The ultimate opportunists: consumers of seston

The seston represents a highly dilute food source to potential consumers. C onsequently, 3 general properties may be expected of sessile filter feeders : (1) high retention efficiency; (2) possession of a low-energy pump system in active filter feeders; and (3) consumption of seston fractions in propo rtion to availability (i.e. opportunistic feeding). Whereas the first 2 pro perties have been well documented, until recently little evidence had been adduced for the third. We assessed whether a pattern across particular stud ies exists that could provide evidence of opportunistic feeding. Recent stu dies of the seasonal variation of seston composition and of natural feeding of species representing 3 contrasting feeding modes were reviewed. For the first time, it was possible to demonstrate in the field that sessile filte r feeders consume a broad spectrum of seston fractions in proportion to the ir availability. We conclude that such opportunistic feeding, within phylog enetically determined broad limits, is a general property of sessile filter feeders, appropriate for exploiting the ubiquitous but dilute and dynamic seston.