DISSERTATION RESEARCH: Biomechanical and Life Historical Challenges to Performance in Early Juvenile Ascidians

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Michael LaBarbara and Kristin Sherrard Unlike land animals, many marine animals are fully independent from the earliest juvenile stages, a tenth of a millimeter long. At this size there are unique challenges to feeding, growth, and survival. Water behaves like honey and is costly to move through, being stepped on by a shrimp is fatal, and the food itself, such as algal cells, is much larger in relation to your mouth. Little is known about how marine invertebrate juveniles face these challenges, although mortality rates are higher than at any subsequent stage, which suggests that early juvenile performance may be a crucial determinant of reproductive success. The researchers are investigating feeding performance, growth rates, and mortality in early juvenile ascidian, or sea squirts. Sea squirts function much like clams, filtering water to feed on microscopic particles. They have a variety of growth forms, and may be colonial, budding off small feeding units, or solitary, increasing greatly in size. Initial juvenile length varies tenfold, and some species have adults of up to 10 cm in length, with a thousand-fold length change in the course of growth. The researchers will compare suspension feeding performance between juvenile and adult sea squirts of the same species, and between juveniles of species with different growth patterns. They will determine whether filter feeding at small size is mechanically less efficient than at larger size, and evaluate the extent to which performance is optimized at different stages in the life cycle. Comparing feeding performance in six distantly related species of sea squirts will reveal whether there are multiple strategies to minimize the difficulties of feeding efficiencies and growth at small size stages.