Molecular Analysis of Predator Scats Reveals Role of Salps in Temperate Inshore Food Webs

Abstract

High precision, high coverage DNA-based diet analysis tools allow great insight into the food web interactions of cryptic taxa. We used DNA fecal-metabarcoding to look for unrecorded taxa within the diet of a generalist central-placed predator, the little penguin Eudyptula minor. We examined 208 scats from 106 breeding pairs throughout August-February in a large colony at Phillip Island, Australia. While we confirmed a largely piscivorous diet, we also recovered DNA sequences from gelatinous and crustaceous plankton groups that have not previously been detected in the little penguin diet using other diet analysis methods. Gelatinous plankton, including salps, appendicularians, scyphozoans, and hydrozoans were present in 76% of samples and represented 25% of all sequences. DNA recovered from minute copepods and appendicularians may indicate links between trophic levels through secondary predation. Percentage frequency of occurrence (%FOO) demonstrated that little penguin diet composition changed over months and stages (incubation, guard, and post-guard) of the breeding season (month: χ 2 = 201.91, df = NA, p < 0.01; stage: χ 2 = 33.221, df = NA, p = 0.015). Relative read abundance (RRA) uncovered variations in the relative abundance of taxa in the diet over months and stages (month: F = 53.18, df = 59, p < 0.001; stage: F = 66.56, df = 29, p < 0.001). The diet became progressively fish-focused over months of the season and stages, while salps were only present in 4 out of 6 months, with a peak in September. Based on their prevalence in this dataset, in this year of very high breeding success (2.15 chicks per pair), salps may constitute a food source for this largely piscivorous generalist. Our work highlights how DNA metabarcoding can improve our understanding of the trophic role of gelatinous plankton and other cryptic taxa.

Trophic niches of a seabird assemblage in Bass Strait, south-eastern Australia

“…While recent studies have observed that jellyfish can contribute a substantial proportion of the little penguin diet (Sutton, Hoskins & Arnould, 2015;Cavallo et al, 2018), no evidence of such prey were found in the present study. This could potentially be due to rapid digestion of gelatinous prey in comparison to fish or crustaceans (Cavallo et al, 2018), emphasising the limitation of traditional stomach content analyses, or reflect inter-annual differences in available prey types. Stomach contents of short-tailed shearwaters in the present study were similar to those of individuals from Tasmania (Weimerskirch & Cherel, 1998;Cherel, Hobson & Weimerskirch, 2005).…”

“…In contrast, winter stomach contents were dominated by jack mackerel, highlighting a seasonal switch in the availability of the main prey of little penguins. Such differences have also been shown in little penguins from Albatross Island in southern Bass Strait (Gales & Pemberton, 1990) and Phillip Island in northern Bass Strait (Cavallo et al, 2018). While recent studies have observed that jellyfish can contribute a substantial proportion of the little penguin diet (Sutton, Hoskins & Arnould, 2015;Cavallo et al, 2018), no evidence of such prey were found in the present study.…”

“…Such differences have also been shown in little penguins from Albatross Island in southern Bass Strait (Gales & Pemberton, 1990) and Phillip Island in northern Bass Strait (Cavallo et al, 2018). While recent studies have observed that jellyfish can contribute a substantial proportion of the little penguin diet (Sutton, Hoskins & Arnould, 2015;Cavallo et al, 2018), no evidence of such prey were found in the present study. This could potentially be due to rapid digestion of gelatinous prey in comparison to fish or crustaceans (Cavallo et al, 2018), emphasising the limitation of traditional stomach content analyses, or reflect inter-annual differences in available prey types.…”

Peer Review #1 of "Trophic niches of a seabird assemblage in Bass Strait, south-eastern Australia (v0.1)"

“…While recent studies have observed that jellyfish can contribute a substantial proportion of the little penguin diet (Sutton et al 2015, Cavallo et al 2018, no evidence of such prey were found in the present study. This could potentially be due to rapid digestion of gelatinous prey in comparison to fish or crustaceans (Cavallo et al 2018), emphasising the limitation of traditional stomach content analyses, or reflect inter-annual differences in available prey types.…”

“…In contrast, winter stomach contents were dominated by jack mackerel, highlighting a seasonal switch in the availability of the main prey of little penguins. Such differences have also been shown in little penguins from Albatross Island in southern Bass Strait (Gales & Pemberton 1990) and Phillip Island in northern Bass Strait (Cavallo et al 2018). While recent studies have observed that jellyfish can contribute a substantial proportion of the little penguin diet (Sutton et al 2015, Cavallo et al 2018, no evidence of such prey were found in the present study.…”