NATURAL ANCHORING OF THE RED ALGA, GRACILARIA CONFERVOIDES (L.) GREV. ON UNSTABLE BOTTOM BY ASSOCIATION WITH AN ANNELID WORM

Clumps of Gracilaria confervoides (L.) Grev. several meters long and several kilograms in weight have been found growing on clean sand bottom. These plants do not arise from the usual discoid holdfast on a buried stone, etc., but each is anchored by enwrapment of main strands to the tube of a worm, Diopatra ornata Moore. This enwrapping was observed to occur by mechanical obstruction of loose hanks of the alga by projecting worm tubes during extreme low tides on winter nights. In three months the alga was cemented to the tube by unexplained action. A coaction of alga and tube worm apparently exists that establishes plant shelter for small animals on an otherwise unsuitable substratum, thus increasing the complexity of the community on such sites. It is suggested that perennating marine algae produce much the same seasonal shelter for animals as do the deciduous plants of terrestrial communities.