Assessment of Invasiveness of the Orange Keyhole Sponge Mycale Armata in Kaneohe Bay, Oahu, Hawaii Based on Surveys 2005-2006, Year 2 of Hawaii Coral Reef Initiative (NODC Accession 0033380)

The Orange Keyhole Sponge, Mycale armata Thiele, was unknown in Hawaii prior to 1996. It was first reported in Pearl Harbor and has been reported in low abundance from a few coral reef locations near harbors, but in Kaneohe Bay it has become a major component of the benthic biota in the south bay in the last 5-10 years. An initial study was conducted in 2004-2005 to determine Mycale armatas distribution, abundance throughout the bay, its growth rates on marked permanent quadrats, and whether mechanical removal would be an effective management technique for its control (Coles and Bolick 2006). Findings in the first year from 190 manta board surveys and 19 quantitative photo-transects on 18 reefs throughout Kaneohe Bay indicated that the sponge had its greatest abundance in the south bay near the Hawaii Institute of Marine Biology (HIMB) pier and Coconut Island. Despite the apparent visual dominance of this conspicuous sponge on many reefs, its maximum coverage measured on any transect in 2004-2005 was 9.2% of the bottom, with a mean of two transects at this site of 6.5%, and sponge was substantially less than coral coverage at all sites. However, measurement of changes in sponge area on ten permanent quadrats photographed quarterly throughout the year indicated a significant average increase in sponge of 13%. Attempts to mechanically remove sponge on ten other permanent quadrats was very time-consuming, requiring up to an equivalent of 22 hr m-2 for removal, and sponge regrew an significant average of 10% during the year following removal. The study was continued for a second year to determine whether changes in sponge coverage and distribution in the bay could be detected, whether the first year's rates of increase in sponge cover on permanent quadrats would continue, and whether a more effective method of sponge control could be devised. Photo-transects repeated at 11 of the 19 sites from Year 1 indicated increased sponge cover at all sites with significant increases at 7 of the 11 sites, and highest sponge coverage still occurring in the vicinity of Coconut Island. The permanent control photo-quadrats remaining from the first year were re-photographed quarterly and showed a further non-significant increase of 1.7% during Year 2. Re-growth of sponge on the remaining removal quadrats averaged a non-significant increase of 6.3%. Four more photoquadrats were deployed in March 2006 and sponge surfaces on two of these were mechanically removed, followed by injection of the sponge with air delivered by a 10 cm long bone necrosis needle. This treatment resulted in mean reduction from initial values of sponge cover of up to 73% a month later. Four more quadrats were deployed in May and these were treated by air injection alone, which showed little visible effect one month later. Sponge on these quadrats were re-injected with air, and one month later showed mean reductions in sponge of 57%. Some regrowth of sponge occurred on these removal quadrats, resulting in a net average reduction of 42% below pretreatment conditions for the five of the six quadrats that remained by the end of the study. Overall, the two-year study suggests that growth and spread of Mycale armata on Kaneohe Bay reefs and may now be slowly but steadily extending beyond its area of highest concentration in the south bay. The air injection method may provide a means for reducing the range expansion and impact of the sponge if substantial resources are directed toward controlling this highly invasive species. Before a large-scale control effort is considered, a pilot study of reducing the sponge by air injection should be conducted and results monitored to determine the effectiveness of this means of control in both the area of highest sponge abundance and at the boundary of present sponge occurrence.

Tags: algae species, and kappaphycus sp., and substratum types within the photoquadrats, benthic, biological survey, biology, central pacific ocean, coastal processes, coastal studies, coconut island, coral reef, coral reef ecology, coral reefs, coral species, corals and other invertebrates, coris_metadata, country/territory, distribution and relative abundance of mycale armata, earth science, frequency of occurrence of species, gracilaria salicornia, hawaii, hawaiian islands, honolulu, invasive/introduced species, kaneohe bay, kaneohe bay (21n157w0004), macroalgae, marine organisms, mhi, nonindigenous and cryptogenic marine taxa, numeric data sets, oahu, oahu (21n157w0003), oahu island, ocean basin, oceans, pacific ocean, percent cover of mycale armata, relative abundance of the invasive algae dictyosphaeria cavernosa, taxa, total biota, united states of america
Organization: National Oceanic and Atmospheric Administration, Department of Commerce