Polychaete Larvae Research Articles

Effects of sedimentary sulfide on community structure, population dynamics, and colonization depth of macrozoobenthos in organic-rich estuarine sediments

An annual field survey and in situ recolonization experiment revealed the effects of sedimentary sulfide (H2S) on macrozoobenthos in a eutrophic brackish lagoon. Species diversity was much lower throughout the year in muddy opportunist-dominant sulfidic areas. Mass mortality occurred during warmer months under elevated H2S levels. An enclosure experiment demonstrated that sedimentary H2S modified community composition, size structure, and colonization depth of macrozoobenthos. Species-specific responses to each sediment type (sand, sulfidic mud, and mud with H2S removed) resulted in changes in the established community structure. Dominant polychaetes (Hediste spp., Pseudopolydora spp., and Capitella teleta) occurred predominantly in a thin surface layer in the presence of H2S. On the other hand, organic-rich mud facilitated settlement of polychaete larvae if it does not contain H2S. These results demonstrate that sediment characteristics, including H2S level and organic content, were key structuring factors for the macrozoobenthic assemblage in organically polluted estuarine sediments.

서해연안 조간대에 서식하는 두줄망둑(Tridentiger trigonocephalus) 자치어의 먹이생물

To investigate the feeding habits of Tridentiger trigonocephalus juveniles captured in the intertidal zone of Dodun-ri, Seocheon-gun from the end of May to early June 2012, the gut contents were observed. Feeding incidence of the juveniles increased twice a day, first in the morning and second in the afternoon. The major food organisms of the juveniles (6.5〜10.0 ㎜ NL) were composed of copepods (65.4%), amphipods (2.0%), shrimp larvae (14.5%), polychaete larvae (22.6%), and etc. These food items held more than 2 percentage in the dry weight of the total food items.

Impact of the 2011 Tohoku earthquake tsunami on zooplankton community in Otsuchi Bay, northeastern Japan

Seasonal changes in abundance and distribution of mesozooplankton were investigated in Otsuchi Bay, northeastern Japan during a 2-year period from May 2011 to May 2013, in order to elucidate the impacts of the 2011 Tohoku earthquake tsunami on plankton communities. Mesozooplankton abundance and composition showed similar seasonal variation in each of the 2 years after the tsunami. Comparison with pre-tsunami data for communities from the bay showed that seasonality in dominant holozooplankton taxa, such as copepods, appendicularians and cladocerans, did not change before and after the tsunami. In addition, there were no observable differences in the seasonal species composition of copepods between pre- and post-tsunami periods. Acartia hudsonica, a dominant copepod in the bay, which has a benthic resting stage, was observed with high abundance immediately after the tsunami (May 2011) as well as 1 and 2 years later (May 2012 and May 2013, respectively). These findings suggest that there were no significant and lasting influences of the huge tsunami on the holozooplankton taxa. In contrast, planktonic larvae of bivalves, gastropods and polychaetes showed reduced abundance at the inner part of the bay in May 2011, possibly reflecting the damage due to the tsunami on their benthic populations.

Swimming speeds of polychaete larvae collected near deep‐sea hydrothermal vents

AbstractFor benthic fauna endemic to hydrothermal vents, larval dispersal in the plankton is required for maintenance of populations and colonization of new vents. Dispersal distances in the plankton are expected to be influenced by vertical positioning into horizontal currents, and larval survival in the plankton as well as encounter rates for settlement cues may be influenced by swimming speed. Here, we present the first quantitative measurements of swimming speeds of polychaete larvae collected near deep‐sea hydrothermal vents. We focused on three polychaete larvae of different morphotypes, with two morphotypes identified genetically to Capitellidae and Spionidae. Mean swimming speeds and helical parameters of the deep‐sea polychaete larvae (measured at 1 atm) were similar to values reported for shallow‐water polychaete larvae, with mean helical 3D swimming speeds ranging from 0.8–1.4 mm·s−1. To account for swimming that deviated from helical patterns, we developed a new method to reconstruct 3D swimming trajectories, using the 2D track and larval orientation. Speeds were generally faster for downward swimming, with mean vertical displacement speeds ranging from 0.6–0.8 mm·s−1 downward as compared with 0.2–0.6 mm·s−1 upward. Mean swimming speeds and helical parameters differed among the individuals. Our results are a first step towards constraining a behavioral component in models of larval dispersal between deep‐sea hydrothermal vents.

Ontogenetic changes in predator–prey interactions between two species of larval fishes and oyster veligers

The naked goby (Gobiosoma bosc), striped blenny (Chasmodes bosquianus), and eastern oyster (Crassostrea virginica) are common resident species in temperate Atlantic tidal waters. All three species produce planktonic larvae, and interactions between their early life stages likely influence recruitment success. Fish predation on oyster veligers requires co-occurrence as well as a match between prey behavior, size, and morphology and the ability of the predator to capture and engulf the veliger (prey). Wild plankton, oyster veligers, and wild plankton enriched with oyster veligers (mixed) were fed to cultured larval fishes during laboratory experiments. Three hypotheses were tested: (1) no fish species-specific differences in oyster veliger consumption exist within similar predator–prey development stage combinations, (2) postflexion blennies and gobies consume more veligers than preflexion fishes, (3) veligers reach a size refuge from fish predation by the umbo developmental stage. The resulting data provide a quantitative description of larval fish feeding behavior with respect to fish (preflexion, postflexion) and veliger (straight hinge, umbo) developmental stage. Selectivity for bivalve veligers as well as ontogenetic effects on the predator–prey interaction were examined. Fish nests were cultured to provide larval fish predators of known age. Overall, 70% of striped blennies and 59% of naked gobies consumed at least one prey item during the 3h experiments. There were fish species-specific differences in oyster veliger consumption between striped blennies and naked gobies. Striped blennies consumed more prey items including a wider range of veliger ages than larval naked gobies of the same developmental stages, regardless of the prey treatment. Fish selectivity was high for copepod nauplii and bivalve veligers and usually low for polychaete larvae, barnacle nauplii, and diatoms. There was a significant positive relationship between standardized consumption and predator development stage in the wild treatment for both fishes and in mixed and veliger treatments for blennies. All fishes consumed straight hinge veligers more often than umbo stage veligers. The largest veligers appear to reach a predation refuge from both fishes. Larval gobies and blennies are generalist predators that use seasonal pulses of zooplankton prey within temperate estuaries. Potential mismatches between predator–prey spatial and temporal overlap that might reduce fish recruitment are likely offset by adult spawning strategies that result in multiple nests within a long spawning season.

Zooplankton community grazing impact on a toxic bloom of Alexandrium fundyense in the Nauset Marsh System, Cape Cod, Massachusetts, USA

Embayments and salt ponds along the coast of Massachusetts can host localized blooms of the toxic dinoflagellate Alexandrium fundyense. One such system, exhibiting a long history of toxicity and annual closures of shellfish beds, is the Nauset Marsh System (NMS) on Cape Cod. In order to measure net growth rates of natural A. fundyense populations in the NMS during spring 2012, incubation experiments were conducted on seawater samples from two salt ponds within the NMS (Salt Pond and Mill Pond). Seawater samples containing natural populations of grazers and A. fundyense were incubated at ambient temperatures. Concentrations of A. fundyense after incubations were compared to initial abundances to determine net increases from population growth, or decreases presumed to be primarily due to grazing losses. Abundances of both microzooplankton (ciliates, rotifers, copepod nauplii and heterotrophic dinoflagellates) and mesozooplankton (copepodites and adult copepods, marine cladocerans, and meroplankton) grazers were also determined. This study documented net growth rates that were highly variable throughout the bloom, calculated from weekly bloom cell counts from the start of sampling to bloom peak in both ponds (Mill Pond range=0.12–0.46d−1; Salt Pond range=−0.02 to 0.44d−1). Microzooplankton grazers that were observed with ingested A. fundyense cells included polychaete larvae, rotifers, tintinnids, and heterotrophic dinoflagellates of the genera Polykrikos and Gymnodinium. Significant A. fundyense net growth was observed in two incubation experiments, and only a single experiment exhibited significant population losses. For the majority of experiments, due to high variability in data, net changes in A. fundyense abundance were not significant after the 24-h incubations. However, experimental net growth rates through bloom peak were not statistically distinguishable from estimated long-term average net growth rates of natural populations in each pond (Mill Pond=0.27d−1 and Salt Pond=0.20d−1), which led to peak bloom concentrations on the order of 106cellsl−1 in both ponds. Experimental net growth rates from the incubations underestimated the observed natural net growth rates at several time intervals prior to bloom peak, which may indicate that natural populations experienced additional sources of vegetative cells or periods of reduced losses that the 24-h incubation experiments did not capture, or that the experimental procedure introduced containment artifacts.

Effects of plankton net characteristics on metagenetic community analysis of metazoan zooplankton in a coastal marine ecosystem

Metagenetic analysis is a recently introduced, taxonomically comprehensive method for characterizing zooplankton communities; however, effects of plankton net characteristics (mesh and opening sizes) on metagenetic data, and biodiversity data in particular, have not been fully evaluated. To this end, we collected zooplankton samples from the subarctic coastal waters off Japan using two plankton nets: 1) Kitahara Quantitative Plankton Net (Kitahara net) with a 0.04-m2 opening and 100-μm mesh and 2) North Pacific Standard Plankton Net (Norpac net) with 0.16-m2 opening and 335-μm mesh. We then conducted 18S rDNA metagenetic and morphological analyses of the resulting catches. Molecular operational taxonomic units (MOTUs) at 97% similarity revealed higher diversity than did the morphological analysis, especially for morphologically unidentified taxa (e.g., Gastropoda and Polychaeta larvae), suggesting the effectiveness of the metagenetic method for characterizing zooplankton communities. Samples obtained with the Kitahara net produced more sequence reads of non-metazoan taxa, mainly derived from phytoplankton, leading to smaller numbers of available sequence reads for metazoan plankton. Numbers of morphological taxa were higher in the Norpac net samples. However, we expected metagenetic analysis to reveal higher diversity for the Kitahara net, due to larger MOTU numbers from smaller-sized taxa. Small-sized taxa also accounted for a larger proportion of sequence reads in the Kitahara net samples. In contrast, the diversity of large-sized taxa was better represented in the Norpac net sample. Although these differences were expected from the morphological analysis, effects of plankton net characteristics were more clearly reflected by metagenetic analysis than the morphological analysis.

Zooplankton variation in relation to hydrology in an enclosed hypoxic bay (Amvrakikos Gulf, Greece)

This study investigated the temporal and spatial variation of the zooplankton community of a hypoxic coastal embayment (Amvrakikos Gulf, western Greece) in relation to hydrological characteristics during an annual cycle. The main hydrological feature was the prolonged water stratification, which determined hypoxic conditions in the deeper layers that became anoxic close to the bottom in September, while vertical mixing occurred for a very short period (October-November). The total zooplankton abundance fluctuated between 44.6 and 159.7 ind l-1. Fourteen groups were recorded, among which copepods dominated accounting on average for 86.4 %. Most of the groups presented higher abundance values in winter and spring when increased chlorophyll-α concentrations were found. Oxygen depletion affects the vertical distribution of most zooplankton groups and the vertical habitat partitioning between copepod orders and their ontogenetic stages. Several taxa were recorded even in the deep, anoxic layers, but only the polychaete larvae increased in abundance with depth. Calanoids, appendicularians and bivalve larvae presented eastward decrease of abundance in the deepest layers following the same pattern of oxygen decrease. Notwithstanding hypoxic conditions in its deepest layers, Amvrakikos Gulf was accounted for a mesotrophic ecosystem, with the nutrient concentration being lower than in the past. Several biotic elements indicate that the gulf is in a transitional phase towards a better quality state and these results reinforce the need for consistent monitoring of this ecosystem.

Mechanisms underlying dual effects of serotonin during development of Helisoma trivolvis(Mollusca)

BackgroundSerotonin (5-HT) is well known as widely distributed modulator of developmental processes in both vertebrates and invertebrates. It is also the earliest neurotransmitter to appear during neuronal development. In aquatic invertebrates, which have larvae in their life cycle, 5-HT is involved in regulation of stages transition including larval metamorphosis and settlement. However, molecular and cellular mechanisms underlying developmental transition in aquatic invertebrate species are yet poorly understood. Earlier we demonstrated that in larvae of freshwater molluscs and marine polychaetes, endogenous 5-HT released from the neurons of the apical sensory organ (ASO) in response to external stimuli retarded larval development at premetamorphic stages, and accelerated it at metamorphic stages. Here we used a freshwater snail Helisoma trivolvis to study molecular mechanisms underlying these dual developmental effects of 5-HT.ResultsLarval development of H. trivolvis includes transition from premetamorphic to metamorphic stages and shares the main features of metamorphosis with free-swimming aquatic larvae. Three types of 5-HT receptors (5-HT1-, 5-HT4- and 5-HT7-like) are functionally active at premetamorphic (trochophore, veliger) and metamorphic (veliconcha) stages, and expression patterns of these receptors and respective G proteins undergo coordinated changes during development. Stimulation of these receptors modulated cAMP-dependent regulation of cell divisions. Expression of 5-HT4- and 5-HT7-like receptors and their downstream Gs protein was down-regulated during the transition of pre- to metamorphic stage, while expression of 5-HT1 -like receptor and its downstream Gi protein was upregulated. In accordance with relative amount of these receptors, stimulation of 5-HTRs at premetamorphic stages induces developmental retardation, while their stimulation at metamorphic stages induces developmental acceleration.ConclusionsWe present a novel molecular mechanism that underlies stage-specific changes in developmental tempo of H. trivolvis larvae in response to endogenous 5-HT produced by the neurons of the ASO. We suggest that consecutive changes in expression patterns of different receptors and their downstream partners in the course of larval development represent the molecular base of larval transition from premetamorphic (non-competent) to metamorphic (competent) state.

Vertical distribution and migration of planktonic polychaete larvae in Onagawa Bay, north-eastern Japan

H.,�Sato-Okoshi,�W.,�Nishitani,�G.�andEndo,�Y.�2014.�Verticaldistributionandmigrationofplanktonicpolychaete� larvae in Onagawa Bay, north-eastern Japan. Memoirs of Museum Victoria�71:�1-9. The planktonic larvae of polychaetes are one of the most numerous and diverse groups in coastal zooplankton; however, little is known about their larval dynamics and the factors that affect their vertical distribution. We investigated the vertical distribution and migration of planktonic polychaete larvae in Onagawa Bay, north-eastern Japan, particularly focusingonthedominantspionidlarvae.�Intotal,�14�familiesofplanktonicpolychaetelarvaeand�14�speciesorgeneraof� spionidlarvaewereidentifiedduringourstudy.�Theirdensitygreatlyfluctuatedaccordingtoseasonanddepth,�withthe� polychaetelarvaegenerallydistributedinthelowerlayersofthewatercolumn.�Furthermore,�trendsinverticaldistribution� ofspionidlarvaevariedbetweenspecies.�Inwinterandspring,�larvaeofPolydora onagawaensis were the most prevalent, withawiderangeinverticaldistribution.�Insummerandautumn,�larvaeofPseudopolydora achaeta and Prionospio spp. were the most prevalent spionid larvae and were primarily distributed in the lower layers of the water column. Trends in larval vertical distribution varied as a result of differences in adult habitat; these variations would enable the larvae to efficientlyrecruitintotheirappropriateadulthabitats.�Spionidlarvaedidnotshowdielverticalmigration.�Larvaeoftwo� spionid taxa, Pseudopolydora achaeta and Prionospio spp., exhibited tidal vertical migration, with larvae appearing to avoiddispersalbymovingtoslower-flowingdeeperwaterduringfloodandebbtides.�Althoughmanypreviousstudies� assume that, because of their limited swimming capacity, polychaete larvae are passively dispersed within the water column, this study indicates that polychaete larvae can control their vertical distribution to some extent, and this small- scale vertical migration may be important as a retention mechanism for polychaete larvae.

Ingestion and transfer of microplastics in the planktonic food web

Experiments were carried out with different Baltic Sea zooplankton taxa to scan their potential to ingest plastics. Mysid shrimps, copepods, cladocerans, rotifers, polychaete larvae and ciliates were exposed to 10 μm fluorescent polystyrene microspheres. These experiments showed ingestion of microspheres in all taxa studied. The highest percentage of individuals with ingested spheres was found in pelagic polychaete larvae, Marenzelleria spp. Experiments with the copepod Eurytemora affinis and the mysid shrimp Neomysis integer showed egestion of microspheres within 12 h. Food web transfer experiments were done by offering zooplankton labelled with ingested microspheres to mysid shrimps. Microscopy observations of mysid intestine showed the presence of zooplankton prey and microspheres after 3 h incubation. This study shows for the first time the potential of plastic microparticle transfer via planktonic organisms from one trophic level (mesozooplankton) to a higher level (macrozooplankton). The impacts of plastic transfer and possible accumulation in the food web need further investigations.

Effects of microalgal exudates and intact cells on subtropical marine zooplankton

Harmful algal blooms (HABs) affect coastal waters worldwide and very often lead to the disruption of seafood harvesting and commercial activities, because of potential hazards to human health associated with the consumption of contaminated mussels, crustaceans and fish. HAB events are frequently caused by outbreaks of toxin-producing dinoflagellates, which are subject to top-down control by zooplankton. The aim of this study was to analyze the effects of dinoflagellate exudates and intact cells on the survivorship and mobility of zooplankton taxa from a subtropical location (Ubatuba, Brazil). Lethal effects were observed in five out of six taxa investigated, three of which (copepod nauplii, tintinnids and gastropod larvae) when exposed to dinoflagellate exudates and two (rotifers and brachyuran zoeae) when exposed to intact cells. In addition, gastropod larvae displayed mobility impairment during exposure to dinoflagellate exudates. Only polychaete larvae were not apparently affected during the course of the experiments. Zooplankton responses usually varied according to the dinoflagellate species tested. For instance, exudates from Alexandrium tamiyavanichii, Gonyaulax sp. and Gymnodinium sp. decreased survivorship of planktonic copepod nauplii but did not affect bottom-dwelling harpacticoid nauplii, which were in turn killed by exudates from Prorocentrum lima, a epibenthic dinoflagellate. These results suggest that HAB events do not cause indiscriminate zooplankton mortality, but may instead generate community shifts and complex cascading effects through the pelagic and benthic food web. Speciesspecific monitoring of zooplankton responses to HABs is therefore an important step to understand the ecological implications of dinoflagellate outbreaks in coastal waters, and their impact on marine farming activities.

Zooplankton diversity and distribution in a deep and anoxic Mediterranean coastal lake

The variation of the smaller size fraction of zooplankton was investigated during a two-year period in a brackish deep and anoxic coastal lake of western Greece (Aitoliko), along with the specific environmental characteristics of this ecosystem. The zooplanktonic community comprised a relatively small number of taxa and it was dominated by brackish-water calanoid copepods (Paracartia latisetosa, Calanipeda aquaedulcis) and in certain periods by rotifers and tintinnids. The zooplankton abundance showed an increase in the warmer period starting from late spring and reached maximum values in July. In the well oxygenated surface layer, temperature was the most important parameter influencing the seasonal cycles of all groups. In contrast, the oxygen depletion a few meters under the surface affected the vertical distribution of most of the zooplankton groups, which were found restricted in the surface layer especially from spring until autumn. Only the meroplanktonic larvae of polychaetes presented increased proportions in the deeper layers. Salinity has not significantly influenced the zooplanktonic assemblages. The results point out the degraded status of the Aitoliko basin where the hypoxic/anoxic layers resulted to a high portion of dead organic material identified as copepod carcasses, and underlines the necessity of monitoring of this ecosystem.

Zooplankton diversity and distribution in a deep and anoxic Mediterranean coastal lake

The variation of the smaller size fraction of zooplankton was investigated during a two-year period in a brackish deep and anoxic coastal lake of western Greece (Aitoliko), along with the specific environmental characteristics of this ecosystem. The zooplanktonic community comprised a relatively small number of taxa and it was dominated by brackish-water calanoid copepods (Paracartia latisetosa, Calanipeda aquaedulcis) and in certain periods by rotifers and tintinnids. The zooplankton abundance showed an increase in the warmer period starting from late spring and reached maximum values in July. In the well oxygenated surface layer, temperature was the most important parameter influencing the seasonal cycles of all groups. In contrast, the oxygen depletion a few meters under the surface affected the vertical distribution of most of the zooplankton groups, which were found restricted in the surface layer especially from spring until autumn. Only the meroplanktonic larvae of polychaetes presented increased proportions in the deeper layers. Salinity has not significantly influenced the zooplanktonic assemblages. The results point out the degraded status of the Aitoliko basin where the hypoxic/anoxic layers resulted to a high portion of dead organic material identified as copepod carcasses, and underlines the necessity of monitoring of this ecosystem.

Metal contamination increases the sensitivity of larvae but not gametes to ocean acidification in the polychaete Pomatoceros lamarckii (Quatrefages)

Ocean acidification is not happening in isolation but against a background of chronic low-level pollution for most coastal marine environments. The reproductive and larval stages of marine invertebrates can be highly sensitive to the impacts of both environmental pollutants and ocean acidification, but very little is currently known regarding the potential impacts of combined contaminant and high CO2 exposures on the health of marine organisms. Ocean acidification research to date has focused heavily on the responses of calcifying marine invertebrate larvae and algae, and as such the polychaetes as a group, despite their ecological importance, remain understudied. Here, we investigate the effects of elevated seawater CO2 (pH range 8.1–7.4, plus an extreme pH of 7.2 in the sperm motility experiments), in combination with the environmental pollutant copper (0.002 μM), on the early life history stages of the intertidal polychaete Pomatoceros lamarckii from two populations. P. lamarckii sperm appear to be robust to elevated seawater CO2. Whilst all three of the sperm motility end points measured showed a response to elevated CO2, these responses were small and not linear. The percentage of motile sperm and sperm curvilinear velocity were significantly reduced in the lower pH treatments of 7.4 and 7.2, whereas sperm straight-line velocity (VSL) was mostly unaffected except for an increased VSL at pH 8.0. Fertilisation success was investigated using two populations from the South West (UK), one from Torquay and one from Plymouth Sound. Fertilisation success was slightly but significantly reduced at the 7.6 and 7.4 pH treatments for both populations (a 9.0 % reduction in fertilisation success from pH 8.1 to 7.4 for Torquay), but with a greater effect observed in the population from Plymouth Sound (a 13.33 % reduction in fertilisation success). No additional impact of 0.002 μM copper exposure on fertilisation success was found. Larval survival was found to be much more sensitive to elevated CO2 than sperm function or fertilisation, and a significant interaction with copper exposure was observed. These results demonstrate the potential for polychaete larvae to be affected by predicted ocean acidification conditions and that chronic coastal pollutants, such as copper, have the potential to alter larval susceptibility to ocean acidification conditions.

Mesozooplankton dynamics in relation to food availability during spring and early summer in a high latitude glaciated fjord (Kongsfjorden), with focus on Calanus

The timing of zooplankton reproduction in relation to spring pelagic bloom is essential in determining grazers' recruitment success and the transport of biomass through the system. At high latitudes marine ecosystems are characterized by extreme seasonality with the production of autotrophes concentrated during the spring. In two consecutive years we studied mesozooplankton during spring and early summer in Kongsfjorden, Svalbard (79°N), aiming at identifying the main grazers and understanding what affects the timing in zooplankton. The main grazers were females and nauplii of holoplanktonic Calanus, together with meroplanktonic Cirripedia nauplii and Polychaeta larvae. The appearing of offspring and larvae showed a correlation with the spring bloom which occurred earlier in 2004 compared to 2003. The Arctic Calanus glacialis reproduced before its Atlantic counterpart Calanus finmarchicus and prior to the bloom. In the Arctic regions decreasing sea ice cover as a result of climate change is expected to alter the timing of the spring bloom which in turn will pose a need for the zooplankton to adjust their reproduction activities. Subsequently, this adjustment will influence ecosystem functioning mainly by modifying particulate organic matter and energy fluxes.

Inter-cohort differences in growth, condition and feeding of juvenile anchovy (Engraulis encrasicolus) in the Gulf of Béjaia (Algerian coast, SW Mediterranean): Implications for recruitment success

Since the spawning season of European anchovy spread over more than six months we compared the growth, condition and feeding of juvenile anchovy originating from two different cohorts (summer and autumn 2007) in the Gulf of Béjaia (Algerian coast, SW Mediterranean). Juvenile anchovy fed predominately on zooplankton, the main prey items being copepods, and to a lesser extent on molluscs larvae, polychaete larvae and ostracods. Prey composition in the diet of the two cohorts differed from each other, and the vacuity index was significantly lower for the autumn cohort (20%) than for the summer cohort (70%). Juveniles from the summer cohort had higher growth (somatic and otolith growth) and better condition than individuals from the autumn cohort. Growth rates were 0.74mmd−1 and 0.59mmd−1 respectively. We also found that otolith daily increments widths were higher for the summer cohort. Sea surface temperature (SST) and sea surface chlorophyll-a concentration derived from satellite imagery (SeaWiFS), were used as the main environmental variables to analyze anchovy growth, condition and feeding. No relationships were observed between chlorophyll-a concentration and juvenile vacuity index, nor growth rates and condition. Our study suggests that growth and condition differences among the two cohorts were mainly due to water temperature differences encountered by the fish during their larval and juvenile periods. High growth rates and condition of individuals from the summer cohort may have conferred them ecological advantages and enhanced their survival. It has been suggested that, in this region, late spawned cohorts contribute less to the recruitment of the adult population.

Diet composition and feeding periodicity of the seahorse Hippocampus barbouri reared in illuminated sea cages

The zooplankton prey composition and feeding periodicity of juvenile and adult seahorses Hippocampus barbouri reared in illuminated and non-illuminated sea cages were compared. Mean frequency of occurrence (%FO), prey composition (%N), and gut fullness of seahorses were calculated from analyses of gut contents. Compared with juvenile seahorses, adults consumed more variety of prey consisting of copepods, larvae of decapods, polychaetes and fish, and euphausid shrimps. Calanoid copedods were found in the gut of more juvenile (%FO=47) and adult (%FO=64) seahorses in illuminated cages but harpacticoid copepods were ingested by more juvenile fish (%FO=50) in non-illuminated cages. Decapod larvae (%N=66) in illuminated cages dominated the diet of juvenile seahorses, whereas in non-illuminated cages harpacticoid copepods (%N=59) did. Calanoid copepods and decapod larvae (%N=91–97) comprised the bulk of ingested prey among adult seahorses in all experimental cages. The gut of caged seahorses was generally full during daytime but declined in the evening, becoming almost empty at midnight, particularly among juveniles. Cage illumination commencing at midnight increased the number of filled guts at dawn (0400h) among juvenile and adult seahorses. Unlike adult seahorses over a 24-h period, the overall incidence of filled guts among juveniles was not different between those in non-illuminated and illuminated cages. These results provide an alternative to growing caged H. barbouri on cultured live food, particularly copepods attracted by night illumination.

Larval abundance and its relation to macrofouling settlement pattern in the coastal waters of Kalpakkam, southeastern part of India

The present work revealed that salinity, water temperature, and food availability were the most crucial factors affecting the abundance of larvae and their settlement as macrofouling community in the coastal waters of Kalpakkam. Quantitative as well as qualitative results showed that late post-monsoon (April-May) and pre-monsoon (June-September) periods were found to be suitable periods for larval growth, development, and survival to adult stages for most of the organisms. Clustering of physico-chemical and biological (including larval and adult availability) data yielded two major clusters; one formed by northeast (NE) monsoon months (October-January) and the other by post-monsoon/summer (February-May) months, whereas; pre-monsoon months (June-September) were distributed between these two clusters. Among all the major macrofouler groups, only bivalves established a successful relationship between its larval abundance and adult settlement. Principal component analysis indicated good associations of bivalve larvae with polychaete larvae and adult bivalves with adult barnacles. However, biotic relation between ascidians and bryozoans was observed both in the larval as well as adult community.

Abundance and distribution of invertebrate larvae in the Bellingshausen Sea (West Antarctica)

The central part of the Bellingshausen Sea has been poorly studied, partly because of the presence of ice during most of the year. The main aim of this study was to analyse the abundance and distribution of meroplankton, and the influence of oceanographic properties were investigated in the Bellingshausen Sea (West Antarctica) during the BENTART-06 cruise carried out in January–February 2006. Zooplankton samples were collected with a 80-μm mesh plankton net hauled vertically from a depth of 200 m to the surface at fifteen stations across the Bellingshausen Sea. Fifteen types of larval benthic invertebrates were found, with echinospira and nudibranch veligers being the most abundant. Hierarchical analysis and non-metric multidimensional scaling revealed a high degree of spatial variability in both larval abundance and larval types across the Bellingshausen Sea. The variability was significantly correlated with total chlorophyll-a and the contribution of large (>5 μm) phytoplankton to total chlorophyll, indicating the availability of food as an important factor determining the larval distribution observed. Nudibranch veligers, nemertean pilidia, echinoderm and planula larvae were more abundant at stations in the central Bellingshausen Sea, which was characterized by low phytoplankton biomass and production. Higher abundances of echinospira veligers and polychaete larvae were found at the more productive stations close to Peter I Island and the Antarctic Peninsula. The abundance and diversity of larval types found in the Bellingshausen Sea during the BENTART-06 cruise support the hypothesis that indirect development through larval swimming stages plays a key role in benthic recruitment in polar areas.