Cheryl Ann Zimmer
My research focuses on the factors that determine where benthic marine invertebrates live (benthic means living on or in the bottom). Distributions of invertebrate populations, including commercially important clams, snail, worms, and crabs, often reflect initial larval settlement sites. What, then, determines settlement locations? The classical view is that settlement is a two-phase process, first dispersal, then “touch-down,” when larvae contact the seafloor. The touch-down process and cues are less well understood than dispersal. Recently, we discovered that a surface layer of fluffy, aggregated particles, known as “floc,” contain very high concentrations of larvae. Larvae can actively enter or get passively entrained in floc, depending on the strength of water currents near the bottom. What floc provides for the larvae remains unknown, but we are investigating the hypotheses of nutrition and protection from predators. A third hypothesis involves larval transport with floc mats that drift along the sea floor. The itinerant aggregates may expose larvae to more potential settlement sites than the animals would encounter by swimming. The discovery of an association of larvae with floc, and floc’s apparent role in settlement, suggests the existence of an important but previously unrecognized third phase in the settlement process. Greater understanding of floc formation may help explain the success, or failure, of settlement in different benthic environments. Because contaminants attach preferentially to the fine particles that make up floc, pollution may also affect the formation and quality of floc, and thus, settlement distributions.