Effects of Fluctuating Environmental Temperature on Development and Hatching Success in the California Grunion

The California grunion, Leuresthes tenuis, a silverside fish, spawns on sandy beaches along the coast of California and Northern Baja California during the highest spring high tides during March-August. Female grunion deposit eggs within the sand while males release sperm to fertilize the eggs. Fertilized eggs develop in the sand and normally hatch only when stimulated by wave action during a subsequent spring high tide. Embryos incubated at 20^oC have a greater hatching rate than those incubated at 15^oC and 25^oC, but no studies have investigated how ambient sand temperature affects the incubating embryos. Sandy beaches are variable environments, and sand temperature may fluctuate by 11^oC within 36 hours. We hypothesized that grunion embryos incubated at variable temperatures similar to those experienced in the sand (experimental) will have reduced hatching success and development when compared with embryos incubated at a constant temperature of 20^oC (control). Batches of eggs from one female fertilized by one male will be divided into experimental and control groups. Once the grunion embryos are competent to hatch (day 5-8), viability and hatching success will be quantified every day. Length and yolk surface area of hatched larvae will be measured using Image J software. We predict that embryos incubated at fluctuating temperatures will have significant lower yolk utilization rates, notochord lengths, and hatching success, when compared to embryos incubated at 20^oC. This study will help us to understand how grunion embryos respond to changes in their environment.