J. mar. biol. Ass. U. K. 57:849-858. Boehlert, G. W., Gadomski, D. M., Mundy, B. C. (1985). Vertical distribution of ichthyoplankton off the Oregon USA coast in the.
Marine Biology113, 549-559 (1992)
Marine Biology 9
1992
Distribution and abundance of marine fish larvae in relation to effluent plumes from sewage outfalls and depth of water C. A. Gray 1, N. M. Otway 1, E A. Laurenson 2, A. G. Miskiewicz 3 and R. L. Pethebridge 1 1 Fisheries Research Institute, P.O. Box 21, Cronulla, New South Wales 2230, Australia z EnvironmentProtection Authority, P.O. Box 367, Bankstown,New South Wales 2200, Australia 3 SydneyWater Board, P.O. Box A53, SydneySouth, New South Wales 2001, Australia Date of final manuscript acceptance: March 20, 1992. Communicatedby G. E Humphrey, Sydney
Abstract. Fish larvae were sampled in and below three separate sewage plumes associated with the cliff-face (shoreline) outfalls at North Head, Bondi and Malabar, and at three control (non-plume) sites located > 8 km away from the sewage outfalls, at Long Reef, Port Hacking and Marley Beach, in nearshore waters off Sydney, south-eastern Australia. Samples were collected at the surface and at 20 m depth during three periods: December 1989, April/May 1990 and August/September 1990. In December 1989, a greater number of taxa were caught at both depths at the plume sites compared to the control sites, but this did not occur during the other two sampling periods. Similarly, in April/May 1990, greater numbers of the clupeid Hyperlophus vittatus but fewer anthiines were caught at both depths near the outfalls (plume sites). Myctophids were more numerous in surface samples, but not at 20 m, at the plume sites in both April/May and August/September 1990, whereas in April/May 1990, labrids and anguilliformes were less abundant at 20 m at the plume sites compared to the control sites. These differences in the numbers of fish larvae caught may have been an effect of the effluent plumes, but these results were only correlative. The results most probably reflect spatial heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney. There were striking differences, however, in the number of fish larvae caught at the surface and at 20 m, and among sampling periods, but these differences were similar across all sites. Of the 46 taxa considered common, 33 occurred in greater numbers at 20 m than at the surface, whereas only 8 taxa were caught in greater numbers at the surface. The composition of the fish larvae also differed markedly among sampling periods; few taxa were common to all three sampling periods. Greater numbers of fish larvae were caught in April/May and August/September 1990 than in December 1989, particularly at 20 m depth. The data highlight the large spatial and temporal heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney and the difficulty of identifying effects that are solely due to sewage plumes.
Introduction The patterns of horizontal and vertical distribution and abundance of plankton are affected by physical phenomena on very different spatial scales, ranging from < 1 to > 1000 km (Haury et al. 1978, Denman and PoweU 1984, Kingsford 1990). Many studies have shown that various types of oceanographic features, including tidal (Epifanio 1987, Clancy and Epifanio 1989), coastal (Zeldis and Jillet 1982, Kierboe et al. 1988), oceanic (Owen 1981) and topographically-controlled fronts (Wolanski and Hamner 1988), eddies (Lobel and Robinson 1986, 1988) internal waves (Shanks 1983, Kingsford and Choat 1986) and plumes from rivers (Mackas and Louttit 1988, Mann 1988, Govoni et al. 1989) influence the distribution and abundance of plankton (including larval fish) at various depths in the water column. Plankton often aggregate in, and along the edges of, such oceanographic convergences (see Kingsford 1990 for review). Consequently, these features can potentially influence the dispersal, survivorship and recruitment of organisms in the plankton. Effluent plumes from sewage outfalls behave in a manner similar to some of the above natural oceanographic features, and thus may affect the horizontal and vertical distribution and abundance of plankton. Effluent plumes differ from these oceanographic features, however, in that they contain varying concentrations of toxic substances. Larval fish are particularly vulnerable to stress, and toxic wastes in effluent plumes could cause increased mortality and sublethal effects (Hoss et al. 1974, Blaxter 1977, Hunt and Anderson 1989, Weis and Weis 1989, Weis et al. 1989). In contrast, however, the increased nutrients and accumulation of food resources in or near sewage plumes may be beneficial to fish larvae (McVicar et al. 1988). Unfortunately, there are relatively few studies that document the effects of sewage effluent on the distributions and abundances of plankton. Arfi et al. (1981) found that the abundances of zooplankton near a sewage outfall in the Mediterranean Sea were reduced close to the outfall; further away a zone of "pollution-tolerant" species was encounted, followed by a zone
C.A. Gray et al.: Fish larvae, sewage plumes and depth
550 of increased a b u n d a n c e s of species similar to n o n - p o l l u t ed areas. I n a n early review, M i l e i k o v s k y (1970) c o n c l u d ed that there were conflicting reports o f the effects o f v a r i o u s types o f p o l l u t a n t s o n the d i s t r i b u t i o n s a n d a b u n dances of p l a n k t o n . F o r example, K a r a s et al. (1991) rep o r t e d lower a b u n d a n c e s o f larvae o f Percafluviatilis in a n area affected b y effluent f r o m a p u l p mill, whereas Scarratt (1969) f o u n d that the effluent f r o m a kraft mill h a d n o effect o n the d i s t r i b u t i o n a n d a b u n d a n c e o f larvae o f Homarus americanus. O f p a r t i c u l a r c o n c e r n to fisheries m a n a g e r s are the positive a n d negative effects t h a t the disposal o f sewage in the ocean m a y have o n the survival a n d r e c r u i t m e n t o f c o m m e r c i a l l y a n d recreationally imp o r t a n t species o f fish a n d invertebrates. Sewage is presently discharged i n t o the Pacific O c e a n n e a r Sydney, s o u t h - e a s t e r n A u s t r a l i a , via three n e w subm a r i n e outfalls situated in 60 to 80 m of water. P r i o r to the c o m m i s s i o n i n g o f these outfalls in 1990/1991, sewage was discharged at several cliff-face (shoreline) outfalls. I n this paper, we c o m p a r e the relative a b u n d a n c e s o f fish larvae in a n d below the effluent p l u m e s associated with the three m a j o r cliff-face outfalls a n d at three c o n t r o l sites located some distance away f r o m outfalls, before the deepwater outfalls were c o m m i s s i o n e d . We assess whether the effects o f the effluent p l u m e s o n larval fish were similar at the surface a n d at 20 m depth, a n d t h r o u g h o u t time.
z
34~ 00'
KING
~'~
Materials and methods Study area a n d s a m p l i n g p r o c e d u r e The three cliff-face sewage outfalls located at North Head, Bondi and Malabar determined the plume sites, whereas the three control sites were located off Long Reef, Port Hacking and Marley Beach (Fig. 1). The minimum distance between a cliff-face outfall (plume site) and a control site was ~ 8 km (between North Head and Long Reef). The depth of water at each site was 25 to 30 m. The primary-treated effluent discharged from these sewage outfalls formed conspicious surface plumes that were usually discoloured and formed distinct fronts with the surrounding ocean. The effluent plumes from these outfalls were usually surface phenomona; water salinity was usually ~ to 3%o less in the top 2 to 3 m at the plume sites than at the control sites (Fig. 2). This difference in salinity was usually consistent throughout time. The size and shape of the plumes varied according to the prevailing winds and currents, but they often extended for several kilometres. The water temperature was similar at all sites and at all depths in the water column in April and August 1990 (Fig. 2). Changes in water temperature between sampling times were similar at all sites (Fig. 2). All sampling was done in daylight and each site was sampled during three periods: December 1989, April/May 1990 and August/ September 1990. During each period, three replicate 15 rain tows were done at the surface and at 20 m depth at each site using cylindrical-conical plankton ring nets, each with a 80 cm-diam mouth, 500 gm mesh in the body and 250 p.m mesh in the codend of the net. The surface and deep samples were collected simultaneously. The surface net was towed at one side of the boat; the nets were towed at 2.0 to 2.2 knots. The "deep" net was fitted with a messenger-operated open-close mechanism (General Oceanics Model 1000-DT) to prevent contamination of the sample during deployment and retrieval. A flow meter (General Oceanics Model 2030R) was fitted in the mouth of each net to determine the amount of water filtered per tow. The average volume of water filtered was
MARLEY
Fig. 1. Location of sampling sites and cliff-face sewage outfalls off Sydney. Plume sites were located near North Head, Bondi and Malabar outfalls, control sites at Long Reef, Port Hacking and Marley
about 280 m 3. Sampling of the outfall sites was always done in and below the visible plume associated with each outfall. Plankton samples were preserved in 10% formalin/seawater. Fish larvae were sorted from the catches in the laboratory using a binocular microscope, identified to the lowest taxonomic level possible (usually family), and enumerated. Larvae were identified using criteria from Fahay (1983), Leis and Rennis (1983), Moser et al. (1984), Miskiewicz (1987) and Leis and Trnski (1989). In the present study, the term "fish larvae" refers to small fish before full attainment of scales, but does not include eggs.
Analysis of d a t a The relative abundances of the fish larvae were standardised to number caught per 250 m 3 of water filtered. When possible, the data were analysed using a partially orthogonal, partially nested, four-factor analysis of variance with the following factors: periods (random); depths (surface vs deep - fixed); treatments (controls vs plumes - fixed) and sites (nested within treatments - random). This design, however, did not permit an evaluation of the depths and treatments main-effects terms, nor did it allow an evaluation of the depths x treatments interaction term. Post-hoc pooling of some of the other non-significantinteraction terms did, however, enable an evaluation of some of these terms and was done when possible. The procedures for post-hoc pooling followed those outlined by Winer (1971) and Underwood (1981). Prior to analysis, data were tested for homogeneity of variances by Cochran's test (Winer 1971) and where necessary, were transformed accordingly. When data remained heterogeneous, the data for each sampling period were
C.A. Gray et al.: Fish larvae, sewage plumes and depth
[] 0 = Control sites Temp. (~ 21
22
23,,31
April 1
9 9 = Plume sites
Temp. (~
Salinity (%o) 32
33
34
35
551
15
36
16
Salinity (%o)
17/,31 A
32 .
i
33 . A I
34
35
36
,
August 1990
~ 5
v
t--
~-10
10
fi5 fi5 5.
5 =5
2o~
!0.
I~
analysed separately using a three-factor analysis of variance similar to that outlined above. This analysis allowed all main effects and interaction terms to be tested. When heteroscedasticity still prevailed, no statistical analyses were done, but the means were examined for trends. All multiple comparisons among means were done using Student-Newman-Keuls (SNK) tests (Winer 1971, Underwood 1981).
Results A total of 127 taxa was caught; 98 taxa were collected at the plume (outfall) sites, 125 at controls. Furthermore, 95 taxa occurred in the surface samples whereas 117 were caught at 20 m depth; 46 taxa were considered common; i.e., their overall occurrence was >20 individuals. Of these 46 taxa, 33 were more numerous in the samples collected at 20 m depth, whereas only 8 taxa were more abundant in the surface samples (Table 1). Five taxa occurred in similar numbers at both depths (Table 1). The total number of taxa and the total number of individuals caught, and the 13 most commonly caught taxa were analysed statistically. No statistical analyses were done on the numbers of the other taxa caught, because too few individuals were caught across both treatments and among sites. All analyses were made on data standardised to 250 m 3 of water filtered. Number of taxa It was not possible to analyse statistically the full data set of the number of taxa caught because of heteroscedasticity, and so three separate analyses were performed. Analyses of the data from each sampling period showed that there were no consistent differences in the number of taxa caught between plume and control sites (Table 2). In December 1989, more taxa were caught at both depths at the plume sites than at control sites (Table 2, analysis ofvari-
2. Salinity-depth profiles of water column in April and August 1990 near cliff-face sewage outfalls at North Head and Malabar (plume) sites and at two control (non-plume) sites at Long Reef and Port Hacking
Fig.
ance, p < 0.05), but there was no evidence for this in April/May 1990 or in August/September 1990 (Table 2, analysis of variance, p>0.05). In December 1989 and August/September 1990, fewer taxa were caught at the surface than at 20 m at most sites (SNK tests based on data in Fig. 3), and although there was evidence for this trend in April/May 1990 (Table 2, analysis of variance, p < 0.05), SNK tests failed to distinguish any differences. The number of taxa caught in April/May 1990 and August/September 1990 differed significantly among sites nested within each treatment (Table 2, analysis of variance, p < 0.01), but, again, SNK tests failed to identify the differences. Examination of the means in Fig. 3 indicated that fewer taxa were caught in December 1989 than in April/May and August/September 1990 at most sites.
Number of individuals Heterogeneous variances prevented a complete analysis of the data, and thus three separate analyses were done. There were no consistent differences in the numbers of individuals caught between outfall sites and controls (Fig. 3). In December 1989, there were no significant differences in the total numbers of individuals caught between treatments and depths (Table 2, analysis of variance, p > 0.05). In contrast, the number of individuals caught in April/May and August/September 1990 significantly differed between depths and among sites nested within treatments (Table 2, analysis of variance, p < 0.01). In April/May, significantly more individuals were caught at 20 m than at the surface at all plume sites and at the Port Hacking and Marley control sites, whereas in August/September greater numbers of individuals were caught at 20 m at all control sites and at the North Head and Malabar outfalls (SNK tests based on transformed data in Fig. 3). Furthermore, it appeared that greater
C.A. Gray et al.: Fish larvae, sewage plumes and depth
552 Table 1. Total overall standardised catches of 46 common taxa (i.e.,
taxa that occurred in > 1 sample, and in which > 20 individuals were caught, pooled over all sites and periods) at surface and at 20 m depth. Total standardised number caught at each depth across Family, species
Surface
20 m
Family, species
Surface
20 m
Group B: surface > 20 m
Group A: 20 m > surface
Gonorynchidae
Carangidae
Pseudocaranx dentex Trachurus sp.
all sites and periods is shown. Group A: taxa that occurred in overall greater numbers at 20 m depth than at surface; Group B: taxa that occurred in overall greater numbers at surface than at 20 m depth; Group C: taxa caught in similar numbers at both depths
115,9 28.4
6 427.9 115.6
179.7
754.4
161.3 1.5
706.9 112.6
Gobiidae
38.0
Labridae
Gonorynchus greyi
205.8
4.9
Cheilodactylidae
68.5
5.1
Mullidae
37.7
0.6
Sphyraenidae
31.8
14.1
Tripterygiidae
21.0
4.3
439.6
Scorpididae
21.9
3.0
29.1
223.4
Blenniidae
Anthiinae
80.8
201.5
20.0
1.3
Bothidae
45.1 1.9
153.8 45.3
17.1
3.3
62.6
162.7
Callionymidae
18.7
119.2
Anguilliformes
12.4
102.9
8.9 2.6
95.4 22.1
12.3
90.9
Myctophidae Clupeidae
Hyperlophus vittatus Sardinops neopilchardus
Pseudorhombus sp. Mugilidae
Liza argentea
Triglidae Trichiuridae Scorpaenidae
5.21
Ambassidae
Velambassis jacksoniensis
56.7
48.7
36.1
31.8
Engraulis austral&
16.6
21.2
Macrorhamphosidae
16.6
16.2
Gonostomatidae
13.1
18.4
Melanostomiatidae
64.4 46.3 87.7
26.6
41.4
0.9
44.8
19.1 9.8
34.0 25.0
Gobiesocidae
2.9
35.6
Pomacentridae
8.9
32.7
Nemipteridae
7.9
25.8
Creedidae
2.5
23.7
Clinidae
Gerres ovatus
Engraulididae
22.5 0
Helicolenus sp.
Gerreidae Group C: surface = 20 m
Platycephalidae
Platycephatus spp. Platycephalus fuscus
Ornobranchius anolius
Sillaginidae
Sillago bassensis Sparidae
Acanthopagrus australis Rhabdosargus sarba
Pinguipedidae
0.0
22.1
Cepolidae
2.5
21.1
2.0
22.3
Berycidae
Centroberyx affinis Notosudidae
3.9
20.6
Pempherididae
4.2
I7.2
Bregmacerotidae
6.4
16.9
n u m b e r s o f i n d i v i d u a l s were c a u g h t a t 20 m in A p r i l / M a y a n d A u g u s t 1990 t h a n in D e c e m b e r 1989 (Fig. 3). Numbers of individual taxa Statistical a n a l y s e s were d o n e o n the n u m b e r o f Bothidae, Triglidae, M y c t o p h i d a e , A n t h i i n a e , G o b i i d a e ,
L a b r i d a e , C a l l i o n y m i d a e , A n g u i l l i f o r m e s , Liza argentea ( M u g i l i d a e ) , Hyperlophus vittatus ( C l u p e i d a e ) , Velarnbassisjacksoniensis ( A m b a s s i d a e ) , a n d Trachurus sp. a n d Pseudocaranx dentex ( C a r a n g i d a e ) caught. T h e n u m b e r o f b o t h i d s c a u g h t e x h i b i t e d significant t e m p o r a l v a r i a t i o n a m o n g sites n e s t e d w i t h i n t r e a t m e n t s a n d b e t w e e n d e p t h s (Table 3, analysis o f v a r i a n c e ,
C.A. Gray et al.: Fish larvae, sewage plumes and depth
C=Control 9 P=Plume [ ]
553
Long Reef North Head
[] []
Port Hacking Bondi
[] []
Marley Malabar
Surface
60
20 m
No. of taxa uJ (n
30
O
~ ~-
0
1551 + 418,~4 c
500
L' \ \ \ \ \
No. of individuals U
E
\ \ \ \ \ \
250
r e-
C
P
I 1 December
C
P
C
I I April/May
1989
1990
P
C
P
I I Aug/Sept
I I December
1990
1989
C
P
I
I
C
P
I I Aug/Sept
April/May 1990
1990
Fig. 3. Mean number of taxa and mean number of individuals of fish larvae caught per 250 m a of water at each site during each of the three sampling periods
Table 2. Summary of analyses of variance of number of species and
number of individuals caught during each sampling period, dfi degrees of freedom; MS: mean square; *, **: Significant at p
