Chan KY et al. (2015), Acidification reduced growth rate but not swimm...

ECB-ART-44001

Sci Rep 2015 May 15;5:9764. doi: 10.1038/srep09764.

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Acidification reduced growth rate but not swimming speed of larval sea urchins.

Chan KY , García E , Dupont S .

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Swimming behaviors of planktonic larvae impact dispersal and population dynamics of many benthic marine invertebrates. This key ecological function is modulated by larval development dynamics, biomechanics of the resulting morphology, and behavioral choices. Studies on ocean acidification effects on larval stages have yet to address this important interaction between development and swimming under environmentally-relevant flow conditions. Our video motion analysis revealed that pH covering present and future natural variability (pH 8.0, 7.6 and 7.2) did not affect age-specific swimming of larval green urchin Strongylocentrotus droebachiensis in still water nor in shear, despite acidified individuals being significantly smaller in size (reduced growth rate). This maintenance of speed and stability in shear was accompanied by an overall change in size-corrected shape, implying changes in swimming biomechanics. Our observations highlight strong evolutionary pressure to maintain swimming in a varying environment and the plasticity in larval responses to environmental change.

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Genes referenced: impact LOC100887844 LOC100893907

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	Figure 1. Micrographs of larval Strongylocentrotus droebachiensis (10 days post fertilization) reared at three nominal pH levels (a).Geometric morphometric techniques were used to analyze shape change in these larvae through identification of landmarks (b), followed by computation and comparison of Procrutes coordinates on transformation grids (c).
	Figure 2. Example of background flow field in shear and swimming behaviors observed in two flow conditions (still and shear).Shear refers to a velocity gradient in the horizontal direction (a, b) and the shear level generated is similar to that in coastal water c). Red indicates upward moving water and blue indicates downward moving water. Swimming trajectories observed over five minutes of larvae reared at pHT 8.0 were overlaid on these flow fields, with the red circles indicating the beginning of the paths (d, e). Under shear condition, larval urchins experienced horizontal transport across flow lines.
	Figure 3. Average relative mortality rate (inset of a) calculated from linear regression of the change in larval density over time did not differ between pH treatments (a).However, pH has a significant effect on larval growth rate computed by logarithmic regression of increase in total body length over time (b). Closed symbols and solid block line represent pH 8.0 replicates, gray symbols and dash line represent pH 7.6, and open symbols and dotted line represent pH 7.2.
	Figure 4. Larval urchins reared at different pHs had significantly different overall shape after accounting for size difference using landmark analysis.The transformation grids render the space between the landmarks with thin plate splines to aid visualization. On these grids each lollipop shows the original starting point of a landmark with a filled circle and the shift of landmark to the target shape is indicated by a line. Each dot represents the canonical variate scores of an individual observed in each of the pH treatments, color of the dots indicate different pH treatment. CV1 and CV2 together account for over 85% of the total variance observed and their transformation grids with the corresponding transformation grids are shown as insets.
	Figure 5. Vertical velocities of both upward and downward swimming larval urchins varied with age and background flow conditions but pH had no effect on larval swimming.Averages and standard errors of larval swimming velocities from each pH treatment are shown.
	Figure 6. Horizontal velocities (Average Â± S.E.) of downward swimming larval urchins varied with age and background flow conditions (c,d).Downward swimming individuals (d) had higher horizontal velocities than upward swimming individuals (b) in shear i.e., larvae were crossing flow lines towards downward moving background flow (grey area). For both groups of larvae, pH had no effect on larval horizontal swimming velocities.

References [+] :

Chan, Biomechanics of larval morphology affect swimming: insights from the sand dollars Dendraster excentricus. 2012, Pubmed, Echinobase