Early life dynamics in tropical western Atlantic and Caribbean snappers (Lutjanidae) and barracudas (Sphyranidae).

摘要

Processes occurring during the early life of marine fishes encompassing the larval, settlement, and juvenile stages can have important impacts on recruitment and subsequent population dynamics. Yet these life stages remain poorly understood, especially in coral reef-associated species of commercial and recreational fisheries interest. Two years (2003-2004) of monthly sampling of 17 stations along a transect spanning the east-west axis of the Straits of Florida revealed consistent spatiotemporal patterns in larval abundance, growth, and mortality of several snapper and barracuda species. Much of the species-specific variability in these patterns tracked adult life history, and spatial (several snapper species) and temporal (Sphyraena barracuda ) patterns in larval growth were related to larval food availability. While no patterns were identified in larval mortality rates, tethering experiments examining relative rates of predation on late-stage Lutjanus griseus larvae in surface waters of the lower Florida Keys revealed that relative predation rate and probability of predation in oceanic areas seaward of the reef was significantly greater than over reef or nearshore seagrass/hardbottom habitats. The combined effects of mortality during these early stages in concert with variability in early life traits caused selective mortality to be pervasive throughout the early life stages of snappers and barracudas. Patterns in selective mortality were investigated by tracking and repeatedly sampling several cohorts of larvae in 2007 and 2008, and for the first time in tropical reef fishes, linking young pelagic larvae with settlement-stage fish and juveniles. In agreement with the growth-mortality hypothesis, large size-at-hatch and fast larval growth conveyed a survival advantage in most species examined, but several switches in the direction of selection with ontogeny and over time occurred, and were contrary to this hypothesis. Consistent patterns of trait-mediated selective mortality lower trait variability in the surviving population, while inconsistencies in these patterns may contribute to the high degree of variability that characterizes these early life stages. Results presented in this dissertation help fill knowledge gaps critical to the understanding and modeling of dispersal and connectivity in several economically valuable snapper and barracuda species. In addition, the identification of life history traits important to the survival of individuals through the larval and into the juvenile stage, has implications for future management of these ecologically and economically valuable species.