The diet of a nocturnal pelagic predator, the Bulwer’s petrel, across the lunar cycle

Abstract

The lunar cycle is believed to strongly influence the vertical distribution of many oceanic taxa, with implications for the foraging behaviour of nocturnal marine predators. Most studies to date testing lunar effects on foraging have focused on predator activity at-sea, with some birds and marine mammals demonstrating contrasting behavioural patterns, depending on the lunar-phase. However, to date no study has focused on how the lunar cycle might actually affect predator-prey interactions in the upper layers of the ocean. Here, we tested whether the diet of the predominantly nocturnal pelagic predator, the Bulwer’s petrel (Bulweria bulwerii) would change throughout the lunar cycle, using molecular analysis to augment detection and taxonomic resolution of prey collected from stomach-contents. We found no evidence of dietary shifts in species composition or diversity, with Bulwer’s petrel always consuming a wide range of mesopelagic species. Other co-variables potentially affecting light availability at-sea, such as percentage of cloud cover, did not confound our results. Moreover, many of the species found are thought not to reach the sea-surface. Our findings reveal that nocturnal predators are probably more specialized than previously assumed, irrespective of ambient-light, but also reveal deficiencies in our current understanding of species vertical distribution and predation-dynamics at-sea.

Antarctic petrels ‘on the ice rocks’: wintering strategy of an Antarctic seabird

“…glacialis), with diet including various proportions of the two groups in most cases (figure 3). The behaviour of petrels was well known to be impacted by the lunar phase, through the influence on their activity level at breeding colonies or on their activity at sea during or outside the breeding period [48][49][50][51]. The lunar cycle is believed to strongly influence the vertical distribution of potential marine prey species, making them more accessible and/or visible to their predators [48,50].…”

DNA metabarcoding in diet studies: Unveiling ecological aspects in aquatic and terrestrial ecosystems

“…Many of the studies reviewed herein allowed the repositioning of species in aquatic trophic webs and uncovered previously unknown species interactions. The difference in relevance of these new findings for aquatic organisms is presumably linked with the fact that the observation of feeding events or collection of feces is generally less feasible in the aquatic ecosystems, and therefore, previous knowledge was more limited (e.g., Waap et al, ). Examples of such relevant novelties include the surprising finding of cartilaginous prey in the diet of the Australian fur seals Arctocephalus pusillus doriferus (Deagle, Kirkwood, & Jarman, ); the cannibalistic predation of the red lionfish Pterois volitans and its ecological meaning (Valdez‐Moreno, Quintal‐Lizama, Gómez‐Lozano, & García‐Rivas, , which led to the subsequent works of Côté, Green, Morris Jr, Akins, & Steinke, ; Dahl et al, ; Maji, Bhattacharyya, & Pal, ); the confirmation of the occurrence of ontogenetic shifts in the dietary preferences in the largemouth sea bass Micropterus salmoides and sunfish Mola mola (Jo et al, 2014; Sousa et al, ); the detection of a much more diverse prey range than expected for the Adelie penguins P. adeliae and the sunfish revealing a much more generalist feeding behavior for these species (Jarman et al, ; Sousa et al, ); or more recently the high diversity and frequency of bony fishes in the diet of Mobula rays (Bessey et al, ).…”

“…For example, an additional 17 taxa were detected in the diet of Cory's shearwater Calonectris diomedea (Alonso et al, ), highlighting the intrapopulation trophic segregation of this species. Moreover, fine‐scale behavioral patterns of predator–prey interactions and feeding ecology have also been uncovered for the nocturnal Bulwer's petrel Bulweria bulwerii dietary habits in relation to the lunar cycle, where no shift was noted, while revealing a more specialized predation, not related to ambient light (Waap et al, ). Lastly, important conservation implications and management decisions may be informed by DNA metabarcoding dietary studies.…”

“…Many of the studies reviewed herein allowed the repositioning of species in aquatic trophic webs and uncovered previously unknown species interactions. The difference in relevance of these new findings for aquatic organisms is presumably linked with the fact that the observation of feeding events or collection of feces is generally less feasible in the aquatic ecosystems, and therefore, previous knowledge was more limited (e.g., Waap et al, 2017). Examples of such relevant novelties include the surprising finding of cartilaginous prey in the diet of the Australian fur seals Arctocephalus pusillus doriferus (Deagle, Kirkwood, & Jarman, 2009) (Jo et al, 2014;Sousa et al, 2016); the detection of a much more diverse prey range than expected for the Adelie penguins P. adeliae and the sunfish revealing a much more generalist feeding behavior for these species Sousa et al, 2016); or more recently the high diversity and frequency of bony fishes in the diet of Mobula rays (Bessey et al, 2019).…”

“…Moreover, fine-scale behavioral patterns of predator-prey interactions and feeding ecology have also been uncovered for the nocturnal Bulwer's petrel Bulweria bulwerii dietary habits in relation to the lunar cycle, where no shift was noted, while revealing a more specialized predation, not related to ambient light (Waap et al, 2017).…”