Jellyfish, Forage Fish, and the World\u27s Major Fisheries

A majority of the world’s largest net-based fisheries target planktivorous forage fish that serve as a critical trophic link between the plankton and upper-level consumers such as large predatory fishes, seabirds, and marine mammals. Because the plankton production that drives forage fish also drives jellyfish production, these taxa often overlap in space, time, and diet in coastal ecosystems. This overlap likely leads to predatory and competitive interactions, as jellyfish are effective predators of fish early life stages and zooplankton. The trophic interplay between these groups is made more complex by the harvest of forage fish, which presumably releases jellyfish from competition and is hypothesized to lead to an increase in their production. To understand the role forage fish and jellyfish play as alternate energy transfer pathways in coastal ecosystems, we explore how functional group productivity is altered in three oceanographically distinct ecosystems when jellyfish are abundant and when fish harvest rates are reduced using ecosystem modeling. We propose that ecosystem-based fishery management approaches to forage fish stocks include the use of jellyfish as an independent, empirical “ecosystem health” indicator

Project Medusa in the Context of its Historical Time

In 2000, the National Science Foundation, in union with Croatian and Slovenian science ministries, provided initial support for the international collaboration that has become Meduza project. The program was started with the goal of international collaboration. Our initial objective was simple - use this international collaboration to develop exiting scientific research involving medusae in Southern Adriatic waters. This international collaborationa has been of great importance personally and professionally to all of the investigators and institutions involved in the project, but we now ask what objective difference has the project made scientifically. We approach this question by comparing what we might accomplish at the project\u27s outset to how we now view of research on gelatinous zooplankton because of research in the Meduza project. Work outside the also has affected our views but we describe here research produced through the project that has contributed substantially to broadening our perspectives in three major areas of investigations: modes of propulsion, mechanics of predation, and trophic significance of medusae

Jellyfish, Forage Fish, and the World’s Major Fisheries

A majority of the world’s largest net-based fisheries target planktivorous forage fish that serve as a critical trophic link between the plankton and upper-level consumers such as large predatory fishes, seabirds, and marine mammals. Because the plankton production that drives forage fish also drives jellyfish production, these taxa often overlap in space, time, and diet in coastal ecosystems. This overlap likely leads to predatory and competitive interactions, as jellyfish are effective predators of fish early life stages and zooplankton. The trophic interplay between these groups is made more complex by the harvest of forage fish, which presumably releases jellyfish from competition and is hypothesized to lead to an increase in their production. To understand the role forage fish and jellyfish play as alternate energy transfer pathways in coastal ecosystems, we explore how functional group productivity is altered in three oceanographically distinct ecosystems when jellyfish are abundant and when fish harvest rates are reduced using ecosystem modeling. We propose that ecosystem-based fishery management approaches to forage fish stocks include the use of jellyfish as an independent, empirical “ecosystem health” indicator

Atlantic Leatherback Migratory Paths and Temporary Residence Areas

BACKGROUND: Sea turtles are long-distance migrants with considerable behavioural plasticity in terms of migratory patterns, habitat use and foraging sites within and among populations. However, for the most widely migrating turtle, the leatherback turtle Dermochelys coriacea, studies combining data from individuals of different populations are uncommon. Such studies are however critical to better understand intra- and inter-population variability and take it into account in the implementation of conservation strategies of this critically endangered species. Here, we investigated the movements and diving behaviour of 16 Atlantic leatherback turtles from three different nesting sites and one foraging site during their post-breeding migration to assess the potential determinants of intra- and inter-population variability in migratory patterns. METHODOLOGY/PRINCIPAL FINDINGS: Using satellite-derived behavioural and oceanographic data, we show that turtles used Temporary Residence Areas (TRAs) distributed all around the Atlantic Ocean: 9 in the neritic domain and 13 in the oceanic domain. These TRAs did not share a common oceanographic determinant but on the contrary were associated with mesoscale surface oceanographic features of different types (i.e., altimetric features and/or surface chlorophyll a concentration). Conversely, turtles exhibited relatively similar horizontal and vertical behaviours when in TRAs (i.e., slow swimming velocity/sinuous path/shallow dives) suggesting foraging activity in these productive regions. Migratory paths and TRAs distribution showed interesting similarities with the trajectories of passive satellite-tracked drifters, suggesting that the general dispersion pattern of adults from the nesting sites may reflect the extent of passive dispersion initially experienced by hatchlings. CONCLUSIONS/SIGNIFICANCE: Intra- and inter-population behavioural variability may therefore be linked with initial hatchling drift scenarios and be highly influenced by environmental conditions. This high degree of behavioural plasticity in Atlantic leatherback turtles makes species-targeted conservation strategies challenging and stresses the need for a larger dataset (>100 individuals) for providing general recommendations in terms of conservation

La metamorfosis de la corvina rubia Micropogonias furnieri (Pisces, Sciaenidae)

Fish metamorphosis is an important ontogenetic process with a key role on early stages survival and on successful recruitment to adult populations. The whitemouth croaker (Micropogonias furnieri) is an important commercial resource for the coastal fisheries of Argentina and Uruguay. Metamorphosis was studied using morphometric and morphological analysis during larval development. Changes in morpho-meristic characters before and after metamorphosis were employed to determine the length interval of this transition by employing Principal Component Analysis. Individuals (n = 430) from 4 to 41 mm standard length (SL) were collected in the Río de la Plata estuary (35.45° S, 56.35° W) in March 2006. Length ranges of individual’s developmental stages were associated with the presence of key morphological characters. During early life stages, M. furnieri changes from a big-headed, robust shape larva to a slender and more elongated body form. Most of the morphometric variables showed an inflexion point at 15.2 mm SL, with a 95% confidence interval of 14.0-16.4 mm. The anterior part of the body grows faster during early stages, probably related to an intense feeding activity strategy. The completion of pectoral fin rays and the onset of squamation determine the beginning of metamorphosis at 11-12 mm SL. At around 18 mm SL, squamation ends, first barbels develop and the sagittae otoliths primordium is closed. The length-at-metamorphosis for M. furnieri was established between 9 to 18 mm SL, since all developmental characters studied highly overlapped at that interval. All those processes are indicative of the beginning of the juvenile period associated to the settlement and the start of a bottom-oriented life-style.La metamorfosis de los peces es un proceso ontogenético importante con un papel clave en la supervivencia de las primeras etapas y en el reclutamiento exitoso a las poblaciones adultas. La corvina rubia (Micropogonias furnieri) es un recurso comercial importante para las pesquerías costeras de la Argentina y Uruguay. Se estudió su metamorfosis mediante análisis morfométricos y morfológicos durante el desarrollo larvario. Se utilizaron los cambios en los caracteres morfomerísticos antes y después de la metamorfosis para determinar el intervalo de duración de esta transición mediante el Análisis de Componentes Principales. Se colectaron individuos (n = 430) de 4 a 41 mm de longitud estándar (LE) en el estuario del Río de la Plata (35,45° S, 56,35° W) en marzo de 2006. Los rangos de longitud de las etapas de desarrollo de los individuos se asociaron con la presencia de caracteres morfológicos clave. Durante las primeras etapas de vida, M. furnieri cambia de una larva de cabeza grande y forma robusta a una forma corporal más delgada y alargada. La mayoría de las variables morfométricas mostraron un punto de inflexión a los 15,2 mm LE, con un intervalo de confianza del 95% de 14,0-16,4 mm. La parte anterior del cuerpo crece más rápidamente durante las primeras etapas, probablemente relacionada con una estrategia de actividad alimentaria intensa. La adquisición del número definitivo de radios de la aleta pectoral y el inicio de la escamación determinan el comienzo de la metamorfosis a los 11-12 mm LE. Alrededor de los 18 mm LE, termina la escamación, se desarrollan las primeras barbillas y se cierra el primordio de los otolitos sagittae. La longitud-de-metamorfosis para M. furnieri se estableció entre 9 y 18 mm LE, dado el alto grado de superposición que presentaron los caracteres de desarrollo estudiados. Todos esos procesos son indicativos del inicio del período juvenil asociado al asentamiento y al comienzo de un estilo de vida orientado hacia el fondo

Removal of the toxic dinoflagellate Alexandrium tamarense (Dinophyta, Gonyaulacales) by Mnemiopsis leidyi (Ctenophora, Lobata) in controlled experimental conditions

The objective of the present study is to estimate the removal capability of the ctenophore Mnemiopsis leidyi (Ctenophora, Lobata) on cultures of the toxic dinoflagellate Alexandrium tamarense (Dinophyta, Gonyaulacales). For this purpose, observations on its clearance and survival rates were made in controlled experiments, using different A. tamarense cell concentrations. Mnemiopsis leidyi is able to remove dinoflagellates actively from the water column only at the lowest density tested (150 cells mL-1). Animals exposed to 300 cells mL-1 presented negative clearance and removal rates (survival= 67%). All ctenophores exposed at the highest concentrations of toxic dinoflagellates (600 cells mL-1) died after 4 h. Removal may occur mainly by incorporating and entangling cells in the mucus strands formed by the ctenophore, and in a lesser way by ingestion. Results indicate that higher concentrations of A. tamarense are fatally toxic to M. leidyi and that this ctenophore could control only the initial development of this dinoflagellate bloom

Spatial Patterns of Large Jellyfish \u3ci\u3eChrysaora plocamia\u3c/i\u3e Blooms In the Northern Humboldt Upwelling System In Relation To Biological Drivers and Climate

In the Northern Humboldt Upwelling System (NHUS), one of the most productive ecosystems in the world, the large jellyfish Chrysaora plocamia exhibits high inter-annual variability in population size, often resulting in massive blooms. In this study, we examined the geographic patterns C. plocamia in the NHUS and their spatial overlap with ichthyoplankton, zooplankton, and chlorophyll a concentration (Chl a) during two El Niño (EN) years (1982–1983 and 1986–1987), and a neutral year (2014). During EN years, the spatial extent of C. plocamia medusae was larger than in the neutral year. In 1982–1983, medusae were concentrated mainly in the central-southern and southern regions of Peru, where they were associated with zooplankton, sardine larvae, and Chl a. In 1986–1987, medusae occurred in the northern and southern regions and spatially overlapped with sardine larvae and Chl a, and with zooplankton and anchoveta larvae, respectively. In 2014, medusae occurred mainly in the northern region, where they were associated with zooplankton, Chl a, and anchoveta eggs and larvae. Our results indicate strong EN effects on the distribution and abundance of C. plocamia, which can have consequences for zooplankton and ichthyoplankton abundance, as well as fisheries, in the NHUS