Trophic ecology of Octopus vulgaris paralarvae along the Iberian Canary current eastern boundary upwelling system.

Our knowledge of the diet of wild octopus paralarvae, Octopus vulgaris, is restricted to the first 2 weeks of its planktonic phase when they are selective hunters found near the coastline. These small paralarvae, bearing only three suckers per arm, are transported by oceanic currents from the coast towards offshore waters, where they complete the planktonic phase over 2 months. Here, we have investigated the trophic ecology of O. vulgaris paralarvae in two contrasting upwelling sub-regions of the Iberian Canary current (ICC) eastern boundary upwelling system and have evaluated dietary change as paralarvae develop (inferred by counting the number of suckers per arm, ranging from three to 15) along the coastal-oceanic gradient during their planktonic phase. Using high-throughput amplicon sequencing, we have characterised the diet of 100 paralarvae collected along the Northwest Iberian Peninsula (n = 65, three to five suckers per arm) and off the west coast of Morocco (n = 35, three to 15 suckers per arm), identifying up to 87 different prey species. The diet of paralarvae varied along the ICC, with crabs (53.4%), siphonophores (12.2%), copepods (12.3%), cnidarians (8.4%) and pteropods (3.7%) accounting for 90% of the variability detected off NW Iberian Peninsula, whereas off W Morocco, crabs (46.2%), copepods (23.1%), cnidarians (12.9%), krill (9.3%) and fishes (4.2%) explained 95.6% of the variability observed using frequency of observance (FOO%) data. Ontogenetic changes in the diet based on groups of paralarvae with similar numbers per arm were evidenced by the decreasing contribution of coastal meroplankton and an increase in oceanic holoplankton, including siphonophores, copepods, pteropods and krill. Trophic niche breadth values ranged from 0.06 to 0.67, with averaged values ranging from 0.23 to 0.33 (generalist = 1 and specialist = 0), suggesting that O. vulgaris paralarvae are selective predators through their ontogenetic transition between coastal and oceanic environments.

Comparative responses to metal oxide nanoparticles in marine phytoplankton.

A series of experiments was undertaken on three different marine microalgae to compare the effect of two metal oxide nanoparticles (NPs) on different physiological responses to stress: zinc oxide (ZnO), a known toxic compound for microalgae, and the never before tested yttrium oxide (Y2O3). The effect of these potential pollutants was estimated for different physiological variables and temporal scales: Growth, carbon content, carbon-to-nitrogen (C:N) ratio, and chlorophyll fluorescence were evaluated in long-term assays, and reactive oxygen species (ROS) production was evaluated in a short-term assay. Population growth was the most susceptible variable to the acute toxic effects of both NPs as measured in terms of number of cells and of biomass. Although Phaeodactylum tricornutum and Alexandrium minutum were negatively affected by ZnO NPs, this effect was not detected in Tetraselmis suecica, in which cell growth was significantly decreased by Y2O3 NPs. Biomass per cell was negatively affected in the most toxic treatments in T. suecica but was positively affected in A. minutum. ZnO treatments induced a sharper decrease in chlorophyll fluorescence and higher ROS than did Y2O3 treatments. The pronounced differences observed in the responses between the species and the physiological variables tested highlight the importance of analyzing diverse groups of microalgae and various physiological levels to determine the potential effects of environmental pollutants.