NICHE VARIATIONS OF TWO CARIBBEAN ACROPORID SPECIES AND THEIR HYBRID

Today, we observe drastic changes in environmental conditions such as increases in ocean acidification and sea surface temperatures. It is predicted that if the current rate of environmental change continues, most Caribbean reefs will perish. The Caribbean genus Acropora has a well-known distribution for the species A. palmata and A. cervicornis but lesser so for the hybrid A. prolifera. Here we analyze differences among adaptability of the Acropora hybrid with respect to A. palmata and A. cervicornis. We hypothesize that the hybrid species can occupy a wider environmental niche compared to its parent species.

Ecoregions within the Caribbean province was set as calibration areas to test our hypothesis. Occurrence data across ecoregions were extracted from Global Biodiversity Information Facility and AGRRA (Atlantic and Gulf Rapid Reef Assessment). The environmental variables necessary for prediction were extracted from BIO- ORACLE. We use 13 environmental variables including pH, temperature, current velocity, photosynthetically available radiation and nutrient availability. We compared the niche size, overlap and the variances across different environmental variables. We found that the acroprid hybrid has a smaller niche size, approximately 1.7 times smaller compared to both the parental species. There is a 55% overlap between the hybrid and each of its parental species and this overlap is not statistically significant. To better understand differences in niche size and overlaps, we compared each environmental variable, and found that 8 out of 13 variables are not significantly different. Among the five variables with significant differences are pH and mean temperature. The hybrid's pH range is slightly higher than that of parent species, while the temperature range is lower than the parent species. Both differences are statistically significant, however we are leading to an acidic and warmer ocean. This implies that the hybrid A. prolifera doe does not have a greater potential for survival in the changing climatic conditions. Thus, addressing the claims that ‘in-between morphotype’ of the hybrid species would provide it with an environmental advantage. However, it is important to understand the risks associated with extensive and thus biased survey of hybrids with respect to their parental species occurrences. These will be addressed in future studies.