Geographic variation in life history of the sand crab, Emerita analoga (Stimpson) on the California coast: Relationships to environmental variables

Abstract

Geographic variation and the influence of environmental factors on life history characteristics of populations of a sandy intertidal decapod, Emerita analoga, Stimpson, inhabiting beaches along 8° of latitude on the California coast in midsummer were investigated for 5 yr. Female size at maturity, largest and smallest ovigerous crab size, and largest male crab size, expressed as carapace lengths, increased from south to north and were 1.5 to 3 times greater in northern than in southern populations. The observed trends in life history were associated with environmental factors that varied on regional (water temperature) and local scales (food availability and physical characteristics related to beach morphodynamics) using simple and multiple linear regression analyses. Incorporating regionally and locally varying environmental factors into a multiple linear regression model provided a better predictor of life history characteristics than any single factor. In every year, the four life history characteristics were negatively correlated with surf zone water temperature, which varied regionally and was correlated with coastline distance. Female size at maturity and the largest and smallest ovigerous crab sizes were positively correlated with food availability, estimated by chlorophyll a concentration, which was not correlated with coastline distance. Life history characteristics were not correlated with any of the beach morphodynamic variables in simple regressions. Removal of variation associated with water temperature and chlorophyll a in multiple linear regression analyses yielded positive correlations between the sizes of the largest and smallest ovigerous crabs and the size of the largest male crab, and a beach characteristic, an index of sediment size and sorting, which was not correlated with coastline distance. Female size at maturity, largest and smallest ovigerous crab sizes and largest male crab size were correlated in each year, implying that these life history traits are influenced by similar mechanisms. Little interannual variation occurred in the geographic patterns observed in life history traits. Life history traits examined in our study were correlated between years, suggesting that interactions between settlement, growth, survival, and enviroment variables were relatively consistent during our study.