MEPS 221:93-104 (2001)  -  doi:10.3354/meps221093

ABSTRACT: This study examined the effects of food limitation, in the form of reduced microalgae, on the recolonization by benthic macrofauna into intertidal saltmarsh-pond mesocosms. Eight tanks (1.4 m diameter) were dug into the intertidal Spartina alterniflora zone of a New Jersey saltmarsh, filled with a layer of defaunated mud, and allowed to recolonize naturally. Shading over 4 of the ponds reduced the light reaching the pond bottoms by 92% and the standing stocks of benthic chlorophyll by 27%. Mean density of the total macrobenthic fauna was 62% lower in shaded ponds relative to controls. This condition persisted over the 2 mo study and showed little change in magnitude during the experiment, suggesting a lower Œcarrying capacity¹ in the shaded habitat instead of a transient effect. Shading caused little change in community composition and had no effect on Shannon¹s index of diversity. Of the 5 most abundant taxa, midge larvae (Chironomus sp.) and the polychaetes Laeonereis culveri and Hobsonia florida densities were significantly lower in shaded ponds. All 3 are known to feed on benthic microalgae. The other 2 dominants, hydrobiid snails and the oligochaete Paranais litoralis, were not significantly affected by shading. Because shading reduced dissolved oxygen levels as well as benthic microalgae, half-way through the experiment continuous aeration was started in 2 of the shaded and 2 of the unshaded ponds in order to maintain high oxygen levels. Oxygenation had no effect on total macrofaunal density, the density of any individual taxon, or species diversity. Results of this manipulative field experiment implicate microalgae as a limiting resource of this macrofaunal community.

KEY WORDS: Saltmarsh · Pond · Benthic macrofauna · Food limitation · Microalgae · Microphytobenthos · Recolonization