DISTURBANCE, COLONIZATION AND SUCCESSION IN A DEEP-SEA SEDIMENT COMMUNITY - ARTIFICIAL-MOUND EXPERIMENTS

Megafaunally produced sediment mounds can be sites of rapid biodeposition and may be important sources of infaunal disturbance at the deep-sea floor. We conducted experiments in the Santa Catalina Basin (1240 m depth) using artificial mounds (approximately 9 cm high by 35 cm wide) to assess macrobenthic disturbance resulting from mound formation and to evaluate modes and patterns of recolonization. To differentiate colonization modes, we created two types of mounds: unfloored (allowing all potential colonists) and floored (excluding burrowing immigrants). Burial beneath an average of 5-6 cm of artificial-mound sediments yielded a 32% reduction in macrofaunal abundance over time scales of less-than-or-equal-to 1 month. All functional groups were disturbed by burial, although subsurface deposit feeders appeared to be the least susceptible. In addition, eight of the 14 dominant background species showed significant population reductions on mound treatments. Macrobenthos in unfloored treatments reached background levels of abundance after 11 months, suggesting colonization rates 3x higher than estimated by previous deep-sea studies using colonization trays. Comparisons between floored and unfloored treatments suggest that burrowing was a significant dispersal mode for colonists. Intermediate peaks in the abundance of two infaunal species on unfloored artificial mounds, as well as changes in trophic-group composition, indicate that community succession proceeded for at least 23 months. At 23 months, these treatments also exhibited enhanced species diversity, providing the first direct evidence that the intermediate disturbance hypothesis helps to explain high macrobenthic diversity in the deep sea.