Form and function in juvenile ascidians: I. Implications of early juvenile morphologies for performance

Newly settled marine invertebrates are typically less than 1 mm tall and face physical and biotic factors distinct from those facing adults, including a fluid environment dominated by high viscosity and deep boundary layers, and a size-specific suite of predators and competitors. If juveniles have distinct morphologies from adults, or morphologies that function differently at small scales, these differences could have important implications for juvenile performance. We compared the ontogenetic scaling of morphological parameters related to suspension feeding in 6 species of ascidians covering a wide taxonomic range. Many aspects of early juvenile morphology differed from those of conspecific adults, though not invariably in ways likely to improve feeding performance at small size. Some juvenile morphologies that are detrimental to efficient suspension feeding may serve other functions, whereas others are the result of commencing suspension feeding before the completion of metamorphosis. Thus, not all ascidian species appear specialized for higher rates of suspension feeding and early growth.