Project: Scope and Consequences of Variability in the Early Life History Traits of a Caribbean Coral Reef Fish

Description from NSF award abstract:
Events occurring during the pelagic larval stage of benthic marine organisms can play an important role in the regulation of open populations. The transition between the pelagic larval stage and the benthic juvenile stage (settlement and metamorphosis) is generally recognized as a critical period in the life of many benthic marine fishes such as coral reef fishes, yet the linkage between these phases had received relatively little attention. Biological traits exhibited during the larval stage can influence not only larval survival, but also the recruitment and survival of subsequent juvenile stages. Patterns of natural variability in early life history (ELH) traits, early juvenile mortality, and trait--related survival are entirely unknown. We currently have no knowledge of which larvae survive to settle successfully, and which of those then survive the early life on the reef, including the energetically expensive process of metamorphosis. While ecological theory concerning the ELH traits that confer higher survival has been developed for larval fishes in temperate systems, rarely has this theory been extended across the transition to juveniles, and very few data are available on the relationship between ELH traits and survival for tropical species such as coral reef fishes.

This field study is designed to investigate patterns of natural variability in the ELH traits of a common Caribbean coral reef fish and the consequences of this variation to the survival of young larvae and juveniles during the transition from the plankton to the reef. Multiple cohorts of newly recruited Thalassoma bifasciatum will be censused and collected from sites in the Florida Keys over several seasons (6 mos.) and hydrographic conditions to identify the relationship between environmental conditions, ELH traits, and recruitment success. Recruits will be collected from replicate sites with high and low densities of resident fishes to examine how variable growth and mortality further influence the distribution of ELH traits of recruits. Examination of the otolith record of late-stage larvae and young juveniles will enable the identification of within--cohort, among-cohort, and among-site differences in ELH traits such as larval growth rates, size-at-age, size and age at settlement, and juvenile growth rates. In addition, cohort-specific condition indices will be measured for late-stage larvae and emerging juveniles (<1 d on the reef). Longitudinal and cross-sectional analyses of otolith records will reveal whether faster-growing, larger or older larvae, or larvae of higher condition preferentially survive, and whether large recruitment events are composed of larvae or recruits with particular ELH traits. An intensive series of juvenile censuses will provide daily age-specific mortality rates, which together with the otolith-derived ELH trait analyses will define the relationship between growth, survival, and selective loss of ELH traits. As such, this field study will be the first broad in situ investigation of the relationship between ELH traits and the survival of larvae and young juvenile reef fishes. Results of this study will contribute to our understanding of the dynamics of this important transitional phase in the life history of coral reef fishes and the factors contributing to recruitment variability in these open populations.