Space as a resource for predatory gastropods on Heron Island Reef, Great Barrier Reef

Brief description

Data on worm-eating gastropod microhabitat use and abundance within microhabitats were collected along transects located on the Heron Island Reef crest between November 1975 and June 1978. All transects were placed parallel with the reef edge within the study area, which was 10-40 m wide by about 1,500 m long, bounded by a rim of coral and coralline algae to seaward and inshore by a rubble bank. The study area was approximately 50 cm above MLW, but remained covered at low tide due to runoff from the reef lagoon.A series of transects were sampled over a period of 4-8 weeks on three occasions: November 1975 (25 transects); June 1978 (20 transects); and June 1978 (20 transects). Each 10 x 1 m transect was divided into forty 0.25 m² quadrats, with 20 quadrats on each side of a 10 m chain. The first two samples were made during daylight low tides and the June 1978 sample was taken on night low tides. Within each transect an estimate of the substratum composition was made by recording the microhabitat type under every 10th link in the chain (17 cm between points). Gastropod use of these microhabitat types was recorded by noting the microhabitat type occupied by each snail, in addition to its species and shell length to the nearest 0.1 mm. All predatory gastropods found in and near the transects were collected in order to determine the gastropods' diets by faecal sample analysis. These gastropods were subsequently returned to within 30 m of their collection sites.Microhabitat resource use was quantified by calculating niche breadth and overlap estimates for all species with numbers of individuals not less than five. These estimates were calculated separately for the November 1975, June 1977 and June 1978 samples. This study of a gastropod assemblage was designed to determine if microhabitat space was a limiting resource at habitat level for predatory gastropods on coral reefs.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The microhabitat categories used are described in:Kohn AJ (1968) Microhabitats, abundance and food of Conus on atoll reefs in the Maldive and Chagos Islands. Ecology 49:1046-1062Kohn AJ, Nybakken JW (1975) Ecology of Conus on eastern Indian Ocean fringing reefs: diversity of species and resource utilization. Mar Biol 29:211-234Microhabitat categories:1. Sanda) Level surfaceb) In depression2. Sand under coral rock3. Coral rubble, with or without sanda) On level limestone surfaceb) In depressionc) Under coral rock4. Very thin layer of sand (5 mm)a) On level limestone surfaceb) In depression5. Reef limestone, bare of sand or algaea) Smoothb) Roughc) In depressiond) Under coral rock6. Beachrock, bare of sand or algae7. Thin layer (1-3 cm) of algal-bound sand on reef limestonea) On smooth surfaceb) On rough surfacec) In depression8. Dead coral head or boulder9. Living coral10. Algaea) Folioseb) Crustose11. Other (e.g. undersurface of rocks)The faecal sample analysis method used to determine gastropod diet is described in:Reichelt RE (1980) Resource utilization strategies of vermivorous gastropods on Heron Reef, Great Barrier Reef. PhD thesis, University of Queensland, Australia.The Shannon-Wiener function used as a measure of niche breadth is discussed in:Colwell RK, Futuyma DJ (1971) On the measurement of niche breadth and overlap. Ecology 52:567-576Hurlbert SH (1971) The nonconcept of species diversity: a critique and alternative parameters. Ecology 52:577-586Pielou EC (1975) Ecological diversity. John Wiley and Sons, New YorkRoutledge RD (1979) Diversity Indices: Which ones are admissable? J Theor Biol 76:503-515Microhabitat resource use overlap between species was calculated using the "percent similarity" overlap index described in:Hurlbert SH (1978) The measurement of niche overlap and some relatives. Ecology 59:67-77

Notes

Credit
Reichelt, Russell E, Dr (Principal Investigator)