Nocturnal Activity & Micro Habitat Preference Introduction H. impatiens are commonly found in the intertidal zone and reef flats (Clark and Rowe 1971). They tend to live under large chunks of corraline rubble, or intricately weaved through the branches and crevices of large coral assemblages within shallow reef flats (Kotpal, 2009). This particular species prefers shallow waters of no more than 37m in depth.  Holothuria impatiens is nocturnal. By day this sea cucumber remains hidden and at night it will only extend half of its body out of its shelter to feed, rarely will this species be found in full view, which makes it extremely difficult to locate at night time. In some species of sea cucumber, the cuvierian tubules are laced with a toxic chemical known as holothurin, however in H. impatiens, the toxin is only located within the body wall (Bakus 19724), this could be a reason as to why it remains hidden during the day and only partially extends its body from it’s shelter to feed. When the sea cucumber is startled, it tenses up the muscles in its body wall, which causes the body to go firm, making it impossible for any predators to pull the animal from its crevice. Study Site Heron Island is a coral cay located in the southern Great Barrier Reef. It is situated 72 km north-east of Gladstone, Queensland and 539 km north of the Brisbane. The island is situated on the western side of Heron Reef, a fringing platform reef of significant biodiversity surrounds the island. Methods During both night and day low tides, belt transects were laid within each of the 3 zones (Lagoon, Reef Flat and Coral Rubble - Reef Crest). Zone distances from the shore were measured. By slowly and carefully walking up the transect from the shore line to the reef crest, abundance of Holothuria impatiens was recorded in each zone. Each coral assemblage was approached and carefully looked at. Boulders were not lifted up, as this would defeat the purpose of calculating day and night abundance. The percentage of ground cover was also recorded for each zone. Observations including, weather, depth and abundant coral types was noted. This process was repeated three times, in three different strips running perpendicular to the shoreline. Each of the three belt transects were 50 m apart. Results Holothuria impatiens were hardly seen during the day however many more were found during the evening belt transects. Commonly, 1 – 3 species were found per coral assemblage (roughly 1m2 – 2m2). As live coral assemblage density increased heading into the reef flat, so too did H. impatiens abundance. By comparison, very little individuals were found on the reef crest amongst the dead coral boulders. A combination of 75% coral assemblages and 25% open sand space was the most successful for H. impatiens abundance at night.

Table 1: Day time abundance of Holothuria impatiens in 3 habitat types; Lagoon, Reef Flat and Reef Crest. Day Time – Low Tide 10am     Distance from shore (m)   % of ground cover Nos. of individuals found over 3 trials   Observations Lagoon       175     10% - 30% 0   - Occasional boulder - Oral patch density increases further away from shore - Quite shallow (knee high) 1 0   Reef Flat       250     75% - 85% 1   - Acropora dominated - Small patches of sand - Individuals extremely cryptic 2 0   Coral Rubble – Reef Crest       270     100%   0 - Dead coral rubble - Mostly large boulders   1 0

Table 2: Night time abundance of Holothuria impatiens in 3 habitat types; Lagoon, Reef Flat and Reef Crest. Night Time – Low Tide 11:30pm     Distance from shore (m)   % of ground cover Nos. of individuals found over 3 trials   Observations Lagoon       175     10% - 30% 3   - Occasional boulder - Oral patch density increases further away from shore - Quite shallow (knee high) 1 5   Reef Flat       250     75% - 85% 12   - Acropora dominated - Small patches of sand - Individuals extremely cryptic, difficult to see in the dark 19 13   Coral Rubble – Reef Crest       270     100%   0 - Dead coral rubble - Mostly large boulders - Moderate wave overlap