Rate of spread of introduced rhodophytes Kappaphycus alvarezii, Kappaphycus striatum, and Gracilaria salicornia and their current distributions in Kane'ohe Bay, O'ahu, Hawaii

Spread of the introduced macroalgae Kappaphycus alvarezii (Doty), Kappaphycus striatum Schmitz, and Gracilaria salicornia C. Ag. was measured on reefs in Kane'ohe Bay, O'ahu, Hawai'i. The red algae Kappaphycus alvarezii and Gracilaria salicornia were introduced to specific sites in Kane'ohe Bay in the 1970s. Since that time their distributions have increased, and the algae have spread through the bay. To assess the current extent of these algae in the bay and determine their rate of spread, we performed surveys with a manta towboard. In addition, abundance of these species was determined by detailed reef transects in the central bay in three habitats: barrier reef, patch reef, and fringing reef. All three species have become well established. These algae were found in all areas of Kane'ohe Bay. Distributions are not uniform within the central bay. Abundance of Kappaphycus spp. was highest on patch reefs in shallow water. Gracilaria salicornia was most abundant on the fringing reef. Kappaphycus alvarezii and K. striatum have spread 6 km from their points of introduction in 1974, an average rate of spread of approximately 250 m yr super(-1). Gracilaria salicornia has spread over 5 km since its introduction in 1978, an average rate of spread of approximately 280 m yr super(-1). High abundance of these introduced species appears to be associated with moderate water motion.