Shallow Soft Bottom Habitats
IV. Long-term Patterns of Natural and Human Disturbance
The most important natural disturbance to the nearshore bottom communities is from wave action (Oliver et al. 1980). The structure of sand bottom communities varies more where the frequency and magnitude of physical disturbance is highest, i.e. in shallow water and at the head of the marine canyon (Oliver et al. 1977). But even near the surf zone, episodic biological interactions also cause major changes in nearshore bottom communities (Fager 1964). Although early studies indicated a relatively constant structure in sand bottom epifaunal communities (Fager 1968), longer term sampling showed significant variations in the same community (Davis and VanBlaricom 1978), like those observed in other benthic environments (Dayton 1992, Barry et al. 1995, Tegner and Dayton 1987).
The reoccupation of much of the MBNMS coastline by sea otters (Enhydra lutris) during the past few decades has also influenced the distribution and abundance of nearshore benthic species (Kvitek and Oliver 1988; also see Sandy Beach, Kelp Forest and Marine Mammals sections). Examples include the demise of the recreational Pismo clam (Tivela stultorum) fishery at Moss Landing co-occurring with the expansion of the sea otter range along the Monterey Bay coast (Stephenson 1977), and the decline in numbers of Gaper and Washington clams (Tresus nutallii and Saxidomus nuttalli) in Monterey Harbor (Hines and Laughlin 1980).
The most significant human disturbances are related to changes in the watershed which led to changes in river inputs, both sediment and water, and to discharges from domestic sewage outfalls (see Human Influences section). No benthic community patterns are known from local river inputs, which have decreased dramatically in the last century (Arnal et al. 1973). Although point sources of sewage input often modify nearby bottom communities (Oakden et al. 1984), local sewer outfalls have no measurable impact on biological communities or sediment chemistry, except that the pipes act like reefs in sand bottoms (Kim 1989). The long-term impacts of fishery trawling on benthic communities (generally beyond scuba depths) are unknown, but likely to be extensive. There are significant reductions in benthic fish and large invertebrates in trawling grounds that are active today (Engel 1995; and see Human Influences section).
Section III. Disruptions of Zonation Pattern