Ecosystem health in Guánica Bay and La Parguera, Puerto Rico: Remote sensing of ocean color and metal analysis of coral tissue and surficial sediments

Author

Jahnelle Howe, CUNY City CollegeFollow

Date of Award

2020

Document Type

Thesis

Department

Earth and Atmospheric Sciences

First Advisor

Karin A Block

Second Advisor

Shakila Merchant

Third Advisor

Maria Tzortziou

Abstract

Guánica Bay is an estuary located in southwest Puerto Rico, with a coral reef ecosystem at its periphery. This ecosystem is affected by sediments, nutrients, and contaminants from the watershed through the Bay and into the offshore water. This project evaluates Guánica Bay and La Parguera coastal areas through remote sensing and chemical analysis to assess coastal ecosystem health. The concentration of metals in two coral species and their associated surface sediments was were analyzed by X-ray fluorescence (XRF) and Direct Mercury Analyzer (DMA- 80). Ocean color remote sensing was used to estimate nutrient inputs and phytoplankton biomass through chlorophyll-a (chl-a) concentrations from Guánica Bay to La Parguera. Chl-a is an indicator of the abundance of phytoplankton and biomass in coastal, and estuarine water. In 2019, chl-a for virtual stations and single-pixel sample sites mirrored each other. Furthermore, high chl-a concentrations were observed for most sites for 2019. This coincides with metal inputs to the ecosystem attributable to an unusually wet dry season which led to more surface runoff and increased algal growth. Higher concentrations of Cu and Zn compared to the Whitall et al. (Whitall et al.) study was found in coral tissue. In the coral Montastraea cavernosa, Cu concentration of 103 ppm is over 69 ppm threshold that affects coral fertilization. Though coral Zn levels found in this study were higher than those reported by Whitall et al. (Whitall et al.), the concentrations are not considered toxic. Moreover, in surficial sediment, all-metal concentrations were low. Geoaccumulation Indices (I_geo) calculated for sediments and corals indicated no contamination for most metals except Cu. I_geo was highest at Baul which is close in proximity to an urbanized area, I_geo for Cu was > 2, and chl-a values were high, indicative of moderate to strong contamination. This strongly suggests that anthropogenic inputs may adversely affect coral health during unseasonably high precipitation in this location. The results of this study provide an update to the baseline of Whitall et al. (Whitall et al.) and add to the knowledge base of metal concentrations in surficial sediment and coral tissues from coastal Puerto Rico, useful for comparisons to future measurements.

Recommended Citation

Howe, Jahnelle, "Ecosystem health in Guánica Bay and La Parguera, Puerto Rico: Remote sensing of ocean color and metal analysis of coral tissue and surficial sediments" (2020). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/846