A baseline environmental assessment to support watershed restoration activities in Guanica Bay, Puerto Rico

Background/Question/Methods

Land based sources of pollution, including nutrients, sediments and toxics, have the potential to adversely affect coastal ecosystems.  In tropical waters, these impacts can include disruption of valuable, yet fragile, coral reef ecosystems.  In Guanica Bay (Puerto Rico), a large effort is underway to reduce land based sources of pollution through watershed restoration activities, such as WWTP improvements, changes in agricultural management practices and stream bank stabilization.  In order to be able to measure improvements to the ecosystem, it is critical to have a baseline assessment against which to measure change. 

The goal of this study was to construct an interdisciplinary environmental baseline, including information on coral reef ecology, surface water nutrients, sedimentation rates and contaminants in surficial sediment and coral tissues.  Additionally, we wanted to determine if the Bay is a source of pollutants to the offshore reef system. 

Here we present information on two components of this project: contaminant stressors and indices of coral reef ecosystem health. Using a stratified random sampling design, divers collected data on benthic cover, fish and selected macroinvertebrate presence at 61 survey sites.  Also using a stratified random design, surface sediments were collected for analysis of over 100 contaminants from 33 sites.

Results/Conclusions

The coral reef community offshore from Guanica Bay was similar to what had been observed elsewhere in Puerto Rico.  Hard coral cover was relatively low (2.2%) and the bottom community was dominated by algae.  Sediment contaminants in the Bay were significantly higher (α=0.05, Wilcoxon test) than the offshore sites for all analytes except Ag and total hexachlorocyclohexanes (HCH).  Targeted sampling in the tributaries of the Bay suggests that some contaminants are coming from watersheds sources (e.g. Cr), whereas, some contaminants are deposited directly into the Bay (e.g. PCBs).  Comparing sediment contaminant concentrations to previously published sediment quality guidelines (SQG) revealed that 22 (of 33) sites had at least one analyte that exceeds the ERL (Effects Range Low; including As, Cr, Cu, Ni, Hg, total PAHs, total PCBs and total DDT) and 17 (of 33) sites had at least one analyte that exceeded the ERM (Effects Range Median; including Cr, Ni, total DDT and total PCBs).  Multiple sites within the Bay had extremely high (>10 times the ERM) levels of PCBs.
These data provide elements of an ecological baseline assessment which will be invaluable for detecting future change in the ecosystem, including potential benefits from ongoing watershed restoration activities.