Larval History Research Articles

The physiological consequences of delaying metamorphosis in the marine ornamental shrimp Lysmata seticaudata and its implications for aquaculture

The timing of metamorphosis has recently been referred as a more suitable proxy to evaluate postlarval quality than size. Indeed, while displaying a larger size at settlement, late settlers that originate from larvae that have delayed metamorphosis commonly display poorer growth performances This delay in metamorphosis is possibly at the expenses of larval endogenous energetic reserves that, once allocated to facilitate the delayed transition to benthic life, will no longer be available to help fuelling early juvenile somatic growth. To further advance our knowledge on this topic, we evaluated the physiological status (energy reserves and allocation, aerobic and anaerobic energy consumption), along with biochemical responses related with detoxification processes, antioxidant defences, oxidative damage, neuromotor activity in early settlers (ES), middle settlers (MS) and late settlers (LS) of postlarvae of the marine ornamental shrimp Lysmata seticaudata. Our results revealed that LS postlarvae presented a higher weight compared to MS and ES, likely related with a lower metabolism and neuromotor activity. Yet, the low metabolism allied with diminished detoxification and antioxidant capacities seemed to result in an increased oxidative stress condition that may negatively condition the growth performance of LS postlarvae. Conversely, ES postlarvae presented a lower weight, likely because of high metabolic costs associated with increased neuromotor activity, detoxification, and antioxidant capacities to avoid oxidative damage. The present study highlights how the physiological, metabolic and biochemical status of L. seticaudata postlarvae is shaped by the timing of their metamorphosis, as well as how this event will shape their early benthic life and confirms that a larger size or weight at metamorphosis may not be good proxies to select premium seedlings for grow-out. Overall, metamorphosis is not a new beginning and does not reset larval history. Crustacean farmers should avoid decoupling larviculture history from grow-out, as only by knowing larval performance to metamorphosis will it be possible to enhance survival and growth performances to commercial size.

Phylogenomic and morphological relationships among the botryllid ascidians (Subphylum Tunicata, Class Ascidiacea, Family Styelidae)

Ascidians (Phylum Chordata, Class Ascidiacea) are a large group of invertebrates which occupy a central role in the ecology of marine benthic communities. Many ascidian species have become successfully introduced around the world via anthropogenic vectors. The botryllid ascidians (Order Stolidobranchia, Family Styelidae) are a group of 53 colonial species, several of which are widespread throughout temperate or tropical and subtropical waters. However, the systematics and biology of this group of ascidians is not well-understood. To provide a systematic framework for this group, we have constructed a well-resolved phylogenomic tree using 200 novel loci and 55 specimens. A Principal Components Analysis of all species described in the literature using 31 taxonomic characteristics revealed that some species occupy a unique morphological space and can be easily identified using characteristics of adult colonies. For other species, additional information such as larval or life history characteristics may be required for taxonomic discrimination. Molecular barcodes are critical for guiding the delineation of morphologically similar species in this group.

Integrative taxonomy revisits the ontogeny and trophic niches of Rimicaris vent shrimps.

Among hydrothermal vent species, Rimicaris exoculata is one of the most emblematic, hosting abundant and diverse ectosymbioses that provide most of its nutrition. Rimicaris exoculata co-occurs in dense aggregates with the much less abundant Rimicaris chacei in many Mid-Atlantic Ridge vent fields. This second shrimp also houses ectosymbiotic microorganisms but has a mixotrophic diet. Recent observations have suggested potential misidentifications between these species at their juvenile stages, which could have led to misinterpretations of their early-life ecology. Here, we confirm erroneous identification of the earliest stages and propose a new set of morphological characters unambiguously identifying juveniles of each species. On the basis of this reassessment, combined use of C, N and S stable isotope ratios reveals distinct ontogenic trophic niche shifts in both species, from photosynthesis-based nutrition before settlement, towards a chemosynthetic diet afterwards. Furthermore, isotopic compositions in the earliest juvenile stages suggest differences in larval histories. Each species thus exhibits specific early-life strategies that would, without our re-examination, have been interpreted as ontogenetic variations. Overall, our results provide a good illustration of the identification issues persisting in deep-sea ecosystems and the importance of integrative taxonomy in providing an accurate view of fundamental aspects of the biology and ecology of species inhabiting these environments.

Evaluating chemical signatures in a coastal upwelling region to reconstruct water mass associations of settlement-stage rockfishes

Vol. 550: 191–206, 2016 doi: 10.3354/meps11704 MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published May 25 O PEN A CCESS Evaluating chemical signatures in a coastal upwelling region to reconstruct water mass associations of settlement-stage rockfishes Sarah G. Wheeler 1, *, Ann D. Russell 2 , Jennifer S. Fehrenbacher 2 , Steven G. Morgan 3 Graduate Group in Ecology at the University of California at Davis and San Diego State University, 5500 Campanile Dr, San Diego, California 92184-4614, USA University of California, Davis, One Shields Ave, Davis, California 95616, USA Bodega Marine Laboratory, University of California, Davis, 2099 Westside Dr, Bodega Bay, California 94923-0247, USA ABSTRACT: Characterizing the behavior of larvae prior to settlement is integral to understanding population dynamics because coastal oceanography may facilitate or limit settlement. Otolith microchemistry can be used to determine patterns of fish movement, although there is a limited understanding of how this tool can be applied in coastal marine systems. Our goal in this study was to evaluate the application of otolith microchemistry to characterize water mass associations of settlement-stage marine fish in a coastal upwelling region using a 3-step approach. First, we characterized seawater chemistry of coastal water mass types across multiple years, finding differ- ences in the chemical signatures of strong upwelling, weak upwelling, and relaxation events. Sec- ond, we experimentally determined the effect of temperature on the partitioning of trace elements in otoliths for 2 rockfishes (Sebastes spp.) to find that the effect of temperature on otolith partition coefficients was element- and species-specific. Finally, we compared coeval changes in seawater and otolith chemistry of settlement-stage rockfishes that were exposed to naturally variable con- ditions over an upwelling-relaxation cycle. We subsequently evaluate whether laser ablation inductively coupled plasma mass spectrometry effectively measures otolith chemistry over eco- logically relevant time scales. We discovered that elemental concentrations in otoliths respond rapidly to changes in seawater chemistry and reflect equivalent proportional changes. This study provides evidence that elemental signatures are valuable tools for reconstructing larval histories of marine fish in coastal upwelling regions. KEY WORDS: Barium · Laser ablation · Inductively coupled plasma mass spectrometry · ICP-MS · Otolith · Seawater INTRODUCTION The elemental compositions of seawater and fish otoliths have numerous applications to ecological research and fisheries management (Campana 1999, Campana & Thorrold 2001, Thorrold et al. 2007, Els- don et al. 2008). Otolith chemistry research capital- izes on differences in the chemical composition of environments to reconstruct fish movements, and heterogeneity in trace elements in freshwater and *Corresponding author: sarahgracewheeler@gmail.com estuarine environments has led to a substantial body of research in these systems (Campana & Thorrold 2001, Gillanders 2005, Elsdon & Gillanders 2006). The validation and application of chemical tags in marine fishes is relatively understudied (Sturrock et al. 2012). However, chemical gradients between near shore and offshore environments and water masses have revealed fish cross-shelf movements (Kingsford et al. 2009), larval dispersal or migrations (Swearer et al. 1999, Hamilton et al. 2008), and settle- © The authors 2016. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com

Contrasting oceanographic conditions during larval development influence the benthic performance of a marine invertebrate with a bi-phasic life cycle

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 546:135-146 (2016) - DOI: https://doi.org/10.3354/meps11629 Contrasting oceanographic conditions during larval development influence the benthic performance of a marine invertebrate with a bi-phasic life cycle Felisa Rey1, Gina M. Silva Neto1, Cláudio Brandão2, Daniela Ramos1, Bruna Silva1,3, Rui Rosa2, Henrique Queiroga1, Ricardo Calado1,* 1Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 2MARE - Marine and Environmental Sciences Centre, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Av. Nossa Senhora do Cabo, 939, 2750-374 Cascais, Portugal 3Present address: Acquacria Piscícolas S.A., Rua do Lavadouro, Quintas do Sul, 3870-304, Torreira, Portugal *Corresponding author: rjcalado@hotmail.com ABSTRACT: The pelagic life and benthic life of marine invertebrates with bi-phasic life cycles have often been studied separately, with the assumption that metamorphosis deletes larval history. However, it is now recognized that larval history can condition the post-metamorphic performance of benthic juveniles and ultimately contribute to the shaping of adult population dynamics. In the present study, we evaluated late larval and early juvenile performance of the green crab Carcinus maenas in Ria de Aveiro (Portugal) over 4 consecutive larval supply events in 2013. Larvae collected from the plankton were kept in the laboratory without food and under controlled conditions. Following metamorphosis, juvenile crabs were either exposed to starvation or provided with food ad libitum (Artemia nauplii). Juveniles were stocked until they either died or reached the 5th juvenile crab instar. Results showed that larval size at metamorphosis shifted along supply events, with this being reflected in early benthic life. Overall, optimal growth conditions did not delete the larval history experienced by the megalopae (and their previous zoeal stages) collected from each supply event. We analysed the influence of upwelling index in larval and early juvenile performance using general additive models, with the upwelling index explaining a significant percentage of the deviance recorded. Overall, contrasting trophic conditions experienced during larval life promoted a variation in larval size at settlement, which was carried over into early benthic life. A unifying integrated framework is therefore needed to better understand the population dynamics of marine invertebrates with bi-phasic life cycles and the role played by latent effects. KEY WORDS: Carcinus maenas · Carry-over effects · Complex life cycles · Megalopa · Phenotypic plasticity · Post-settlement performance · Upwelling Full text in pdf format PreviousNextCite this article as: Rey F, Silva Neto GM, Brandão C, Ramos D and others (2016) Contrasting oceanographic conditions during larval development influence the benthic performance of a marine invertebrate with a bi-phasic life cycle. Mar Ecol Prog Ser 546:135-146. https://doi.org/10.3354/meps11629 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 546. Online publication date: March 21, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

The usefulness of otolith chemistry to determine the life history of the honeycomb grouper around Reunion Island (SW Indian Ocean)

Due to the relative geographical isolation of Reunion Island the grouper Epinephelus merra is assumed to be self-recruited but almost nothing is known about its larval history. We used elemental composition of the otoliths (Ba, Sr, Mn, Mg, Na) of fifty-eight one year-old groupers collected from four main coral reefs on the west coast of Reunion Island, to determine environmental variations during their early life history. Hierarchical clustering analysis of the otolith chemical composition of core and early larval phase, allowed the identification of three groups of larvae. Larvae from the first group (cluster 1) were born and dispersed in Ba-enriched water bodies, while the second and third groups included larvae that had crossed Ba-poor water masses. Larvae of group 1 were primarily found in the southern sector (74%) decreasing northward, while group 3 were more abundant in the northern sector (56%) and cluster 2 showed a scattered distribution. Such opposite spatial distributions might suggest that clusters 1 and 3 originated from opposite dispersal kernels, south and north respectively. It is possible however that larvae from both groups came from the same spawning ground but represented different cohorts that experienced changing geochemical conditions either at the spawning site or within the surrounding pelagic environment, over the course of the breeding season. Both scenarios on the origin and dispersion may thus suggest significant influence of hydrographic features causing or preventing larvae from becoming displaced far from their natal area.

Carbon isotope ratios document that the elytra of western corn rootworm (Coleoptera: Chrysomelidae) reflects adult versus larval feeding and later instar larvae prefer Bt corn to alternate hosts.

In much of the Corn Belt and parts of Europe, the western corn rootworm, Diabrotica virgifera virgifera LeConte, is the most important insect pest of maize. The need for additional basic knowledge of this pest has been highlighted while developing resistance management plans for insecticidal genetically modified crops. This study evaluated the possibility of tracking feeding habits of western corn rootworm larvae using stable carbon isotope signatures. Plants accumulate different ratios of (13)C:(12)C isotopes, usually expressed as δ(13)C, according to whether they use the C3 or C4 photosynthetic pathway. Herbivore biomass is expected to reflect the δ(13)C of the food they eat. For the current experiment, western corn rootworm larvae were grown on different species of plants exhibiting different δ(13)C values. The δ(13)C values were then measured in elytra of emerged beetles. When beetles were unfed, biomass reflected larval feeding. When beetles were fed for 31 d postemergence, δ(13)C values of elytra almost exclusively reflected adult feeding. These results suggest the use of caution in the interpretation of δ(13)C data aiming to document larval diet history when adult feeding history is unknown. The technique was also used to evaluate western corn rootworm larval choice between alternate hosts and maize with and without genetically modified (Bt) traits aimed at their control. Propensity for feeding on alternate hosts versus maize was biased toward feeding on maize regardless whether the maize had Bt or not, suggesting western corn rootworm larvae were not repelled by Bt. These data will be helpful for regulators in interpreting western corn rootworm feeding data on Bt maize.

Growth history and intrinsic factors influence risk assessment at a critical life transition for a fish

Making the appropriate decision in the face of predation risk dictates the fate of prey, and predation risk is highest at life history boundaries such as settlement. At the end of the larval phase, most coral reef fishes enter patches of reef containing novel predators. Since vision is often obscured in the complex surroundings, chemical information released from damaged conspecific is used to forewarn prey of an active predator. However, larvae enter the reef environment with their own feeding and growth histories, which will influence their motivation to feed and take risks. The present study explored the link between recent growth, feeding history, current performance and behavioural risk taking in newly settling stages of a coral reef damselfish (Pomacentrus amboinensis). Older and larger juveniles in good body condition had a stronger response to chemical alarm cues of injured conspecifics; these fish spent a longer time in shelter and displayed a more dramatic decrease in foraging behaviour than fish in lower body condition. Feeding experiments supported these findings and emphasized the importance of body condition in affecting risk assessment. Evidently, larval growth history and body condition influences the likelihood of taking risks under the threat of predation immediately after settlement, thereby affecting the probability of survival in P. amboinensis.

Variation in the effects of larval history on juvenile performance of a temperate reef fish

For organisms with complex life cycles, the transition between life stages can act as a significant demographic and selective bottleneck. Variation in developmental and growth rates among individuals present in one stage (e.g. larvae), due to initial differences in parental input and/or environmental conditions experienced, can propagate to future stages (e.g. juveniles), and such ‘carry-over effects’ can shape fitness and phenotypic distributions within a population. However, variation in the strength of carry-over effects between life stages and the intensity of selective mortality acting on intrinsic variation, and how these might be mediated by environmental variability in natural systems, is poorly known. Here, we evaluate variation in the strength to which larval growth histories can mediate juvenile performance (growth and survival), for a reef fish (Forsterygion lapillum) common to rocky reefs of New Zealand. We used otoliths to reconstruct demographic histories of recently settled fish that were sampled across cohorts, sites and microhabitats. We quantified sources of variation in the strength of carry-over effects and selective mortality that operate on larval growth histories. We found overall that individuals that grew fast as larvae tended to experience proportional growth advantages as juveniles. However, the strength of growth advantages being maintained into the juvenile period varied among cohorts, sites and microhabitats. Specifically, a stronger growth advantage was found on some microhabitats (e.g. mixed stands of macroalgae) relative to others (e.g. monocultures of Carpophyllum maschalocarpum) for some cohorts and sites only. For other cohorts and sites, the degree of coupling between larval and juvenile growth rates was either indistinguishable between microhabitats or else not evident. Similarly, the intensity of growth-based selective mortality varied among cohorts, sites and microhabitats: for the cohort and site where carry-over effects differed between microhabitats, we also observed difference in the intensity to which fish with rapid larval growth rates were favoured. Overall, our results highlight how this spatial and temporal patchiness in extrinsic factors can interact with intrinsic variation of recruiting individuals to have a major influence on the resulting distribution of juveniles and their phenotypic traits.

Larva and pupa of Amyna axis (Guenee, 1852) and affirmation of its taxonomic placement in Bagisarinae (Lepidoptera, Noctuidae)

Th e larva and pupa of Amyna axis (Guenee, 1852) are described and illustrated, and observations are provided on the insect’s life history and larval biology. Larval, adult, and life history characters support the transfer of Amyna Guenee from Acontiinae Guenee, 1841 to Bagisarinae Crumb, 1956. Th e phylogenetic placement of the Bagisarinae is enigmatic; some adult and larval features indicate that the subfamily is a basal trifi d proximate to Acontiinae, whereas other larval and life history characters suggest an association with Scoliopteryginae, a basal quadrifi d group. Larvae exhibit a green-to-black color polyphenism presumably linked to larval density, with darker phenotypes occurring during outbreak densities. Parallel color shifts that occur in other Lepidoptera are briefl y discussed.

Ontogenetic effects of diet during early development on growth performance, myosin mRNA expression and metabolic enzyme activity in Atlantic cod juveniles reared at different salinities

This study investigates the effect of diet during early development on growth and metabolic capacity in the juvenile stage of Atlantic cod. Growth in three groups of Atlantic cod juveniles (10–70 g) was measured at two salinities (15‰ or 32‰) in combination with two temperatures (10 °C or 14 °C). Groups of cod from a single egg batch differed by having been fed with rotifers (R) or natural zooplankton (Z) during the first 36 days post hatch. A third group was fed zooplankton from 1 to 22 dph, after which diet changed to rotifers from 22 to 36 dph (ZRZ). All fish were weaned at 36 dph. Juveniles from the Z and ZRZ groups performed equally well under all experimental conditions, but fish that had received rotifers as a larval diet showed overall significantly lower growth rates. Growth was significantly enhanced by reduced salinity. Metabolic enzyme activity and relative myosin mRNA expression levels were not affected by larval diet. Muscle AAT and MDH were affected by salinity while these enzymes in liver tissue were affected by the interaction between salinity and temperature. Metabolic enzymes were stronger correlated with fish size than growth rates. Our results indicate that larval diet has a pronounced effect on juvenile growth rates under varying environmental conditions as optimal larval diet (zooplankton) increased juvenile growth rates significantly. Metabolic enzyme activity and relative myosin mRNA expression were not affected by larval history, which suggests that the persisting juvenile growth difference is not a result of differing metabolic capacity.

Spatially variable larval histories may shape recruitment rates of a temperate reef fish

Several long-standing hypotheses purport variation in recruitment to be positively cor- related with pelagic environmental conditions that enhance larval growth, survival, and/or delivery to recruitment sites. However, the relationship between recruitment intensity and larval environmen- tal conditions (or more directly, larval condition) is difficult to evaluate and poorly known for most species. We evaluate this relationship for the reef fish Forsterygion lapillum that commonly inhabits rocky reefs throughout New Zealand. We quantified variation in recruitment of F. lapillum using a nested sampling design, and found that the largest source of variation was between 2 nearby regions (a semi-enclosed harbour and an adjacent open coast system). We estimated 'settler condition' as the composite of residual body mass and 2 measurements of larval growth (reconstructed from otolith microstructure) and found that recruitment intensity was positively correlated with settler condition for sites within the harbour, but negatively correlated with settler condition for sites on the open coast. Mean pelagic larval duration of recruits to the harbour was ~3 d shorter than recruits to the open coast. These results suggest that larval experience and relationships between recruitment and settler condition are spatially variable. We speculate that (1) larval retention within a productive embayment facilitates a positive relationship between recruitment and settler condition while (2) dis- persal through a less productive environment drives a negative relationship for replenishment on the open coast. These putative differences may have important implications for patterns of recruitment, the strength of post-settlement density-dependent interactions, and dynamics of local populations.

Larval and pupal descriptions for the genera Podischnus and Heterogomphus (Scarabaeidae: Dynastinae: Oryctini)

The larva and pupa of Heterogomphus dilaticollis Burmeister and Podischnus agenor (Olivier) (Scarabaeidae: Dynastinae: Oryctini) are described for the first time based on specimens from Colombia. Podischnus agenor is the first species in the genus to have its immature stages described. Keys to the third-instar larvae of genera in the tribe Oryctini and species of Heterogomphus are included. Data on larval natural history for both species are provided.

Phenotypic plasticity in sperm traits in scorpionflies (Mecoptera: Panorpidae): Consequences of larval history and seasonality on sperm length and sperm transfer

We examined effects of seasonality, larval food availability and larval rearing density on sperm length, sperm transfer rates and body size in the bivoltine scorpionfly Panorpa vulgaris. Males of the first annual generation were larger and had larger sperm. Comparing individuals of two summer generations showed that adult males resulting from group bred, ad libitum fed larvae were larger but had smaller sperm than males resulting from singly kept, food deprived larvae. Thus, sperm size is not a simple function of body size. Instead, we suggest that sperm size modification was caused by varying rearing densities. Group bred individuals produced smaller sperm but transferred at higher rate. This indicates a trade-off between sperm number and sperm size as predicted by evolutionary models of sperm production. Given the strong influence of larval history in our present work, we recommend that future studies investigating the consequences of varying sperm competition risk or intensity on male gametic strategies should also control for larval history in order to avoid distorting effects.

Larval history influences post-metamorphic condition in a coral-reef fish

Upon settlement, many fishes undergo an energetically costly metamorphic period that requires substantial nutritional reserves. Larval growth and the accumulation of lipids prior to metamorphosis are likely to influence growth and survival following this critical period. On the Caribbean island of St. Croix, I investigated relationships between larval growth, early life-history characteristics, and post-metamorphic lipid content in the bluehead wrasse Thalassoma bifasciatum. Lipid reserves remaining after metamorphosis were positively related (r2 = 0.62) to the width of the metamorphic band; thus, this otolith-derived trait may be used to estimate the condition at emergence of survivors collected at some later time. In contrast, pelagic larval duration, average larval growth, and otolith size at settlement were negatively related to post-metamorphic lipid content. Interestingly, the trend for slower growth among fish in good condition was not consistent over the entire pelagic larval duration. Analyses of daily larval growth histories indicated that fish with high lipid reserves grew rapidly in the last week prior to settlement, but relatively slowly during the early phases of larval life; those emerging with low lipid concentrations, however, displayed strikingly opposite patterns. These contrasting patterns of growth and energy storage were consistent at two sites and over three recruitment events. Otolith chemistry data suggested that differences in growth histories and body condition were consistent with the hypothesis of larval development in distinct oceanic environments (characterized by Pb concentration); but, within a water mass, differences reflected life-history trade-offs between growth and energy storage. The results have implications for understanding the processes driving juvenile survival, which may be condition dependent.

Postsettlement survival linked to larval life in a marine fish.

There is a growing realization that the scale and degree of population connectivity are crucial to the dynamics and persistence of spatially structured populations. For marine organisms with complex life cycles, experiences during larval life may influence phenotypic traits, performance, and the probability of postsettlement survival. For a Caribbean reef fish (Thalassoma bifasciatum) on an oceanic island, we used otolith (ear stone) elemental profiles of lead (Pb) to assign recent settlers to a group that developed in waters elevated in Pb concentrations throughout larval life (i.e., nearshore signature) and a group that developed in waters depleted in Pb (i.e., offshore signature), potentially dispersing from upstream sources across oceanic waters. Larval history influenced early life history traits: offshore developers initially grew slowly but compensated with fast growth upon entering nearshore waters and metamorphosed in better condition with higher energy reserves. As shown in previous studies, local production contributed heavily to settlement: at least 45% of settlers developed nearshore. However, only 23% of survivors after the first month displayed a nearshore otolith profile. Therefore, settlers with different larval histories suffered differential mortality. Importantly, selective mortality was mediated by larval history, in that the postsettlement intensity of selection was much greater for fish that developed nearshore, potentially because they had developed in a less selectively intense larval environment. Given the potential for asymmetrical postsettlement source-based survival, successful spatial management of marine populations may require knowledge of "realized connectivity" on ecological scales, which takes into account the postsettlement fitness of individuals from different sources.

Environmental influences on the relationship between juvenile and larval growth of Atlantic croaker Micropogonias undulatus

For marine organisms with bipartite life cycles, there is growing recognition that juve- nile traits may be dependent on previous larval history. The potential correlation between juvenile and larval stages is important to recognize, as growth rates in juvenile fish have been proposed to be an indicator of habitat quality. We investigated whether juvenile and larval growth are positively or negatively related using the estuarine-dependent fish Atlantic croaker Micropogonias undulatus as a model species. The relationship between juvenile and larval growth was examined using both a laboratory study, in which fish were held in individual containers with constant water temperature and salinity, and replicated field experiments, which spanned a range of environmental conditions. There was no relationship between juvenile and larval growth rates in the laboratory experiment. However, results from the field study suggest that a positive relationship between juvenile and larval growth was associated with high levels of freshwater runoff that displaced juvenile croaker from nursery areas to downstream habitats, in which they had reduced feeding success. Variability in the correlation between juvenile and larval growth for the 27 cohorts examined (fish hatched during the same 1 wk period) was independently explained by change in salinity (a proxy for freshwater runoff) and feeding ability (percentage of fish with empty stomachs). Future research should recognize the role that variable environments play in our ability to detect the relationship of life-history traits between ontogenetic stages.

Larval otolith growth histories show evidence of stock structure in Northeast Atlantic blue whiting (Micromesistius poutassou)

Abstract Brophy, D., and King, P. A. 2007. Larval otolith growth histories show evidence of stock structure in Northeast Atlantic blue whiting (Micromesistius poutassou). – ICES Journal of Marine Science, 64: 1136–1144. Oceanographic modelling studies suggest that blue whiting (Micromesistius poutassou) larvae released on the Northeast Atlantic spawning grounds split into two branches, one following a northerly drift trajectory and the second drifting towards the south. This mechanism is proposed to restrict gene flow between northern and southern stock components. This study examined larval growth histories recorded in otoliths of adult blue whiting from three regions of the main spawning area and three feeding areas for evidence of divergent dispersal pathways. Increment measurements show that fish from the south of the spawning area on average grew significantly faster as larvae than those from the north of the spawning area, confirming that blue whiting spawning west of Ireland and Scotland do not form a randomly mixing unit, and that larval dispersal influences the subsequent distribution of spawning adults. Larval otolith growth rates in feeding blue whiting from the Bay of Biscay were significantly faster than those of fish from the Norwegian Sea feeding grounds, showing that mixing of fish from these areas is limited. Fish from the Bay of Biscay grew faster as larvae than fish from all regions of the main spawning area. The results support the proposed split in the blue whiting stock and signal caution for managing the fishery.

Natural variability in size and condition at settlement of 3 species of marine invertebrates

Experimental studies have demonstrated that for many marine invertebrate species, variability in larval condition or quality at settlement may have important effects on post-settlement, early juvenile performance. Relatively few studies, however, explicitly examine natural variability in larval condition at settlement. This study examines natural variability in larval attributes (size and lipid index) at settlement for terminal-stage larvae of intertidal mussels (Mytilus sp.) and barnacles (Pollicipes polymerus and Chthamalus dalli) from southern California. Despite significant differences among cohorts in larval attributes, for all 3 species a greater percentage of the variance in larval length (80-100%) and lipids (58-83%) occurred among individuals within a cohort, rather than among cohorts. For all 3 species, coefficients of variation within a cohort for length were much smaller (3-8%) than those for lipid index (30-93%), suggesting that lipid storage is a much more plastic attribute than size for larvae. For mussels, settlement intensity and larval attributes were decoupled, such that average larval condition of a cohort was not related to the number of larvae that settled. At the cohort level, Mytilus and Pollicipes settling together across 3 dates showed similar trends of decreasing lipid index over time, suggesting that environmental conditions may influence co-occurring planktonic larvae similarly across species. This work highlights the need for further experiments in the field on the effects of larval history on recruitment success in natural populations, and further studies to determine what factors influence larval attributes for planktonic larvae in the field.

VARIABLE TIMING OF LARVAL FOOD HAS CONSEQUENCES FOR EARLY JUVENILE PERFORMANCE IN A MARINE MUSSEL

For organisms with complex life cycles, larval history is increasingly being found to influence later juvenile or adult performance; however, most experiments maintain manipulations in the larval environment at a constant level. Here, I assess the effects of constant vs. variable larval food availability on the marine mussel Mytilus galloprovincialis. In the laboratory, I raised larvae in four food concentrations: constant high, constant low, initial low switched to high, and initial high switched to low. After settlement, I outplanted juveniles to the field for two weeks. Changes in food availability affected larval size and lipid stores, and covariance between the two. Losses of juveniles were greater, and juvenile growth was lower, for those that had been reared as larvae in constant low food compared to those reared in constant high larval food. For the switched treatments, losses were greater, and growth was lower, for juveniles that had experienced initial low larval food relative to those that had experienced initial high larval food, regardless of average larval size or lipid stores from the different treatments. Thus, the timing of pulses of larval food may impact dynamics of later stages.