MEPS 192:163-172 (2000)  -  doi:10.3354/meps192163

ABSTRACT: Since phytoplankton abundance can constitute a highly unpredictable source of food for suspension feeders, we examined whether early juvenile Bugula neritina, Hydroides elegans, and Balanus amphitrite can use bacteria to achieve extended survival or growth when phytoplankton is scarce. At bacterial concentrations of ~2 to 3.5 x 10⁶ cells ml^-1, within the range of values observed in the field, early juvenile B. neritina and H. elegans were effective bacterivores, obtaining enough energy and nutrients from bacteria to sustain survival and growth. When provided with bacterial concentrations of ~3 x 10⁶ cells ml^-1, early juvenile B. neritina grew as rapidly as individuals provided with abundant phytoplankton, and completed the development of a second zooid slightly earlier. At bacterial concentrations of ~1 x 10⁶ cells ml^-1, however, early juvenile B. neritina fared only slightly better in terms of growth and survival than in controls where bacterial concentrations were kept to a minimum. Growth of early juvenile H. elegans at ~2 x 10⁶ bacteria ml^-1 was significantly faster than in the controls, but was nevertheless slower than in the phytoplankton treatment. Finally, Balanus amphitrite did not obtain any detectable benefit from bacteria, despite being provided with bacterial concentrations of ~9 x 10⁶ cells ml^-1, well in excess of values observed in the field. These results indicate that early juveniles of some species are effective at using bacteria as an alternative food source, and may use bacteria as a food supplement or even as a sole source of particulate matter, if necessary, to support survival and growth. Starvation may therefore be a minor natural cause of mortality, if a cause at all, in early juvenile H. elegans and B. neritina which can use bacteria and possibly other alternative food sources when phytoplankton is scarce.

KEY WORDS: Starvation · Suspension feeding · Bacteria · Mortality · Development · Post-settlement