Abstract
Food web linkages, or the feeding relationships between species inhabiting a shared ecosystem, are an ecological lens through which ecosystem structure and function can be assessed, and thus are fundamental to informing sustainable resource management. Empirical feeding datasets have traditionally been painstakingly generated from stomach content analysis, direct observations and from biochemical trophic markers (stable isotopes, fatty acids, molecular tools). Each approach carries inherent biases and limitations, as well as advantages. Here, using 27 years (1991–2016) of in situ feeding observations collected by remotely operated vehicles (ROVs), we quantitatively characterize the deep pelagic food web of central California within the California Current, complementing existing studies of diet and trophic interactions with a unique perspective. Seven hundred and forty-three independent feeding events were observed with ROVs from near-surface waters down to depths approaching 4000 m, involving an assemblage of 84 different predators and 82 different prey types, for a total of 242 unique feeding relationships. The greatest diversity of prey was consumed by narcomedusae, followed by physonect siphonophores, ctenophores and cephalopods. We highlight key interactions within the poorly understood ‘jelly web’, showing the importance of medusae, ctenophores and siphonophores as key predators, whose ecological significance is comparable to large fish and squid species within the central California deep pelagic food web. Gelatinous predators are often thought to comprise relatively inefficient trophic pathways within marine communities, but we build upon previous findings to document their substantial and integral roles in deep pelagic food webs.
Highlights
Food webs are networks of feeding interactions that encompass overall energy flow between resources and consumers within a given ecosystem
Given the complexity of the predator– prey relationships and the inter-changeability of these roles, we present data according to broad ecological groups
In situ observations reveal that a large proportion of the central predatory groups in midwater ecosystems are soft-bodied gelatinous animals
Summary
Food webs are networks of feeding interactions that encompass overall energy flow between resources and consumers within a given ecosystem. Gathering quantitative feeding data for all members of an ecosystem is challenging, if not impossible for vast habitats with high species diversity, and food webs are commonly constructed from compiled observations or diet studies often limited in space or time, or by taxonomic resolution [3]. These approaches are often limited by their inability to resolve prey taxonomic identities, providing instead, general trophic trends Another source of diet data for documenting food webs comes from in situ observations of feeding Video annotations of feeding interactions were processed to identify unique predator– prey feeding events, based on ROV dive number, depth and tape time code, and were tabulated according to identified taxonomic levels for both predators and prey. Tabulated predator – prey interactions were used to compile an ecosystem-level network, or food web, connected by relationships from all documented feeding events. More detailed groupings are provided as electronic supplementary material, as well as raw data and reproducible analysis code (electronic supplementary material S1)
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