Transport dynamics and survival of the pelagic larval stages of a coral reef fish, the bicolor damselfish, Stegastes partitus (Poey).

摘要

Coral reef fish population variability is driven by variability in the number of larvae settling onto the reef as young juveniles and from settlement and post-settlement processes. The focus of this thesis research is on describing the mechanism by which retention occurs by tracking larval cohorts throughout their pelagic duration, quantifying larval transport variability, and estimating ontogenetic larval survival rates in relation to the near-field circulation. The system represented by the island of Barbados and the bicolor damselfish (Stegastes partitus Poey) served as a proxy for general mechanisms in coral reef fish recruitment.; As an initial analysis, the local circulation was analyzed, revealing significant sub-mesoscale fluctuations of the velocity field. Current reversals of a periodicity of ∼20 d and salinity fronts, signature of North Brazil Current Rings (NBCR) impinging on the island, dominated the near-field circulation. However, the flow field was coherent and mostly baroclinic indicating that the NBCR structure was retained during the low salinity intrusions.; Objective statistical interpolation of the velocity field combined to a Lagrangian random-flight scheme and larval vertical behavior were utilized to predict discrete larval patch trajectories in real-time flow conditions. Results indicated that (1) retention resulted from the ontogenetic vertical migration of larvae through vertically sheared currents, (2) coral reef fish larvae initially dispersing as patches tended to remain aggregated in patches throughout their pelagic duration, (3) observed variability in recruitment strength was largely explained by differences in retention rates.; Finally, the survival of 3-d larval cohorts throughout their pelagic duration was estimated as a function of advection and diffusion, as well as a function of natural mortality, thereby closing the larval loop. Advective losses were consistently higher than natural mortality rates (estimated mean value of 0.38 d−1 and 0.20 d−1, respectively), both decreasing with cohort age. This decline was coincident with increased growth rate and larger size. Hydrodynamics, timing of hatching pulses, and the vertical distribution of larvae resulted in differential larval transport and survival. The mortality rates reported here consisted of the first estimates of instantaneous mortality coefficients for coral reef fish larvae. (Abstract shortened by UMI.)