TEMPORAL FACTORS INFLUENCING KILLIFISH ABUNDANCE AND RECRUITMENT IN GULF OF MEXICO SALT MARSHES

Killifish (Fundulus grandis and F. similis) were seined monthly for two years near the mouths of three tidal creeks in each of two north Florida [USA] salt marshes. Abundance patterns were identified by a combination of multivariate analyses and quantitative graphical techniques. Abundance (numbers and biomass) peaked in the summer and fall as successive waves of juveniles accumulated. Relative abundance of age groups that reached their second breeding and growing seasons was low; the largest individuals of both species were less than two years old. Most killifish reproduced frequently in their first year of life. Temporal abundance patterns were regulated significantly by tidal phase, water depth, water temperature, and dissolved oxygen, but not by salinity or percent cloud cover. There were no significant differences between populations in the various creeks and marshes. Killifish apparently moved over submerged marsh surfaces at high tide, then retreated to tidal creeks at low tide, resulting in high abundance near creek mouths at low tide. However, these tidal movements were modulated by water depth; regardless of tidal phase, abundance at creek mouths was correlated negatively with water depth, indicating that killifish remained in the salt marsh when its surface was inundated. Thus, tidal movements of killifish were flexible and influenced by environmental conditions producing variation in water depth (e.g. wind-driven effects). Abundance correlated positively with water temperature and dissolved oxygen, reflecting juvenile recruitment peaks during warmer seasons and increased recruitment in year 2 of this study when dissolved oxygen values were higher. In both abundance and recruitment, Fundulus grandis and F. similis responded similarly to varying temporal enviornmental conditions.