Flow in the Subtidal Zone: How fluid flow might determine organism distribution in microhabitats of the San Juan Channel.

Abstract

The Salish Sea of Washington State, USA and British Columbia, Canada is characterized by deep narrow channels with saltwater input from the Pacific Ocean and freshwater input from the Frasier River. The San Juan archipelago sits right at the intersection of these two inputs. This region experiences mixed semidiurnal tides and has many narrow passes and abrupt sills that characterize local flow dynamics. A steep drop off close to shore typifies the bathymetry of the sub-tidal habitat. Some of the more obvious parameters that control where benthic sub-tidal organisms live are light and availability of food, but a few studies have sought to shed some light on how microhabitats created by flow regimes also are an important consideration. Small scale studies on how flow affects benthic communities have shown pieces of how communities and individual species of benthic filter feeders have the highest performance when they are within their target flow range. This range is determined mainly by the physiology of how organisms feed.