SHERRARD, K.M.: Transient Lilliputians: Suspension feeding performance in early juvenile sea squirts (Tunicata: Ascidiacea).

Early juvenile stages of marine invertebrates typically experience high mortality. The causes remain obscure, but nutritional stress is likely to play a role. Sea squirts include solitary species whose juveniles begin suspension feeding at a length of 200 microns, and grow rapidly to several cm, as well as colonial species with larger and more precocious juveniles. Scaling considerations imply that internal suspension feeding is disproportionately costly at the small end of the size range. To what extent is ascidian juvenile suspension feeding performance reduced compared with that in conspecific adults? Here I examine suspension feeding rates in four ascidian species, the solitary Corella inflata and Ciona intestinalis, and the colonial Distaplia occidentalis and Botrylloides violacea. I videotaped incurrent flow of algal particles using a trinocular microscope and cooling stage, and calculated volumetric flow rates from measured velocity profiles. Size was measured as lateral area and was tied to dry mass and ash-free dry mass. In all species, relative volumetric flow rates were initially lower than conspecific adults�, and increased with positive allometry. In the solitary species, later ontogeny was characterized by isometric increase. The colonial species’ volumetric flow rates were comparable to same-sized solitary juveniles, but covered a wider range of values. Increases in siphon size and stigmatal perimeter (lined with flow-driving cilia) and body size were isometric. The relatively poor feeding performance and lack of compensatory morphology (such as larger siphons or relatively more stigmatal perimeter) in early ontogeny suggests that juvenile ascidians are not specialized for suspension feeding at small size.