Trophic indices for micronektonic fishes reveal their dependence on the microbial system in the North Atlantic

The importance of microbes for the functioning of oceanic food webs is well established, but their relevance for top consumers is still poorly appreciated. Large differences in individual size, and consequently in growth rates and the relevant spatial and temporal scales involved, make the integration of microorganisms and large metazoans in a common food web framework difficult. Using stable isotopes, this study estimated the trophic position of 13 species of micronektonic fishes to examine the microbial and metazoan contribution to mid trophic level consumers. Vertically migrant species displayed higher trophic positions than non-migrant species in all depth layers. The estimated trophic positions agreed well with those from the literature, but all species displayed mean increases between 0.5 and 0.8 trophic positions when taking into account microbial trophic steps. Trophic position, but not the relative importance of the microbial food web, increased with individual size, suggesting that current estimates of the trophic position of top consumers and of the length of oceanic food webs are too low because they are based only on metazoan trophic steps. This finding calls for a review of trophic position estimates and of the efficiency of trophic transfers along oceanic food webs.

Ease into Climate Change Instruction through Ocean Acidification

Although climate change garners the bulk of headlines, ocean acidification is an equally important issue that also results from our increasing consumption of fossil fuels. As atmospheric CO2 dissolves into the ocean, the ocean’s pH decreases, making it increasingly difficult for organisms that build calcium carbonate skeletons to grow and thrive. Given that these marine calcifiers – such as corals, snails, shellfish, crustaceans, and plankton – often form the base of oceanic food webs and are habitat and food resources for larger oceanic plants and animals (including humans), ocean acidification poses a serious threat. In this article, we present a series of investigations that provide evidence that increases in anthropogenic sources of CO2 contribute to the acidification of the ocean, and that an increasingly acidic ocean can negatively impact marine calcifiers.

Pelagic deep-sea fauna observed on video transects in the southern Norwegian Sea

Observations of the diversity, distribution and abundance of pelagic fauna are absent for many ocean regions in the Atlantic, but baseline data are required to detect changes in communities as a result of climate change. Gelatinous fauna are increasingly recognized as vital players in oceanic food webs, but sampling these delicate organisms in nets is challenging. Underwater (in situ) observations have provided unprecedented insights into mesopelagic communities in particular for abundance and distribution of gelatinous fauna. In September 2018, we performed horizontal video transects (50–1200 m) using the pelagic in situ observation system during a research cruise in the southern Norwegian Sea. Annotation of the video recordings resulted in 12 abundant and 7 rare taxa. Chaetognaths, the trachymedusaAglantha digitaleand appendicularians were the three most abundant taxa. The high numbers of fishes and crustaceans in the upper 100 m was likely the result of vertical migration. Gelatinous zooplankton included ctenophores (lobate ctenophores,Beroespp.,Euplokamissp., and an undescribed cydippid) as well as calycophoran and physonect siphonophores. We discuss the distributions of these fauna, some of which represent the first record for the Norwegian Sea.

Luciferin production and luciferase transcription in the bioluminescent copepod Metridia lucens

Bioluminescent copepods are often the most abundant marine zooplankton and play critical roles in oceanic food webs. Metridia copepods exhibit particularly bright bioluminescence, and the molecular basis of their light production has just recently begun to be explored. Here we add to this body of work by transcriptomically profiling Metridia lucens, a common species found in temperate, northern, and southern latitudes. In this previously molecularly-uncharacterized species, we find the typical luciferase paralog gene set found in Metridia. More surprisingly, we recover noteworthy putative luciferase sequences that had not been described from Metridia species, indicating that bioluminescence produced by these copepods may be more complex than previously known. This includes another copepod luciferase, as well as one from a shrimp. Furthermore, feeding experiments using mass spectrometry and 13C labelled L-tyrosine and L-phenylalanine firmly establish that M. lucens produces its own coelenterazine luciferin rather than acquiring it through diet. This coelenterazine synthesis has only been directly confirmed in one other copepod species.

CRABS AS BIOINDICATORS OF TRACE ELEMENT ACCUMULATION IN MEDITERRANEAN LAGOON (BIZERTE LAGOON, TUNISIA) / CARANGUEJOS USADOS COMO BIOINDICADORES DE ACUMULAÇÃO DE METAIS NUMA LAGUNA MEDITERRÂNEA (LAGUNA DE BIZERTE, TUNÍSIA)

Nine crab species samples, males and females, were collected after homogeneously prospection of sediment surface of Bizerte Lagoon. Crabs were caught by dip net from Bizerte Lagoon during spring 2012. Concentrations of metals (Zn, As, Cd, Cr, Cu, Fe, Ni, Pb and Zn) were evaluated in the carapace and muscle tissue of crabs and in surface sediment samples. Concentrations of metals accumulated in the benthic crabs tissues were compared to the reactive metals content that constitute the bioavailable fraction of the sediments. Total organic carbon and carbonate contents were also determined, since they are principal requirements associated with crab development.Results of this work indicate that, in the study area, the metals that reach the highest concentrations in the sediments-water interface are by decreasing order Zn, Cr and Pb. The reactive concentrations of these metals are also the highest. However, the trace elements that are being accumulated in the carapace and muscle of crabs are mainly As and Cu.Continental waters flowing into the Bizerte Lagoon are the main source and the principal cause of the enrichment of trace elements in sediment. Results highlight that the reactive concentrations of metals in sediments were the principal cause of their bioaccumulation in the crabs tissues.The important results of this work highlight that cabs can be very useful on studies of monitoring and evaluation of environmental quality in addition to data obtained from the sediment as they also give information about the bioaccumulation of metals through the oceanic food webs. ResumoNove amostras de espécies de caranguejos, machos e fêmeas, foram coletadas na superfície do sedimento da Laguna de Bizerte. Os caranguejos foram capturados com uma rede na Laguna de Bizerte, na primavera de 2012. Foram avaliadas nas carapaças e no tecido muscular dos caranguejos e em amostras de sedimentos superficiais, concentrações de metais (Zn, As, Cd, Cr, Cu, Fe, Ni, Pb e Zn). As concentrações de metais acumuladas nos tecidos de caranguejos bênticos foram comparadas com o teor de metais reativos que constituem a fração biodisponível dos sedimentos. Os teores totais de carbono orgânico e carbonato também foram determinados, uma vez que são requisitos principais associados ao desenvolvimento dos caranguejos.Os resultados deste trabalho indicam que, na área de estudo, os metais que atingem as maiores concentrações na interface sedimentos-água são, por ordem decrescente, Zn, Cr e Pb. As concentrações reativas desses metais também são as mais elevadas. No entanto, os metais que estão sendo acumulados nas carapaças e nos músculos dos caranguejos são principalmente As e Cu. As águas continentais que desembocam na Laguna Bizerte são a principal fonte e a principal causa do enriquecimento de metais nos sedimentos. Os resultados sugerem que as concentrações reativas de metais nos sedimentos foram a principal causa de sua bioacumulação nos tecidos dos caranguejos.Os resultados deste trabalho revelam que para além dos dados sedimentológicos, os caranguejos podem ser muito úteis em estudos de monitoramento e avaliação da qualidade ambiental, pois fornecem informações sobre a bioacumulação de metais através das cadeias alimentares oceânicas.

Observation of a Gelatinous Octopod, Haliphron atlanticus, along the Southern West Mariana Ridge: A Unique Cephalopod of Continental Slope and Mesopelagic Communities

The circumglobal deep-sea gelatinous giant octopod, Haliphron atlanticus, reaches 4 m in length and uses both benthic and pelagic habitats in the upper 3000 m of the ocean during different life history stages, but it is rarely observed due to the deep-depths where it typically lives. It has been collected in trawls and observed a few times near continental margins or islands and has been identified in the stomach contents of deep-diving predators such as sperm whales and blue sharks or detected as body fragments after predation events. An individual H. atlanticus (~1 m in total length) was video-recorded at 12:21 for about 3 minutes in front of the Shinkai 6500 submersible at 586–599 m (6.5°C, salinity 34.4) along the West Mariana Ridge. It made no escape attempt as the submersible approached and it moved slowly up or down in front of the submersible. It was over the outer seamount-slope (bottom depth ~3208 m) ~50 km west of seamounts (≥1529 m summits), but how it fits into the mesopelagic food web along the ridge is unclear. More information is needed to understand the role of H. atlanticus in oceanic food webs and if it typically lives along seamount ridges.

Low occurrence rates of ubiquitously present leptocephalus larvae in the stomach contents of predatory fish

Leptocephali, the larvae of eels, grow to large sizes and are widely distributed in tropical and subtropical oceans. Their role in oceanic food webs is poorly known because they are rarely reported as food items in fish stomach content studies. Data from 13 years of research on the trophic dynamics of Pacific Ocean predatory fish indicate that among 8746 fish of 76 species/taxa (33 families) that had been feeding, only 16 fish of 6 species had remains of 34 leptocephali in their stomachs. Only 0.013% of the 256 308 total prey items were leptocephalus larvae, and 0.03% of the total prey items were juvenile or adult eels (mostly snipe eels: Nemichthyidae). There were 10 fish of 2 species of lancetfish (Alepisaurus spp., n = 152), 2 rainbow runners (Elagatis bipinnulata, n = 222), and 2 yellowfin tuna (Thunnus albacares, n = 3103) that had leptocephali in their stomach contents, but all except one T. albacares (contained 15 leptocephali) had each eaten ≤3 leptocephali. A swallower, Pseudoscopelus sp., and a frigate tuna, Auxis thazard, had eaten single leptocephali. Twenty-eight bigeye tuna, Thunnus obesus, had eaten 76 juvenile/adult nemichthyid or serrivomerid eels. A literature survey found that only 15 out of 75 examined publications listed leptocephali in the stomach contents of a total of 6 species out of ∼ 42 300 predatory fish of 40 species. The transparency of leptocephali and their apparent mimicry of gelatinous zooplankton could contribute to lower rates of predation. Their soft bodies likely digest rapidly, so although this study and existing literature indicate that leptocephali sometimes contribute to predatory fish diets, particularly for fish that do not exclude gelatinous prey types, and fish with low digestion rates in their stomachs such as lancetfish, their levels of contribution to fish diets and the impacts of predators on eel recruitment remain uncertain.