MACROBENTHIC COLONIST GUILDS AND RENEGADES IN MONTEREY CANYON (USA) DRIFT ALGAE: PARTITIONING MULTIDIMENSIONS

Accumulations of sunken drift macrophytes are known to stimulate high secondary production in submarine canyon heads, but the details of macroinvertebrate colonization of these subsidies are poorly known. I conducted a series of algal and macrofanual sampling programs and manipulative algal‐placement experiments in different Monterey Canyon head sub‐habitats and seasons from 1988 to 1991 to elucidate the dynamics of macroinvertebrate associations with sunken drift macrophytes, severe annual sediment‐flushing events, and the physical and chemical changes associated with these agents of subsidy and disturbance. Conducting these investigations in such a highly disturbed and subsidized setting, i.e., with multiple niche axes, would enable novel insights into how biological communities are structured. Up to 5.7 × 10 5 individual macrofauna/m 2 inhabited naturally occurring patches of sunken drift algae in Monterey Canyon's s shallow head (Monterey Bay, California, USA), and the seasonally changing mosaics of macrophyte subsidies led to conspicuously converse responses of amphipods and polychaetes. Amphipods dominated natural patches of sunken algae during winter and spring, while polychaetes dominated during late summer and fall. This community shift corresponded with temporal changes in algal composition, dissolved oxygen (DO), and annual flushing disturbances. Repeated algal‐colonization experiments in different habitats further highlighted the contrasting responses of amphipods and polychaetes to drift algae and other habitat characteristics. Mean abundances of motile amphipods increased between 8‐ and 148‐fold within five days after placement of Enteromorpha patches (up to >4 × 10 5 individuals/m 2 ) while abundances less than doubled in Macrocystis treatments. Amphipod species colonized Enteromorpha treatments in significantly greater numbers than any controls irrespective of date and sub‐habitat. Polychaete species did not colonize algae treatments in significant numbers within five days, but experiments did reveal significant temporal and habitat differences in this group. Sampling of swimming macrobenthos in different canyon habitats and depths (including 30, 100, 300, and 500 m) revealed temporal and habitat patterns in crustaceans and provided explanations of guild functional contrasts. Attributes of two “evolutionary renegades,” the phytic polychaete Platynereis bicanaliculata and the hypoxia‐tolerant crustacean Nebalia sp., indicated that adaptive constraints inherent in the phenologies and life histories of the two partitioned guilds help reinforce normal functional boundaries. Maximum species richness at intermediate DO and time since disturbance resulted from complementary responses of the two guilds to temporal and habitat characteristics that are shaped by an interacting regime of algal subsidy, hypoxia, and severe flushing disturbance. Corresponding Editor: R. V. Etter.