P3.111 Friday, Jan. 6 Effects of blastocoel geometry and density on swimming ability in early-stage larvae TIMM, L*; GRUNBAUM, D; Texas A&M University, Galveston; University of Washington, Seattle email@example.com
Planktonic larval phases are seen across marine taxa. Recent evidence suggests that early development of swimming capabilities may play a crucial role in larval survival. As marine environments vary most rapidly in the vertical direction, vertical swimming is likely to be an important performance criterion for early-stage larvae. However, vertical swimming requires an effective mechanism for larval orientation. The relatively simple external morphology of most early-stage larvae, and their lack of internal sensory structures, suggest that these larvae orient primarily through a passive gravitational mechanism, i.e., by having a center of buoyancy anterior to their center of gravity. This mechanism may depend strongly on a morphological feature seen in many early-stage larvae: an anterior blastocoel. We hypothesize that larvae are able to manipulate their blastocoel density by preferentially transporting ions in or out, and that the blastocoel plays a crucial role in oriented swimming. This hypothesis implies that altered environmental conditions would require compensating changes in blastocoel characteristics to maintain swimming. For example, in fresher water the blastocoel may be enlarged to maintain larval buoyancy. To test the effects of salinity on early-stage larval blastocoels, we reared Dendraster excentricus larvae at higher and lower salinities and measured their blastocoels at three pre-pluteus stages. We used observed morphologies to parameterize hydrodynamic models of early swimming across a range of blastocoel densities. Larval blastocoel size differed significantly between treatments, with larger blastocoels developing in lower salinity. Model results suggest that blastocoel geometry and density have important consequences for swimming performance rates, possibly indicating new biomechanical constraints on early-stage larvae across a broad range of marine taxa.