Seasonal changes in resident zooplankton sampled by emergence traps in one tree lagoon, great barrier reef

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Small resident Zooplankton species which rise from the substratum after sunset were sampled during the winter and summer seasons of 1977 and 1978. Modified emergence traps were used to obtain quantitative overnight samples from five habitats on and around two lagoonal patch reefs: live coral, and coralline rock, both on top of the reefs, sand at undercut and at vertical reef bases, and open sand 1–3 m away from the reef. In summer, at each habitat, many more animals and more species rise off the substratum than in winter. Estimated mean densities of animals rising overnight ranged from 664.9 · m −2 in winter (at undercut reef base) to 5034.7 · m −2 in summer (rock on top of reef). In winter the abundance of animals rising from open sand is significantly lower than that from the top of the reef. A total of 261 taxa was recognized. Samples from all habitats are dominated by copepods, mainly small calanoid and harpacticoid species. The most abundant of these include Stephos sp., Pseudodiaptomus cornutus Nicholls, Peltidium spp., Tisbe sp., and an unidentified thalestrid. In summer, additional copepod and peracarid species become numerous at night over the reef and over open sand. Other major taxonomic groups collected were ostracods, polychaetes, mysids, cumaceans, tanaids, gammarids, and the zoeae of some carid species. Most species appear to have a limited vertical range. Fauna rising from the top of patch reefs is rich compared with that from open sand, and significantly richer in summer than in winter. Faunal analyses indicate the localized distribution of a “coral” fauna and a “sand” fauna. Spatial distribution of these characteristic faunas is more discrete in winter than in summer. The reef base habitats appear to be a transitional faunal zone which contains elements of both “coral” and “sand” faunas. Seasonal fluctuations in abundance, composition and spatial distribution are similar to seasonal trends found in light-trap sampling of resident Zooplankton in the same seasons, and in similar locations, on Heron Reef. Sampling techniques, limitations, and results are compared with those of single-season emergence trap studies in other coral reef regions.