Quantifying Kāneʻohe: Coral Bleaching Conditions through Color Card Analysis

Abstract

The Nutrient Addition Experiment underscores the importance of monitoring coral reef health in the face of global climate change, focusing on how nutrient enrichment influences mass coral mortality during thermal stress events. Previous research from Palmyra Atoll demonstrates that nutrient-rich seabird guano contributes to coral resilience to thermal stress. Contrastingly, wastewater effluent, an anthropogenic nutrient source, has been found to be detrimental to coral health and thermal tolerance. This study, utilizing seabird guano and wastewater effluent, aimed to understand the coral color responses, a proxy of symbiont density, of coral fragments to these different nutrient treatments. The study involved collecting 288 Porites compressa (P. compressa) and Montipora capitata (M. capitata) fragments from Kāneʻohe Bay, Oʻahu, and conducting a three-week experiment with stable temperature conditions, randomized tank placements, and consistent nutrient dosing concentrations of 6 𝜇mol/L. Nutrient treatments included seabird guano, wastewater effluent, inorganic nitrogen and phosphorus, and an ambient control. The Hawaiian Ko’a Coral Color Card was used for coral color assessment using photographs analyzed in ImageJ. Results revealed an overall decrease in color values for P. compressa and an increase for M. capitata over the experimental period. Red Green Blue (RGB) values of P. compressa showed an inconsistent trend across treatments, while M. capitata exhibited significant increases, except for effluent-treated corals, which experienced a decline from week 1 to week 2. The study suggests additional coral conservation experiments that explore symbiont diversity, photosynthetic material, and temperature stressors for a comprehensive understanding of coral health in diverse nutrient conditions.