Patterns of selective predation by juvenile,benthivorous fish on estuarine macrofauna

Benthic feeding on macrofauna was studied in juveniles of the sparids Lithognathus lithognathus and Rhabdosargus holubi in the upper reaches of the Gamtoos Estuary, South Africa. Fish and benthic macrofauna were sampled simultaneously, and the selection of invertebrate prey assessed. Both fish species strongly selected for corophioid amphipods and consumed other benthic taxa in low numbers. R. holubi also exploited aquatic autotrophs, while L. lithognathus had a narrow prey-spectrum, feeding almost exclusively on the tube-dwelling amphipod Grandidierella lignorum. G. lignorum was the most abundant prey species, both in the benthos and the fish's diet. This species also showed prominent behavioural differences between the sexes; males were markedly more active on the sediment surface than females, who rarely left their tubes during the day. Males switched from an infaunal to epifaunal microhabitat in search of receptive females, concurrently increasing their exposure to fish predators. Consequently, L. lithognathus selected significantly more males than female amphipods, causing a marked bias towards females in the sex ratio and age-structure of the amphipod population. Juvenile amphipods were less preyed upon, presumably as a result of lower prey-detection or capture efficiency by the predators. Accepting current notions about predation as an important structuring element for benthic communities, our data also stress the prominence of size-and sex-selective predation in structuring individual prey populations.     

Scavenging abyssal amphipods from the North-East Atlantic ocean

A baited trap set on the bottom (4855 m) in the eastern North Atlantic Ocean caught over 600 specimens belonging to 7 species of lysianassid amphipods. Photographic evidence showed a slow build up of numbers and demonstrated fluctuations apparently related to current and pressure changes and to the presence of fish. Length-frequency distributions for the more abundant species reveal size classes related to growth stages. Paralicella caperesca produces a single brood of about 90 eggs. Maturity in this species may be attained in 7 to 11 moults, the precise number possibly being determined by food availability. Orchomene gerulicorbis requires about 11 moults to reach maturity, and females are double-brooded. Mortality within the trap is discussed. A comparison of species of Paralicella and Orchomene based on morphological, developmental, reproductive and ecological characters indicates that the former genus are specialized necrophages whereas the latter are opportunist generalists. The abundance and mobility of necrophagous amphipods indicate that they play a very significant role in the trophic web.     

Effect of tidal submersion on lysozyme activity in Mytilus edulis and Tellina tenuis

Changes in mean style weight and in lysozyme activity of the style, digestive gland, gill and mantle of Mytilus edulis and Tellina tenuis from the Clyde Sea area, Scotland, were investigated over tidal cycles in March and August, 1981. For M. edulis, significant changes occurred in the style weight, style lysozyme activity and digestive gland lysozyme activity during a 22 h period. These appear to be related to a diurnal cycle rather than a tidal cycle. Changes in the weight of the style of M. edulis may be caused by dissolution during feeding, and style lysozyme may be secreted independently of the style matrix. The activity of lysozyme in T. tenuis is unaffected by the tide, suggesting that this intertidal bivalve can feed throughout the tidal cycle.     

The occurrence of marine Cladocera on the west coast of Sweden

The present paper is based on a 3-year field study of marine Cladocera in the waters off Gothenburg on the Swedish west coast. The group mainly occurred from May to September, when there was a temperature stratification of the waters. The dominant species, Evadne nordmanni Lovén, may occur in large numbers during the entire warm period, both in offshore and inshore waters. The species Podon leuckarti G.O. Sars, P. intermedius Lilljeborg, and Pleopis (=Podon) polyphemoides (Leuckart) occurred separately both in time and space. The occurrence of different species may primarily be regulated by abiotic factors, e.g. temperature and currents, but may also be modified by competition for food between closely related species. During the early summer, the populations of E. nordmanni and Podon leuckarti seem to be comprised of specimens brought in by the sea, while the estuarine species Pleopis polyphemoides seems to be more indigenous within the area.     

Spatio-temporal variations in the diet and stable isotope composition of the Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 of the continental shelf of southeastern Brazil

The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m). The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio. δ¹⁵N and δ¹³C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7 for M. hubbsi was estimated using δ¹⁵N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels.     

Dispersal mechanisms in amphipods: a case study of <Emphasis Type="Italic">Jassa herdmani</Emphasis> (Crustacea,Amphipoda) in the North Sea

Jassa herdmani (Walker 1893), a tube-building amphipod typical of hard substrates, was found in large densities on shipwrecks from the Belgian part of the North Sea, in association with the hydrozoan Tubularia indivisa. In this area, shipwrecks only represent the source of hard substrates in an environment dominated by soft sediments. Nevertheless, the long-distance dispersal of Jassa species has never been investigated. Therefore, we tested the hypothesis of dispersal with currents, by investigating the behaviour of J. herdmani in the laboratory. Size distribution revealed that newly released juveniles (<1 mm) predominated throughout the year and the lower frequency of the size class 1–3 mm indicates a high mortality or a dispersal at this life stage. Individuals of J. herdmani may initiate actively the transport by tidal or surface currents by swimming to the surface of the water or by floating at the surface, as suggested by behaviours noted in the laboratory. The reaction of the amphipods to a current was investigated in the laboratory. We could not detect any sexual function associated with drifting and there was also no preponderance of a size class in the drifting individuals. When testing different substrates, we observed a significant influence of the substrate type on the frequency at which drifting occurred: J. herdmani showed a better adherence on T. indivisa compared to other substrates. Finally, the amphipod showed also a preference for its host compared to other substrates, which suggests a possible detection mechanism.     

Diurnal and lunar patterns of larval recruitment of Brachyura into a mangrove estuary system in Ranong Province, Thailand

The present study followed the temporal recruitment pattern of brachyuran larvae in a mangrove tidal creek on the Andaman Sea coast of Ranong Province, Thailand, based on the assumption that the processes governing recruitment are important for the overall population dynamics of mangrove brachyuran crabs. Plankton net samples were taken on five occasions: on two new moon spring tides, one waxing moon neap tide, one full moon spring tide and one waning moon neap tide during October and November 1997. In addition collectors for larval crab megalopae were employed every 3 days through one dry season and one wet season (March–October 1998). Both the plankton net samples and collector samples revealed four major brachyuran groups in three families: Ocypodidae, Grapsidae and Portunidae. The grapsid group was further separated into two morphotypes which were identified as Metaplax and sesarmid species. Identified group mean numbers per cubic metre were ocypodids 3.0, sesarmids 0.8 and Metaplax 0.5, while portunid megalopae were very scarce (≪0.1 m⁻³). Further analysis of plankton net samples showed that when considering the parameters date, depth, current direction and the diel cycle, Metaplax and ocypodids distribute differently in the tidal and lunar cycle. Metaplax recruitment dominates on flood tides and on bottom layers, followed by middle and surface layers. Conversely, ocypodid abundance varied significantly with date only. Notably recruitment was not dependent on the diel cycle for either group. The collector samples of megalopae showed that recruitment of ocypodids, Metaplax and sesarmids occurred on full and new moon spring tides, while portunid megalopae preferred to settle on full moon spring tides. Since tidal currents were related to the lunar cycle megalopa groups are also cross-correlated with tidal amplitude, except for the portunid group. It is concluded that megalopae recruit in a similar manner to what has been found in other regions of the world, except that the abundance of ocypodids and Metaplax is not influenced by the diel cycle. Received: 14 February 2000 / Accepted: 24 November 2000     

Seasonal and spatial differences in the fish assemblage of the non-estuarine Sulaibikhat Bay,Kuwait

In the period September 1986 to August 1987 fish were captured once a month, using an otter trawl, from the intertidal and subtidal regions of Sulaibikhat Bay, Kuwait. Correlation analysis revealed that numbers were not directly related to temperature at the time of sampling. The recruitment of large numbers of young of the year Liza carinata (Valenciennes) during March was related to low temperatures in November, the probable time of spawning of this species. Salinity at the time of sampling was inversely correlated with numbers. This result indicates that large numbers of 0+fish recruit to the Bay during the period of maximum fresh water outflow through the Shatt-al-Arab. Numbers of fish were significantly greater in the intertidal region, where they were present almost entirely as 0 group fish, than in the subtidal. The three dominant species of the assemblage are shown to use the two depth intervals in differnt ways. L. carinata was capture a almost exclusively in the intertidal region as 0+ fish. Pomadasys stridens (Forsskål) was captured as 0+ fish in both the intertidal and subtidal regions but in greater numbers in the intertidal region. Leiognathus brevirostris (Valenciennes) was captured as small, mostly 0+ individuals in the intertidal region and as larger fish in the subtidal region. The use made by the smaller fish of the intertidal region is related to the avoidance of sublittoral predators and reduction of intraspecific competition, whilst larger fish in the sublittoral region may be avoiding predation by piscivorous birds.     

Feeding ecology of juvenile rockfishes off Oregon and Washington based on stomach content and stable isotope analyses

The feeding habits of pelagic, juvenile rockfishes (Sebastes spp.) collected off Oregon in 2002, and Oregon and Washington in 2006, were examined using stomach content and stable isotope analyses. Sampling occurred along a series of transects across the shelf between Crescent City, California (Lat. 41°54.0′), and Newport, Oregon (Lat. 44°39.0′), in 2002, and off Willapa Bay, Washington (Lat. 46°40.0′), and the Columbia River, Oregon (Lat. 46°10.0′), in 2006. Species composition varied both years with distance from shore, but the predominant species were darkblotched (Sebastes crameri), canary (S. pinniger), yellowtail (2006 only; S. flavidus), and widow (S. entomelas) rockfishes. Stomach content analysis revealed that darkblotched rockfish had highly variable diets, and canary, yellowtail, and widow rockfishes exhibited a high degree of overlap in 2006. Multivariate analysis showed significant differences in diet based on distance from shore where caught, fish size, and species. Stable isotope analysis indicated that all species were feeding at about the same trophic level within each year, with a 1.5 ‰ difference in δ¹⁵N between years and regions. The difference in δ¹⁵N values may indicate a greater contribution of mesotrophic zooplankton such as euphausiids, hyperiid amphipods, and chaetognaths to fish diets in 2006. Depleted ¹³C values were indicative of diets based on primary production from a more offshore origin, suggesting that these rockfish had previously inhabited offshore waters. These results add to our understanding of some of the important environmental factors that affect young-of-the-year rockfishes during their pelagic phase.     

A flume study of drift in marine infaunal amphipods (Haustoriidae)

Amphipods of the infaunal family Haustoriidae are characteristic of high-energy marine sands and occur both in the sediment and the overlying water column. Sediments in this habitat are subject to constant reworking by tidal currents, suggesting that resident amphipod populations are affected by this disturbance in a phenomenon similar to freshwater invertebrate drift. A controlled-velocity laboratory flume was used to examine the effect of haustoriid density, current velocity, illumination, and food availability on drift rates to determine a causal basis for drift. Drift is densityindependent and greatest at night and during high current flow; it is also greater at night from sterile sediment than from untreated sand. Flume transport was usually less than 10% of amphipods present in the sediment. Haustoriids captured downstream were mostly adults occurring in a 1:1 sex ratio, suggesting no obvious function of drift in reproduction. Current-induced displacement of haustoriids may produce the patchiness in distribution observed in nature. Disturbance of the bed could also function to keep amphipod densities below the carrying capacity of the local environment. In certain cases, food limitation may cause amphipods to actively leave the substrate. Under all conditions, greater drift rates in darkness are probably adaptive in avoidance of predators. Despite the nature of sediment movement in a high-energy environment, haustoriid drift may have an active as well as passive component.     

Short-term temporal patterns of early recruitment of coral reef fishes in the tropical eastern Pacific

Short-term temporal patterns of recruitment have been described in a variety of coral reef fishes and have often been related with lunar and tidal cycles. While the relative importance of lunar and tidal factors in determining recruitment patterns has been difficult to assess, most studies have been done in the Caribbean and Indo-Pacific, where tidal amplitudes are small. We studied the short-term temporal dynamics of fish recruitment at Gorgona Island (tropical eastern Pacific), where there is a large tidal amplitude (~4.4 m). Every other day during three consecutive months in 1998, we directly measured the magnitude of reef fish recruitment to standardized coral units (SCUs) isolated from natural reefs. A total of 40 species from 21 families settled on the SCUs. Of 11 species with sufficient numbers for meaningful statistical analyses, two (Lutjanus guttatus and Pomacanthus zonipectus) had lunar recruitment with peaks near the new moon; three combined species of antennariids showed semilunar recruitment with peaks near moon quarters; and eight other species showed sporadic and aperiodic recruitment pulses. The contribution of lunar (moonlight intensity) and tidal factors (tidal amplitude and net tidal flow) to recruitment dynamics varied among species, although it was generally low (<18%) even among species with periodic patterns, except perhaps in L. guttatus. In this species, recruitment magnitude correlated negatively with moonlight intensity, accounting for 34.5% of the variance. Post-settlement predation by roving predators may be one cause of this relationship. In the remaining species, particularly those with sporadic and aperiodic recruitment pulses, stochastically varying weather and oceanographic events may be more important in determining temporal variation in recruitment.     

Photographic and acoustic tracking observations of the behaviour of the grenadier Coryphaenoides (Nematonurus) armatus the eel Synaphobranchus bathybius,and other abyssal demersal fish in the North Atlantic Ocean

Using an autonomous free-fall vehicle (AU-DOS), observations were made of demersal fish attracted to baits and baited acoustic transmitters at two stations in the North Atlantic Ocean. A comparison was made between Station PAP (48°50N; 16°30W), 4800 m deep on the Porcupine Abyssal Plain which is relatively eutrophic, and Station MAP (31°N; 20°W), 4900 m deep on the Madeira Abyssal Plain, which is oligotrophic. Experiments were conducted during summer, in 1989 and 1990. Four species of fish were observed at Station MAP, the grenadier, Coryphaenoides (Nematonurus) armatus, the eel, Synaphobranchus bathybius, and the ophidiids Spectrunculus grandis, and Barathrites sp. At Station PAP, C. (N.) armatus and H. (S.) bathybius were attracted to bait on all deployments and only two other individuals of different species, probably ophidiids, were seen. The mean first grenadier arrival time was 30 and 138 min at Stations PAP and MAP, respectively. Mean first eel arrival time was 29 and 151 min at Stations PAP and MAP, respectively. Estimated population densities of fish were 167 grenadiers km^-2 and 180 synaphobranchid eels km^-2 at Station PAP and 8 grenadiers km^-2 and 7 eels km^-2 at Station MAP. Only the grenadier C. (N.) armatus definitely ingested transmitters, and this species dominated fish activity around the baits. Mean time of departure of grenadiers with transmitters in their stomachs across an acoustic horizon at 1000 m range was 371 and 488 min at Stations PAP and MAP, respectively. Grenadiers had a longer mean staying time at the food source at the more oligotrophic Station MAP (364 min) than at Station PAP (141 min). This corresponds with predictions of optimal foraging theory.     

Using surface drifter observations to measure tidal vortices and relative diffusion at Aransas Pass,Texas

Tidal vortices play an important role in the flushing of coastal regions. At the mouth of a tidal inlet, the input of circulation by the ebb tide may force the formation of a starting-jet dipole vortex. The continuous ebb jet current also creates a periodic sequence of secondary vortices shed from the inlet mouth. In each case, these tidal vortices have a shallow aspect ratio, with a lateral extent much greater than the water depth. These shallow vortices affect the transport of passive tracers, such as nutrients and sediment from the estuary to the ocean and vice versa. Field observation of tidal vortices primarily relies on ensemble averaging over several vortex events that are repeatable in space and can be sampled by a fixed Eulerian measurement grid. This paper presents an adaptive approach for locating and measuring within tidal vortices that propagate offshore near inlets and advect along variable trajectories set by the wind-driven currents. A field experiment was conducted at Aransas Pass, Texas to measure these large-scale vortices. Locations of the vortices produced during ebb tide were determined using near real-time updates from surface drifters deployed near or within the inlet during ebb tide, and the paths of towed acoustic Doppler current profiler (ADCP) transects were selected by analysis of the drifter observations. This method allowed ADCP transects to be collected within ebb generated tidal vortices, and the paths of the drifters indicated the presence of both the starting-jet dipole and the secondary vortices of the unstable ebb tidal jet. Drifter trajectories were also used to estimate the size of each observed vortex as well as the statistics of relative diffusion offshore of Aransas Pass. The field data confirmed the starting-jet spin-up time (time until the vortex dipole begins to propagate offshore) measured in the laboratory by Bryant et al. [6] and that the Strouhal condition of \(St=0.2\) predicts the shedding of secondary vortices from the inlet mouth. The size of the rotational core of the vortex is also shown to be approximated physically by the inlet width or by \(0.02UT\) , where U is the maximum velocity through the inlet channel and T is the tidal period, and confirms results found in laboratory experiments by Nicolau del Roure et al. [23]. Additionally, the scale of diffusion was approximately 1–15 km and the apparent diffusivity was between 2–130  \(m^2/s\) following Richardsons law.     

Diets of clupeoid,stomiatoid and salmonoid fish of the Rockall Trough,northeastern Atlantic Ocean

The trophic interactions of species of fish of the continental slopes have not been investigated previously in detail. The present study examines the diets of the clupeoid, stomiatoid and salmonoid species occurring demersally and pelagically in the Rockall Trough to the west of Scotland and Ireland. Pelagic fish were collected between the surface and about 2 500-m depth between 1973 and 1978. Demersal fish were sampled at 250-m intervals of depths between 500- and 2 900-m depth during the years 1975 and 1981. Of the 28 species caught, 18 were strictly pelagic and dominated by the stomiatoids while five were strictly demersal. The remaining five species occurred in both the pelagic and demersal environment. The commonest clupeoid was Alepocephalus bairdii, which is a dominant species within the demersal fish associations at depths of 750 to 1 250m. This species, along with the deeper-living A. agassizi, and 3 other alepocephalid species feed primarily on benthopelagic prey but also exploit the epibenthos. The stomiatoid species, such as Cyclothone microdon, C. braueri, Maurolicus muelleri and Argyropelecus hemigymnus, dominate the associations of pelagic fish in the Trough. They feed on different proportions of ostracods, copepods and amphipods. Of the salmonoids, only Argentina silus and Bathylagus euryops occurred commonly and both feed on benthopelagic fauna, the latter at much greater depths than the former. The principal factor acting to prevent direct competition between species is the modal centres of bathymetric distribution of the species. Other contributing factors are briefly discussed.     

Scavenging abyssal benthic amphipods trapped under oligotrophic central North Pacific Gyre waters

Two traps baited with fish were placed on the bottom (5720 m) of the central North Pacific Gyre. A total of 1793 lyssianassid amphipods were collected no ovigerous females and no identifiable males were caught. Five amphipod species were represented [1 undescribed species of Orchomene; 2 undescribed species of Paralicella; Eurythenes gryllus (Lichtenstein); and Cyclocaris sp.], 2 by single specimens. Amphipod samples give no evidence of size-classes. Evidence for scavenging as the amphipods' primary mode of existence is discussed. Forty-four copepods, of a single harpacticoid genus (Tisbella), were also collected.     

Under-ice amphipods in the Greenland Sea and Fram Strait (Arctic): environmental controls and seasonal patterns below the pack ice

During three "Polarstern" cruises to the ice-covered Greenland Sea (spring 1997, summer 1994, autumn 1995) studies on the under-ice habitat (morphology, hydrography, ice-algal biomass) and on the macrofaunal, autochthonous under-ice amphipods (species diversity, abundance) were carried out in order to describe environmental controls and seasonal patterns in this community. In spring, the ice underside was rather smooth and whitish, while in summer melting structures and sloughed-off ice-algal threads were observed, in autumn detritus clumps accumulated in depressions at the ice underside. Only in summer, a thin layer of warm (up to -0.6°C) and less saline (as low as S=6.3) water was found at the ice-water interface above Polar Water. Integrated ice-algal biomass was highest during autumn (2.6 mg chl a m^-2) and lowest during summer (1.2 mg chl a m^-2). Four species of under-ice amphipods occurred in spring and summer (Apherusa glacialis, Onisimus glacialis, O. nanseni, Gammarus wilkitzkii), but only the last species was observed at the ice underside in autumn. A. glacialis and G. wilkitzkii were equally abundant in spring; A. glacialis dominated in summer. The highest total abundance of amphipods occurred during summer (31.9 ind. m^-2), compared to lower abundances in spring and autumn (5.3 and 1.1 ind. m^-2, respectively). A factor analysis revealed seasonal patterns in the data set, which mainly influenced A. glacialis, and species-specific relations between several environmental factors and the distribution of under-ice amphipods. Abundance of A. glacialis was closely related to the under-ice hydrography and ice-algal biomass, whereas the other amphipod species were more influenced by the under-ice morphology. It is therefore stated that the observed thinning of the Arctic sea ice and the resulting increased meltwater input and change in morphology of floes will have a profoundly adverse effect on the under-ice amphipods.     

Temporal and spatial use of stranded wrack by the macrofauna of a tropical sandy beach

During two field studies the macrofauna associated with wrack stranded on a tropical sandy shore was analysed. During the first period all animals present in small wrack deposits were randomly collected with cores. During the second field study active animals were sampled in larger wrack deposits for an entire lunar period, and tube traps were used. After a comparison between the two studies, only the data from the tube traps were examined from a temporal and spatial point of view. The aim of the present work was to gain information on how, when and where wrack was colonised by invertebrates, keeping in mind cyclical aspects such as lunar, diel and tidal phases. Predatory taxa, such as Staphylinoidea and the amphipods Talorchestia martensii, were most abundant, whereas Diptera larvae and Tenebrionidae were scarce. Successional changes of beach wrack colonisation were evident throughout a semi-lunar period, with molluscs invading wrack during the first days of deposition and histerids during the last ones. Strictly nocturnal or diurnal surface-active species were found to be active in the wrack during both the day and the night. The analysis of the tidal component of species activity in the wrack showed that some species moved at ebbing tide, and others moved at rising tide. Differences were found also in the mean hours of tidal activity, calculated separately during day and night periods. The study of the zonation of each species showed that in some cases wrack deposits were closely followed by the fauna as their position changed during the semi-lunar phase. In other cases differences occurred between species zonation during day and night periods and tidal phases. Cluster analysis indicates that most species exploit the wrack in different ways (as refuges and/or feeding site), both in space and in time. Received: 11 July 1999 / Accepted: 20 January 2000     

Intertidal slope of coral sand beach as a unique habitat for fish: meiobenthic diet of the transparent sand dart, <Emphasis Type="Italic">Kraemeria cunicularia</Emphasis> (Gobiidae)

Coral sand beaches harbor gobiid sand darts (genus Kraemeria), the only fish known to live in the sand throughout their adult life. Despite the uniqueness of sand-dwelling habitat as a vertebrate, the biology of this fish remains unclear. To explore how this unique fish utilize an unusual habitat, we investigated diurnal patterns of microhabitat use and prey consumption by the transparent sand dart, Kraemeria cunicularia, at a sandy beach on Iriomote Island, the Ryukyu Archipelago, Japan. Sand darts were found in sediment in the lower intertidal zone throughout the daytime regardless of changes in tidal level, whereas at nighttime these fish were found swimming. Gut content analyses revealed that the sand dart diet was dominated by harpacticoid copepods throughout the day. Analyses of meiobenthic distribution indicated that these copepods were most abundant at lower intertidal zones where highest numbers of sand darts were found during the daytime; thus, it is possible that microhabitat use of the fish is largely determined by food availability. An extensive distributional survey throughout the Ryukyu Archipelago further indicated that sand darts prefer sandy beaches with well-sorted, coarse sand. These results provide novel insights into how sand darts respond to the tidal rhythm and highlight putative key environmental factors that determine their distribution at both regional and microhabitat scales. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Impact of salt-marsh management on fish nursery function in the bay of Aiguillon (French Atlantic coast), with a focus on European sea bass diet

The Bay of Aiguillon is a national French Nature Reserve of great importance for birds. Recently, the managers of the Reserve (ONCFS-LPO) paid attention to the influence of saltmarshes management on the nursery function for fish feeding in creeks at high tide. A study carried out from March to July 2012 aimed to evaluate the use of saltmarshes by fish juvenile fraction according to the mowing intensity in salt marshes surrounding creeks: ceased, irregular or annual mowing. This community approach was completed by a focus on the European sea bass Dicentrarchus labrax individual diet, vacuity index and growth, and the biomass of a main potential prey (the amphipod Orchestia gammarella). Whatever the mowing intensity, the juvenile fraction was very high for the main species, which were the grey mullet Liza ramada, the European sea bass, undetermined clupeid and the European flounder Platichthys flesus. Adult and subadult for these species were anecdotic or totally absent. Despite very different biomasses of amphipods between mown and natural sites, vacuity index, prey composition and their relative abundance in the diet of European sea bass juveniles were little different, contrary to their hypothetical growth (i.e. when assuming site fidelity), which appeared higher in non-mown site. The low distance between sampling sites could allow fish exchange over time between optimal and suboptimal creeks to feed on, as a hypothesis to explain such results. Because mowing was subsidized by European Union (EU) to favour open habitats for geese and maintain an economic activity, indirect impacts on nursery for fish called into question the appropriateness of such agro-environmental measure on natural habitats, and related fish nursery function.     

Distribution of squid paralarvae, <Emphasis Type="Italic">Loligo opalescens</Emphasis> (Cephalopoda: Myopsida), in the Southern California Bight in the three years following the 1997–1998 El Niño

Large numbers of paralarvae of the California market squid, Loligo opalescens (10,560 paralarvae from 422 plankton samples), were collected in the Southern California Bight in 1999, 2000, and 2001 during the spawning season. Paralarval abundance increased dramatically (P<0.0041) from 1.5 squid/1,000m³ in 1999 to 77.9 squid/1,000m³ in 2000, and 73.6 squid/1,000m³ in 2001, following the El Niño of 1997-1998. The effects on the squid fishery of the 1997-1998 El Niño were thus extended for two years, with larval abundance reduced until the 1999-2000 spawning season. Paralarvae were abundant close to shore for up to a month after hatching in 2000 (P<0.003), with tidal surface currents adjacent to shore in the Channel Islands strongly affecting paralarval abundance. Tidally reversing currents within 1-3 km of shore created a boundary layer of "sticky water" within which paralarvae remained entrained inshore immediately after hatching. Neritic currents farther from shore dispersed older paralarvae within the Southern California Bight. The greatest change in paralarval abundance, for all transects, was observed within 1 km of the transition between these two flow regimes. Age of paralarvae (from statolith increments) entrained within the Catalina Island boundary layer averaged 13-16 days, but some individuals remained nearshore for up to a month. Paralarvae in the boundary layer occurred above 80 m depth both day and night, and exhibited a statistically significant pattern of vertical diel migration (P<0.01). Paralarvae at sea were disproportionately abundant adjacent to fronts associated with uplifted isotherms.