Patterns and Effects of Direct Contact Between Coral and Macroalgae on Shallow Reefs Around O‘ahu, Hawai‘i.

Abstract

O‘ahu’s reefs are vulnerable to increased macroalgal growth, which can have severe negative effects on reef corals. While experiments investigating these interactions have increased in recent years, most are short (less than 20 days) and naturally-occurring coral-algal interactions are rarely surveyed. Surveys of nearshore O‘ahu reefs seeking to quantify naturally-occurring coral-algal interactions for the first time found significant differences in the number and severity of interactions experienced by different coral species as well as between sites. This research provides a valuable baseline and springboard for future research. A three-month experiment exposed Porites lobata coral to mats of the invasive Gracilaria salicornia and observed higher prevalence and severity of bleaching, reduced photosynthetic pigment concentrations, and altered lipid content in treatment corals. However, differences in physiological metrics over time suggest that the response may be more immediate and acute than chronic.