Assessment of nonindigenous species on coral reefs in the Hawaiian Islands, with emphasis on introduced invertebrates

Coles, SL; Eldredge, L; Kandel, F; Reath, P; Longenecker, K

Coral reefs on the islands of Kauai, Moloka¿i, Maui, Hawaii and Oahu were surveyed for the presence and impact of marine nonindigenous and cryptogenic species (NIS) using a rapid assessment method that standardized search effort for approximately 312 m2 at each site. A total of 41 sites were surveyed by three investigators for a total of approximately 120 hours search time on the five islands. Algae, invertebrate, and fish taxa were identified on site or returned to laboratory for identity confirmation. Only 26 NIS, comprised of three species of algae, 19 invertebrates, and four fishes were recorded from a total of 486 total taxa on the entire study, and 17 of the NIS occurred at only one or two sites. The most NIS that occurred at any site was six, and 21 of the sites had less than three. If the three species of fish that were introduced in the 1950s and known to occur throughout Hawaii are excluded, over half the sites had less than two NIS. The numbers of NIS occurring at each site were compared with values measured or assigned to a number of factors that may influence the spreading and proliferation of introduced marine species. These factors included distances from harbors, boat launching ramps, stream mouths and shorelines, and subjective ranking values on a scale of 1 to 5 for shoreline urbanization, artificial surfaces in the water, reef condition, and the degree to which sites were isolated from the open ocean (non-exposure). The number of total native taxa at each site determined from the reef assessments was also included as a predictor variable, on the basis that high species richness could act to limit the establishment of introduced species. A best subsets regression model explained over 65% of the variance in NIS from two predictor variables: non-exposure, number of native taxa and their interaction. Most of the variance was explained by a highly significant relationship of NIS with non-exposure to open ocean conditions, i.e. NIS increased going from open coastlines to embayments and semi-protected harbors. A highly significant interaction between ocean non-exposure and native species richness suggested that higher species diversity may act to restrict NIS occurrence in embayments and semi-enclosed environments where they are most likely to establish themselves. Due to the relatively low frequency of occurrence and few invertebrate NIS found on these surveys, no eradication or control management efforts are recommended at this time. However, two introduced species encountered in the surveys, the Orange Keyhole Sponge, Mycale armata Thiele, and the Snowflake Octocoral, Carijoa riisei (Duchassaing & Michelotti), appear to be increasing in both abundance and distribution on some coral reef areas. These species should be considered invasive, monitored and research conducted to obtain basic biological and ecological information that may be utilized in their control. Other management efforts should focus on preventing the initial introduction of nonindigenous marine species into Hawaiian waters and their transport among the islands, and in preserving the integrity of coral reef species richness, especially in semi-enclosed embayments and other areas most likely to be the first locations to be colonized by introduced species.

Assessment of nonindigenous species on coral reefs in the Hawaiian Islands, with emphasis on introduced invertebrates

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