Meeting Abstract
Ocean acidification (OA), the reduction of ocean pH due to dissolution of anthropogenic carbon dioxide, has been shown to negatively affect fertilization of various marine invertebrates. Thus far, most studies have focused on how reduction in pH affects sperm motility without considering the potential impacts on eggs. Sea urchin eggs have a characteristic layer of jelly coat, which is suggested to increase target size for sperm and for species recognition. Here, we exposed the gametes of a tropical sea urchin, Heliocidaris crassispina, to a broad range of pH (pH 6.5 – 8) and quantified jelly coat thickness, sperm motility, and fertilization success over time. Consistent with previous studies, sperm swimming velocity decreased with pH reduction. Thickness of jelly coat also changed with pH: eggs that were spawned into low pH had significantly thinner jelly coats. In the extreme pH treatment (6.5) the jelly coats were on average ~20% thinner than those in the control (pH 8). Despite the observed reduction in sperm motility and jelly coat thickness, fertilization success remained high (>80%) even at the lowest pH treatment. Our results suggest that even gametes were negatively impacted by OA, fertilization could still occur provided there was sufficient sperm density. And yet, the fertilized embryos exposed to pH 7.4 or below failed to divide beyond the two-cell stage, suggesting sensitivity to acidification in later developmental stages could be more detrimental to urchin populations than fertilization.
