Abstract

A simulation of natural disturbance at the bathyal seafloor evoked rapid response from dominant infaunal species, for the first time providing experimental evidence that similar disturbances structure normal deep-sea communities. Parcels of dead fish (1–40 kg) were placed on the seafloor at a depth of 1310 m in the Santa Catalina Basin and monitored with Alvin and free-vehicle cameras for up to 8 wk. Dense aggregations of fish and ophiuroids were rapidly attracted to the baitfalls; in the process of consuming the bait, these megafaunal scavengers disrupted sediment surface structures and resuspended substantial amounts of sediment. The predominant macrofaunal effect was reduction of infaunal species diversity and community abundance around treatments. The most strongly depressed species was the community dominant Tharyx monilaris, a near-surface-dwelling cirratulid polychaete. Disturbance effects were low in intensity, however, with a large number of background species persisting within the perturbed area. Three macrofaunal species rapidly colonized the areas of disturbance/enrichment near baitfalls; two of these species, the paraonid polychaete Levinsenia oculata and the cirratulid polychaete Chaetozone sp. A, were dominant members of the surrounding community, while the third respondent, the cumacean (?)Cumella sp. A, was rare in background sediments. L. oculata and (?)Cumella apparently responded as post-larvae, suggesting that "adult" colonization of disturbed habitats may be important in deep-sea environments. The opportunistic response of two common species indicates that normal components of the Santa Catalina Basin fauna can rapidly exploit disequilibrium conditions, such as those resulting from a variety of low-intensity disturbance sources (e.g., conveyor-belt species, megafaunal "croppers", skates, flatfish, carcasses of megafauna, kelp falls) commonly observed at the basin floor. Low-intensity disturbance may thus contribute materially to the structure of this, and other, deep-sea communities.

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