The Influence of Oxygen, Temperature, and Salinity on Ostracod Body Size in the Gulf of California and the Pacific Coast of North America

Abstract:

The study of body size and its evolution is important to paleontological understanding of ecological niches that different organisms have occupied. Ostracods, with frequent occurrences throughout the geological record beginning in the Ordovician, are useful in analyzing how body size has changed. Therefore, understanding the impact of environmental variables is crucial to understanding patterns of body size evolution in extinct ostracods. In order to further investigate this question, ostracod populations in the Gulf of California and the Pacific Coast of North America were studied. By compiling data from Ostracoda from the Gulf of California (Swain, 1967), Marine Holocene Ostracoda from the Pacific Coast of North and Central America (Swain and Gilby, 1974), and the National Oceanographic Data Center, we compare environmental factors, including oxygen levels, temperature, salinity, and depth with anteroposterior length measurements of about 180 recent ostracod species in order to determine the impact of these variables. Using R, we constructed graphs of oxygen levels, temperature, and salinity versus average body size. Using a correlation test, the correlation coefficient for oxygen is -0.193, temperature is -0.398, and salinity is -0.322, with the corresponding p-values of 0.067, 9.196 x 10-5, and 0.002; only the latter two p-values are significant at the alpha = 0.05 level. The correlation test for depth was calculated but showed no trends. The statistically significant correlation coefficient between temperature and body size suggests a strong negative correlation. Because oxygen levels and salinity levels are, to some extent, dependent upon temperature, this may explain the smaller, yet still statistically significant, correlation between body size and salinity. Relationships between ostracod body size and temperature may be relevant to our understanding of the impacts on ecological structure as the ocean temperatures fluctuate in the future.