Not so sluggish: movement and sediment turnover of the world’s heaviest holothuroid, Thelenota anax

Abstract

Ecology of many sea cucumbers, including the world’s heaviest holothuroid Thelenota anax, remains understudied, hindering effective fisheries management and conservation. We located, measured and weighed 38 T. anax over 10 days at Lizard Island, northeast Australia. Body length alone was a suitable predictor of body weight for this species. Short-term (1–4 h) rates of displacement and sediment defecation were measured on 30 animals across three sites. The animals were highly mobile, moving, on average, 57 cm h⁻¹ (± 11 SE), and reworking 34 g dry weight of sediment h⁻¹ (± 7 SE). The animals moved more and defecated more sediments in areas where surrounding sediments had lower levels of organic matter. Defecation rates increased through daytime hours. The high mobility of T. anax should confer an advantage for mate-finding but also could increase spillover from small marine reserves into fishing grounds. Our findings galvanise a pattern of high mobility in larger holothuroids and show that food resources and time of day modulate the extent of sediment reworking by deposit feeding holothuroids. The high sediment turnover rate highlights the detrimental effect that overfishing of these large holothuroids will have on the health of coastal marine ecosystems.