Abstract.Large quantities of drifting algal mats have become a common phenomenon on shallow sandy bottoms in the northern Baltic Sea. A decomposing algal mat rapidly induces hypoxic or anoxic conditions in the underlying sediment and interferes with the normal living‐mode of the benthos, i.e., mobility, feeding, and predator‐prey relationships. Field surveys have shown that bivalves, such asMacoma balthica, avoid the unfavourable anoxic conditions by emerging at the sediment surface. Due to low reburrowing rates these bivalves are exposed to epibenthic predators once the drift algae disperse. A series of aquarium experiments were conducted to test for differences in the survival ofM. balthicawhen exposed to continuous predation without prior stress and short‐term predation after hypoxic stress induced by algae (= 20 02‐saturation). Sublethally stressed adultM. balthica, that normally are outside the size‐range of the isopod predatorSaduria entomon, became significantly more susceptible to predation when lying exposed at the sediment surface. The same effects were found with two other predators, the brown‐shrimpCrangon crungonand the flounderPlatichthysflesus. Drift algal mats induced an escape‐reaction in the infauna more rapidly than mere hypoxia. This response is affected by temperature. which further underlines the importance of drift algae influencing prey availability. This paper discusses the role of the drift algae as a regulating factor for the infauna and demonstrates the importance of external structuring factors, such as hypoxic stress and algal mats, on predator‐pr
展开▼
