Trophic Structure of Neuston Across Tropical and Subtropical Oceanic Provinces Assessed With Stable Isotopes

Abstract

The marine neuston, organisms living in the vicinity of the ocean surface, is one of the least studied zooplankton groups. Neuston occupies a restricted ecological niche and is affected by a wide range of endogenous and exogenous processes while also being a food source to zooplankton fish migrating from the deep layers and seabirds. In this study, the neustonic communities were characterized along the Malaspina global expedition sampling tropical and subtropical oceanic provinces using stable carbon and nitrogen isotopes to explore their trophic structure and relationships with environmental variables. The differences in stable isotopes mirrored the patterns in environmental characteristics of each province. High δ13C values were associated with atmospheric carbon inputs, while the presence of dinoflagellates, coccolithophorids, and upwelling influence is related to low δ13C values. Similarly, provinces presenting high δ15N values were associated with denitrification and nitrate diffusive fluxes, whereas the presence of low δ15N is attributable to nitrogen supplied through N2 fixation by diazotrophs. Neuston showed a large overlap among the isotopic niches of four functional groups, with chaetognaths and detritivores generally exhibiting a smaller degree of overlap compared to carnivores and omnivores/herbivores. These results support the hypothesis of a common trophic structure in the neuston community across the ocean. However, the size of the niche, small in coastal areas and those influenced by upwelling and large in oligotrophic regions, and their overlap, low in more productive provinces and high in oligotrophic provinces, may be associated with food availability. Small trophic niches are associated with a dominance of specialized over-opportunistic feeding in productive environments.

Hydrographic fronts shape productivity, nitrogen fixation, and microbial community composition in the southern Indian Ocean and the Southern Ocean

“…Differences in P B usually arise from physiological changes due to variabilities in irradiance (Geider, 1987), nutrient concentrations (Behrenfeld et al, 2008;Chalup and Laws, 1990), or differences in phytoplankton community structure, where cyanobacteria have the highest PP efficiency and diatoms the lowest (Talaber et al, 2018). Thus, our observations suggest that either (1) there is a lack of selective pressure on photosynthetic efficiency between provinces or (2) mechanisms driving P B are different between provinces, and the sum of beneficial (e.g., increased nutrient concentrations in the SO) and detrimental mechanisms (e.g., low irradiance and photoinhibition through deep vertical mixing, reported from the Antarctic circumpolar current (ACC); Alderkamp et al, 2011) result in similar P B . The slight variation around the frontal system is hard to interpret, as the complex interplay between factors may result in stochasticity.…”

Estimating the impact of new high seas activities on the environment: the effects of ocean-surface macroplastic removal on sea surface ecosystems

“…Little is known about interspecific interactions in the neuston, so a multispecies model is currently beyond our capabilities. There is recent evidence of interspecific competition in the neuston from stable isotope studies ( Albuquerque et al, 2021 ). However, the general claim that interspecific interactions are weaker than intraspecific interactions ( Mutshinda, O’Hara & Woiwod, 2009 ) appears to be supported by specific models for aquatic systems ( e.g.…”

Mesoscale structure of neuston assemblages across the southern Indian Ocean subtropical gyre

“…Kerambrun and Champalbert, 1995). And this can be seen very clearly in the overlapping isoplots of Albuquerque et al (2021). In other words, not only do the organisms that occupy the sea-surface interphase look different from those occurring at depths greater than 30 cm (Helm, 2021a), but the assemblages of which they are part likely function in slightly different waysat least towards the centre of subtropical ocean gyres.…”

“…Although it is customary to take a single neuston sample at any station (e.g. Jeong et al, 2014;Albuquerque et al, 2021), here we collected three neuston samples (total = 84) at each. Individual stations were not occupied for a full day-night cycle, but were sampled sequentially along the transect line, so there is no corresponding set of day and night samples for any station.…”

“…The euneuston is dominated by carnivores: Physalia (Bieri, 1970;Holdway and Maddock, 1983a), Velella (Purcell et al, 2015;Betti et al, 2019;Helm, 2021b), Porpita (Sahu et al, 2020), Janthina (Churchill et al, 2011;Helm, 2021b), Glaucus (Thompson and Bennett, 1970;Sahu et al, 2020;Helm, 2021b) and Halobates (Cheng, 1985) all eat "meat". And carnivores dominated the abundance of the non-copepod neuston westward of 95 • E. Yet euneuston only represented 11% of the fauna between 70 and 85 • E (Table 1), less than 6% of assemblages in most other samples there and only 2% of that eastward of 95 • E. The carnivorous nature of the neuston is largely down to its facultative members, because chaetognaths (Albuquerque et al, 2021), siphonophores (Mackie et al, 1988) and most hyperiid amphipods (Shulenberger, 1977) also eat "meat". Although we should be cautious in our interpretation of these data because information about copepods is missing, neustonic copepods show a greater tendency towards carnivory/omnivory than herbivory (e.g.…”