Researcher(s)
- Elizabeth Roros, Marine Science, University of Delaware
Faculty Mentor(s)
- Mark Warner, School of Marine Science and Policy, University of Delaware
Abstract
Rising ocean temperatures are a major threat to many reef-building corals as well as their endosymbiotic algae that are critical for coral growth. High temperature damages the photosystem II (PSII) reaction center and decreases photosynthetic capacity, often leading to algal expulsion and coral bleaching. Two genotypes of a Caribbean symbiotic dinoflagellate, Breviolum minutum, were recently found to adapt to heating in the lab and could withstand higher temperatures than their wild-type (WT) counterparts. This project set out to determine if these thermally selected (TS) algae retained thermal tolerance after being held at the original control temperature of 28°C for two years. Algal photochemistry was monitored by active chlorophyll a fluorescence in each TS and WT genotype across a range of temperatures and exposure times. When subjected to short-term acute heating (32–38°C for 3 hrs), the maximum PSII quantum yields in the dark and light ( Fv/Fm , Fq’/Fm’) decreased in a similar fashion across all algal samples. However, in an ongoing chronic heating experiment (>2 weeks at 32°C), thermally selected algae retained higher photosynthetic function than their wild-type counterparts and clear differences were noted in how each algal genotype reacts to heating. This work shows that acute heating assays may not reveal ecologically relevant thermal tolerance in all symbiotic algae. Further, successful development of thermally adapted Symbiodiniaceae could allow these dinoflagellates to maintain photosynthesis and, if successfully transplanted into corals, possibly maintain the health of their animal hosts in the face of global climate change.