The Effect of Temperature on the Vertical Distribution and Swimming Speeds of Pycnopodia helianthoides and Pisaster ochraceus Larvae in haloclines

Abstract

We investigated the effect of high temperatures on the vertical distribution and swim speeds of Pisaster ochraceus and Pycnopodia helianthoides larvae in haloclines. The haloclines were kept at 12-13 °C for the low temperature treatment and 18 °C for the high temperature treatment. We saw that larvae kept in low temperatures showed higher proportions of larvae at the halocline or swimming just above the bottom of the chamber than larvae kept in high temperatures, who tended not to swim. Data analysis suggests that these differences were not significant, though we expect that they would be significant with increased sample sizes. We also saw no significant difference in swimming speeds between species and temperatures, likely due to low sample size. These results suggest that high ocean temperatures experienced during heatwaves in the Pacific Northwest would have a significant effect on the distribution of these species in the water column and therefore their ability to feed, as the phytoplankton they eat is mainly distributed within or at the base of haloclines.