Environmental assessment of coral reef ecosystems at Jobos Bay National Estuarine Research Reserve

Natural and anthropogenic inputs have degraded Jobos Bay National Estuaries Research Reserve (JBNERR) coral reefs. Better tools to monitor reef health and accurate communication of the science are needed to improve stakeholders’ decisions and support proper management actions in the reserve. Resources managers in the bay need to understand how to integrate science-based strategies into managing and monitoring reefs in the reserve. This pilot project proposed to apply the FORAM Index (FI) as a non-invasive and low-cost tool to assess water quality conditions at the reefs using benthic foraminifers as bioindicators.

This thesis work aims to test: the feasibility of the FI as a reliable tool to address the water quality condition of coral reefs at JBNEER, identify which physicochemical parameter(s) (if any) are influencing the FI-values, determine if other ecological indices are associated with the parameters, and evaluate differences on physicochemical parameters, foraminiferal richness and Shannon-Index within fore-reef and back-reef sites. Differences in foraminiferal assemblages are expected to reflect FI-values and inform interpretations of reef conditions. Also, environmental conditions would reflect differences in the relationships between physicochemical parameters and ecological indices.

To test the hypothesis, three reefs: Cayo Morillo, Cayo Pájaros, and Cayo Caribe, were sampled along transects in the front and back of each reef. Physicochemical parameters and nutrients were measured through the water column and ~20 g superficial sediment samples. Limited variations in water quality parameters were observed among reefs: pH (8.1-8.2), salinity (37.24-37.94), temperature (26.0-27.0 oC), DO (90 -120 %), orthophosphate (0.04-1.0 µM), total chlorophyll (0.22-1.2 mg/L) and ammonium (0.04-0.30 µM). These findings support the expected oligotrophic environmental conditions on coral reefs. The foraminiferal assemblage in the front to fore-reef settings is dominated by symbiont-bearing foraminifers (Amphistegina). However, the interior of the reefs is mainly dominated by heterotrophic species (Discorbis). The predominance of sand-sized sediments and abraded specimens reflects the active hydrodynamic regime. Unexpected limitations such as low foraminifera shells (6 individuals per gram) in samples limit the validation of the FI and assessment of the water quality at Jobos Bay.

Spearman r(s) show relationships between ecological indicators such as foraminiferal richness and the Shannon-Index and physicochemical parameters such as temperature, salinity, and calcium carbonate, among others. These relationships suggest how living foraminiferal assemblages respond to changes in abiotic factors. Mann-Whitney test results showed median differences between back-reef and fore-reef sites on parameters such as temperature, salinity, and pH. These results show the differences in environmental settings for the lagoonal and fore-reef areas. Kruskal-Wallis’ test results show differences in physicochemical parameters between August/September, March, and December. These fluctuations are evidence of differences in wet and dry seasons in Jobos Bay.

It is promising that indicator species of good water-quality were found in fore-reef stations. It is also reassuring to see heterotrophic species in the back-reef sites, such as rotaliids and miliolids, species that prefer finer grains and high organic content. These results show that foraminiferal assemblages respond to their environment. However, due to the low density of foraminifers found in sediment samples, FI interpretation was a challenge, compromising the feasibility of the FI in coral reefs at Jobos Bays. Because of that, a better understanding of the spatial foraminiferal distribution in coral reefs is needed to better inform the FI's applicability in coral reefs at Jobos Bay.