Bottom-up regulation of food webs in a high-latitude environment depends on season and habitat type

Abstract

Food source and quality influence benthic trophic pathways and health status of scavengers at high latitudes. We hypothesised that benthic responses to food sources differing in nutritional value vary across habitats and seasons. We therefore deployed Baited Remote Underwater Video systems with four different types of bait in coastal waters (≤20 m) of the Nain Archipelago (Labrador, Canada). Strong seasonality and a variety of habitat types (e.g., mud and rhodolith beds) characterize this high latitude environment. We deployed an in situ feeding experiment in those habitats during the ice-covered spring and ice-free fall. We selected bait commonly found in the region that fluctuates according to environmental conditions and biotic interactions: herring (Clupea harengus), lion's mane jellyfish (Cyanea capillata), kelp (Laminaria sp.), and crab (Chionoecetes opilio). We deployed herring and kelp in both seasons but the absence of lion's mane in spring only allowed for fall deployments, and we therefore used the crab treatment in spring instead. We observed significantly lower feeding activity in the spring compared to the fall deployments regardless of bait type. The highly structural rhodolith beds supported higher feeding activity than any other habitat and more diverse species composition than the flat muddy habitat. In all habitats, the number of visitors feeding on the fish treatment was significantly higher than to the lion's mane, likely reflecting its higher nutritional value. Species composition between treatments differed significantly, where toad crab Hyas spp. and whelk Buccinum undatum dominated the fish treatment. Only one species consumed kelp and crab treatments, sea urchin Strongylocentrotus droebachiensis and whelk, respectively. Overall, season tempered the intensity of scavenger initial response to a food fall deployments whereas habitat and treatment regulated key players and intensity. Bottom-up effects on benthic scavengers therefore depend on season, habitat, and food source.