Advances in early life history study of fish

The relationship between fish larvae and their zooplanktonic prey has not been fully explored for late-stage larvae of coral-reef fish in lagoonal environments. However, compared to most temperate taxa, these larvae are characterized by strong sensory and swimming abilities, which may influence their feeding behaviour in the water column. The present study aims to determine the relative importance of the water column and zooplankton variables for the structure of pre-settlement larval fish assemblages within a single Season in three bays of the coral reef lagoon of New Caledonia, southwest Pacific. The structure of larval assemblages was found to be explained better by water column variables in two out of the three bays examined. Zooplankton variables only played a role in one bay out of the three, probably due to the lower variability in the water column variables. Moreover, the relationship between total larval fish abundance and zooplankton density was not significant in any of the three bays. These results suggest that the relationship between late-stage coral-reef fish larvae and their prey: 1) is difficult to detect at small spatial and temporal scales, 2) is probably complex and non-linear, 3) depends on environmental conditions, and 4) probably varies between fish taxa

Importancia relativa de las variables de la columna de agua Vs las del zooplancton en la determinación de la estructura de los grupos de larvas de peces en última fase de desarrollo en las aguas costeras de una laguna de arrecife coralino

The relationship between fish larvae and their zooplanktonic prey has not been fully explored for late-stage larvae of coral-reef fish in lagoonal environments. However, compared to most temperate taxa, these larvae are characterized by strong sensory and swimming abilities, which may influence their feeding behaviour in the water column. The present study aims to determine the relative importance of the water column and zooplankton variables for the structure of pre-settlement larval fish assemblages within a single season in three bays of the coral reef lagoon of New Caledonia, southwest Pacific. The structure of larval assemblages was found to be explained better by water column variables in two out of the three bays examined. Zooplankton variables only played a role in one bay out of the three, probably due to the lower variability in the water column variables. Moreover, the relationship between total larval fish abundance and zooplankton density was not significant in any of the three bays. These results suggest that the relationship between late-stage coral-reef fish larvae and their prey: 1) is difficult to detect at small spatial and temporal scales, 2) is probably complex and non-linear, 3) depends on environmental conditions, and 4) probably varies between fish taxa.La relación entre las larvas de peces y sus presas zooplanctónicas sigue siendo poco estudiada para las larvas en últimas fases de desarrollo de peces coralinos en ambientes lagunares. además estas larvas se caracterizan por tener grandes habilidades natatorias y sensoriales respecto a la mayoría de peces en mares templados, habilidades que pueden influenciar su comportamiento alimenticio en la columna de agua. El presente estudio tiene como objetivo determinar la importancia relativa de las variables de la columna de agua y del zooplancton sobre la estructura de las larvas de peces próximas al asentamiento durante una única estación y en tres bahías de la laguna coralina de Nueva Caledonia en el Pacífico sur. La estructura de los grupos de larvas de peces se explica mejor por las variables de la columna de agua en dos de las tres bahías estudiadas, pero las variables zooplanctónicas desempeñan un papel importante en la tercera bahía, seguramente debido a la mayor variabilidad de las condiciones de la columna de agua. La relación entre la abundancia total de las larvas de peces y la densidad total del zooplancton no fue significativa en ninguna de las tres bahías. estos resultados sugieren que la relación entre las larvas de peces coralinos en última fase de desarrollo y sus presas es 1) difícilmente detectable a tan pequeña escala espacial y temporal, 2) probablemente compleja y no lineal, 3) variable según las condiciones medioambientales y 4) probablemente variable según los taxones

Change and Recovery of Coastal Mesozooplankton Community Structure During the Deepwater Horizon Oil Spill

The response of mesozooplankton community structure to the Deepwater Horizon oil spill in the northern Gulf of Mexico was investigated using data from a long-term plankton survey off the coast of Alabama (USA). Environmental conditions observed in the study area during the oil spill (2010) were compared to historical observations (2005–2009), to support the contention that variations observed in zooplankton assemblage structure may be attributed to the oil spill, as opposed to natural climatic or environmental variations. Zooplankton assemblage structure observed during the oil spill period (May–August) in 2010 was then compared to historical observations from the same period (2005–2009). Significant variations were detected in assemblage structure in May and June 2010, but these changes were no longer significant by July 2010. The density of ostracods, cladocerans and echinoderm larvae were responsible for most of the differences observed, but patterns differed depending on taxa and months. Many taxa had higher densities during the oil spill year, including calanoid and cyclopoid copepods, ostracods, bivalve larvae and cladocerans, among others. Although this result is somewhat surprising, it is possible that increased microbial activity related to the infusion of oil carbon may have stimulated secondary production through microbial-zooplankton trophic linkages. Overall, results suggest that, although changes in zooplankton community composition were observed during the oil spill, variations were weak and recovery was rapid

Assessment of fish trophic status and relationships by stable isotope data in the coral reef lagoon of New Caledonia, southwest Pacific

This study examines the trophic status and relationships of coral reef fish in the lagoon of New Caledonia, southwest pacific. The feeding habits of 34 fish species collected at three contrasted sites were first described using a compilation of gut contents observations and data from the literature. The carbon and nitrogen isotope signatures of these fish and of some of their potential ultimate food sources were also determined at each site. Despite some spatial variations in the isotopic signatures of most food sources and fish trophic groups, the overall trophic structures of fish assemblages were similar at the three sites. Stable isotope data were then used to re-assign fish species to trophic groups based on the δ15N signatures of fish and their food sources. Herbivorous fish species were clearly distinguished from the other trophic groups by their lower δ15N signatures, consistent with an estimated trophic position of ~2 for all species examined. Scaridae were however characterized by relatively higher δ13C and lower δ15N, which is probably linked with the role of detritus in their diet. The estimated trophic positions of planktivorous fish species were consistent with their gut contents-based classification. Conversely, the isotopic signatures of carnivorous and piscivorous fish species largely overlapped, and their estimated trophic positions were much lower than expected. This suggests that these species feed over a broader range of trophic levels and food sources than implied by the gut contents observations, and indicates that their diet is partly omnivorous. Finally, the relationships between body mass and the isotopic signatures of four fish species were significant for at least one isotopic ratio for each species. Since ontogenetic variations and omnivorous diets are difficult to assess with gut contents data only, stable isotopes revealed essential in estimating the actual trophic status and relationships characterizing the fish species under study

Environmental Influences on Juvenile Fish Abundances in a River-Dominated Coastal System

We investigated the influence of climatic and environmental factors on variations in juvenile abundances of marine fishes in a river-dominated coastal system of the north-central Gulf of Mexico, where an elevated primary productivity sustains fisheries of high economic importance. Fish were collected monthly with an otter trawl at three stations near Mobile Bay from 1982 to 2007. Fish sizes were used to isolate juvenile stages within the data set, and monthly patterns in juvenile fish abundance and size were then used to identify seasonal peaks for each species. The average numbers of juvenile fish collected during these seasonal peaks in each year were used as indices of annual juvenile abundances and were related to corresponding seasonal averages of selected environmental factors via a combination of principal components analysis and co-inertia analysis. Factors contributing the most to explain interannual variations in juvenile fish abundances were river discharge and water temperature during early spring–early summer, wind speed and North Atlantic Oscillation index during late fall–winter, and atmospheric pressure and wind speed during summer–fall. For example, juvenile abundances of southern kingfish Menticirrhus americanus during summer–fall were positively associated with atmospheric pressure and negatively associated with wind speed during this period. Southern kingfish juvenile abundances during late fall–winter were also negatively associated with wind speed during the same period and were positively associated with river discharge during early spring–early summer. Juvenile abundances of the Atlantic croaker Micropogonias undulatus during early spring–early summer were negatively associated with river discharge and North Atlantic Oscillation during late fall–winter. Overall, the importance of river discharge for many of the species examined emphasizes the major role of watershed processes for marine fisheries production in coastal waters of the north-central Gulf of Mexico

Multiscale analysis of factors that affect the distribution of sharks throughout the northern Gulf of Mexico

Identification of the spatial scale at which marine communities are organized is critical to proper management, yet this is particularly difficult to determine for highly migratory species like sharks. We used shark catch data collected during 2006–09 from fishery-independent bottom-longline surveys, as well as biotic and abiotic explanatory data to identify the factors that affect the distribution of coastal sharks at 2 spatial scales in the northern Gulf of Mexico. Centered principal component analyses (PCAs) were used to visualize the patterns that characterize shark distributions at small (Alabama and Mississippi coast) and large (northern Gulf of Mexico) spatial scales. Environmental data on temperature, salinity, dissolved oxygen (DO), depth, fish and crustacean biomass, and chlorophyll-a (chl-a) concentration were analyzed with normed PCAs at both spatial scales. The relationships between values of shark catch per unit of effort (CPUE) and environmental factors were then analyzed at each scale with co-inertia analysis (COIA). Results from COIA indicated that the degree of agreement between the structure of the environmental and shark data sets was relatively higher at the small spatial scale than at the large one. CPUE of Blacktip Shark (Carcharhinus limbatus) was related positively with crustacean biomass at both spatial scales. Similarly, CPUE of Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) was related positively with chl-a concentration and negatively with DO at both spatial scales. Conversely, distribution of Blacknose Shark (C. acronotus) displayed a contrasting relationship with depth at the 2 scales considered. Our results indicate that the factors influencing the distribution of sharks in the northern Gulf of Mexico are species specific but generally transcend the spatial boundaries used in our analyses

Connectivity through allochthony: Reciprocal links between adjacent aquatic and terrestrial ecosystems in South Africa

An important aspect of the dynamics of nutrients and pollutants in natural systems is captured in the concept of allochthony, founded on the observation that nutrients and energy in a variety of forms are transferred between adjacent habitats, com-munities and ecosystems that are not routinely considered as connected. Different forms of nutrients and energy move across the conceptual boundaries of habitats via organisms’ activities or physical processes such as wind or water currents, and these transfers can represent important food subsidies. Such cross-partition ecolog-ical subsidies can augment the nutritional condition, biomass and biodiversity of communities, particularly where local production (or autochthony) alone may be inadequate to support local food webs. Furthermore, organic subsidies can influ-ence population dynamics, community interactions and ecosystem processes, and can represent dominant flux inputs in ecosystem budgets. Our intention was to ex-plore organic nutrient fluxes in relation to a primarily lotic (i.e. flowing) aquatic sys-tem at the scale of a hydrological catchment

Les assemblages de larves de poissons deans le lagon de Nouvelle-Calédonie : structure spatio-temporelle et relations avec les facteurs abiotiques et biotiques de l'environnement

The understanding of the most influential factors on larval survival in the water column is crucial in order to predict local variations in fish abundances. This dissertation describes the composition and diversity of assemblages of fish larvae at the end of the pelagic stage in the bays and lagoon of New Caledonia, and examines the relationships between their spatial and temporal structures and various abiotic and biotic environmental factors. The peaks in abundances and diversity of larvae were observed during the warm season, between September and February. The number of sun hours per day and wind conditions at the scale of sites, water surface temperature and the concentration in chlorophyll at the scale of stations, were found to be the greatest contributors, in decreasing order of importance, to the variations in abundance of larvae from different families. Similar hierarchies were observed in contrasted sites, suggesting that these variables represent relevant predictive factors for future spatially-explicit models of assemblages structures. Moreover, in seagrass habitats, similitudes of structures were found between adult assemblages and assemblages of larvae sampled nearby, suggesting that adult communities also may play a part. Since feeding success is paramount for larval survival, the diets of different taxa were examined. The densities and relative proportions of larvae's favourite zooplanktonic prey categories were observed to be higher in bays than in lagoonal areas; yet no significant relationship between larvae and larval prey distributions could be detected in these bays. However, larval assemblages structures were positively related to prey density along an inshore-offshore gradient. This suggests that the detection of any relationship between larval assemblages structure and prey assemblages will depend on the spatial scale under consideration. Overall results reveal the importance of bays for the abundances, diversity and diet of larvae at the end of the pelagic stage in the lagoon of New Caledonia.La compréhension des facteurs susceptibles d'influencer la survie des larves dans la colonne d'eau est d'une importance capitale pour prévoir les fluctuations des abondances de poissons en un site donné. L'objectif de cette thèse est donc de décrire la composition et la diversité des assemblages de larves de poissons en fin de phase pélagique dans les baies et le lagon de Nouvelle-Calédonie, et de mettre en relation leur structure spatiale et temporelle avec divers facteurs abiotiques et biotiques de l'environnement. Les abondances et la diversité de larves sont apparues maximales pendant la saison chaude, entre septembre et février. La durée d'ensoleillement par jour suivie par les conditions de vent à l'échelle du site, et la température de surface de l'eau suivie par la concentration en chlorophylle à l'échelle de la station ont le mieux expliqué les variations d'abondance des larves de différentes familles. La hiérarchie de ces différents facteurs est apparue similaire dans des sites contrastés, suggérant que ces variables constituent de bons facteurs prédictifs pour de futurs modèles spatialisés de la structure des assemblages. Des similitudes de structure entre les assemblages d'adultes résidant dans les herbiers et les assemblages de larves collectés à proximité suggèrent que les communautés d'adultes peuvent également jouer un rôle. Comme l'alimentation constitue un processus essentiel de la survie des larves, le régime alimentaire de différents taxons a été analysé. Les densités et proportions relatives des catégories de proies zooplanctoniques préférées par les larves sont apparues plus élevées dans les baies que dans les zones lagonaires, mais aucune relation significative entre la distribution des larves et celle de leurs proies n'a pu être détectée au sein de ces baies. Pourtant, la structure des assemblages de larves et la densité de zooplancton ont varié de manière concomitante le long d'un gradient côte-large. Ce résultat suggère que la détection des relations liant la structure des assemblages de larves et celle de leurs proies dépend de l'échelle d'étude considérée. L'ensemble des résultats obtenus met en évidence l'importance des baies pour les abondances, la diversité et le succès de l'alimentation des larves de poissons en fin de phase pélagique dans le lagon de Nouvelle-Calédonie

Spatio-temporal structure of pelagic larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific

This study aims at describing the diversity and composition of larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific, and identifying the environmental factors that influence the seasonal and spatial patterns of these assemblages. A total of 97 taxa belonging to 7 orders and 26 familis were captured in three bays near Noumea by light trapping every month between January 2002 and June 2003. The assemblages were dominated by Clupeiform larvae and juveniles (96.4% of total abundance) and followed by Perciform larvae (3%). The number of taxa per sample varied from less than five in July-August to more than ten in October-November and abundances followed the same seasonal pattern. Analyses of similarity showed significant differences in the assemblages caught in the three bays and analyses of contribution to the dissimilarity revealed that these differences were due to the most abundant families. The constant part of the relationship between environmental variables and the composition of assemblages was assessed by the partial triadic analysis STATICO, a statistical approach that takes into account the strong seasonality of the data. Rainfall, wind direction and thermal stratification of the water column were found to play a major role in the structure of the assemblages, although tidal amplitude and wind speed became important when Clupeidae and Engraulididae were excluded from the analyses. The richness, relative abundances and seasonal variations of the assemblages caught in three bays under study are close to what has been observed elsewhere in the tropics. This study shows the efficiency of the STATICO analysis for identifying the environmental factors that have a permanent effect on assemblages and sorting them out from those which act temporally or on specific locations. The high abundances and diversity of coral-reef fish larvae observed in coastal zones of New Caledonia suggest that further studies are needed to fully explore the role of the coastal zones of New Caledonia as nurseries