Living in a potentially toxic environment: comparisons of endofauna in two congeneric sponges from the Great Barrier Reef

The abundance and community composition of the endofauna in 2 species of sponge, Haliclona sp. 1 and Haliclona sp. 2 (phylum Porifera: order Haplosclerida), were examined at different sites on the slope at Heron Island Reef, in the southern Great Barrier Reef, on 2 separate occasions. Both species of Haliclona Occupy Similar habitats on the reef slope and are often found living adjacent to each other, but the major groups of secondary metabolites and the gross external morphology in the 2 species of sponge are different. The 2 species of sponge supported significantly different endofaunal communities, with Haliclona sp. 2 Supporting 3 to 4 times more individuals than Haliclona sp. 1. Fewer demersal zooplankton (copepods), nematodes and some peracarid crustaceans were found in Haliclona sp. I compared with Haliclona sp. 2. There were also differences in the numbers of spionid, nereidid and syllid. polychaetes living in the 2 species of sponge. The only taxon that was more abundant in Haliclona sp. 1 than Haliclona sp. 2 was the spionid Polydorella prolifera, and this difference was only evident on 1. of the 2 occasions. The amount of free space (pores, channels, cavities) for a given weight of sponge was only 19% greater in Haliclona sp. 2 than in Haliclona sp. 1, suggesting other factors, such as the differences in the allelochemicals, may have a role in determining the numbers and types of animals living in these 2 species of sponge.

Emergence rates from the benthos of the parasitic juveniles of gnathiid isopods

Variation in the rate at which parasitic gnathiid isopod juveniles emerged from the benthos at Lizard Island, Great Barrier Reef, Australia, was examined (I) every 4 or 8 h throughout the day and night over a 24 h period, (2) over a 12 h period during the day or night, and (3) during different lunar phases (weeks). The number of gnathiids sampled per 4 or 8 h was low, with only 30% of the traps containing gnathiids and the abundance ranging from 0 to 3 gnathiids m(-2). The number of gnathiids that emerged over 12 h, in contrast, ranged from 0 to 36 m(-2). During the third and fifth weeks sampled, more gnathiids emerged during the day than at night. This coincided with the full moon and new moon. Most gnathiids that emerged from the reef during the day (98 %) had not fed, in contrast to those sampled at night (71%). Of the gnathiids with no engorged gut, most (97 %) of those collected during the day were small (II. mm) compared to those collected at night (19%), the latter being mostly >1 mm. Of the gnathiids with an engorged gut, most were sampled at night (83 %) and 97 % were >1 mm in size. These percentages suggest differences in the emergence behaviour among Life stages or species of gnathiids. This study, which shows that gnathiids do emerge during the day and supports other studies showing that gnathiids also attack fishes during the day, has important implications for understanding the role of cleaner fish and their main food source, gnathiids, as it shows there is a constant source of gnathiids emerging from the reef during the day and night in search of hosts.