Comparison between the life cycles of two Soleidae, the common sole, Solea solea, and the thickback sole, Microchirus variegatus, in the Bay of Biscay (France)

The life history of two Soleidae, the common sole, Solea solea, and the thickback sole, Microchirus variegatus, were compared in the Bay of Biscay in an attempt to set out factors which could explain settlement styles known to be different between juveniles of each species. Common sole juveniles had been shown to depend on coastal and estuarine nurseries, and the thickback sole to develop in open-sea nurseries, although the spawning grounds and spawning season of both species overlapped (offshore and at springtime, respectively). For this study, data on adult, juvenile and larva distributions were obtained from cruises carried out in the Bay of Biscay during the last decade. In addition, growth rate of larvae and planktonic interval duration, estimated by means of otolith increment analysis, were compared, as well as literature-derived information on behaviour of larvae. By comparing larval features, it appeared that thickback sole did not obtain the advantage of a slightly longer pelagic life span for an increased dispersal, due to an early shift to benthic behaviour. Other evidence was given by more specifically stated distributions that the further and deeper offshore spawning of M. variegatus, compared to S. solea, was a likely key-factor of the juvenile settlement process. This could explain why the thickback sole, contrary to the common sole, never reach coastal areas and thus settle offshore, in waters deeper than 30 m.     

Ontogenic migration of Pleuronectes flesus larvae in the eastern English Channel

Along the French coast of the eastern English Channel there is a strong separation in the hydrology, zooplankton community and ichthyoplankton assemblages, between a coastal ecosystem of continental influence and an offshore ecosystem of Atlantic influence. During April and May 1995, two surveys (60 stations) were conducted to describe the early life history of fishes in this area, and especially the influence of hydrodynamics on Pleuronectes flesus larval transfer from the spawning grounds to the nurseries. Ontogenic changes in larval distributions were described by variograms and path analysis. P. flesus eggs and young larvae were found in the southern offshore area. Their distributions were mainly influenced by sediment and cold temperature found in the central part of the Channel. Older larvae were found at more northern stations, showing a clumped distribution near estuaries, in areas of low salinity. Apparently, young stages of this species were transported from the south central spawning area to coastal waters by residual currents. Behavioural changes in older larvae facilitate the move to nurseries along the French coast.     

Vertical Distribution and Feeding Activity of Metamorphosing Sole, Solea Solea, Before Immigration to the Bay of Vilaine Nursery (Northern Bay of Biscay, France)

To evaluate the impact of metamorphosis on the vertical distribution and feeding activity of sole, Solea solea, larvae passing from offshore spawning grounds to the Bay of Vilaine, sampling series at fixed stations were carried out in April 1991 and April 1993 at depths from 50 to 30 m. Comparisons between plankton and bottom samplin series indicated differences in vertical distribution of larvae in pre-metamorphic and metamorphic steps. Metamorphosing larvae displayed a tendency to concentrate in the lower part of the water column, mainly during the day. Gut contents, analysed for prey identification, fullness index and carbon content, indicated that metamorphosing larvae fed mostly on plankton. Variations in fullness index were observed not only during the day, but also depended on tide and wind-induced mixing conditions. Larvae sampled in mixed spring-tide waters had highly variable carbon estimates, resulting in unclear diel activity. More larvae fed actively at neap-tide, which allowed the observation of a diurnal feeding activity through hourly changes in carbon estimates. It is concluded that immigrating sole were not yet able to settle but prepared themselves for demersal life (i) without undergoing starvation and (ii) by modifying the patterns of vertical distributions. The presence of a larval swimbladder suggests they can adjust their vertical movements, depending on tidal cycles, which could in turn favour coastal accumulation of metamorphosing larvae and pulses of new settlers entering the nursery grounds.     

Testing adaptive hypotheses on the evolution of larval life history in acorn and stalked barnacles

Despite strong selective pressure to optimize larval life history in marine environments, there is a wide diversity with regard to developmental mode, size, and time larvae spend in the plankton. In the present study, we assessed if adaptive hypotheses explain the distribution of the larval life history of thoracican barnacles within a strict phylogenetic framework. We collected environmental and larval trait data for 170 species from the literature, and utilized a complete thoracican synthesis tree to account for phylogenetic nonindependence. In accordance with Thorson's rule, the fraction of species with planktonic‐feeding larvae declined with water depth and increased with water temperature, while the fraction of brooding species exhibited the reverse pattern. Species with planktonic‐nonfeeding larvae were overall rare, following no apparent trend. In agreement with the “size advantage” hypothesis proposed by Strathmann in 1977, egg and larval size were closely correlated. Settlement‐competent cypris larvae were larger in cold water, indicative of advantages for large juveniles when growth is slowed. Planktonic larval duration, on the other hand, was uncorrelated to environmental variables. We conclude that different selective pressures appear to shape the evolution of larval life history in barnacles.     

Semilunar postlarval settlement periodicity ensuing from semilunar larval release cycle in the Nihonotrypaea harmandi (Crustacea,Decapoda, Axiidea,Callianassidae) population on an intertidal sandflat in an open marine coastal embayment

Many decapod crustaceans in marine intertidal habitats release larvae toward coastal oceans, from which postlarvae (decapodids: settling-stage larvae) return home. Decapodid settlement processes are poorly understood. Previous studies showed that in Kyushu, Japan, the callianassid shrimp population on an intertidal sandflat of an open bay joining the coastal ocean near a large estuary released eight batches of larvae basically in a semilunar cycle from June through October and that decapodids performed diel vertical migration, occurring in the water column nocturnally. We conducted (a) frequent sampling for population density and size-composition on the sandflat through one reproductive season, (b) planktonic and benthic sampling for decapodids around the bay mouth, and (c) current meter deployment at three points across the bay mouth for tidal harmonic analysis. On the sandflat, six batches of newly-settled decapodids (settlers) occurred in a semilunar periodicity until October, with peaks occurring 0–3 days before syzygy dates except for the first one. For larval Batches 1–4, buoyancy-driven shoreward subsurface currents during July to mid-October would transport some pre-decapodid-stage larvae (zoeae) toward the bay. The absence of expected settler Batches 7–8 would be due to the converse subsurface currents caused by water-column mixing and seasonal winds after mid-October, carrying zoeae offshore. Once in the bay, phasing of night and nighttime-averaged shoreward tidal current explained the settlement pattern for Batches 1–4. For Batches 5–6 occurring in mid-September to mid-October, water currents generated by seasonal wind and tidal forcings may have caused peak settlement after the time expected from tidally-driven decapodid transport.     

Seasonal dynamics and grazing rate of zooplankton in Yueqing Bay,China

The species composition,biomass,abundance,and species diversity of zooplankton were determined for samples collected from August 2002 to May 2003 from 14 stations in Yueqing Bay,China.Phytoplankton growth rate and microzooplankton grazing rate were obtained by using the dilution method developed by Landry and Hassett.The spatial and temporal variations of zooplankton and its relationship with environmental factors were also analyzed.The results showed that the zooplankton in the Yueqing Bay could be divided into four ecotypes,namely coastal low saline species,estuary brackish water species,offshore warm water species,and eurytopic species.A total of 75 species of zooplankton belonging to 56 genera and 17 groups of pelagic larva were identified in the Yueqing Bay.The coastal low saline species was the dominant ecotype in the study area,and the dominant species were Labidocera euchaeta,Acartia pacifica,Acrocalanus gibber,Pseudeuphausia sinica,and Sagitta bedoti among others.There was considerable seasonal variation in zooplankton biomass and abundance in the surveyed areas.The peak biomass appeared in August,descending in November and in May,and the lowest biomass appeared in February.Similarly,the highest abundance of zooplankton was observed in August,with the abundance descending in the following months:May,November,and February.There were similar horizontal distribution patterns for the biomass and the abundance of zooplankton.They both increased from the upper to the lower bay in February and May,but decreased from the upper to the lower bay in August.Biomass and abundance were evenly distributed in the Yueqing Bay in November.Moreover,there was marked seasonal variation in the species diversity of zooplankton,which conformed to the abundance of zooplankton.Results of the dilution experiments indicated that there was grazing pressure of microzooplankton on phytoplankton in the Yueqing Bay throughout the year though the rate of microzooplankton grazing on phytoplankton varied seasonally.Phytoplanktons were growing at 0.26-2.07/d and grazed by microzooplankton at a rate of 0.15--0.48/d in different seasons.     

The Effects of Anthropogenic Structures on Habitat Connectivity and the Potential Spread of Non-Native Invertebrate Species in the Offshore Environment

Offshore structures provide habitat that could facilitate species range expansions and the introduction of non-native species into new geographic areas. Surveys of assemblages of seven offshore oil and gas platforms in the Santa Barbara Channel revealed a change in distribution of the non-native sessile invertebrate Watersipora subtorquata, a bryozoan with a planktonic larval duration (PLD) of 24 hours or less, from one platform in 2001 to four platforms in 2013. We use a three-dimensional biophysical model to assess whether larval dispersal via currents from harbors to platforms and among platforms is a plausible mechanism to explain the change in distribution of Watersipora and to predict potential spread to other platforms in the future. Hull fouling is another possible mechanism to explain the change in distribution of Watersipora. We find that larval dispersal via currents could account for the increase in distribution of Watersipora from one to four platforms and that Watersipora is unlikely to spread from these four platforms to additional platforms through larval dispersal. Our results also suggest that larvae with PLDs of 24 hours or less released from offshore platforms can attain much greater dispersal distances than larvae with PLDs of 24 hours or less released from nearshore habitat. We hypothesize that the enhanced dispersal distance of larvae released from offshore platforms is driven by a combination of the offshore hydrodynamic environment, larval behavior, and larval release above the seafloor.     

Premetamorphic bonefish (Albula sp.) leptocephali from the Gulf of California with comments on life history

Synopsis Ten early premetamorphic bonefish (Albula sp.) leptocephali were collected in MOCNESS plankton tows in the Guaymas Basin area of the Gulf of California from 27 July–1 August, 1985. Initial captures of five larvae showed that these were found only in surface waters (0–100 m) at temperatures of 15–29° C. A shallow tow made from 200 m to the surface resulted in the capture of five additional larvae that were distributed in the upper 50 m of the water column at temperatures of 21–29° C. Both pre-flexion larvae (<17.0 mm notochord length, NL) and larvae with flexed notochords were captured. The size range was from 12.0 mm NL to 27.0 mm standard length. Drawings of representative larvae are given. This is apparently the first report of premetamorphic bonefish larvae for the Gulf, although metamorphic larvae have been known to be abundant in coastal areas of this region for almost 100 years. Distribution records for metamorphic larvae are reviewed. This, together with observations on seasonal distribution of ripe adults in coastal waters near Guaymas, Sonora, Mexico, has allowed us to speculate on various aspects of life history. Our data suggest that spawning occurs during late spring and summer and that early development takes place offshore. The premetamorphic interval is postulated to last approximately 6–7 months. Larvae then return to coastal areas during the winter and spring to complete metamorphosis.     

Comparison of inshore and offshore fish larval assemblages within the wider Yangtze River estuary (China)

It is hypothesized that fish larvae undertake vertical movements in estuarine waters. To test this hypothesis, a sampling period was selected during times when many spring‐spawning fish reach maximum abundance in coastal waters so that spring and summer variations in larval fish assemblages could be determined in the Yangtze River estuary. Six oceanographic surveys were conducted across the salinity gradient of an inshore (freshwater) and offshore area (brackish intersection) during spring (May) and summer (August) between 2010 and 2012. The fish larval community was dominated by species of Engraulidae, Gobiidae, Champsodontidae and Mugilidae. The pre‐flexion and flexion larval stages of euryhaline marine species, which are dependent on estuaries as nursery areas, were common. The brackish and marine larval assemblage was the most abundant with taxa such as Coilia mystus and Engraulis japonicus accounting for more than 57.3% of the total catch. Spatial differences in the taxonomic composition of larval fish assemblages were evident between the inshore and offshore areas. Additionally, the Yangtze River runoff regulatory functions as affected by the Three Gorges Reservoir operational mode (hydrological alternating operations) showed weak influences on fish and habitat environments. Low salinities from high freshwater inflow limited bay anchovy production in the inshore area.     

Decapod Larvae: Dispersal, Mortality, and Ecology. A Working Hypothesis

TWO topics on decapod larval biology are discussed: retentionand recruitment of decapod larvae to the parental populationand the ecological role of decapod larvae in the water column. Most decapods have retained a planktonic larval phase whichis generally interpreted as a mechanism for increased dispersal.Evidence of restricted gene flow and biological/physical interactionresearch have suggested that larvae can be retained and recruitedto the parental population via mesoscale processes. To fullyunderstand recruitment processes improved estimates of mortalityrates for planktonic larval stages will be required. Recentevidence suggests that mortality rates are not constant overthe complete larval developmental period but decrease with time. During some seasons meroplankton including decapod l arvae canconstitute more than 50% of the plankton biomass. The quantityof energy transferred into the water column can be significant.Their role in planktonic ecology may be significant and additionalresearch is required.     

Orientation and navigation in coastal and estuarine zooplankton

The axiom that zooplankton species exhibit upwards migration behaviour at night is challenged by recent findings. Such behaviour is not universal, may vary during ontogeny, and is occasionally reversed. Moreover, in some estuarine and coastal zooplankton species vertical migration rhythms are of tidal, not diel, periodicity. There is evidence for several species that vertical migrations are endogenously controlled, occurring in constant conditions in the laboratory, suggesting that they have arisen under considerable selection pressure. They appear to play a significant role in orientation and navigation of coastal and estuarine zooplankton, predicated on the selective advantage of closure of life cycles. Vertical migrations between water masses moving in different directions at tidal, diel or longer timescales permit dispersal and recruitment, or retention, of planktonic larvae and adults in favourable ecological locations. Exogenous factors serving as cues for, or directly controlling, vertical migration rhythms include light, hydrostatic pressure, salinity, temperature, water movements and gravity responses, besides biological factors such as the timing of larval release, duration of larval life and predator/prey interactions. Behavioural characteristics should be quantified and factored into dispersal models which assume that zooplankton adults and larvae are advected as passive particles.     

Observations on the incidence and seasonal fluctuations of certain crustacean larvae in the plankton of the South-West Coast of India

The seasonal fluctuations in the incidence of planktonic organisms and the larval forms of certain crustaceans such as crabs, barnacles and post larvae of prawns in the plankton of the south-west coast of India have been followed for a period of three years from 1963. South-west monsoon period is the least productive period for zooplankton in this area. Brachyuran zoeae, post larvae of prawns and barnacle nauplii occur in the plankton throughout the year with distinct peaks for different groups. The zoeae ofUca annulipes occur in the plankton from September to May with a peak during November–December. The zoeae ofPortunus pelagicus are present in the plankton from September to June and their abundance is in February–March. The post larvae ofMetapenaeus affinis are found in the inshore plankton from November to June with the peak in March. The nauplii ofBalanus amphitrite communis occur in the plankton in all the months of the year, the peak incidence has been during November January. The zoeae ofU. annulipes are found to tolerate better the medium saline conditions. Of the ecological factors, salinity of the ambient water and the availability of planktonic food for the larvae seem to influence the seasonal fluctuations of these crustacean larvae in this locality.     

Cross-shelf dispersion of Dover sole (Solea solea) eggs and larvae in Biscay Bay and recruitment to inshore nurseries

We studied the cross-shelf dispersion of Dover sole (Solea solea)eggs and larvae from the offshore spawning grounds to the coastalnurseries of Biscay Bay in 1987. Eggs and larvae were retainedover the spawning grounds from late February to early April,consistent with the limited movement of satellite-tracked Lagrangiandrifters at different depths in the water column. The distributionof the larvae coincided with maximum zooplankton abundance.In mid April, both sole larvae and drifters moved northwardin response to wind forcing but the advection rate of the larvaewas about one-third that of the drifters. No significant onshoreadvection of the pelagic stages was observed. No evidence wasfound for a behavioural selection of tidal currents by the pelagiclarvae that could lead to onshore transport Unless that behaviourdeveloped after settlement to the bottom, cross-shelf diffusionof the pelagic stages would represent the main avenue of transportto the coastal nursery grounds. This dispersion strategy wouldimply that the vast majority of sole larvae fail to recruitto the bays and estuaries and arc lost to the population.     

Seasonal dynamics and grazing rate of zooplankton in Yueqing Bay, China

The species composition, biomass, abundance, and species diversity of zooplankton were determined for samples collected from August 2002 to May 2003 from 14 stations in Yueqing Bay, China. Phytoplankton growth rate and microzooplankton grazing rate were obtained by using the dilution method developed by Landry and Hassett. The spatial and temporal variations of zooplankton and its relationship with environmental factors were also analyzed. The results showed that the zooplankton in the Yueqing Bay could be divided into four ecotypes, namely coastal low saline species, estuary brackish water species, offshore warm water species, and eurytopic species. A total of 75 species of zooplankton belonging to 56 genera and 17 groups of pelagic larva were identified in the Yueqing Bay. The coastal low saline species was the dominant ecotype in the study area, and the dominant species were Labidocera euchaeta, Acartia pacifica, Acrocalanus gibber, Pseudeuphausia sinica, and Sagitta bedoti among others. There was considerable seasonal variation in zooplankton biomass and abundance in the surveyed areas. The peak biomass appeared in August, descending in November and in May, and the lowest biomass appeared in February. Similarly, the highest abundance of zooplankton was observed in August, with the abundance descending in the following months: May, November, and February. There were similar horizontal distribution patterns for the biomass and the abundance of zooplankton. They both increased from the upper to the lower bay in February and May, but decreased from the upper to the lower bay in August. Biomass and abundance were evenly distributed in the Yueqing Bay in November. Moreover, there was marked seasonal variation in the species diversity of zooplankton, which conformed to the abundance of zooplankton. Results of the dilution experiments indicated that there was grazing pressure of microzooplankton on phytoplankton in the Yueqing Bay throughout the year though the rate of microzooplankton grazing on phytoplankton varied seasonally. Phytoplanktons were growing at 0.26–2.07/d and grazed by microzooplankton at a rate of 0.15–0.48/d in different seasons. __________ Translated from Acta Ecologica Sinica, 2005, 25(8): 1853–1862 [译自: 生态学报, 2005, 25(8): 1853–1862]     

The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides

Abstract. Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typically are not well understood. The purpose of this study was to examine the pre-settlement impacts of different seawater temperatures on the size and population density of dinoflagellate symbionts in brooded larvae of the Caribbean coral Porites astreoides. Larvae were collected from P. astreoides at 14–20 m depth on Conch Reef (Florida) in June 2002, and incubated for 24 h at 15 temperatures spanning the range 25.1°–30.0°C in mean increments of 0.4±0.1°C (±SD). The most striking feature of the larval responses was the magnitude of change in both parameters across this 5°C temperature range within 24 h. In general, larvae were largest and had the highest population densities of Symbiodinium sp. between 26.4°–27.7°C, and were smallest and had the lowest population densities at 25.8°C and 28.8°C. Larval size and symbiont population density were elevated slightly (relative to the minimal values) at the temperature extremes of 25.1°C and 30°C. These data demonstrate that coral larvae are highly sensitive to seawater temperature during their pelagic phase, and respond through changes in size and the population densities of Symbiodinium sp. to ecologically relevant temperature signals within 24 h. The extent to which these changes are biologically meaningful will depend on the duration and frequency of exposure of coral larvae to spatio-temporal variability in seawater temperature, and whether the responses have cascading effects on larval success and their entry to the post-settlement and recruitment phase.     

Early life history of kitsune-mebaru,sebastes vulpes (scorpaenidae), in the sea of japan

The larval and juvenile stages of kitsune-mebaru,Sebastes vulpes, based on 50 wild specimens collected in, the Sea of Japan, are described and illustrated, and some ecological aspects of the early life history (feeding, horizonal distribution and habitat shift) included. Preflexion larvae became extruded between 3.9–4.6 mm body length (BL) and notochord flexion occurred between 4.7–7.1 mm BL. Transformation from postflexion larvae to pelagic juventiles occurred between 13–17 mm BL. Compared with other rockfish species,S. vulpes is deep-bodied, throughout both larval and, juvenile stages. Larval and juvenileS. vulpes inhabit mainly coastal water surface layer (usually on the continental shelf), but do not occur offshore region (northwest of Oki Islands). Although someS. vulpes juveniles are associated with drifting seaweed, such clumps are not indispensable habitats for any stages. Surface-to-benthie migration of juveniles occurs at about 25 mm BL. Preflexion and flexion larvae feed mainly on copepod nauplii, and postflexion, transforming larvae and pelagic juveniles mainly on calanoid copepodites (Parracalanus parvus).     

Mesoscale advection of Upogebia pusilla larvae through an upwelling filament in the Canaries Coastal Transition Zone (CTZ)

Larval transport has a strong influence on marine populations and ecosystem function. Traditional hypotheses establish that larvae of coastal species are swept offshore during strong upwelling periods producing low recruitment rates; however, recent studies have demonstrated that this hypothesis is not supported by larval distribution data. The present study examines the influence of upwelling filaments on larval advection and wastage. During August 1993, the transport of Upogebia pusilla was analysed in relation to an offshore filament off Northwest Africa. This mesoscale structure was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf and extended 150?km westward into the oligotrophic open ocean waters. The horizontal distribution depicted by U. pusilla larvae was strongly influenced by the oceanographic features of the Canaries Coastal Transition Zone (CTZ). Specifically, the larvae were closely associated with upwelling front and filament position, showing that these neritic larvae can be advected 10–100s of kilometres offshore through the filament. However, the low larval densities observed in the samples suggest that many larvae might remain close to the coast, thus avoiding seaward transport. This implies that filaments probably do not significantly affect the recruitment success of intertidal invertebrates such us U. pusilla in upwelling systems.     

Seasonal variation in dry weight and elemental composition of the early developmental stages of Petrolisthes laevigatus (Guérin, 1835) (Decapoda: Porcellanidae) in the Seno de Reloncaví, southern Chile

In the Seno de Reloncaví, southern Chile, seasonal changes in dry weight (DW) and elemental composition (CHN) were studied in embryo (initial embryonic stage), newly hatched zoeae, and newly settled megalopae of a porcelain crab, Petrolisthes laevigatus. Samples were taken throughout the seasons of egg laying (March-December), hatching (August-February), and settlement (October–February). Values of DW and CHN per embryo or larva, respectively, were consistently minimum in the middle of each season and maximum near its beginning and end. Patterns of seasonal variation in early embryonic biomass may thus be carried over to larvae at hatching and, possibly, to the settlement stage. Such carry-over effects may be selectively advantageous, as zoeae released at the beginning or near the end of the hatching season face conditions of poor planktonic food availability in combination with low winter temperatures or decreasing temperatures at the end of summer (enforcing long development duration). Hence, an enhanced female energy allocation into egg production may subsequently translate to enhanced yolk reserves remaining at hatching, allowing for a larval development under unfavourable winter conditions. In summer, by contrast, plankton productivity and temperatures are generally high, allowing for fast larval growth and development. This coincides with minimal biomass and energy contents both at hatching and settlement. In conclusion, our data suggest that seasonal patterns in the biomass of early developmental stages of P. laevigatus may reflect phenotypic variability as an adaptive response to predictable variations in environmental conditions, allowing this species to reproduce in temperate regions with marked seasonality in water temperature and plankton productivity.     

Seasonal variation in horizontal and vertical structure of larval fish assemblages off south-western Australia, with implications for larval transport

The coastal ocean off south-western Australia is characterisedby the southward-flowing Leeuwin Current, which suppresses theupwelling typically associated with other eastern boundary currentsin the southern hemisphere. This results in a unique environmentfor the transport and survival of planktonic fish larvae. Thehorizontal and vertical structure of larval fish assemblagesoff south-western Australia was investigated during winter (August2003) and summer (January 2004), and related to these unusualregional oceanographic and biological processes. Larval fishwere sampled along a four station transect running from theinner continental shelf to offshore waters, using depth-integratedbongo net tows and depth-stratified EZ net tows. The distributionof taxa across the shelf and offshore was strongly influencedby the current regime at the time of sampling. Larval fish assemblagestructure reflected the distinctive oceanographic conditionsfound during each season, and vertical depth distributions oflarvae affected their horizontal location. Continental shelfsamples were dominated by larvae of pelagic fishes, such asclupeiform species (e.g. Sardinops sagax), whereas offshoreassemblages were characterised by larvae of oceanic families,such as Myctophidae and Phosichthyidae. The winter cruise (August2003) was completed during a time of strong, southerly LeeuwinCurrent flow, whereas the northward-flowing Capes Current, incombination with surface offshore Ekman transport, predominatedduring summer. The vertical depth preferences of larvae wereparticularly influential in affecting their horizontal position;especially so for surface-dwelling larval fishes found duringsummer. This study represents the first documentation of thevertical structure of ichthyoplankton assemblages in the oligotrophicwaters off south-western Australia.     

Long-Term Changes in the Distributions of Larval and Adult Fish in the Northeast U.S. Shelf Ecosystem

Many studies have documented long-term changes in adult marine fish distributions and linked these changes to climate change and multi-decadal climate variability. Most marine fish, however, have complex life histories with morphologically distinct stages, which use different habitats. Shifts in distribution of one stage may affect the connectivity between life stages and thereby impact population processes including spawning and recruitment. Specifically, many marine fish species have a planktonic larval stage, which lasts from weeks to months. We compared the spatial distribution and seasonal occurrence of larval fish in the Northeast U.S. Shelf Ecosystem to test whether spatial and temporal distributions changed between two decades. Two large-scale ichthyoplankton programs sampled using similar methods and spatial domain each decade. Adult distributions from a long-term bottom trawl survey over the same time period and spatial area were also analyzed using the same analytical framework to compare changes in larval and adult distributions between the two decades. Changes in spatial distribution of larvae occurred for 43% of taxa, with shifts predominately northward (i.e., along-shelf). Timing of larval occurrence shifted for 49% of the larval taxa, with shifts evenly split between occurring earlier and later in the season. Where both larvae and adults of the same species were analyzed, 48% exhibited different shifts between larval and adult stages. Overall, these results demonstrate that larval fish distributions are changing in the ecosystem. The spatial changes are largely consistent with expectations from a changing climate. The temporal changes are more complex, indicating we need a better understanding of reproductive timing of fishes in the ecosystem. These changes may impact population productivity through changes in life history connectivity and recruitment, and add to the accumulating evidence for changes in the Northeast U.S. Shelf Ecosystem with potential to impact fisheries and other ecosystem services.