Fewer, faster, leaner: a seabird's-eye view of chasing fish in a warming ocean; mechanisms from cell membranes to body-size selection

• Main Authors: 3rd World Seabird Conference 2021, Diamond, Tony
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Ornithology; Environmental Engineering; FOS Environmental engineering; Arctic; Phytoplankton
• Online Access: https://dx.doi.org/10.48448/7dtr-w263; https://underline.io/lecture/34836-fewer,-faster,-leaner-a-seabird's-eye-view-of-chasing-fish-in-a-warming-ocean-mechanisms-from-cell-membranes-to-body-size-selection

Abstract: Recent changes in our long-term study site (25 yrs) in the Bay of Fundy/Gulf of Maine have drawn us to examine the variety of mechanisms that might be affecting the alcids breeding there, given recent exceptionally rapid ocean warming and associated changes in diet. Seabirds are endotherms so manage their own temperature internally; but their prey are ectotherms whose physiology responds directly to changes in the marine environment. I consider some consequences of this 'metabolic asymmetry' on the availability of fish to seabird predators. Fish metabolic rate rises with water temperature, so more energy is needed for metabolism leaving less for growth; yet their ability to secure oxygen declines both because of haemoglobin's reduced affinity to bind oxygen in warmer water, and because warmer water holds less oxygen. The 'burst speed' of fish also increases with temperature, so fish prey are not only fewer (from reduced survival) and smaller (from slower growth) but harder to catch. It is to this increasing mismatch of predator and prey that the dearth of pursuit-diving seabirds in tropical oceans has been attributed. Changes lower in the food-chain add to these challenges for marine birds. In many phytoplankton communities, diatoms tend to be replaced by dinoflagellates; diatoms are the major source of 'essential' (unsaturated) fatty acids (UFAs) in marine ecosystems, which therefore become depleted. UFAs are important in maintaining flexibility in cell membranes, allowing cells to adjust to low temperatures, and therefore predominate in cold-water fish; warm-water fish have no need to maintain cell structure at low temperatures and contain less lipid, in which saturated fatty acids predominate. Fish prey available to seabirds as the ocean warms are likely to be fewer, smaller, faster, and less nutritious ('junk food') than those currently available to seabirds in boreal and arctic waters. Authors: Tony Diamond¹ ¹University of New Brunswick