Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Marine Science

Major Professor

Frank Muller-Karger, Ph.D.

Committee Member

Pamela H. Muller, Ph.D.

Committee Member

Cameron Ainsworth, Ph.D.

Committee Member

Matt McCarthy, Ph.D.

Committee Member

Lauren Toth, Ph.D.

Keywords

coral reef health indices, coral reef indicators, ecosystem services, fisheries, Florida Keys Reef Tract, reef fish diversity

Abstract

The general decline in coral-reef ecosystem health throughout the Caribbean between the 1970’s and late 1990’s seems to have slowed down or stopped, with only slight decreases in coral reef cover observed in the 2000’s through 2019. The earlier decline can be attributed to many different local and regional stressors that have acted together, and include naturally occurring (hurricanes, diseases) and anthropogenic pressures (increased sedimentation, fishing). These ecosystems provide a range of services to people, including food and protection from storms, with an annual benefit of billions of dollars. This has driven a desire to better understand these ecosystems. The declines in coral reef cover have also forced policy makers and scientists to work together to find ways protect these marine ecosystems.

One focus of this dissertation is to examine data that may help understand the health of coral reefs in the Florida Keys National Marine Sanctuary (FKNMS) in southern Florida. Chapter One lays out the structure of the dissertation. Chapter Two details the history of the coral-reef ecosystem in the FKNMS and discusses three robust datasets and their importance in monitoring different aspects of the ecosystem. The Coral Reef Monitoring Project (CREMP) of the Florida Fish and Wildlife Research Institute began collecting data in 1996, a year before the unprecedented world-wide 1997-1998 El Niño event, reporting an average of ~11% stony coral cover. As of 2020, coral cover was ~5%. The decline has been attributed to bleaching events and disease outbreaks. A group monitoring water-quality [Southeast Environmental Research Center] has noted a large-scale decrease in total organic carbon and nitrogen, and an increase in dissolved oxygen in waters of the FKNMS from 1995 to 2020. A reef-fish monitoring group under National Oceanic and Atmospheric Administration’s South Florida National Coral Reef Monitoring Program has indicated fish populations have remained relatively constant from 1999–2020, with the highest values in high-relief strata areas.

In Chapter Three, I combined the coral-reef benthic-cover estimates, coral-reef assemblage data (i.e., whether coral or algae), and the reef-fish data into three coral-reef health indices. Health indices can help synthesize a large amount of biological data about ecosystem health. These specific indices were developed to share coral-reef health trend estimates with policymakers, the public, and other scientists studying the ecosystem. Survey data were used to compute the coral-health indices, with all but one indicating declining trends over the study period. The “healthiest” reefs were in patch-reef environments, with coral cover having the most influence on the health indices. Macroalgae did not account for a large amount of explained variation but exhibited higher values in offshore sites. Reef-fish assemblages were most diverse in patch-reef habitats, but had higher biomass values in offshore, higher relief reef sites. The result of this work provides baseline information for restoration efforts occurring in the FKNMS.

Chapter Four combines fisheries-independent, fisheries-dependent, and economic data to evaluate the value of economically-important reef fish. The fishing industry and ecotourism divisions that rely on reef fish are billion-dollar industries that rely on tens of thousands of workers per year. By combining these databases, I identified high-relief coral reef strata and protected areas to have the highest “value” of fish per year sustained over time.

The reef fish data also show that the average trophic level of the fish assemblages is higher in patch-reef environments. High-relief areas have more reef-fish biomass and more individuals of species that show high specificity and fidelity to the habitat. Unprotected areas also had high trophic-level averages for all indicator fish species.

Groupers and snappers were the most economically and ecologically important based on landings data (101 grouper species, 71 snapper species) and biomass values (43 grouper species, 26 snapper species). However, other fish families were shown to be indicator species in our analysis (75 of the 86 reef fish species identified were not a grouper or snapper) likely due to being less migratory through their life cycle and relying more on substrate for protection and food.

Ultimately there was no significant difference in “value ($/m2)” among the Upper, Middle, and Lower Florida Keys. But the average trophic level of indicator species was highest in the Lower Keys followed by the Middle Keys and then the Upper Keys. This may be a consequence of higher trophic levels in the Lower Keys being less exposed to the high fishing pressure likely experienced closer to the Miami urban area.

This dissertation research exemplifies how large-scale monitoring networks can be combined and analyzed to provide a better understanding of the marine ecosystem and biodiversity shifts occurring in large coral-reef ecosystems like the FKNMS.

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