Publication Date

2010-05-12

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2009-12-04

First Committee Member

Su Sponaugle - Committee Chair

Second Committee Member

Robert K. Cowen - Committee Member

Third Committee Member

Michael C. Schmale - Committee Member

Fourth Committee Member

Dean A. Williams - Committee Member

Fifth Committee Member

G. Todd Kellison - Outside Committee Member

Abstract

Processes that influence the early life stages of fishes can significantly impact population dynamics, yet they continue to be poorly understood. This dissertation examined relationships between the environment, early life history traits (ELHTs), behavior, and post-settlement survival for a coral reef fish, Stegastes partitus, in the upper Florida Keys, to elucidate how they influence juvenile demography. Otolith analysis of settlers and recruits coupled with environmental data revealed that S. partitus surviving the early juvenile period settled at larger sizes and grew slower post-settlement. Water temperature also influenced the ranges of these and other ELHTs as well as the intensity and direction of selective mortality processes acting on some of these traits (i.e., pelagic larval duration, mean larval growth). Otolith analysis was paired with behavioral observations of newly settled juvenile S. partitus in the field to reveal that the relationship between size-at-settlement, early juvenile growth and survival is behaviorally-mediated. Individuals that were larger at settlement were more active (i.e., spent less time sheltered, swam farther from shelters) and grew more slowly post-settlement. Likewise, slower juvenile growth was associated with greater activity, more conspecific aggression, and faster escape swimming speeds. A six-year time series of recruitment densities revealed substantial temporal (interannual, seasonal, lunar) and spatial (by microhabitat, conspecific density) variability in recruitment which influenced the composition of recruits. For instance, larvae settling during the darkest phases of the moon were larger at settlement, but selective mortality processes during brighter periods removed more of the smallest settlers, resulting in juveniles with similar sizes-at-settlement regardless of when they arrived to the reef. Because recruitment strength and composition varied temporally, genetic markers (6 microsatellite and 1 mitochondrial loci) were used to determine if the genetic composition of monthly cohorts of settling larvae and juveniles also varies interannually, monthly, or across life stages. A lack of genetic structure suggested that S. partitus has a large effective population size and variation in ELHTs is not likely the result of successful spawning of a disproportionately small group of adults. As a whole, these results reveal processes associated with larval supply and post-settlement life that collectively shape juvenile demography.

Keywords

Population Connectivity; Development; Metamorphosis; Fitness; Behavioral Traits; Population Genetics

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