Predation in marine reserves and its impact on the survival and early life histories of newly-settled coral reef fishes

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Su Sponaugle, Committee Chair


Higher densities of piscivores on reefs may affect the mortality of newly-settled coral reef fishes, leading to lower survival and increased selective pressure. Therefore, survivors are often individuals with advantageous traits acquired during early life. To examine the carryover effects of larval history on early juvenile survival, nine cohorts of newly-settled bluehead wrasse, Thalassoma bifasciatum, were collected over multiple seasons and years from reefs in the upper Florida Keys, USA, and the life history traits of survivors were compared using otolith analysis. Selective mortality was not pervasive, but the trait most frequently important for survival was higher condition at settlement (wider otolith metamorphic bands). Behavioral advantages associated with condition were identified using recruits with natural and artificially-created differences in condition. Laboratory experiments demonstrated that high condition recruits swim better, take fewer risks by foraging less in the presence of a predator, and evade a predator threat at faster speeds. In the field, an accumulation of predators in marine reserves may affect post-settlement processes since surveys showed higher densities or biomass of large and small piscivores in marine reserves of the Florida Keys National Marine Sanctuary. To identify the effect of increased predation pressure on recruit mortality, mesocosm experiments exposed recruits to different densities of predators (reserve treatment = numbers of piscivores reflecting reserve densities, non-reserve treatment = number of piscivores reflecting non-reserve densities, control treatment = no piscivores). Results demonstrated that higher densities of predators can lead to lower survival and condition-based selective mortality. The impact of predators in marine reserves may be altered due to variable larval supply and recruitment, but collections of late-stage larvae and newly-settled recruits illustrated site-specific differences in the abundance of early life stages unrelated to protection level. Small-scale oceanographic features in this region can alter population replenishment among sites. Thus, while condition-based selective mortality of recruits occurs and is mediated by predation, the outcome of these interactions in reserves and non-reserves is not yet evident. Mortality of newly-settled coral reef fishes is a dynamic process, and an increased knowledge of the factors influencing recruit survival will aid in the protection of future populations.


Biology, Ecology; Biology, Oceanography

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