ECOLOGY/EVOLUTION

Rapid Fin Movement Sleep

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Science  10 Sep 2004:
Vol. 305, Issue 5690, pp. 1533
DOI: 10.1126/science.305.5690.1533a

Coral and fish species often live in mutualistic associations, in which both partners benefit from the other's presence. For the fish, the association is usually obligatory, as they depend on the coral for both shelter and foraging (for zooplankton). The corals can survive on their own, but nevertheless show faster growth and greater reproductive output when fish are present; fish enhance nutrient input to corals via excretion and can protect them from predators and clear them of sediment.

Goldshmid et al. have documented another mechanism by which fish can benefit coral. In a reef of branching coral near the Red Sea port of Eilat, sleeping zooplanktivorous fish aerate their coral hosts at night. The fish, which were filmed by infrared video camera in their resting positions among the coral branches, spend the night sleep-swimming with their fins in vigorous motion. In the absence of fish, measurements showed that oxygen availability to the corals was severely reduced, to less than 30% of ambient levels. These observations may explain how dominant branching corals (whose morphologies hinder the free flow of water) can inhabit zones of relatively calm water. — AMS

Limnol. Oceanogr. 49, 1832 (2004).

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