Inverse modeling reveals efficient salp‐mediated energy flow to higher trophic levels

Abstract

While pelagic tunicates are known to exert strong influences on ecosystem trophic and biogeochemical function, it has long been assumed that their shortcutting of traditional planktonic food webs results in a dead‐end with respect to higher trophic levels given their poor nutritional quality. Growing reports of salps as prey in various fish diets challenge this notion. Here we combine insights into salp feeding with a variety of other in‐situ rate measurements of New Zealand's Chatham Rise to reconstruct the most likely energy flows within the ecosystems using linear inverse ecosystem modeling. We then utilize model results to assess diets, production, and ecosystem efficiency for each of the key functional groups in the system, including economically important higher trophic levels and fisheries. We find that rather than acting as a trophic dead‐end, the shorter energetic pathways introduced by salps increase overall ecosystem efficiency. Through their direct consumption by fish such as myctophids and oreo, these salp‐driven energetic savings are efficiently passed on to higher trophic levels, increasing NPP‐normalized secondary production by 130% relative to areas with background salp abundances. This finding challenges the hypothesis that an increased dominance of gelatinous zooplankton (brought on by climate change) will negatively impact global fisheries and instead suggests that species able to directly or indirectly access enhanced gelatinous production may instead benefit from the tighter coupling to lower trophic levels.

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