Molecular assessment of sub-lethal stress in the Hawaiian coral, Pocillopora meandrina, exposed to elevated inorganic nutrient concentrations and an acute temperature increase

Today, coral reef ecosystems worldwide exhibit a general decline because of chronic and acute damaging events on inshore and offshore reefs. Two key threats coral reefs currently face are elevated seawater temperatures and exposure to nutrient enriched water. Increased sea surface temperatures have severely impacted coral reefs around the world, but the Hawaiian islands have not yet been heavily impacted by bodies of warm water and mass-scale coral bleaching. Inshore coral reefs of Hawaii are, however, often exposed to elevated levels of inorganic nutrients, especially nitrogen. This happens because coastal coral reefs of the main Hawaiian islands are chronically affected by land activities more immediately than other locations due to the islands' high gradient geography. This study investigated the use of Heat Shock Protein 70 (Hsp70) expression at the protein level, in addition to the density of symbiotic dinoflagellates, to examine the multiple stress events of long-term ammonium exposure followed by an acute exposure to elevated seawater temperature on reef building corals. Hsp70 was quantified using western blotting. Corals in a manipulative experiment exposed to long-term inorganic nutrients and acute elevation of sea-water temperature expressed more HSP70 and had less symbiotic dinoflagellates than corals exposed to an acute elevation of seawater temperature alone. These results suggest corals in nutrient-exposed reefs are more physiologically susceptible to anomalous bodies of warm water than corals in an oligotrophic environment.