Factors influencing rates of sediment ingestion by Parastichopus parvimensis (Clark), an epibenthic deposit-feeding holothurian

Abstract

Rates of sediment ingestion and organic matter uptake by Parastichopus parvimensis , an epibenthic deposit-feeding holothurian have been examined in relation to intraspecific patterns of age-size distribution, differences in sediment type ingested seasonal variations in temperature and annual evisceration events. Individuals living in areas of rock rubble along cove margins in the vicinity of the Isthmus, Santa Catalina Island, southern California were 27% smaller and seven times more numerous than holothurians living on granular sediments on cove bottoms. Animals feeding on the fine particulate matter on rock surfaces removed three times more organic material per gram of ingested sediment than animals feeding on the coarser grained sediments of the cove floor, but the quantity reworked was eight times less. As a result, animals feeding on granular sediments consume almost eight times the quantity of organic matter per animal per day than those feeding on sediment from rock surfaces. P. parvimensis is non-selective with respect to grain size ingested. By only ingesting the top few millimeters of sediment it does, however, exploit the sediment layer with the highest and most readily utilizable organic matter. Annual evisceration events, which affected 60% of the population during October and November, caused a cessation in feeding for approximately 4 weeks until minimal gut connections were formed, and can result in an annual decrease of 10% in rates of sediment reworking and organic matter removal by the entire population. Seasonal variations in temperature did not significantly affect these rates.