Natural feeding of coral reef holothurian, Holothuria atra on microalgae and meiofauna from seagrass beds in Chuuk, FSM

Abstract

The coral reef holothurian, Holothuria atra has an important role in nutrient recycling as a sediment-feeder in coral reef ecosystems. This recycling of nutrients contributes to the high productivity in coral reefs. Limited information is available on the main food sources of H. atra, despite their importance on the reefs. This study investigates the food items (i.e. microalgae and meiofauna) consumed by the sediment feeding holothurian, H. atra. Sediment samples in front of the mouth and faeces at the posterior of the sea cucumbers, and the intestines were taken from each individual. The different sediment samples were fixed in 10% formalin for later qualitative and quantitative analysis of microalgae and meiofauna. Taxonomical determination of microalgae was performed with an inverted microscope. Extraction of the meiofauna was performed using Ludox HS 40 and the species were identified to the class level. Total number of microalgae and meiofauna was identified to 25 species and 10 classes in three different samples, respectively. Microalgae and meiofauna in before feeding sediment was recorded 349 ind. ml–1 and 12.2 ind. ml–1 with the major groups of Bacillariophyceae and Polychaeta, respectively. After feeding, the microalgae and meiofauna were ingested up to 85.6% and 79.1% by the holothurians. In the intestine content, the abundance of Bacillariophyceae without chlorophyll was higher than other groups while the abundance of Polychaeta was lower than other groups. This data demonstrated that Bacillariophyceae and Polychaeta were main ingested food items of H. atra.