Structural aspects of the surf-zone fish assemblage at King's Beach,Algoa Bay,South Africa: Long-term fluctuations

Regular collections of fish were obtained from the surf-zone at King's Beach, Algoa Bay. A total of 3970 fish, representing 50 species was caught with a coarse net and 16 857 fish, representing 37 species, were caught with a fine net. Predominant species were the blacktail, Diplodus sargus; the sand steenbras, Lithognathus mormyrus; the mullet, Liza richardsoni; the gorrie, Pomadasys olivaceum; the white stumpnose, Rhabdosargus globiceps; the sandshark, Rhinobatos annulatus; and the streepie, Sarpa salpa. No seasonal trends were discernible in the overall abundance or species diversity. The species composition of the dominant component of the fish assemblage varied considerably. This indicated instability in the community structure and cast doubts on the applicability of a classic community concept and the use of diversity indices. Neither classification nor correspondence analysis were of any use in identifying a characteristic species component. Multiple regression analysis indicated that short-term variations in wind conditions might be a primary determinant of fluctuations in abundance. The lack of seasonality in the community parameters may reflect the fact that short-term variability masks seasonal perturbations.     

Influences of diel and tidal cycles on fish assemblage in eelgrass (Zostera marina) bed of southern Korea during autumn

Short-term tidal and diel variations of autumn fish assemblage in a Zostera marina bed were investigated using 3 h interval samplings for 24 h in both spring and neap tide using a small beam trawl. A total of 1 346 fishes belonging to 19 species were collected at spring tide, whereas 1 115 fishes belonging to 17 species were at neap tide. The common fish species were Nuchequula nuchalis, Acanthogobius flavimanus, Takifugu niphobles, Acentrogobius pflaumii, and Pholis nebulosa with the former three species dominating at spring tide, while the latter two species being abundant at neap tide. Diel variation in abundance was significant with higher abundance at night than day, but there were no significant differences between spring and neap tides, and between ebb and flood tides (three-way ANOVAs). Diel variation in the abundance of fishes may be influenced by tidal range and cycle, and day-night differences of food availability and behaviors of fishes indirectly. Non-metric multidimensional scaling (nMDS) ordination and analysis of similarity (ANOSIM) results revealed significant differences in species compositions both between day and night, and between spring and neap tide. Eelgrass beds are highly productive marine ecosystem, and thus, our results will contribute to conservation of seagrass ecosystem in the study area.     

Implication of salt marsh foraminiferal assemblages in Suncheon Bay,South Korea

Analyses of the compositions of benthic foraminifera and sediment, observations of tidal level and salinity, and a geographic survey of the tidal salt marsh in Suncheon Bay were conducted to examine the vertical distribution of foraminifera and evaluate their potential use for sea level studies. The salt marsh is composed mainly of fine-grained silty clay sediment and its salinity is below approximately 11 psu. The tidal current flows in the southwest-tonortheast direction with an average velocity of 26.57 cm/s. A total of 33 species of foraminifera (17 agglutinated and 16 calcareoushyaline) belonging to 24 genera was identified. The species diversity (1.1 on average) was relatively low. Dominant species were Ammonia beccarii, Miliammina fusca, Haplophragmoides wilberti, and Jadammina macrescens. Calcareous foraminifera (29.5%) were dominantly represented by the Ammonia beccarii assemblage, which characterized the region between mean tide level and mean low high water (MLHW). Agglutinated species (70.5%) were represented mostly by Miliammina fusca, Miliammina fusca-Haplophragmoides wilberti, and Haplophragmoides wilberti assemblages, which characterized the MLHW–mean high water (MHW), MHW–mean highest high water (MHHW), and MHHW–Approx. highest high water tide levels, respectively. In particular, the Haplophragmoides wilberti assemblage is believed to represent the highest elevation zone of foraminifera in the salt marshes of Suncheon Bay and is considered to be a reliable indicator of sea level as a result of its narrow vertical range.     

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.     

Species composition and dietary relationships in a brackish shallow water fish assemblage in the Bothnian Sea,Sweden

A nearshore fish assemblage inhabiting a shallow bay in the southern Bothnian Sea, Sweden, with demanding environmental conditions (c. 5‰; >15°C during 4 months 1980 and 1 month 1981) was studied during a two-year period, in 1980 and 1981. Seasonal distribution patterns, dietary relationships, and growth rates were studied in Pungitius pungitius (L.), Pomatoschistus minutus (Pallas.), Gasterosteus aculeatus (L.), Phoxinus phoxinus (L.), Pomatoschistus microps (Krøyer) and Gobius niger L. The structure of the juvenile populations changed both over seasons and years but the adult populations remained constant. Lower water temperature, fewer individuals, lower and delayed fish growth, and lower interspecific food overlaps were found in 1981 compared to 1980. Few significant correlations were found in both years between the following community parameters: diversity, niche width, food overlap, and the proportion of each species in the fish assemblage.According to these results it is suggested that food competition and resource partitioning were of minor importance for the structuring of the fish community in the present area. Rather, the extreme salinity and the fluctuations in temperature regulated the fish populations. One may conclude that the populations of juveniles were more influenced by short-term changes in the environment than those of the adults.     

Tidal,diel and semi-lunar changes in the faunal assemblage of an intertidal salt marsh creek

The utilisation of a brackish estuarine marsh by nekton was investigated over a semi-lunar cycle in August 1994. Nekton migrating in and out of the intertidal creeks of the marsh ‘Het Verdronken Land van Saeftinghe’ in the Westerschelde estuary, SW Netherlands, was sampled passively during seven complete tidal cycles. Sampling one tidal cycle yielded three consecutive flood samples and four consecutive ebb samples. Sampling occurred every 2–3 days, covering diel, tidal and semi-lunar situations, thus allowing comparison of tidal, diel and semi-lunar influences on the composition of the intertidal fauna.Two different tidal-migration modes were observed. The mysid shrimp, Mesopodopsis slabberi, showed maximum abundance around high tide. For the remaining common species, the mysid (Neomysis integer), the shrimp (Palaemonetes varians), the crab (Carcinus maenas) and the goby (Pomatoschistus microps) and the amphipod (Corophium volutator), highest densities were recorded during lower water heights. The faunal assemblage shifts between the different tidal stages.On two occasions, consecutive day and night samples were taken. Total densities were higher during the night samples. During spring tide, difference in community composition was noticed between the night and the day samples. During neap tide, day–night differences were less clear. Recorded total densities were highest during spring tide and lowest during neap tide. At maximum water levels, a drop in total density was observed. A shift in community composition occurred between spring and neap tides.     

Larval fish distribution in shallow coastal waters off North Western Iberia (NE Atlantic)

Monthly sampling for ichthyoplankton was conducted at three stations very near to the coast (near to shore shallow stations before the surf zone in direction to the shoreline) of Atlantic northwestern Portugal within contrasting localities: rocky shore, in front of a sandy beach receiving an estuary and a fishing port with heavy anthropogenic impact. Sampling was conducted from August 2002 to October 2003, always at full moon, at low tide and high tide in daylight hours, at the water column using a 48 cm diameter plankton net with 335 μm mesh. Analysis of the physico-chemical parameters pointed out the spatial (horizontal) homogeneity of the sampling area. Fish larvae from 41 taxa belonging to 17 families were identified; Blenniidae, Labridae, Ammodytidae, Clupeidae, Gobiidae, Soleidae and Gobiesocidae were the most representative during the study period. Parablennius gattorugine, Ammodytes tobianus, Symphodus melops, Sardina pilchardus, Lipophrys pholis and Coryphoblennius galerita were the most representative species (percentage contribution to total abundance). Peak abundance of fish eggs occurred during May, June and August 2003 and fish larvae occurred during May and July 2003 and August 2002 and 2003; there was a pronounced winter/early spring (March 2003) peak in larval abundance dominated by the small sandeel A. tobianus. This study identifies the occurrence of a conspicuous assemblage of larval fishes at very nearshore shallow environments of a variety of species with different adult habitats: the fish larvae assemblage was dominated by intertidal species. The present study has shown that temporal and spatial variations in the larval fish assemblage are related to environmental conditions and biological dynamics: the results suggest that abiotic conditions mediate biotic parameters, and that both abiotic and biotic characteristics regulated the larval fishes at very nearshore shallow environments.     

Seasonal changes in community composition and trophic structure of fish populations of five salt marshes along the Essex coastline, United Kingdom

European intertidal salt marshes are important nursery sites for juvenile fish and crustaceans. Due to the increasing threat of habitat loss, the seasonal changes of salt marsh fish communities need to be understood in order to appreciate the ecological and economic importance of the saltmarsh habitat. This study was the first in Great Britain to investigate the seasonal changes of salt marsh fish communities and the variation in community structure between closely located marsh habitats. Between February 2007 and March 2008, five marshes on three estuaries of the Essex coastline were sampled using flume nets to block off intertidal creeks at high tide. Fourteen fish species were caught. The community overall was dominated by three species that made up 91.6% of the total catch: the common goby Pomatoschistus microps (46.2% of the total catch), juvenile herring Clupea harengus (24.3%), and juvenile and larval sea bass Dicentrarchus labrax (21.2%). Cluster analysis demonstrated clear seasonal patterns, with some community structures unique to specific marshes or estuaries. The marsh fish community shifts from a highly diverse community during spring, to a community dominated by D. labrax and P. microps in autumn, and low diversity during winter months. Gravimetric stomach content analysis of fish community identified three main trophic guilds; macroinvertivores, planktivores and omnivores. The macroinvertivore feeding guild contained D. labrax and P. microps, the two most frequently occurring species. This investigation demonstrates the importance of British salt marshes as nursery habitats for commercial fish species.     

Fish assemblage structure of Koycegiz Lagoon–Estuary, Turkey: Spatial and temporal distribution patterns in relation to environmental variation

Spatial and temporal variation in fish assemblage structure of Koycegiz Lagoon–Estuarine System (KLES), located on the northwestern Turkish coast of Mediterranean, was investigated along an estuarine gradient where salinity ranged from 5 in upper reaches to 40 in lower reaches during October 1993–September 1994. Throughout the study, 42 species, consisting of marine (25), marine–estuarine-dependent (12), freshwater (3), catadromous (1), and estuarine resident (1) forms, were collected in trammel nets. Although species richness of marine species was greater than that of other groups, numerical contribution by marine species to the total catch was only 16%. Tilapia spp., the most abundant species mostly during summer and early spring at upper reaches, contributed 17% of the total samples. Among the seven species of Mugilidae, which contributed 42% of the total catch, Mugil cephalus, Liza aurata, and Liza salines contributed 10, 13, and 10% of the total catch, respectively. Consistent with findings from other studies, species richness and abundance were highest during late spring and summer and the lowest during winter and early spring. Samples from sites at or near the sea had more marine species. Samples from upper reaches had more freshwater and marine–estuarine-dependent species. Canonical correspondence analysis (CCA) indicated that salinity and turbidity were the most important environmental parameters affecting fishes. Sites near the sea were associated with high salinity and low turbidity, and sites in upper reaches had low salinity and high turbidity. Thus, the pattern observed in fish assemblage structure appears to be strongly influenced by species' responses to dominant salinity and turbidity gradients.     

Amphipod-supported food web: Themisto gaudichaudii, a key food resource for fishes in the southern Patagonian Shelf

The trophic role of the hyperiid amphipod Themisto gaudichaudii in the southern Patagonian shelf food web was assessed from the analysis of stomach contents of the local fish assemblage. A total of 461 trawl samples were collected during seven seasonal cruises. A total of 17 out of 38 fish species were found to ingest T. gaudichaudii. This amphipod was a main prey item in five of these species, showing high values of alimentary index: Seriolella porosa (99.9%), Macruronus magellanicus (68.8%), Micromesistius australis (59.1%), Patagonotothen ramsayi (48.6%), and Merluccius hubbsi (10.9%). The contribution of T. gaudichaudii, in weight, to their summer diet was 60%, on average. This contribution was minimal in winter and maximal in summer. Fisheries studies have indicated that these five species, mainly M. magellanicus, account for almost 85% of the fish biomass in the area. Although the remaining 15% did not feed heavily on T. gaudichaudii, they are known to prey on the main hyperiid predators. Our study shows that T. gaudichaudii contributes greatly, both directly and indirectly, to supporting the fish community. We thus proposed that T. gaudichaudii plays a key role as a “wasp-waist” species in the sub-Antarctic region, similar to that of krill in Antarctic waters, channeling the energy flow and enabling a short and efficient food chain.     

Food utilisation by coastal fish assemblages in rocky and soft bottoms on the Swedish west coast: Inference for identification of essential fish habitats

The concept of essential fish habitats (EFHs) is widely accepted for conservational and management purposes. EFHs are often considered as high quality habitats for fisheries species and subsequently of high values for society. In this study, fish and Substrate-Associated Prey (SAP) were sampled during the productive summer season 1998 (fish) and 2003 and 2004 (SAP) in shallow coastal rocky- and soft-bottom habitats on the Swedish west coast. The aim was to study the spatial and monthly variation of SAP as well as abundance and biomass of fish, and to examine if food items found in the diet of the fish assemblage were derived from SAP. We also examined if the diet of Ctenolabrus rupestris, a resident and abundant fish species in the shallow coastal habitats, and the diet of four seasonally abundant and commercially important fish species (Gadus morhua, Pleuronectes platessa, Salmo trutta and Scomber scombrus) were derived from SAP. There were significantly higher mean species number and abundance of the SAP assemblage on rocky compared to soft bottoms and the highest values were found on the rocky bottoms in August and in the shallowest (0–3 m) depth strata. There were no significant differences in number of fish species caught in the two habitats, although mean number of fish and mean biomass were significantly higher on rocky bottoms. Both habitats showed the same seasonal variation and the highest values of number of fish species, abundance and biomass were observed in June. On rocky bottoms, gastropods and amphipods were the most frequent food items in the diet of the entire fish assemblage and these items were also the most abundant SAP in this habitat. The dominant food items of the soft-bottom fish assemblage were decapods and fish, which were not common SAP. However, except for S. scombrus, the diet of the selected fish species showed a strong association to the SAP availability. Gadus morhua displayed the strongest association to SAP on rocky bottoms and P. platessa and C. rupestris to SAP on soft bottoms. Further, for C. rupestris, multivariate statistical analysis showed a significant association to the SAP assemblage on both rocky and soft bottoms. These results provide vital new information for the management and conservation of Essential Fish Habitats on the Swedish west coast.     

Influence of summer conditions on the larval fish assemblage in the eastern coast of Tunisia (Ionian Sea,Southern Mediterranean)

The structure of the summer larval fish assemblage off the eastern coast of Tunisia and its relation to environmental conditions was studied, from ichthyoplankton samples taken during a survey conducted between 23rd June and 9th July 2008. A total of 68 larval fish taxa were identified, 52 to species level. The taxonomic composition and abundance of the larval fish assemblage showed high spatial heterogeneity. Mesoscale hydrographic features, such as eddies, seem to play an important role in the spatial distribution of fish larvae in the area, enhancing concentration and retention. The larval fish assemblage was dominated by the small pelagic species Sardinella aurita (26.6% of the total larval fish abundance), followed by Engraulis encrasicolus (22.6%), Spicara spp. (8.6%) and Mullus barbatus (6.8%). Shannon–Weaver index (H′) ranged between 0 and 2.62. The highest values were found offshore, at 95 miles east of Sousse, over depths around 250 m. The diversity was higher in this region as a result of transport by currents and retention by eddies. It has also been shown that the eastern coast of Tunisia is a spawning ground for the tuna species Auxis rochei, Thunnus thynnus and Thunnus alalunga. Larvae of mesopelagic fishes represented 5.46% of the total abundance, with Cyclothone braueri, Ceratoscopelus maderensis and Lampanyctus crocodilus being the most important species. Canonical correspondence analysis (CCA) indicated that depth was the most important environmental factor in explaining species distribution.     

Physical factors influencing immature-fish communities in the surf zones of sandy beaches in northwestern Kyushu Island,Japan

We aim to understand the relationships between physical conditions and characteristics of the immature-fish community in surf zones of sandy beaches. Therefore, we obtained fish samples between March 2007 and February 2008 and analyzed certain physical conditions in the surf zones of 21 sandy beaches on the coastline of the northwestern Kyushu Island, Japan. We collected a total of 83 species and 6458 immature individuals. In a BIO-ENV analysis, the highest correlation was observed between fish assemblage and S20 (i.e., the slope from the shoreline to the sites where the depth was 20 m) and current velocity (CV) values. Stepwise multiple linear regression analyses revealed that the number of species and individuals decrease with an increase in the S20 and CV values. These results show that species richness and the abundance of immature-fish increase under shelving and calm conditions. Thus, immature-fish assemblages are strongly influenced by the prevailing physical conditions. Moreover, in six of the 10 dominant species, a negative correlation was observed between CV and abundance. On the other hand, S20 was found to be the explanatory variable only in the case of the most dominant species, i.e., Gymnogobius breunigii. Furthermore, a positive correlation was observed between S1 (i.e., the slope from the shoreline to the sites where the depth was 1.0 m at the mean tidal level) and median particle size (i.e., MPS of the sediments) and the abundances of Sillago japonica and Favonigobius gymnauchen, respectively, and a negative correlation with salinity, in the case of Acanthogobius lactipes. We conclude that the characteristics of the fish community in surf zones on sandy beaches are determined by not only the shelving and calm conditions, which influence fish assemblages and abundances, but also the habitat diversity, which influences the diversity of fish species.     

Spatio‐temporal dynamics of the surf‐zone faunal assemblages at a Southern Oregon sandy beach

Sandy beach/surf‐zone ecosystems are unique environments that, despite the harsh and highly variable hydrodynamic conditions, present a diverse and heterogeneous fauna. However, the dynamics of these ecosystems are currently poorly understood. In this study we tested the hypothesis that surf‐zone assemblages vary with temporal factors such as time of day, tide and tidal height. To test this hypothesis, the surf‐zone community of Bastendorff, a Southern Oregon sandy beach was sampled during the summer of 2006. Samples were collected to (i) describe the smaller, benthic and larger swimming assemblages, (ii) determine whether assemblage compositions, densities, species richness and diversity vary with time of day, tide and tidal height, (iii) explore potential reasons for the variation by correlating environmental factors to the assemblages, and (iv) identify particular species that most strongly exhibit these variations. A hyperbenthic sledge, a sediment corer and a beach seine were used to collect the smaller swimming, benthic and larger swimming fauna, respectively. Sampling occurred during day and night, spring and neap tide, and high, mid and low tide. A total of 76,743 individuals belonging to 105 species were collected. Ninety‐one invertebrate (72,904 individuals), 15 invertebrates (2234 individuals), and 19 invertebrate and vertebrate species (1605 individuals) were collected with the sledge, corer and seine, respectively. Nine species of fish were caught, 98% of which were juveniles. The smaller and larger swimming assemblages varied most strongly with the time of day, suggesting certain species will actively move to the shallow surf‐zone at night. The three assemblages also varied with the tide, potentially due to the larger waves and higher abundance of detached macrophytes observed during spring tides when compared to neap tides, which could push individuals into the surf zone. The benthic assemblage most strongly varied with tidal height and sand grain size, confirming the presence of different faunal zones within Oregon sandy beaches. Finally, several variables of the swimming assemblages varied with temperature and salinity, suggesting that downwelling favorable conditions may have transported species close to shore. Bastendorff presents a complex and diverse surf‐zone community that appears to be influenced by diel species movements, environmental variables such as wave height and abundance of detached macrophytes, and regional oceanographic conditions.     

Spatial variability of epifaunal communities from artificial habitat: Shipwrecks in the Southern Bight of the North Sea

We investigated the cover, community structure and abiotic environment of nine shipwrecks lying at increasing distance from the Belgian coast. Results indicated that all shipwrecks were strongly dominated by cnidarians in terms of biomass and by amphipods in terms of abundances. Based on their epifaunal composition, three groups of shipwrecks could be determined. Metridium senile dominated a species poor community of the coastal sites. On the same sites, a Tubularia larynx community with a more species-rich assemblage was also developing. The T. larynx community had a lower biomass value (102 g AFDW m⁻²) and significantly lower species richness compared to the other sites. The coastal sites were characterized by periodic salinity decreases, large seasonal temperature fluctuation, high total suspended matter load and reduced current velocity. Channel water masses influence the offshore sites causing a more stable temperature and salinity environment, less turbid waters and high current speed. Tubularia indivisa dominated this community, with an average biomass of 229 g AFDW m⁻². Intermediate sites were also dominated by T. indivisa, but a higher biomass (424 g AFDW m⁻²) was observed. They showed intermediate results for the abiotic parameters and fast current velocities. Hypotheses for the observed variation in community structures are discussed in the light of the abiotic characterization of the shipwrecks.     

Fish faunal and habitat analyses using trawls,camera sleds and submersibles in benthic deep-sea habitats off central California

Beam trawl, camera sled and submersible data from 2 000–3 300 m off central California produced similar fish faunal composition, but different density estimates. All species caught in trawls were observed in camera-sled and submersible observations. However, some rare species that were observed were not caught in trawls. The fish fauna was dominated by the families Macrouridae, Zoarcidae, Moridae, and Rajidae. Fishes both trawled and observed were the macrourids Coryphaenoides armatus, C. filifer and C. leptolepis; the zoarcids Bothrocara spp., Pachycara lepinium and Lycenchelys spp.; the morid Antimora microlepis; the rajid Bathyraja trachura, the ophidiid Spectrunculus grandis, and the liparidid Careproctus ovigerum. One unidentified liparidid (Paraliparis sp.) and two unidentified Lycenchelys spp. were trawled and may have been seen but also could not be identified to species from photographs. Observed only in photographs were the liparidids Paraliparis rosaceus and Careproctus melanurus, synodontid Bathysaurus mollis, and notocanthid Notacanthus chemnitzii. These three techniques differed in their ability to provide specimens for accurate identification, counts, and later life history (feeding habit, age and growth, and reproduction) studies, and to provide information on dispersion, habitat utilization, behavior and interactions. Accurate density estimates were undoubtedly hampered by trawl and camera sled avoidance, escape, and uncertainties concerning the area trawled. Camera sleds produced higher (and perhaps better) estimates of density. Submersible observations from the DSV Alvin produced a similar species list but little additional, quantitative information. Both visual techniques allowed habitat characterization, but no strong faunal associations with habitat types were observed.     

Diel Fluctuations of a Shallow Water Fish Community in the Inner Oslofjord, Norway

Abstract. A shallow water fish community in the inner Oslofjord, Norway, was sampled with a beach seine at 4h intervals over two 36 h periods (25-26th May and 28-29th September, 1982). Night length varied from 1 h in May to 11 h in September. Differences in the community composition were observed between May and September. The diversity of the fish community changed between the two months although the interpretation of the change was dependent on the method used to analyse the community. The three dominant species ( Gasterosteus aculeatus, Sprattus sprattus , and Ammodytes tobianus ) showed diel variations in catch rate which were out of phase with each other. The percentage overlap in abundance of the dominant species was low. The summation of the individual periodicities resulted in aperiodicity at the community level. There were fluctuations, over a diel cycle, in all the community parameters (number of individuals, number of species, species diversity [H'J, species richness [D] and evenness [J']) which affect measures of resource partitioning in fish communities and which should therefore be considered in ecological studies. Diel fluctuations in abundance of some individual shallow water species varied between seasons causing problems in population estimates.     

Short-term variation in copepod community and physical environment in the waters adjacent to the Kuroshio Current

A continuous survey examined short-term variations in the zooplankton community and physical ocean environment from the northeastern Izu Islands to Boso Peninsula in Japan. High copepod abundance and small upwellings in the surface layer and salinity minimum layer in the subsurface were observed on the north side of coastal fronts in the westernmost transect, moving southward as the Kuroshio Current left the Boso Peninsula. Thus, the salinity minimum layer might be a key factor forming upwelling and the fronts, leading to large abundance of coastal copepods off the northeastern Izu Islands. A community structure analysis of calanoid copepods revealed an intermediate belt assemblage between coastal and offshore (Kuroshio) assemblages. Copepod abundance was remarkably low and Ctenocalanus vanus dominated (nearly 37%) in the intermediate belt zone, indicating that C. vanus has a relatively high tolerance to adverse environments for calanoid copepods. As the Kuroshio Current left the Boso Peninsula, the coastal assemblage expanded in the same direction, and the intermediate belt assemblage off the northeastern Izu Islands disappeared. The largest population of Calanus sinicus was found along the two western transects off the northeastern Izu Islands (>1000 m depth), which was assumed to be transported from Sagami Bay and advanced southwestward while growing from copepodite stages CIII to CV. Larvae of C. sinicus would be an important food for fish larvae in addition to Paracalanus parvus s.l., the numerically dominant species in the coastal assemblage, and C. vanus under the adverse conditions for coastal copepods.     

Estuarine production of resident and nursery fish species: Conditioning by drought events?

The production of resident (Pomatoschistus minutus and Pomatoschistus microps) and marine juvenile fish species using the Mondego estuary (central Portugal) as nursery grounds (Dicentrarchus labrax, Platichthys flesus, Solea solea), was assessed in order to: (1) understand the potential of the estuary for fish production; (2) know the production of nursery fish species likely to be exported to the coastal stocks; and (3) how anthropogenic and natural stress could influence the estimated production. Sampling occurred from June 2003 to May 2006 and together the 5 species in study comprised around 70% of the whole fish community numbers and biomass. Increasing drought conditions were observed, starting with a normal hydrological year in 2003 until attaining a severe drought in 2005, which resulted in low river discharges (1/3 of the mean river discharges in 2003). Additionally, high water temperatures were observed in 2003 and 2005 (24 and 26 °C, night temperatures). The secondary production was estimated using the increment summation method, after recognition of the cohorts. Production was in general lower in the Mondego estuary when compared to other systems, which was associated to the estuary's small area (only 3.4 km², less than 1/4 of area compared to other studied systems). Dicentrarchus labrax was among the most productive species. Production decreased in the drought year for all species, especially evident for D. labrax, P. minutus and P. flesus. No direct effects could be attributable to the salinity and temperature variations and to the low freshwater discharges (resulting from the drought and high temperatures), yet these were pointed as probable major reasons for the decreased production. A significant reduction (15–45% reduction in the estuarine production) was also concluded for the potential production to be exported for coastal areas by the nursery species in the drought conditions.