New information from fish diets on the importance of glassy flying squid (Hyaloteuthis pelagica) (Teuthoidea: Ommastrephidae) in the epipelagic cephalopod community of the tropical Atlantic Ocean

Squids of the family Ommastrephidae are a vital part of marine food webs and support major fisheries around the world. They are widely distributed in the open ocean, where they are among the most abundant in number and biomass of nektonic epipelagic organisms. In turn, seven of the 11 genera of this family (Dosidicus, Illex, Martialia, Nototodarus, Ommastrephes, Sthenoteuthis, and Todarodes) are heavily preyed upon by top marine predators, i.e., birds, mammals, and fish, and currently support fisheries in both neritic and oceanic waters (Roper and Sweeney, 1984; Rodhouse, 1997). Their commercial importance has made the large ommastrephids the target of many scientific investigations and their biology is consequently reasonably well-known (Nigmatullin et al., 2001; Zuyev et al., 2002; Bower and Ichii, 2005). In contrast, much less information is available on the biology and ecological role of the smaller, unexploited species of ommastrephids (e.g., Eucleoteuthis, Hyaloteuthis, Ornithoteuthis, and Todaropsis)

Trophic ecology of three sympatric batoid species (Dasyatis pastinaca, Raja clavata, and Raja maderensis) from the Azores, NE Atlantic

ABSTRACT: Describing the trophic structure and interactions of demersal elasmobranch assemblages is fundamental to understanding food web dynamics and developing ecosystem-based management approaches. Stomach content analysis (SCA) and stable isotope ratios (SIA) of carbon (δ13C) and nitrogen (δ15N) from muscle were used to examine the dietary habits and intra- and interspecific trophic ecology of three sympatric batoid species (Dasyatis pastinaca, Raja clavata, and Raja maderensis) from the Azores, Northeast Atlantic. Data were nalyzed with respect to sex and maturity stages. SCA showed that D.pastinaca feeds mostly on crustaceans, whereas R. clavata and R. maderensis prey almost exclusively on teleosts, but not on the same species. Dasyatis pastinaca displayed higher δ13C and lower δ15N values compared to R. clavata and R. maderensis. Trophic niche breadth was variable, D. pastinaca and R. clavata had the broadest and the narrowest trophic breadth, respectively. Relative trophic position categorized D. pastinaca as a mesopredator, while R. clavata and R. maderensis occupied higher trophic positions. With size, R. clavata and R. maderensis shifted from small prey such as crustaceans to larger prey such as teleosts, and they also exhibited significant increases in δ15N with size. Dietary and isotopic overlap was overall low among species, but it was higher between R. clavata and R. maderensis, suggesting more similarity in diet and habitat use between them than with D. pastinaca. This study depicts trophic interactions and functional roles of three co-existing batoid species in the Azorean food webs. In addition to presenting new information on the trophic ecology of D. pastinaca and R. clavata, the present study provides, to our knowledge, the first description of the diet composition and trophic level of the Macaronesian endemic batoid R. maderensis.info:eu-repo/semantics/publishedVersio

Effect of body length, trophic position and habitat use on mercury concentrations of sharks from contrasted ecosystems in the southwestern Indian Ocean

International audienceThe non-essential metal mercury (Hg) can have deleterious effects on health of organisms, and tends to bioaccumulate with age in long-lived organisms and to biomagnify along food chains. Because sharks are fished for human consumption and their Hg levels are frequently above the maximum Hg concentration recommended for fish consumption, understanding the drivers of Hg concentration is of considerable interest. Total Hg concentrations were analysed in muscle tissues of 14 shark and 2 batoid species (n = 339 individuals) sampled across multiple habitats (coastal, oceanic and bathyal) in the southwestern Indian Ocean. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were analysed to assess whether relative trophic position and foraging habitats affected Hg concentrations. Hg concentrations increased with δ15N and body length, highlighting the mechanisms of bioaccumulation and biomagnification in relation with the trophic position and size of the individuals. Habitats where elasmobranchs were collected also affected their Hg concentrations. Bathyal sharks had high Hg concentrations that were almost similar to those of oceanic species, despite their lower relative trophic position. Higher bioavailability of Hg due to its enhanced methylation in deeper waters was considered as the most likely explanation for this result. These results highlight that multiple factors contribute to mercury accumulation in elasmobranchs

Geographic variation in the trophic ecology of an avian rocky shore predator, the African black oystercatcher, along the southern African coastline

International audienceThe reflection of baseline isotopic signals along marine food chains up to higher trophic levels has been widely used in the study of oceanic top predators but rarely for intertidal predators. We investigated variation in the δ13C and δ15N ratios of a sedentary, rocky shore predator, the African black oystercatcher Haematopus moquini, over ~2000 km of the southern African coastline, which is characterized by strong biogeographic patterns in primary productivity and intertidal communities. Blood and feathers from breeding adults and chicks and muscle tissues from primary prey items (mussels and limpets) were sampled between southern Namibia and the southeast coast of South Africa. 15N enrichment was observed between the southeast and west coasts in oystercatcher tissues and their prey, mirroring an isotope shift between the oligotrophic Agulhas Current on the east coast and the eutrophic Benguela upwelling system on the west coast. Oystercatcher blood showed δ13C values that varied between those of the carbon-depleted mussels and the carbon-enriched limpets along the coastline, which reflected changes in the proportion of grazers and filter feeders in the oystercatcher diet across the sampling range. The geographic shift in diet, dominated by mussels on the west coast and composed of mixed proportions of mussels and limpets on the southeast coasts, strongly reflected regionally high abundances of the invasive Mediterranean mussel Mytilus galloprovincialis. Finally, isotope signatures of blood and feathers displayed a strong correlation throughout the study area, indicating seasonal stability in environmental conditions and feeding habits of the adults. There were, however, local discrepancies on the south coast that indicated movement of adults occurred outside the breeding season possibly in response to a lower abundance of food in this region. Overall, the results indicate that the influence of regional oceanic conditions on the base of the food web can penetrate to the predator level, but that local effects can be incorporated within this pattern

Rôle des oiseaux marins tropicaux dans les réseaux trophiques hauturiers du sud-ouest de l'océan Indien

The study of the food web requires the understanding of natural processes related to the distribution and abundance of organisms in their environment. Tropical seabirds show a hierarchical distribution that depends on the position of their colonies in relation to the physical structures of the environment, which favours biological production and to their dispersion capability, which is strongly affected by their status (breeder, migrant, ...). At macro-scale (103km), this distribution reflects the boundaries of their habitat, at meso-scale (10²km) the presence of structure aggregating prey, and at micro-scale (101km), the temporary presence at the surface, of prey driven by foraging marine predatory schools, mostly tunas. In the south-west Indian Ocean, more than 6 million of birds are present, of which 99% are sooty terns. They breed seasonally, in austral winter, at the Seychelles and at Europa, in austral summer at Juan de Nova. High chlorophyll concentration found around islands during breeding season favours the development of the food web that leading to the terns. The location of the Glorieuses Islands drives a sub-annual breeding regime, led by the presence of prey in the vicinity of the colony all year round. Sooty tern biomass removed during the reproduction, is estimated at 55,000 tons yearly, in the Mozambique Channel. The ain preys are squids, pelagic fishes and fish larvae, in various proportions according to the location.L'étude des réseaux trophiques nécessite une compréhension des phénomènes naturels relatifs à la distribution et l'abondance des organismes dans leur environnement. Les oiseaux marins tropicaux ont une distribution hiérarchique qui dépend de la position de leurs colonies vis à vis des structures physiques du milieu favorisant la production biologique, et de la capacité de dispersion des oiseaux, qui est fortement influencée par leur statut (reproducteur, migrateur, ...). A macro-échelle (103km) cette distribution reflète les limites de leurs habitats, à méso-échelle (10²km) la présence de structures qui agrègent les proies et à micro-échelle (101 km), la présence temporaire en surface, de proies rendues accessibles le plus souvent par les bancs de prédateurs en chasse, tels que les thons. Dans le sud-ouest de l'océan Indien, plus de 6 millions d'oiseaux sont présents, dont 99% sont des sternes fuligineuses. Elles se reproduisent de façon saisonnière en hiver austral aux Seychelles et à Europa, en été austral à Juan de Nova. La concentration en chlorophylle plus élevée autour des colonies saisonnières favorise le développement de chaînes alimentaires qui aboutissent aux sternes. La position des Glorieuses semble avoir favorisé une reproduction sub-annuelle,soutenue par la présence de proies autour des colonies toute l'année. Les rélèvements de biomasse effectués par les sternes en reproduction sont estimés à plus de 55 000 tonnes par an, dans le canal du Mozambique. Ces prélèvements concernent des calmars, des poissons pélagiques et des larves de poissons, avec des proportions variables suivant les sites

Short NotePostfledging parental care and unexpected foraging behaviour of juvenile Sooty Terns Onychoprion fuscata in the southern Mozambique Channel

No Abstract.OSTRICH 2010, 81(3): 271–27

Study in South Africa sheds light on ecological gradient between two oceans. WIOMSA Annual Report 2008

Rapport sur Study in South Africa sheds light on ecological gradient between two oceans. WIOMSA Annual Report 200

A first assessment of marine litter on a beach of an uninhabited island in the Mozambique Channel

Marine litter is ubiquitous and associated with both ecological and socio-economic consequences. Beaches are major sinks of marine litter and as such its assessment and monitoring are needed. An opportunistic marine litter survey was performed for 12 consecutive days on the island of Juan de Nova in the central Mozambique Channel in February 2007. Plastic dominated the marine beach litter with daily accumulation of plastic positively related to the tide height (R2 = 0.768, p<0.01). Annual deposits could reach an average of 1 t.km-1, suggesting that regular cleaning of the coastline should be conducted to limit the impact on the local wildlife of this protected area

Effects of urea and lipid removal from Carcharhinus leucas and Galeocerdo cuvier white muscle on carbon and nitrogen stable isotope ratios

International audienceThe analysis of stable isotope ratios of carbon and nitrogen is a tool commonly used in trophic ecology. However, the presence of nitrogen compounds and lipids in tissues of studied organisms can bias the ratio measurements. Treatments to eliminate problematic compounds have been highlighted in the literature. In this study the effects of two different treatments and their combination on the δ15N and δ13C ratio values of Carcharhinus leucas and Galeocerdo cuvier white muscle samples were tested. All sharks were caught along the west coast of Reunion Island (western Indian Ocean), within the framework of a shark-control programme. Deionized water rinsing proved to be the most effective treatment for nitrogen compound removal and the lipid extraction, using a 2:1 chloroform-methanol solution, the most effective treatment for lipid removal. The combination of both treatments was as effective as deionized water rinsing for nitrogen compound removal but produced an unexpected decrease of δ13C ratio values.Deionized water rinsing caused a similar decrease on some δ13C values in the bull shark. Some differences on the effects of the different treatments appeared when considering the sexes separately. Analytical normalization equations for the different treatments on the two stable isotope ratios are provided

ReefTEMPS-OI - Réseau d'observation des eaux côtières de l'Océan Indien

GEOSUR est le catalogue de données de l'OSU- RéunionReefTEMPS is a network created by the IRD, initially covering some twenty territories and island states in the South, South-West and West Pacific. ReefTEMPS-OI is the Indian Ocean version. The network uses temperature, pressure, salinity and other coastal observables to monitor climate change and its effects on coral reefs and their resources over the long term. ReefTEMPS is part of the French national federative Research Infrastructure for coastal ocean and seashore observations named IR I-LICO, accredited as a National Observation Service (SNO) by the CNRS-INSU Ocean-Atmosphere Commission. ReefTEMPS is operated by ENTROPIE since 2019, and before by the GOPS (South Pacific integrated observatory for the environment, terrestrial and marine biodiversity) in 2010-2017, and by LEGOS in 2018. ReefTEMPS-OI is operated by OSU-Reunion since 2020.ReefTEMPS est un réseau créé par l'IRD qui couvre initialement une vingtaine de territoires et états insulaires à l’échelle du Pacifique Sud, Sud‐Ouest et Ouest. ReefTEMPS-OI est sa déclinaison dans l'Océan Indien. Ce réseau repose sur des capteurs de température, pression, salinité et autres observables dans le domaine côtier pour le suivi à long terme du changement climatique et de ses effets sur l’état des récifs coralliens et de leurs ressources. ReefTEMPS est un service d’observation de l’infrastructure de recherche nationale française « milieux littoraux et côtier » IR ILICO, labellisé Service National d'Observation (SNO) par la commission Océan-Atmosphère du CNRS-INSU. Le réseau ReefTEMPS est piloté par l’UMR ENTROPIE depuis 2019, par le GOPS (un consortium d'observatoires de recherche dans le Pacifique Sud) avant sur la période 2010-2017, et par le LEGOS en 2018. ReefTEMPS-OI, sa déclinaison dans l'Océan Indien, est pilotée par l'OSU-Réunion depuis 2020