Movement and growth of the coral reef holothuroids Bohadschia argus and Thelenota ananas

Tropical sea cucumbers are among the largest mobile invertebrates on coral reefs and are widely regarded as sedentary. Mark-recapture methods provide empirical estimates of movement and growth but have often been unsuccessful with sea cucumbers. We applied a new photographic mark-recapture technique to measure rates of short-term displacement (over a few days), long-term displacement (over 2 yr) and growth of Bohadschia argus and Thelenota ananas on the Great Barrier Reef, Australia. Recapture rates were 50–100% in the short-term study and 50–77% in the long-term study. In the short-term studies in 2010 and 2012, average movement rates ranged 2–8 m d-1 for B. argus and 5–9 m d-1 for T. ananas. Long-term movement averaged 15–47 m over 2 yr, with some individuals displacing less than 5 m and several others moving more than 100 m. Our study shows that some tropical sea cucumbers can be highly mobile, and many appear to display home ranging. Growth rates were positive yet modest for smaller individuals, but many of the large individuals lost weight over the 2 yr study. Classical growth models indicated that B. argus attain an average maximum size in 15–20 yr, and the empirical data on growth show that they can lose or gain weight thereafter. Hence, longevity appears to be at least several decades. The 2 species are slow growing, and the negative growth in large individuals undermines previous estimates of growth and longevity based on size-frequency data.