COLONY FORM AND THE EXPLOITATION OF SPATIAL REFUGES BY ENCRUSTING BRYOZOA

Summary The sheet‐runner continuum model of unilaminar encrusting colony growth is reassessed for cheilostome Bryozoa. It is concluded that the model does not adequately account for the existence of spatially predictable refuges from mortality, which can be selected by the larva at the time of settlement. A third end‐point category of colony form, named the spot colony, is recognized for species settling in small spatially predictable refuges and growing to small, early maturing colonies of determinate or semi‐determinate size. Similar colonies are reported from spatially restrictive substrates such as flexible algal fronds and single sediment grains on particulate seabeds. Runner growth is also reappraised. In some cases, uniserial growth may be regarded as a primary adaptation for growth in linear refuges, or on maze‐like or strongly three‐dimensional surfaces where multiserial growth is impossible, rather than as a general fugitive strategy adopted by competitively inferior forms. A revised classificatory model for encrusting growth is proposed. This consists of two continua, sheet‐ribbon‐runner and sheet‐patch‐spot. It is suggested that an improved ecological classification of encrusting growth might be framed as a series of coupled settlement/growth strategies.