Microzooplankton grazing and selective feeding during bloom periods in the Tolo Harbour area as revealed by HPLC pigment analysis

Dilution experiments were conducted to investigate microzooplankton grazing impact on phytoplankton of different taxonomic groups and size fractions (< 5, 5–20, 20–200 μm) during spring and summer bloom periods at two different sites (inner Tolo Harbour and Tolo Channel) in the Tolo Harbour area, the northeastern coastal area of Hong Kong. Experiments combined with HPLC pigment analysis in three phytoplankton size fractions measured pigment and size specific phytoplankton growth rates and microzooplankton grazing rates. Pigment-specific phytoplankton growth rates ranged between 0.08 and 3.53 d^− 1, while specific grazing rates of microzooplankton ranged between 0.07 and 2.82 d^− 1. Highest specific rates of phytoplankton growth and microzooplankton grazing were both measured in fucoxanthin in 5–20 μm size fraction in inner Tolo Harbour in summer, which coincided with the occurrence of diatom bloom. Results showed significant correlations between phytoplankton growth and microzooplankton grazing rates. Microzooplankton placed high grazing pressure on phytoplankton community. High microzooplankton grazing impact on alloxanthin (2.63–5.13) suggested strong selection toward cryptophytes. Our results provided no evidence for size selective grazing on phytoplankton by microzooplankton.     

Estimation of submarine groundwater discharge in Plover Cove, Tolo Harbour, Hong Kong by Rn

Algal blooms in Tolo Harbour, Hong Kong have received much attention and submarine groundwater discharge is speculated to be a significant pathway carrying nutrients into the constricted estuary. Plover Cove, a small cove in the Harbour, was selected for SGD analysis using ²²²Rn budget. The volumetric SGD rates are estimated to be about 8000 m³/day for neap tide and about 17,000 m³/day for spring tide. Result of nutrient analysis of the porewater indicates that the nutrient loading through this pathway is speculated to be crucial for eutrophication in Tolo Harbour. Current practice for the management of algal blooms in Hong Kong, in which nutrient loading through SGD was ignored, has to be reviewed and the control measures of groundwater contamination are obviously required.     

Pollution studies on Tolo Harbour,Hong Kong

Eight stations were chosen for this 14 month survey of Tolo Harbour in Hong Kong, four of them in the harbour proper and four in the estuaries of the major streams entering the harbour. Various chemical and physical factors were measured twice each month. Water samples were collected for nutrient, phytoplankton, chlorophyll and bacteriological analysis.The annual discharge of nutrients from the four streams into Tolo Harbour has been estimated, based on the nutrient analyses and computation of annual discharge (QA) values for these streams. The seasonal and spatial variations in nutrient content are discussed in relation to the increasing organic pollution of Tolo Harbour. Calculations of various ratios between SiO₃, PO₄, NO₃ and total inorganic N reveal that excessive amounts of phosphate are entering the harbour and subsequently accumulating in the bottom waters and sediments, leading to changes in the trophic condition of this water body and the development of anoxic conditions in the bottom layer.Significant correlation has been demonstrated between standing crop and various environmental parameters in both estuarine and marine waters and similarly between chlorophyll a concentration and various environmental parameters. However, no significant correlation values were obtained between either standing crop or chlorophyll a concentrations, SiO₃Si (the latter presumably due to the predominance of diatoms in the phytoplankton). Neither standing crop nor chlorophyll determinations reveal any evidence of alternating periods of high productivity and decomposition which could explain the deteriorating bottom water conditions. This again is taken as evidence that the high organic inputs are responsible for such deterioration.Increasing TC, FC and FS densities have been noted in Tolo Harbour as a direct result of the increasing organic pollution and ratios between FC and FS densities indicate that in 55% of the samples pollution was derived from human sewage. The bacterial levels well exceeded various international standards for bathing waters and shellfish collection for at least a part of the survey period and at a number of stations for the entire survey period. Pathogenic organisms were also present. This underlines the potential health risks in these waters.Finally, the future prospects for this harbour are discussed in relation to activities such as reclamation and the development of new towns and their impact on water quality.     

Changes in the nutrient ratios and phytoplankton community after declines in nutrient concentrations in a semi-enclosed bay in Hong Kong

Tolo Harbour is a landlocked bay with poor tidal flushings in the northeastern part of Hong Kong. During the 1980s, excessive nutrient loading led to dramatic increase in nutrient concentrations, accompanied by lower N:P ratios, higher algal biomass and shifts in the phytoplankton community. We studied the effects of nutrient loading reduction measures on nutrient concentrations, nutrient ratios and phytoplankton dynamics in Tolo Harbour by comparing data collected before the full implementation of nutrient loading reduction measures (1986-1997) to those after the implementation (1998-2008). Such measures led to declines in nutrient concentrations, changes in N:P and N:Si ratios, lower chlorophyll-a concentrations and fewer algal blooms. Diatoms were the most abundant phytoplankton group in Tolo Harbour both before and after declines in nutrient concentrations. The density of dinoflagellates did not change, but substantial increase in other algal group abundance was recorded.     

Molluscan lysosomal responses as a diagnostic tool for the detection of a pollution gradient in Tolo Harbour, Hong Kong

Sub-cellular perturbations in the lysosomal compartment of molluscan haemocytes were examined in mussels (Perna viridis), collected along a pollution gradient. The neutral red technique was validated using a well defined contamination gradient among indigenous populations from five stations along Tolo Harbour, Hong Kong. Condition indices (shell length:dry tissue wt) and tissue metal concentrations were also measured in an attempt to identify a relationship between contamination level and adverse physiological effects. Correlations were found between lysosomal retention time and condition along the pollution gradient. There were significant differences between mussels collected from stations on offshore islands and those collected from inner harbour sites (p < 0.05). There was, however, little correlation between metal concentrations and retention time or condition (p > 0.05).     

Diet of the West Coast rock lobster Jasus lalandii: influence of lobster size,sex, capture depth,latitude and moult stage

Diets of male and female West Coast rock lobster Jasus lalandii in South Africa were compared across a large size range of 10–85 mm carapace length (CL). The diets of male rock lobsters were compared between two different depths, different seasons, across the moult cycle, and among eight sites along the South-Western Cape coast. There was no significant difference in diet between male and female rock lobsters for any of the size-classes examined. Male rock lobsters showed large differences in diet between small and large size-classes. The diet of small lobsters (<75mm CL) consisted of a wide range of species, which included, in order of importance, coralline algae, barnacles Notomegabalanus algicola, sponges and ribbed mussels Aulacomya ater. However, prey items rich in inorganic material were not dominant in their diet, as had been predicted. By contrast, large rock lobsters (>80mm CL) fed on few species, and fish and ribbed mussels were their most abundant prey items. There were some dietary differences between individuals captured at 20 m and those collected at 50 m, but these differences were less marked than between the two sampling sites (the Knol and Olifantsbos). There was seasonal variation in diet at the Dassen Island and Olifantsbos sites. Cannibalism was highest during the moulting periods. Gut fullness varied seasonally at Dassen Island, and was consistently high at Olifantsbos. However, the proportion of the population feeding showed marked seasonal trends at both sites, tracking the commercial catch per unit effort of rock lobster. Ribbed mussels were a ubiquitous and dominant component of the diet at the eight sites sampled. However, south of Dassen Island, black mussels Choromytilus meridionalis were scarce in the diet of rock lobster and sponges predominated. Gut fullness was lowest at the northernmost sites.     

Copepod feeding in a coastal area of active tidal mixing: diel and monthly variations of grazing impacts on phytoplankton biomass

This study examined monthly feeding rates and grazing impact on phytoplankton biomass, as well as diel feeding rhythms of four key copepod species in a tidally well mixed estuary (Asan Bay, Korean Peninsula). Monthly ingestion rates estimated based on gut pigment analysis were closely associated with their peak densities, but not with phytoplankton biomass, implying high ingestion may be related to reproductive output for population growth. The three smaller copepods, Acartia hongi, Acartia pacifica and Paracalanus parvus, showed feeding preference for smaller phytoplankton (<20 μm) with higher clearance rates, whereas the larger Calanus sinicus preferred larger phytoplankton. Acartia pacifica and P. parvus showed distinct increased nocturnal feeding rates as measured with gut fluorescence, whereas A. hongi showed no significant day–night differences. Copepod diel feeding patterns were not associated with food quantity, and endogenous physiological rhythm might be hypothesized as responsible for the observed diel feeding patterns. Grazing impact on phytoplankton biomass by the four copepods in the estuary was on average 8% (range 0.2–29.8%) of the phytoplankton standing stock, similar to values reported in other coastal waters. Very high copepod abundances but low daily carbon ration (<20% for all copepods) provided by feeding on phytoplankton indicate that copepods also grazed on other non‐phytoplankton foods in Asan Bay.     

Vertical Migrations and Feeding Rhythms of Acartia clausi and Pseudodiaptomus hessei (Copepoda: Calanoida) in a Tropical Lagoon (Ebrié, Côte d'Ivoire)

Diel changes in vertical distribution and gut pigment contents of Acartia clausi andPseudodiaptomus hessei were studied during several 24-h time series performed between 1993 and 1997 in four sites of the Ebrié Lagoon (Côte d'Ivoire). The sites differed by their morphology and their hydrological structure and by the vertical distribution of chlorophyll biomass. Both species showed classical diel vertical migrations (DVM). Copepodites and adult stages of P. hessei were almost benthic during the day and evenly distributed through the water column at night. The amplitude of DVM of A. clausi increased from copepodites I–III to adults. Copepodites and adults of A. clausi increased significantly their gut fluorescence at night, whereas those of P. hessei showed no clear diel feeding rhythm (DFR). These results suggest that A. clausi feed mostly at night on phytoplanktonic particles and P. hessei feed mostly on benthic algal particles during the day and on sestonic particles at night. No relationship was observed between DFR and DVM because both patterns occurred when food was either vertically homogeneous or vertically stratified. The daily average gut fluorescence of A. clausi increased with ambient chlorophyll concentration until around 12–15 μg l⁻¹, whereas no relationship was found for P. hessei. The implication of these patterns on the adaptation capacities and the behaviour of the two species are discussed. The DVM of P. hessei should explain its rarity in the estuarine area. The comparison of our results with previous ones suggests an evolution of A. clausi DFR between 1981–1982 and 1996–1997, in relation to an intensification of eutrophication.     

Reproductive pattern of the epifaunal amphipodPontogeneia rostrata (Crustacea) on dolsando sandy shore in Korea

Reproductive patterns of an epifaunal amphipod,Pontogeneia rostrata, were studied on Dolsando sandy shore in Korea. The life history pattern was iteroparous, with recruitment mainly occurring from winter to spring. The sex ratio was male-biased, especially during breeding periods. The mean body length of females was significantly larger than that of males. Brood size and egg volume were positively related to the body length of ovigerous females. There was no significant difference in brood size between successive breeding periods, but egg volumes were significantly higher in early winter (December) than in late spring breeding (May and June), increasing the probability of survival to hatching. These traits contribute to more reproductive potential in early winter than in late spring breeding. The mean brood size of epifaunalP. rostrata was larger but the mean egg volume smaller than that of infaunal amphipods in this sampling area. We suggest that reproductive effort for epifaunal species may be proportionally greater than for infaunal species in risky environments.     

南海北部大鹏湾中DOP的分布、滞留时间、自养生产和异养降解

The importance of dissolved organic phosphorus(DOP) as a potential nutrient source for primary producers in marine systems has been recognized for up to eight decades, but currently, the understanding of the biogeochemistry of DOP is in its infancy. In the present study, monthly data between 2000 and 2014 were used to analyze the temporal and spatial distributions of DOP in the Mir Bay, the northern South China Sea. The DOP residence time(T_(DOP)) was also investigated using a simple regression analysis in combination with chlorophyll a(Chl a) measurements while excess DOP(ΔDOP), produced by the biogeochemical processes of autotrophic production and heterotrophic removal, was determined using a two-component mixing mass-balance model in combination with salinity measurements. The results showed that the DOP concentration was(0.017±0.010) mg/L higher in the surface-water compared with the bottom-water and higher in the inner Tolo Harbour and waters adjacent to Shatoujiao compared with the main zone of the bay. Although seasonal changes and annual variability in the DOP were small, the surface DOP concentration was higher in the wet season(April–September)than in the dry season(October–March) due to the impacts of seaward discharges and atmospheric deposition into the bay. Measurement and regression results showed that the DOP release rate from phytoplankton production was about 1.83(gP)/(gChl a) and the T_(DOP) was about 7 d, which implied that the DOP cycle in the bay was rapid. The ΔDOP was calculated from the model to be about 0.000 mg/L in the main zone of the bay and about 0.002 mg/L in the inner Tolo Harbour and waters adjacent to Shaotoujiao, suggesting that the autotrophic production of DOP was almost balanced by the heterotrophic removal in the main zone of the bay and dominated in the inner Tolo Harbour and waters adjacent to Shaotoujiao. In conclusion, the Mirs Bay is very productive and fairly heterotrophic.     

Seasonal settlement of shipworms (Bivalvia: Teredinidae) in Tauranga Harbour and Wellington Harbour

The seasons of settlement of shipworms in Tauranga and Wellington harbours in 1970–72 were studied using Pinus radiata test‐blocks. At Wellington the seasonal abundance of late‐stage shipworm larvae was monitored in the plankton. In Tauranga Harbour Bankia australis, Lyrodus medilobatus, Lyrodus pedicellatus, and Nototeredo edaxspawned and settled predominantly in summer, when water temperatures were above 17–18°C. Bankia neztalia had peak periods of settlement in winter and early summer and there was no correlation of settlement with water temperature. In Wellington Harbour B. neztalia spawned and settled mainly during winter when water temperatures were 11–15°C. Total larval abundance at the 2 test sites in Wellington Harbour was an approximate indication of the relative intensity of settlement, but seasonal larval abundance did not correlate well with seasonal settlement. B. neztalia larvae settled on air‐dried Pinus radiata wood within 6 days of the immersion of the wood. Annual variations in patterns of settlement of shipworms in the 2 harbours are related to variations in water temperatures.     

Diel and seasonal variability in the fish community structure of a mud‐bottom estuarine habitat in the Gulf of Mexico

We hypothesized that temporal variation in fish species composition and community structure in a low complexity habitat in the Pueblo Viejo Lagoon, Mexico, is influenced by diel light/dark cycles and tidal stage, and by seasonal changes in salinity and temperature. We collected a total of 17,661 individuals during 2‐h interval sampling over six bi‐monthly 24‐h sampling cycles representing 53 species, of which 11 (～20%) were previously unknown in the system. Diel variation indicated that significantly higher numbers of individuals and species were caught at night, whereas diversity and evenness were higher during the day. Species richness was significantly higher in July and January, whereas diversity and evenness peaked around May; both were correlated with temperature. Diel variation in species composition was influenced primarily by the light/dark cycle. Cluster analyses of each diel cycle separated fish assemblages from midday samples from those of nocturnal samples, separated by an extended wide transition period as fish moved at dawn and during the late afternoon/dusk. Significant shifts (as determined by MANOVA) in assemblage structure occurred between months. Canonical correspondence analysis showed that temperature and day/night effects were the most important environmental variables structuring the fish community. This constrained ordination also defined species with specific habitat preferences as follows: (i) diurnal, warm temperature species (mainly planktivores) (Brevoortia gunteri, Cetengraulis edentulus, Diapterus auratus, and Membras martinica); (ii) nocturnal, warm temperature species (mainly predators) (Citharichthys spilopterus, Cathorops melanopus, and Bairdiella spp.); and (iii) low temperature, diurnal species (Brevoortia patronus and Mugil curema) or those with twilight and nocturnal distributions (Anchoa mitchilli, the most numerically abundant species). Our results indicate that diel and seasonal changes in fish community structure were mainly related to day/night cycles and temperature regimes.     

The Fish Assemblage of a Newfoundland Estuary: Diel, Monthly and Annual Variation

Twice monthly sampling over two 16 month periods at a shallow site on Newfoundland's east coast showed the fish assemblage to be dominated by four taxa (Gasterosteus aculeatus, G. wheatlandi, Osmerus mordax, Gadus spp.) that accounted for 96% of the individuals collected. Of the 16 479 fish measured, 65% were adults based on the estimated size of first spawning. The fish assemblage was dominated (86%) by species with demersal eggs, several of which spawn at the same shallow sites used by juveniles as nursery sites. Coastal spawning and demersal eggs maintain offspring in coastal nursery areas where survival is thought to be increased. Number of species and number of fish were both correlated with water temperature being highest from mid-summer to early autumn and lowest in winter. Temperature, time of spawning, and movements of juveniles and adults facilitated grouping species into five assemblages based on seasonal abundance: seasonal periodic species (summer and winter), regular species, regular species collected in all seasons except winter, and occasional (rare) species. At the diel scale, two consistent species groupings were observed: species that showed no significant difference between day and night and species caught primarily at night. Number of night species exceeded day species by a factor of two. No seine-caught species in shallow water exhibited significantly higher catches during the day. Observations by SCUBA divers indicated some species were more abundant during day time at slightly deeper depths. This observation in conjunction with day and night seining in shallower water, suggests these species aggregate in deeper water during day and move to shallow waters at night.     

Common bivalve larvae from New Zealand: Leptonacea

The late stage larvae of three erycinid bivalves (Mollusca: Pelecypoda: Leptonacea) taken from the brood chamber of the adult are described (Kellia cycladiformis, Lasaea rubra hinemoa, and L. maoria), and the provisionally identified late stage larva of the erycinid Arthritica bijurca taken from the plankton is described. Also, the D‐shaped larvae of the erycinid bivalves Kellia cycladiformis, Borniola reniformis, Arlhritica crassijormis, and A. bifurca taken from the parent brood chamber are described. The seasonal occurrence of each late stage larva in the plankton at the Bay of Islands (35° 15'S, 174° 10'E), Wellington Harbour (41° 16'S, 174° 51'E), and Raumati Beach (40° 56'S, 174° 58'E), New Zealand is described. Aspects of the reproductive cycles of Lasaea rubra hinemoa and Arthritica bifurca are presented.     

Reproductive output of male seahorses,Hippocampus abdominalis,from Wellington Harbour,New Zealand: Implications for conservation

This investigation examines aspects of reproductive output in brooding wild male seahorses, Hippocampus abdominalis, from Wellington Harbour, New Zealand. Previously undocumented, such information is crucial to the management and protection of this species in relation to the CITES Appendix II‐listing of all seahorse species. Brooding males (n = 46) were captured and kept captive until the release of their juveniles, whereupon the number of juveniles was counted and sampled for standard length (SL) and dry weight (DW). SL (mean ± 1SE) of brooding males was 18.1 ± 0.6 cm and wet weight (WW) 17.6 ± 1.6 g. Number (mean ± 1SE) of juveniles released per brood was 271.2 ± 27. The number of juveniles produced was positively correlated with parent SL, WW, and brood pouch volume. Brood pouch volume was positively correlated with male SL. SL (mean ±1SE) of juveniles released was 16.7 + 0.2 mm and DW 1.2 ± 0.1 mg. Mean SL and DW of juveniles were not correlated with the number of juveniles per brood, parent male SL or parent male pouch volume. The percentage of pouch contents which were non‐viable (i.e., premature or non‐viable eggs) upon juvenile release was low (1.1 ± 0.2%; mean ±1SE of the total pouch contents). Based on findings in this study it is suggested that the CITES 10 cm minimum height restriction, which can be used in lieu of non‐detriment findings to allow sustainable exploitation of seahorses, is not suitable for H. abdominalis from Wellington Harbour as it would appear to only protect small males that produce low numbers of juveniles.     

Occurrence patterns of mesopelagic fish larvae in Sagami Bay, central Japan

The species composition, seasonal abundance, and vertical distribution of mesopelagic fish larvae are described based on discrete depth sampling from the surface down to 1000 m depth during four cruises at a fixed sampling station in Sagami Bay. The abundances of total mesopelagic fish larvae in April, July, September, and December were 65.7, 13.6, 118.9, and 17.2 individuals per 10 m² sea surface, respectively. Twenty species or types of mesopelagic fish larvae belonging to 10 families were collected. Diaphus garmani, Lipolagus ochotensis, Diogenichthys atlanticus, Sigmops gracile, and Maurolicus japonicus were the five most abundant larvae and accounted for 43.1, 14.5, 7.4, 6.3, and 5.9% of the total mesopelagic fish larvae, respectively. These five species showed clear seasonal changes in abundance, i.e. L. ochotensis, D. atlanticus, and S. gracile larvae mainly occurred during winter— spring; D. garmani and M. japonicus were collected during summer—autumn. No obvious diel vertical migration was found in these larvae. The larvae of D. garmani and M. japonicus were concentrated in the 25–50 and 50–100 m depth layers, respectively. The transforming stage of L. ochotensis, S. gracile, and D. atlanticus occurred at 400–1000 m depth, while their larvae (<8 mm standard length) occurred in the upper 100 m layer, indicating that metamorphosis of these species takes place in the 400–1000 m layer. Based on the occurrence of mesopelagic fish larvae and oceanographic processes in Sagami Bay, with the exception of D. garmani and M. japonicus, most larvae are considered to originate from the Kuroshio region where their main spawning grounds are formed.     

南海大鹏湾夜光藻种群在其生态群落中的地位和功能

分析了１９９１年上半年南海大鹏湾盐田水域夜光菏和浮游动、植物之间的种群动态关系，结果表明，在春季高峰期３月至５月初，调查海域共出现１２个夜光藻和浮游动、植物高峰。其中，以发生４次赤潮的夜光藻种群占主导地位，其次是枝角类的鸟啄尖头蚤，其最高数量高达９６２３８ｉｎｄ／ｍ＾３。相比之下，在夜光藻和枝角类岛啄尖头捕食压力的影响下，浮游植物的春季高峰并不显著。调查结果表明夜光藻的过度繁殖，不但对产浮游性卵的     

Diel changes in the abundance and size composition of invertebrate drift in five rivers in South Island,New Zealand

Drift was collected over 24‐h periods in five rivers in South Island, New Zealand, to determine whether diel periodicity was consistent across a range of river types, and whether the pattern was similar for different life stages/sizes of selected taxa. Total drift density (numbers per 100 m³ ) of aquatic invertebrates was greater at night than during the day in all rivers; peak abundance occurred shortly after sunset in clear water rivers and shortly before sunrise in a turbid, glacier‐fed river. Densities of drifting Deleatidium spp., Nesameletus spp. (both Ephemeroptera), Aoteapsyche spp., and Hydrobiosidae (both Trichoptera), were generally greater at night than during the day. However, the timing of peak abundance in the drift for other common taxa varied between rivers. Larger Deleatidium spp. larvae (> 1.00 mm head width) were more common in the drift at night than during the day in all rivers. However, this was not apparent for Aoteapsyche spp. and Hydrobiosidae, for which diel differences in the size of drifting animals were not consistent even within the same river. The propensity for some aquatic invertebrates to drift at night may influence fish feeding behaviour, particularly with respect to the timing of feeding and the species or life history stages of their prey.     

Zooplankton Feeding Ecology: Grazing by Marine Copepods and Cladocerans upon Phytoplankton and Cyanobacteria from Kingston Harbour, Jamaica

Abstract. Grazing by the copepods Temora turbinata and Acartia lilljeborgii and the marine cladoceran Penilia avirostris on natural phytoplankton and cyanobacteria assemblages from Kingston Harbour. Jamaica, was examined in summer 1992. Food assemblages were often dominated by an unidentified filamentous cyanobacterium. with abundances of up to 1.16 × 10⁴ filaments. ml^-1. Other abundant phytoplankters included microflagellates and diatoms of the genus Niteschia. Mean clearance rates for the entire food assemblage ranged from 0.10 to 2.41 ml animal^-1. h^-1, although most mean clearance rates were between 0.5 and 1.5 ml. animal^-1 h^-1. Patterns of selection of different food items by various grazers on different dates were variable and inconsistent. Microscopic measurements revealed that cyanobacterial filament lengths were shorter in grazed than initial aliquots during a cyanobacterium bloom in August. This suggests that grazers reduced lengths of many filaments by biting off portions, in addition to consuming entire filaments. Such ‘filament clipping’ of cyanobacteria filaments has been recorded previously in freshwater studies and suggests that grazers impact a larger portion of the phytoplankton assemblage than is accounted for by ingestion and clearance rates based only upon removal of filaments. Grazers exhibited no adverse effects from consuming cyanobacteria. Cyanobacterkd are often considered to be toxic or of poor food quality for planktonic grazers. but due to the high abundance and dominance of filamentous cyanobacteria in Kingston Harbour. if these cyanobacteria were ungrazed. there would at times be little alternative phytoplankton food for copepods and cladocerans. Our results suggest that the trophic role of tilamentous cyanobacteria in pelagic food webs of the tropical ocean should be further investigated and possibly reconsidered.     

Spatial, temporal and diel variations of fish assemblages at two sandy beaches in the Sepetiba Bay, Rio de Janeiro, Brazil

Fish assemblages from two beaches, one in the inner and the other in the outer Sepetiba Bay (latitude: 22°54′–23°04′S; longitude: 43°34′–44°10′W), Southeast Brazil, were sampled by beach seine net, simultaneously, on both seasonal and diel scales, between August 1998 and June 1999. Sites were selected to encompass different environmental conditions which reflect the two bay zones, thus providing a comprehensive assessment of the factors influencing surf zone fish assemblages, and their spatial, seasonal and diel variations. A total of 55 fish species was recorded, mostly young-of-the-year. Anchoa tricolor, Micropogonias furnieri, Gerres aprion, Diapterus rhombeus, Harengula clupeola, Atherinella brasiliensis and Mugil liza were numerically dominant and contributed to 95.2% of the total fish catches. Strong differences in fish assemblages were observed between the two areas, with higher number of species in the outer bay. Increases in fish numbers occurred in winter, while the highest biomass occurred in winter and summer. Transparency, followed by salinity, was responsible for most of the spatial variability and played an important role in structuring fish assemblages. Overall, diel patterns did not reveal any significant trends; however, if we consider each season separately, an increase in fish numbers during the day with peak at sunset was observed in winter, and a higher biomass occurred at night in winter and summer. Species preferences for various combinations of environmental variables are responsible for shifts in the structure and overall abundance of assemblages and dictated some patterns. The sciaenid M. furnieri, the second most abundant species, occurred only in the inner zone, being more abundant in winter. The species of Engraulidae were more abundant in the outer zone in winter/spring during the day. The gerreids G. aprion and D. rhombeus occurred mainly in summer. Overall, temporal fluctuations act more at a specific level than at a structural one, and may be linked to some particular stages of the fish life cycle, but do not significantly influence the spatial organization.