MEPS 131:61-73 (1996)  -  doi:10.3354/meps131061

Egg production by the bay anchovy Anchoa mitchilli in relation to adult and larval prey fields

Peebles EB, Hall JR, Tolley SG

Abundances of copepod nauplii, copepodite/adult copepods, and the larvae of iteroparous anchovies (primarily the bay anchovy Anchoa mitchilli) were monitored in Tampa Bay, Florida (USA) at 2 wk intervals for 2 yr. All possible pairings of the 3 time-series variables yielded significant positive correlations. Nearly all (>98%) of the collected anchovy larvae occurred with prey (nauplius) densities higher than those reported to affect larval starvation (<100 l-1). The larval association with abundant prey could be explained as (1) the remnants of earlier larval starvation, or (2) spawning being concentrated in zooplankton-rich waters. To evaluate the 2 explanations, the diet of adult A. mitchilli was analyzed, and egg/adult prey surveys were conducted across a 290 km2 area of Tampa Bay. In 5 of the 6 spatial surveys, A. mitchilli egg abundance was correlated with the abundance of calanoid copepods, a principal adult prey item. Calanoids (primarily adult Acartia tonsa) were never correlated with net plankton biomass or with the eggs of the bay anchovy's congener, Anchoa hepsetus. Calanoids were aggregated near sites of stable freshwater discharge during a dry season, but became dispersed as discharge increased during a rainy season. Among spatial surveys, egg abundance exhibited a strong nonlinear relationship with calanoid aggregation (r2 = 0.96, n = 6, p = 0.001). Collectively, these findings suggest that the bay anchovy's size-specific fecundity is related to adult prey availability, with adult prey availability being represented by a combination of abundance and patchiness. We discuss relationships between spawning pattern and environmental instability, and suggest that iteroparity serves to fine-tune reproductive effort to environmental parameters that are relevant to larval survival.

Variable fecundity . Larval survival . Plankton patchiness . Life-history strategy . Spawning season . Spawning location

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