Effects of temperature and salinity on Pisaster ochraceus and Pycnopodia helianthoides larvae

Abstract

Increasing global temperatures are resulting in marine heating events which can increase temperature in these environments up to 22℃. These marine heating events are becoming more frequent and intense, increasing the physiological stress on marine invertebrates and their larval forms in the water column. In the Salish Sea, Pisaster ochraceus and Pycnopodia helianthoides are important ecosystem predators which maintain the structure of the systems they dominate through predation. A decrease in the abundance of these species attributed to lessened juvenile recruitment from heat-induced morphological variation, could result in cascading effects for the balance of their ecosystems. This study implemented conditions of decreased seawater salinity and increased water temperatures to determine the effects on sea star larval growth over time. Pisaster ochraceus larvae were exposed to 4 treatments with 3 replicate jars per treatment: Three jars at low temperature and low salinity (LTLS), 3 jars at low temperature and high salinity (LTHS), 3 jars at high temperature and low salinity (HTLS), and three jars at high temperature and high salinity (HTHS). Pycnopodia helianthoides were kept under two temperature treatments: A high temperature treatment between 15 and 18°C and a low temperature treatment between 9 and 14°C. Total larval length and width were measured for 12, 24 and 32 day-old Pisaster bipinnaria and early brachiolaria larvae, and for 60 and 63 day-old Pycnopodia brachiolaria larvae. Our results indicate that temperature had a significant effect on larval length and width for both species and that the variation in these variables decreases as larvae age. These findings suggest that the timing of marine heat waves may be critical for successful larval development to metamorphosis of these species.