stables isotopes, and tracking: unraveling the trophic ecology of a winter-breeding storm petrel (Hydrobates castro) with a multimethod approach. Marine Biology 167 ( 14) , -

There is a growing search for less invasive methods while studying the diet of Antarctic animals in the wild. Therefore, we compared the diet of gentoo penguins from stomach contents (i.e. through visual identification of prey remains) and scats (i.e. faeces), and further compared prey DNA assay in fresh and old scats. Prey remains identified visually in stomach contents and scats were broadly comparable: the crustaceans and fish were the most important components, with Themisto gaudichaudii clearly being the most frequent and numerous prey species in both sampling methods. By mass, differences in species frequency were observed in stomach contents (Parachaenichthys georgianus) and scats (Champsocephalus gunnari), with the former fish species absent in scats.Differences were detected in the most frequent prey (T. gaudichaudii and Euphausia superba) and in various fish species, most with bigger sizes in scats. Allometric equations to estimate most crustacean's sizes (i.e. relationships between carapace and mass/total length) are needed. For DNA studies, when comparing DNA from fresh and old scats, both provided similar results that, in general, were also similar to the visual analysis. In order to use penguin scats (along with the use of DNA analyses) for monitoring purposes, allometric equations to estimate mass and size of prey (most crustaceans) and better designed species-specific primers are needed for targeting key prey species (e.g.Euphausia superba, T. gaudichaudii). These DNA methodologies can complement other methods (i.e. visual analyses and stomach contents analyses) in monitoring programs of penguins.

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Although studying the diet of threatened species is crucial in terms of conservation, the diet of the Madeiran Storm Petrel Hydrobates castro and the vulnerable and Azores-endemic Monteiro's Storm Petrel H. monteiroi is mostly unknown. The only information available to date comes from anecdotal observations, analysis of mercury levels and stable isotopes. Here is presented the first insights into prey consumption by adults and chicks from the two species breeding in the Azores. The rapidly developing field of metabarcoding was used to identify dietary items from fecal samples, to species level where possible. A total of thirteen fish, five cephalopod, one crustacean and two oligochaete operational taxonomic units (OTUs) were detected. Results suggest that both petrel species feed mainly on myctophid fish. However, differences were detected between the prey species consumed by (i) H. monteiroi and H. castro, (ii) two distinct H. castro populations (Vila and Praia islets), and (iii) chicks and adults within the same population.

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Plastic pollution is distributed patchily around the world’s oceans. Likewise, marine organisms that are vulnerable to plastic ingestion or entanglement have uneven distributions. Understanding where wildlife encounters plastic is crucial for targeting research and mitigation. Oceanic seabirds, particularly petrels, frequently ingest plastic, are highly threatened, and cover vast distances during foraging and migration. However, the spatial overlap between petrels and plastics is poorly understood. Here we combine marine plastic density estimates with individual movement data for 7137 birds of 77 petrel species to estimate relative exposure risk. We identify high exposure risk areas in the Mediterranean and Black seas, and the northeast Pacific, northwest Pacific, South Atlantic and southwest Indian oceans. Plastic exposure risk varies greatly among species and populations, and between breeding and non-breeding seasons. Exposure risk is disproportionately high for Threatened species. Outside the Mediterranean and Black seas, exposure risk is highest in the high seas and Exclusive Economic Zones (EEZs) of the USA, Japan, and the UK. Birds generally had higher plastic exposure risk outside the EEZ of the country where they breed. We identify conservation and research priorities, and highlight that international collaboration is key to addressing the impacts of marine plastic on wide-ranging species.

Predator-prey interactions provide key information on the role of each species in the community and an overall assessment of the stability of food webs. DNA metabarcoding has the potential to provide highly informative data which substantially enhance trophic interactions analysis, by providing higher taxonomic detail compared to earlier methods. Here we show, using the Cabo Verde seabird community, that the integrated analysis of trophic networks based on DNA metabarcoding of faecal samples can increase considerably our understanding of the trophic interactions in whole communities. Results revealed that these seabird species prey mostly on fish, with most seabirds relying heavily on very few prey species, which are also targeted by fisheries. This community shows high specialization and modularity levels, i.e., is dominated by seabird species with specialized diets. Such network structure has implications for its management and conservation because specialist predators are especially vulnerable to prey depletion. The Cape Verde shearwater (Calonectris edwardsii), identified as the main network connector species, was confirmed to be a suitable sentinel species of changes in this marine food web. Our results clearly show that network analysis can be used effectively to maximize the potential of DNA metabarcoding in studying trophic interactions of complex communities.