Assessment of an Invasive Tropical Sponge on Coral Reefs in Hawai‘i

Sponges are ecologically important components of many marine ecosystems and are abundant benthic fauna on coral reefs. Mycale grandis is an alien invasive sponge found on many partially degraded shallow water coral ecosystems in Hawai‘i. Mycale grandis is known to compete spatially with dominant native reef building coral such as Montipora capitata and Porites compressa. Since its appearance in the late 1990s, M. grandis has established itself in a number of coral reef ecosystems around the main Hawaiian Islands. Within south Kāne‘ohe Bay, sponge coverage in 2014–2017 ranged from 2.1% on fringing reefs to 32.3% within the mangrove habitat along the northern edge of Coconut Island, which is similar to coverage found in 2006–2007 surveys. Sponges are prolific filter feeders and pump seawater for the dual purpose of obtaining resources and removing metabolic wastes, and thus process large amounts of water in their environment. Mycale grandis pumps 0.0027 L seawater s−1 L−1 sponge, equivalent to 115 times its own volume per day. These pumping rates were combined with biomass estimates, depth, and circulation parameters in south Kāne‘ohe Bay to show that M. grandis can cycle a substantial amount of the overlying water column and therefore has the potential to influence the biogeochemistry of overlying reef water in south Kāne‘ohe Bay.