Publication Date

2015-11-21

Availability

Embargoed

Embargo Period

2016-11-20

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2015-10-29

First Committee Member

Su Sponaugle

Second Committee Member

Robert K. Cowen

Third Committee Member

Michael C. Schmale

Fourth Committee Member

Joseph E. Serafy

Fifth Committee Member

James A. Bohnsack

Abstract

Coral reef fish populations are composed of subpopulations across a range of depths and geographic locations that are connected through larval dispersal. As reefs decline, coral reef organisms may become dependent up habitats at the periphery of their distributions. The objectives of this dissertation were to determine the influence of habitat variability on population demographics, reproduction, survival, and the consequences to population connectivity of a common coral reef fish (bicolor damselfish: Stegastes partitus) across the Florida Shelf and the depth distribution of the species. Assessing demographic plasticity and habitat suitability for a model species across depth strata (SS: shallow shelf <10 m and DS: deep shelf 20-30 m in the Florida>Keys, and MPR: mesophotic 60-70 m at Pulley Ridge) provides insight into the potential for DS and mesophotic reefs (30-150 m) to be sources of larvae and coral reef refuges. Otolith-derived traits of young fish revealed that higher productivity in the lower Florida Keys compared to the upper Florida Keys led to faster growth after only 4 days post-settlement to the reef. Habitat variation continued to affect fish throughout their life cycle, indicated by a shift toward slower growth rates and larger asymptotic sizes based on otolith-derived ages, and populations dominated by older and larger individuals in deeper habitats. Per capita reproductive investment in spawning batch, measured as gonado-somatic index (GSI), batch fecundity, and oocyte area, was highest in MPR habitats, followed by SS, then DS. Assessment of the drivers of demographic variation suggested that low reproductive investment in DS habitats was the result of high predator densities, risk-avoidance behavior, and decreased access to planktonic food. Higher C:N ratio (lipid content), higher trophic position, and longevity, traits associated with MPR habitats, were linked with high GSI, whereas in shallower habitats there was a trade-off between fast growth and low reproductive investment per spawning batch. The consequences of habitat suitability to population connectivity were assessed based on total subpopulation egg production using depth-specific demographic parameters, population densities, and habitat availability. Fish on SS and mid-shelf (10-20 m) reefs in the Florida Keys had the highest subpopulation reproductive output, whereas fish in DS habitats had the lowest egg production. MPR fish had the lowest population densities but high habitat availability, resulting in an estimate of 14% of the total egg production from the study region sourced from Pulley Ridge. Coral reef fish exhibit a broad range of demographic plasticity, and as a result, mesophotic coral reefs are suitable environments for reef fish, with long-lived individuals and high reproductive investment per spawning batch. Mesophotic reefs are potential refuges for reef fish that can provide high condition larvae, but may be less resilient than shallower habitats due to their dependence upon long-lived individuals for population persistence. Incorporation of such spatially explicit demographic plasticity in the assessment of habitat suitability and resilience should inform and enhance the effectiveness of management strategies.

Keywords

Demographic plasticity; Reproduction; Population connectivity; Mesophotic; Coral reef refuge; Habitat quality

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