 2 45

Log iN+ 1) 1.97 13.49*** 0.92

Log (B+l) 2.89 8,24** 1.75

Log (N, Liza + 1) 2.24 11.78** 1.26

ITL,

Log Liza)

Log (TLO+Liza)

53,42*** 10.05** 0.48

242.54*** 2643*** 0.23

The diet data for L. carinata in the seines suggested a shift in diet from detritus and chlorphytes on 22 February 1988 (88.0 and 6.3O,, proportional weighted points respectively) to be a larger proportion of chlorophytes on 8 March 1988 (73.5 and 26.5”,, detritus and chlorophytes respectively) and finally to a diet of almost entirely detritus on 25 March 1988 (99,9O,,), (Figure 5). The detritus observed in all stomachs was fine grey amorphous material and did not seem to be derived from the chlorophytes. The diet of the fish captured in the trawls was analysed only for the latter two sampling days as less than 20 examples of any particular species were captured on 18 February 1988. L. breuirostris had

Detached

chlorophytcs

as nursery

areas forf;sh

101

I r,E Figure 5. Histograms showing mean percentage proportional weighred points of rhe food items in samples of twenty fish from the seine and trawl catches. (Har, harpacticoid Copepods; Dia, Diatoms; Chl, chlorophytes; Amp, Amphipoda; Ost, Ostracoda; Pal, Polychaeta; Nem, Nematodes.)

consumed a greater proportion of chlorophytes on 12 March 1988 than on 28 March 1988 respectively). On the last day of sampling, 28 March 1988, Liza carintitu 138.1 and 4,5”,,, had consumed entirely detritus (Figure 5).

Discussion A comparison of the mean size of the trawl catches of chlorophytes in the spring of 1987 and 1988 shows that the bloom in 1988 was much smaller than the bloom in 1987. The volumes of weed recorded in this survey range between O-18.1 1, much smaller than the range reported in Western Australia on surf-zone beaches of O-535 1 for a swept area of approximately 60 m2 (Robertson & Lenanton, 1984). The fish assemblage of the shallow water, sampled using seines, did not show a correlation between numbers or biomass with weed volume, an observation at odds with that of Robertson and Lenanton (1984), who observed a positive relationship between numbers of fish and quantity of detached macrophytes taken in a surf-zone environment. There was a significant relationship between these biological variables and the presence or absence of patches with higher numbers and biomass occurring in association with patches of weed. On surf-zone beaches of Western Australia a similar relationship has been shown between numbers and the presence or absence of patches of macrophyte detritus (Robertson & Lenanton, 1984). The lack of correlation between weed volume and both fish numbers and

192

3. M. Wright

biomass, and the significant association between both numbers and biomass of fish with the relatively small patches of weed in this survey suggests that the size of the patches is of no importance. The dominant species of the assemblage in shallow water, L. carinata, was more abundant amongst patches of weed, with smaller fish found amongst the patches of weed and larger fish away from the patches. If the 1 + or older fish are removed from the length data set this latter relationship becomes more pronounced suggesting that the 1 + or older fish were associated with the weed accumulations. Throughout the sampling period there was a significant difference in length between dates of sampling reflecting growth. The fish assemblage from the deeper water, sampled using an otter trawl, showed a change from a positive correlation between weed volume with biomass at the beginning of the study to a pronounced negative correlation between weed volume with numbers and biomass at the end of the study. As the bloom progressed the weed became more patchy and the fish were not associated with the large patches of weed in the deeper water. L. car&am, the dominant species in the shallow water, consumed chlorophytes particularly during early March. In late March this species had returned to its normal diet of detritus (Wright, 1988~). In the deeper water L. brevirostris also made direct use of the weed during early March but by late March this species returned to its generalist diet (Wright, 1988~). It is noticeable that amphipods did not constitute a major part of the diet in either shallow or deep water fish during the sample period, nor did an examination of the weed reveal any amphipods. Previous work (Lenanton et al., 1982; Robertson & Hansen, 1982; Robertson & Lenanton, 1984) has shown that weed associated amphipods are an important dietary constituent for fish associated with macrophyte detritus particularly on surf-zone beaches. Macrophyte detritus from different sources is not of equal value to amphipods as food or shelter (Robertson & Lucas, 1983). Examination of the chlorophytes during this survey revealed very low populations of amphipods. The chlorophytes may not have been suitable for the establishment of amphipod populations, or the amphipod population had not established themselves at the time of sampling. This study has shown that the near shore accumulations of chlorophytes are temporarily important for young of the year of L. carinata both as a physical refuge and as a dietary resource. Accumulations of chlorophytes are considered to be a refuge from piscivorous birds and in Western Australian estuary may be responsible for a pronounced rise in abundance of fish (Lananton et al., 1984). In surf-zone environments detached macrophyte detritus is also considered to provide protection against piscivorous birds (Lenanton et aZ., 1982; Robertson & Lenanton, 1984). In the deeper water the negative correlation between weed volume with both numbers and biomass suggests that the patches, which had become benthic by the end of the programme, were not acting as a refugee from predators. Considering the assemblage as a whole it seems that 0 group L. carinata utilize the accumulations as a physical and dietary resource whilst the remainder of the assemblage make incidental use of the patches. Although Sulaibikhat Bay is considered to be an important nursery area for nine species of fish only L. carinata, S. elongata (Day) and I’. stridens (ForsskHl) recruit as young of the year during the period January to March (Wright, 1988a). S. elongata is a demersal species that would not be expected to use the accumulations as a physical refuge and the peak recruitment of P. stridens occurs during the summer months with few fish occurring in March, In Western Australia there was an increase in numbers of species, of between two and ten times, in areas with macrophyte detritus compared to areas without accumulations (Robertson & Lenanton, 1984). In the

Detached

chlorophytes

as nursery

areas forfish

193

present study the number of species was always low and this variable was not used in the analysis. The spring bloom of chlorophytes is a short term resource that is patchily distributed within Sulaibikhat Bay. When present, the patches of chlorophytes are expected to have a beneficial effect on the L. carimta population in particular by providing a food resource and protection from piscivorous birds. Acknowledgement

This study was supported by Kuwait University, grant-SZ027. References Al-Sdirawi, F. A. 1984 Wintering birds of Sulaibikhat Bay. 1984 Annual Research Report, 30-33. Kuwait: Institute for Scientific Research. Dames&Moore. 1983 Aquatic biology investigations. Volumes I and II: Studies for the Sabiya area, Kuwait Bay and development of electrical networks. Ministry of electricity and water report. Government of Kuwait. pp. 900. Haram, 0. J. &Jones, J. W. 1971 Some observations on the food of the Gwyniad Coregonus cl~peoidespennatiz Velenciennes of the Llyn Tegid (Lake Bala), North Wales. Jourd ofFish Biology 3,287-295. Houde, E. D., Almatar, S., Leak, J. C. & Dowd, C. E. 1986 Ichthyoplankton abundance and diversity in the western Arabian Gulf. Kuwait Bulletin of Marine Science 8, 107-393. Hull, S. C. 1987 Macroalgal mats and species abundance: a field experiment. Estuarinr, Coastal arrd Shelf Science 25, 519-532. Hynes, H. B. N. 1950 The food of the freshwater sticklebacks (Gasterosteus act&am and Pygortruspurgitimi wirh a review of methods used in the study of the food of fishes. Journal of Animal Ecology 19,36-58. Hyslop, E. J. 1980 Stomach content analysis: a review of methods and their application. 3ournal (11’Fzsh Biology 17, 41 l-429. Kuronuma, K. &Abe, Y. 1986 Fishes ofthe Arabian Gulf. Tokyo: International Academic Printing, pp. 356. Lenanton, R. C. J., Loneragan, N. R. &Potter, I. C. 1985 Blue-greenalgal blooms and the commercial fishery of a large Australian estuary. Mark Pollution Bulletin l&477-482. Lenanton, R. C. J., Potter, I. C., Loneragan, N. R. & Chrystal, I’. J. 1984 Age structure and changes in abundance of three important species of teleost in a eutrophic estuary (Pisces: Teleostei). Jottrnal ojZoology, Loizdon 203,31 l-327. Lenanton, R. C. J., Robertson, A. I. &Hansen, J. A. 1982 Nearshore accumulations of detached macrophytes as nursery areas for fish. Marine Ecology Progress Series 9,51-57. Robertson, A. I. & Hansen, J. A. 1982 Decomposing seaweed; a nuisance or vital link in coastal food chams? CSIRO Diwixion of Fisheries Research Report 1980-1981, 75-83. Robertson, A. I. & Lenanton, R. C. J. 1984 Fish community structure and food chain dynamics in the surf zone of sandy beaches: the role of detached macrophyte detritus. Journal of Experimental Marine Bio1ot.v arid Ecology, 84,265-283. Robertson, A. I. & Lucas, J. S. 1983 Food choice, feeding rates and turnover of macrophyte biomass by a surf-zone inhabiting amphipod. Journal of Experimental and Marine Biology and Ecology 72,99-l 24. Rosenberg, R. 1985 Eutrophication-the future marine coastal nuisance? Marine Pollution Bull&t 16, 27-231. Wright, J. M. 1988~ Recruitment patterns and trophic relationships of fish in Sulaibikhat Bay, Kuwait. jrourrtal of Fish Biology 33, 671-687. Wright, J. M. 19886 Seasonal and spatial differences in the fish assemblage of the non-estuarine Sulaibikhat Bay, Kuwait. Marine Biology in press.