Damselfish territories and primary productivity on coral reefs from the Great Barrier Reef and Papua New Guinea

Brief description

The territories of herbivorous damselfish from two coral reefs in the central Great Barrier Reef (Davies Reef and Myrmidon Reef) and a fringing reef in Papua New Guinea (Motupore Island) were measured for algal biomass and primary productivity and compared to surrounding epilithic algal communities. Three automatic data-logging respirometers were deployed for periods of 24 hours in the field to measure productivity parameters, light (as irradiance, Li-cor), temperature and oxygen concentration at 1 minute intervals. Primary productivity was estimated from diel patterns in oxygen flux using data from: photosynthesis-irradiance relation (Ik, Icomp and alpha); rates of photosynthesis (P) and respiration (R); primary productivity expressed as the area1 gross (Pg) and net (Pna) rates and as the net turnover (Pnb) of community biomass (B, g C m-¹). These results were compared to the parameters: damselfish species; reef location; date; inside/outside fish territories.Algal productivity inside and adjacent to the territories of Stegastes fasciolatus at Myrmidon Reef and Plectroglyphidodon lacrymatus at Motopure Island was measured using square blocks (8 x 8 x 2 cm) of Porites which had been attached to the respective reef substrata for a period of 12 months prior to measurement. At Davies Reef, coral blocks with established algal covering from non-territory substrata were caged with wire mesh to exclude all large grazers for 30 days, then the productivity of the increased algal biomass on these blocks was measured by respirometry, uncaged blocks were measured at the same time. The surface area of Acropora sp. branches was calculated. Algal biomass was determined by drying coral rock samples at 60°C and scraping the surface to a depth of 2 mm. Scrapings were ground, redried, and then analysed for total organic carbon.Surveys of algal community distribution were carried out in May 1986 across the northern, central and southern sections of Davies Reef, from the front reef slope to the back reef slope. Up to 14 sites were established along each of these sections. At each of these sites, a 100 m tape transect was surveyed perpendicular to the section lines and the length of intercept to the nearest 1 cm for each major substratum category and damselfish territory was recorded. Four major substratum categories were surveyed: fish territories with dense mats of turf algae; closely-cropped filamentous and encrusting coralline algae; bare sand; organisms other than algae. This research was initiated to:1. quantify differences in reef epilithic algal community metabolism within and outside damselfish territories.2. assess the significance of these differences in the context of total reef primary productivity. Epilithic algal communities include coralline algae, turf algae (filamentous forms and thick turfs), corallines mixed with short turf.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The method used to survey algal community distribution is described in:Reichelt RE, Loya Y and Bradbury RH (1986) Patterns in the use of space in two coral reefs of the Great Barrier Reef. Coral Reefs 5: 73-79.

Notes

Credit
Klumpp, David W, Dr (Principal Investigator)