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The annual pattern of burial depth in natural populations of the infaunal bivalves Tagelus dombeii (Tellinacea) and Venus antiqua (Veneracea) is described in relation to annual food availability in both the water column and the sediment and abiotic factors (temperature and salinity) at Coihuín tidal flat, in southern Chile. A field experiment in which burial depth was measured in situ each month (over 14 months), with the aid of a fixed-length nylon thread attached to the shell. For T. dombeii the results showed a significant increase in burial depth with increasing bivalve size and syphon weight. Tagelus dombeii had a mean burial depth of 17·5 cm, which was three times more than in V. antiqua (5·30 cm). The burial depth dynamics for both species displayed a strong correlation with food availability in the water column. Approximately 60% of the variability in burial depth in T. dombeii and V. antiqua was explained by concentration of chlorophyll-a in the water column. Food concentration on the sediment surface did not effect burial depth, i.e. deposit feeding seems to be of minor significance in either species.

Periodic sampling from April 1997 to December 1998 of a population of the deposit-feeding protobranch Yoldia hyperborea from the deep depositional zone (250 m) of Conception Bay, Newfoundland, indicated that this species was exposed to subzero temperatures (Ϫ0.63ЊC) throughout the year. However, the standing stock of phytoplankton in the photic zone showed strong seasonal fluctuations with primary peaks always occurring in April (4.26 and 5.09 g L Ϫ1 chlorophyll a in 1997 and 1998, respectively). In addition, sediment chlorophyll a started to increase (from a low of ϳ6 ng mg Ϫ1 dry weight of sediment) as the sinking of a smaller, secondary bloom, reached the bottom in the first 2 months of 1997 and 1998, although higher concentrations were reached by mid-April and May 1997 (21.32 ng mg Ϫ1 sediment) and remained relatively high until February 1998. An increase of digestive cell height and protein content occurred as soon as sinking organic material from the spring bloom reached the benthic zone, suggesting storage of metabolic energy during spring and summer. Sharp increases in digestive enzyme activity occurred primarily in early spring of each year, coinciding with the timing of the primary spring bloom fallout, suggesting activation of the formerly depressed digestive system after a prolonged period of low food availability (i.e., late summer to autumn). Results suggest that Y. hyperborea strongly depends on the input of fresh algal material despite the high availability of organic matter in the sediment.Carbon supply to the aphotic benthic zone of the sea is largely based on the timing of climatic events (e.g., snow and ice melt, rainfall), tidal exchange, and, most importantly, the sinking of phytoplankton blooms (Wassman 1991;Graf 1992). The organic fraction of the particle input to the sediment is a potential energy source for benthic organisms. It is well established that in shallow water the input of fresh organic matter of high nutritional value from primary production creates a burst of activity in the benthic population (Clarke 1988;Boon et al. 1998). Graf et al. (1982) showed that the response to organic matter input is more rapid in those species that utilize the organic matter directly rather than those species that feed on meiofauna and sediment. However, the availability of food particles decreases with increasing depth and becomes more episodic at higher latitudes, imposing specific constraints on the organisms, which must be able to withstand periods of reduced food availability. Thus energy-demanding metabolic processes such as growth and reproduction are often restricted to periods of high food abundance. For example, antarctic suspension feeders show a marked seasonal variation in feeding rates, with the highest activity occurring in the short but very productive summer, whereas most animals cease feeding during