Flow around phoronids: Consequnces of a neighbor to suspension feeders

Dye visualization was used to assess the effects of closely spaced conspecifics to the flow microhabitat of the benthic suspension feeder Phoronopsis viridis Hilton (Phoronida), which lives in dense populations over a wide range of natural densities. Spacing between upstream‐downstream neighbors affected water movement near the animals and the source of water processed by their filter‐feeding tentacles. Visualization of flow around and between pairs consisting of living and model P. viridis revealed that water encountered tentacle crowns (lophophores) via upward transport from near the sandy substratum rather than from above the lophophore, close spacing of individuals (<1 lophophore diam) inhibited this upward flow for the upstream neighbor, and turbulence generated by an upstream neighbor increased the useful area of feeding surface of the lophophore in the downstream individual. Upward movement of water is important because benthic food particles are an important component of the diet of P. viridis . Thus the presence of neighbors within populations of P. viridis could enhance the incorporation of benthic food particles into their diets. The consequences to feeding of having a neighbor should shift from positive at low densities (>1 lophophore apart) to negative at high densities (≤1 lophophore apart).