Meeting Abstract
63.4 Sunday, Jan. 6 Intertidal cobble field ecology: Does the Intermediate Disturbance Hypothesis hold for less exposed shores with smaller rocks? MCCLINTOCK, James B*; ANGUS, Robert A; MCCLINTOCK, Ferne E; Univ of Alabama at Birmingham; Univ of Alabama at Birmingham; Univ of Alabama at Birmingham mcclinto@uab.edu
The community structure of macroinvertebrates occurring beneath cobbles during tidal emersion was investigated on the south island of New Zealand. To test if the IDH holds in less exposed shores comprised exclusively of smaller rocks (cobbles) we measured 1) the size frequency distribution of cobbles, 2) the incidence of barnacle encrustation as an indirect measure of cobble disturbance, 3) the abundances of the dominant macroinvertebrates occurring beneath cobbles, and 4) macroinvertebrate fidelity beneath a range of cobble sizes. Only large cobbles were encrusted with barnacles, indicative of their greater resistance to physical disturbance. Fidelity to a given cobble over two tidal cycles was 11-14% for crabs and did not vary with cobble size. In contrast, fidelity to medium and large cobbles was higher for chitons (26-45%) and snails (17-31%) and generally increased with increasing cobble size. In contrast to the predictions of the IDH, there was a positive correlation between increasing cobble size and increasing species diversity of organisms found under the cobbles. This pattern is not attributable to greater space beneath large cobbles as there was a greater density of macroinvertebrates beneath medium and large, compared to the small cobbles. Increasing species diversity with increasing cobble size appears to be independent of patterns of species recolonization associated with small cobbles being subject to high disturbance or interspecific competitive hierarchies associated with low disturbance beneath large cobbles. Instead, factors such as aggregative behaviors, and reducing vulnerability to predators and desiccation stress are likely to explain the relationship between cobbles and their associated macroinvertebrate communities.
