Meeting Abstract
Filter feeding by glass sponges, especially in dense communities such as reefs, is an important process that couples a pelagic microbial food supply – typically not an accessible food source to other animals – with benthic communities. Filtration of bacteria supplies carbon to sponge reefs, but given high densities and feeding rates in reefs, how do sponges capture enough food and what is the flow of carbon that passes through the reefs? We studied the feeding behavior, from particle capture to excretion, of Aphrocallistes vastus fed 0.1 µm, 1 µm beads, and bacteria using scanning electron microscopy and tracking 13C-labeled bacteria. At 15 minutes post feeding (mpf) bacteria and beads were in canals and actively phagocytized into the primary and secondary reticulum. However, 60 mpf, phagocytic vesicles full of undigested bacteria were visible in other tissues distant from flagellated chambers. By 8 hours pf (hpf), larger phagocytic vesicles were visible in the primary reticulum. By 24 hpf, phagocytized particles were seen in vesicles in the trabecular syncytium. Pulse-chase feeding of 13C-labeled bacteria showed a rate at which carbon consumed by the sponge passed through its body and how much remained in its tissue. The water that washes over sponge reefs comes from deep and surface water, from the nearby Fraser River, and from sediments resuspended among sponges. Stable isotope data show that different reefs feed on distinct food sources, which supports previous findings that reefs require trophic subsidies from currents and which may explain their ability to form dense reefs. Reef sponges, which live at densities of up to 46 m-2, manage to sustain themselves through highly efficient particle capture and by growing in regions with a variety of food inputs.
