MEPS 237:257-269 (2002)  -  doi:10.3354/meps237257

ABSTRACT: Bay anchovy egg abundance in the Manatee River estuary, Florida, was compared with conditions in the spawning ground before and after spawning to distinguish prey-supply-based spawning responses from post-spawning advective effects. Plume fronts were a prominent feature of the spawning ground. Egg distribution, copepod distribution and front development were surveyed 25 times across a wide range of freshwater inflow conditions. Surface-front strength (maximum interpolated salinity slope) was strongly correlated with the size of the frontal zone, as defined by surface areas having slopes >1 psu km^-1. Eggs were most abundant landward of the frontal zone at a location with consistently high abundance of the copepod Acartia tonsa, which is consumed by adult and larval bay anchovies. Large, significant changes in egg abundance were observed over both long (seasons) and short (<3 d) periods (Tukey 95% HSD multiple range tests). An El Niño-associated flood event caused the rapid evolution of a large, seaward-moving frontal system that initially had a negative effect on egg abundance. Spawning resumed in reduced salinity following passage of the front, demonstrating a level of plasticity in spawning response to salinity change. A stepwise regression model explained 92% of the variation in egg abundance and suggested that tidal amplitude was not a significant determinant of abundance. Instead, egg abundance appeared to be determined initially by pre-spawning prey supply and temperature, and subsequently by variable retention behind the frontal zone.

KEY WORDS: Iteroparity · Egg development · Population dynamics · Stock recruitment · Life history strategy · Plankton patchiness · Estuarine retention · Tampa Bay