MS THESIS DEFENSE: SHANNON KEALA MURPHY CRANSTON – CONTRASTING METABOLIC RESPONSES TO NUTRIENT ENRICHMENT AND THERMAL STRESS IN HAWAIIAN CORALS: INSIGHTS FROM NET AND GROSS PRIMARY PRODUCTIVITY
Abstract: Anthropogenic inputs of excess nutrients, including effluent from sewage outfalls, promote algal dominance and are associated with coral reef decline. In contrast, natural nutrient enrichment, e.g., from seabirds, may enhance thermal resilience and coral growth rates. Such instances are observed in Palmyra Atoll, where seabird nesting and roosting concentrate nitrogen and phosphorus as guano to nearby reefs. Endosymbiotic dinoflagellates in corals assimilate the nutrients, potentially increasing primary production, which may increase coral resistance or resilience during temperature-induced bleaching events. This study aims to compare the effects of anthropogenic (primary-treated sewage effluent), biotic (seabird guano), and mineral nutrient sources (inorganic nitrogen pellets) on the metabolism of two coral species in Hawai‘i, Montipora capitata and Porites compressa, during a simulated marine heating event. Physiological performance was quantified using light and dark respirometry, measuring oxygen production and consumption as photosynthesis (P) and respiration (R) rates, respectively. The results indicate that nutrients increased net and gross primary production (NPP & GPP) for M. capitata but did not affect P. compressa. With elevated temperature, heated M. capitata fragments maintained high NPP and GPP rates in the effluent and guano treatments, suggesting thermal buffering from the anthropogenic and biotic nutrient addition. In contrast, control and inorganic-enriched fragments experienced reduced P in the heated treatment. In the simulated thermal stress event, nutrient addition did not alleviate heat stress for P. compressa corals. In the recovery phase, both coral species exhibited similar NPP and GPP, regardless of nutrient and temperature treatments. While nutrient enrichment during a marine heatwave may aid metabolic maintenance in M. capitata, the combination of nutrients and heat impairs P. compressa metabolism. Evaluating the production of harmonious reef systems versus individual coral fragments during thermal stress events may help decipher this nutrient paradigm.
Location: WEB 203
Date & Time: Wednesday, April 30, 2025 at 9:00am
You can also connect via Zoom:
https://hawaii.zoom.us/j/84994131421
Meeting ID: 849 9413 1421
Passcode: 793370
