The physiological ecology of digestion in Arenicola brasiliensis, a deposit-feeding polychaete (Annelida)

Quantifying food resources for deposit feeders has been problematic because sources of food materials are variable and often unidentifiable, and traditional methods that compare the nutritional composition of ambient sediment with the composition of egested sediment are subject to a number of problems that confound the results. I avoid some of the problems associated with traditional methods by inferring the nutritionally important components of the diet of the deposit-feeding polychaete worm Arenicola brasiliensis from measurements of its digestive capabilities. I investigated two potential proxies for diet, (1) changes in digestive enzymes complements and activities in digestive fluids of the worm and (2) comparisons of lipid biomarkers in sediments and worm tissues.; Arenicola brasiliensis has a broad complement of digestive enzymes as would be expected for an animal that exploits sedimentary food resources that vary widely in digestibility and nutritional content. Its digestive enzymes have high temperature optima and high Q₁₀ values indicating temperature sensitivity. Field studies showed that activities of its digestive enzymes vary seasonally with changes in the suite of organic components in the sediments in which it lives. From this research it appears that plant materials (vascular plant macroalgae and microalgae) are the sediment components that these worms are tracking physiologically? Changes in digestive enzyme activities similar to those seen in the field were induced in laboratory manipulations of food availability.; Sediments and body wall tissues of Arenicola brasiliensis contained a diversity of steroidal compounds. The ubiquitous sterols, cholesterol and its degradation products, were, not surprisingly, most abundant in sediments and tissues. Among the plant sterols β-sitosterol, a sterol derived predominantly from vascular plants, was most abundant in sediments and tissues. Overall, the results of sterol analysis show that A. brasiliensis does digest and assimilate plant material from ingested sediments. Vascular plant and algal wrack contributes a large seasonal input of organic material to the sediment at the site I studied, and the vascular plant components of the wrack seem to comprise the most important plant-derived fraction of diet of the worms.