Mission 5 — The physiological ecology of symbiotic dinoflagellates across a depth gradient: Underst

Mission 5 — The physiological ecology of symbiotic dinoflagellates across a depth gradient: Understanding the influence of physical and biological factors on photosynthetic processes and population distribution.

Principal Investigator: Dr. Mark Warner, University of Delaware
Training: September 7-11
Mission: September 13-22

The ecological success of reef-building corals is due in part to the small symbiotic algae that live within the stomach cells of these animals. These algae, commonly called zooxanthellae, provide food in the form of photosynthetically fixed carbon which is transferred to the coral and eventually used for growth and reproduction. While we know quite a lot about how these small plants interact with their coral hosts, changes in climate and degradation of coral reef ecosystems worldwide have prompted a desire understand these symbiotic interactions in greater detail, as they appear to be quite fragile in some circumstances. Our goal is to have a better understanding of the diversity, ecology, and physiology of multiple zooxanthellae populations across many spatial scales, as knowledge of these symbionts and their associations with different host corals at this level remains limited. This project focuses on the physiology of these algae within multiple species of reef corals at different depths. We are investigating the genetic diversity of these algae, and several aspects of their photo-biology.

Some corals will contain the same type of algae at all depths, while other species may contain algae that are quite different. Over the course of several days, we will follow several photosynthetic processes of selected corals while they reside within their natural environment. In order to better understand how certain corals and their algae react to elevated water temperature, we will conduct short-term thermal stress experiments by placing corals within small flow chambers that are subsequently heated to simulate coral bleaching where some types of zooxanthellae become damaged by the higher temperatures. In addition to our thermal stress experiments, we will place other corals inside small chambers and then expose them to chemicals that block certain metabolic pathways within the zooxanthellae. This will allow us to estimate how quickly some key proteins used in photosynthesis are degraded over time. Other experiments will be performed to investigate how different species of corals and their algae may utilize small pulses of nutrients that appear on the reef by supplying corals with 15N labeled nitrate or ammonium as well as 13C labeled carbonate. After the corals are frozen and transported back to our home laboratory, we will separate the zooxanthellae from the coral tissue and then analyze how much of these compounds are found in the algae and the coral.