Complex drivers of invasive macroalgae boom and bust in Kāne'ohe Bay, Hawai'i

Abstract

Invasive macroalgae Eucheuma sp. and Kappaphycus spp. (E/K) became a dominant benthic feature in Kāne'ohe Bay throughout the past four decades - occurring on up to 74 ha of reef area and growing up to three meters thick, which prompted intensive management action. In 2013, E/K cover began decreasing at managed and unmanaged sites. This study examined the extent and timing of the E/K decline and evaluated environmental and ecological drivers beyond management contributing to the decline. E/K continued to recede into 2017 and remains sparse in Kāne'ohe Bay today. Increasing over the sampling period, herbivore biomass was negatively correlated with E/K cover, and other significant, non-linear relationships emerged between E/K cover and coral cover, sea surface temperature, wind, and rainfall. This study uncovers several possible mechanisms explaining a boom and bust in E/K abundance, emphasizes the importance of herbivory, and highlights the resilience of coral reefs in Kāne'ohe Bay.

Keywords: Coral reef; Eucheuma; Herbivory; Invasive species; Kappaphycus; Management.