Consequences of ocean change for ecological function:Observational and modeling case studies of larval echinoderms
Chan, Kit Yu Karen
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Planktonic larvae of many marine invertebrates play important roles in connecting and sustaining disjunct adult populations. Most larvae are denser than seawater and rely on swimming to regulate their vertical positions. Because environmental variables including direction and strength of advective currents and prey and predator concentrations vary with depth, larval swimming behaviors can significantly impact larval survival and transport. Quantification of larval movement is therefore essential for understanding population dynamics, especially in the face of global climate change because of the need to predict possible shifts in ecosystems. Larval swimming is physically constrained by their morphologies, which are often complex and highly variable. Behavioral responses to surrounding environmental variables modulate the actual swimming performance within physical limits. This study took a two-pronged approach to understand larval swimming through 1) quantifying larval behaviors under changing environmental conditions and 2) modeling larval morphology-flow interactions. This study applied novel non-invasive video motion analysis techniques to quantify effects of environmental variations. Ocean acidification is considered one of the major threats to marine ecosystems and larvae are suggested to be particularly vulnerable. When reared under elevated pCO<sub>2</sub> level, larval sand dollars <italic>Dendraster excentricus</italic> maintained their swimming performance but had lower feeding success. By combining feeding and respiration experiments with motion analysis, we observed similar tradeoffs among larval purple urchins, <italic>Strongylocentrotus purpuratus</italic>, and heart urchins, <italic>Brissopsis lyrifera</italic>. These two echinoids also underwent budding under acidified conditions, an asexual reproduction strategy that has not been previously reported. These results suggest that sublethal OA impacts could be carried over from planktonic stages to later development stages and affect population dynamics. Previous studies suggest that larval swimming performance peaks within a tight morphospace. Larval sand dollars are phenotypically plastic and develop longer arms when starved. Starved individuals swam with higher oscillatory speeds than their fed counterpart. To distinguish the biomechanical constraints associated with morphological changes from behavioral adjustments, we developed a detailed 3-dimensional model of individual larvae using laser confocal microscopy and finite-element mesh generation. This novel modeling approach can easily be adapted for other taxa to help understand constraints that swimming imposes on the evolution of larval form.
- Oceanography