The interactive effects of nutrient and salinity stress on corals from distinct environments on the Belize Barrier Reef System

Global climate change has induced shifts in local weather patterns near many coral reef ecosystems, resulting in greater frequency and intensity of major rainfall events. These changes in precipitation, combined with land use changes, have resulted in greater nutrient loading and more severe seasonal decreases in seawater salinity surrounding coral reefs. In order to investigate how different populations of corals might respond to these stressors, we are quantifying the effects of salinity and nitrate (NO₃^-) concentrations on calcification across corals from nearshore and forereef environments. Colonies of Siderastrea siderea, a commonly found highly stress tolerant species in the southern portion of the Belize Barrier Reef System (BBRS) were collected, fragmented, and reared in four salinity/nutrient treatments that simulate natural seasonal conditions: 1) local average salinity (32 psu) and nutrient concentration ([NO₃^-] = 2.5 μmol), 2) low salinity (24 psu) with average nutrient concentration, 3) average salinity and increased nutrient concentration (([NO₃^-] = 5.5 μmol), and 4) low salinity and increased nutrient concentration. S. siderea were collected from nearshore, where nutrient loading and depressed salinity occur regularly during the rainy season , and the forereef, where corals are less commonly exposed to these stressors. Changes in coral calcification and symbiont density were monitored for 60 days in order to simulate the duration of one rainy season in southern Belize, which experiences 2-3 months of heavy rainfall each year. Understanding these interactive roles of nutrients and salinity, as well as the role that local environments play in coral survivorship, will be important considerations for the future of coral reefs in the face of climate change.