Life in the fast lane: macrobenthos use temporary drifting algal habitats

In coastal waters filamentous algal growths have increased due to eutrophication. At some stage, algal filaments come loose and start drifting in the water column where they become important transient resources for ambient invertebrates, before they gather at the bottom and start decaying. By field experiments, we have quantitatively studied how macrofauna temporarily utilise these filamentous algae, and whether large water depths or long distances from the shore restrict or promote the colonisation process. Further we have compared macrofauna colonisation rates to algae in the water column and to algae lying at the sediment. sults show that macrofauna colonisation rates are fastest in late July. The colonisation of the drifting algae occurred mainly by juvenile individuals. Species colonising algae at the sea bottom partly originated from the sediment, while species colonising algae in the water column were mobile crustaceans and pelagic juvenile molluscs. Water depths exceeding 10 m restricted colonisation rates, while the distance from the shore seems to be less important as a barrier for migrating fauna from the algal belts. clude that drifting algae serve as important nutrient-rich temporal habitats after they have become detached and been transferred to other areas. Drifting algae also transport species and enhance the recolonisation of previously defaunated sediments, and hence function as floats for Baltic macroinvertebrates.