Abstract:
ABSTRACT: Sedimentary habitats are complex associations of biotic, chemical, and physical processes
comprising ‘ecosystem function’. The relative importance of these processes to biogeochemical
cycling in highly reactive, permeable sediments remains poorly understood. We report results
from several field experiments in a muddy-sand intertidal flat dominated by 2 functionally different
types of bioturbating macrofauna in False Bay, Washington, USA: (1) the arenicolid polychaete
Abarenicola pacifica and (2) 2 species of thalassinid shrimp (Upogebia pugettensis and Neotrypaea
californiensis). Experimental plots composed primarily of one of the study taxa or mixed communities
of both were evaluated for their effects on porewater advection, solute concentrations, and sediment
characteristics. Fluorescein-impregnated acrylamide gels were used to infer rates of transport, and
acrylamide gel peepers were used to record porewater concentrations of diagenetically important
constituents among experimental plots. Laboratory studies evaluated rates of diffusive transport in
non-bioturbated sediments for comparative analysis. We found that (1) functionally different macrofauna
affect rates of porewater advection in permeable sediments, (2) organism effects are not attributable
to changes in average measures of sediment granulometry, (3) species interactions may
further complicate the advective environment and the resulting diagenetic processes, and (4) species
effects vary according to reaction rate kinetics. We hypothesize that species-related effects on transport
are due to inhibition of arenicolid feeding by thalassinid tubes that serve to block sediment
fluidization and advective flow. Thus, specific behaviors and interactions among organisms appear to
affect transport rates and sediment function in advectively permeable habitats. The results indicate
the importance of integrating behavior, kinetics, and transport into future studies of sedimentary
biodiversity and ecosystem function.
