Mangrove fish, zooplankton and forest epifauna at Dickson Inlet, Port Douglas, north Queensland

Brief description

Three areas in Dickson Inlet were sampled intensively in the wet season (16-18 March 1989) and the dry season (24-27 October 1989) during daylight hours. The first area (FRONT) was slightly north of Magazine Island adjacent to the mangrove stands at the mouth of a small creek. Low tide water depth was between 0.5 and 1.0 m at this site and small patches of seagrass were present. The second area (MID) was in the middle reaches of the inlet, and included parts of the mainstream and small mangrove creeks draining into the mainstream. Area 3 (UPPER) contained small creeks and sections of the mainstream at the extreme upper limits of the inlet.In Dickson Inlet fish were sampled with three net types. A small seine net (6 m x 2 m, 3 mm mesh) was dragged by two people for 10 m at low tide to capture very small post larval and juvenile fish inhibiting shallow creeks. A large seine net (30 m x 1.5 m, 18 mm mesh), was used to sample larger, more mobile fish species, which use shallow accreting mud-banks as a habitat at low tide. Gill nets (15 m x 1.5 m, 20 mm mesh) were set at high tide at the entry points of small creeks into the mainstream, and left to fish for 3 hours on the ebb tide. Three replicate samples were taken for each net type in each of the three areas. All fish were identified and counted in the field. Measurements of water temperature (°C), salinity (ppt), turbidity (secchi disc (m)) and dissolved oxygen concentrations were taken in each area.Dip Creek, approximately halfway between Port Douglas and Cooya Point, was sampled during the dry season field trip to determine if fish community structure varied in the region. In Dip Creek, only the two types of seine net were used for sampling.Zooplankton were sampled at 4 sites in the inlet (FRONT, MID1, MID2, UPPER) in the wet season, but only at 3 sites (FRONT, MID1, UPPER) in the dry season, using oblique tows of a zooplankton net (mouth diameter 0.5 m, mesh size 105 µm, with a center-mounted General Oceanics flow meter). Tows were for 2 minutes duration, and there were 3 and 4 replicates per site in the wet and dry seasons respectively. Zooplankton were preserved in the field and returned to the laboratory for analyses. In addition to the quantitative sampling of fish and zooplankton, many areas of the intertidal forested areas were also surveyed, and a record was kept of the degree of leaf litter accumulation and the relative abundance of crabs (Family Grapsidae, Sub-Family Sesarminae). Surveys were undertaken to describe the status of fish communities and zooplankton inhabiting mangrove waterways of the Dickson Inlet. Juvenile fish and prawns were targeted, since mangroves are known nursery grounds. The aims of this study were to determine:- if the fish and zooplankton communities of Dickson Inlet were similar to those in other tropical, north Queensland estuaries- if the abundance and community structure of the fish and zooplankton faunas varied with distance upstream in Dickson Inlet- if fish community structure varied in the region between Port Douglas and Cooya Point.A qualitative assessment of the macro-fauna inhabiting the intertidal forested areas of the inlet was also undertaken. This survey of the mangrove fish, zooplankton and intertidal macrofauna of Dickson Inlet was undertaken as part of the Marine and Estuarine Studies section of the Port Douglas and Environs Planning Study, in accordance with the brief from the Premier's Department, through Environment Science and Services.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The same sampling procedures as those employed in previous detailed work on north Queensland mangrove fish and zooplankton were used so that comparisons among estuaries were possible. These procedures are described in:Robertson AI (1988a) Abundance, diet and predators of juvenile banana prawns Penaeus merguiensis in a tropical mangrove estuary. Aust. J. Mar. Freshw. Res. 39, 467-478.Robertson AI (1988b) Links between nearshore fisheries and mangroves in tropical Australia: management implications for South Pacific nations. Information paper No 24. Workshop on Pacific Inshore Fisheries, South Pacific Commission, Noumea, 45 p.Robertson AI and Duke NC (1987) Mangroves as nursery sites: comparisons of the abundance and species composition of fish and crustaceans in mangroves and other nearshore habitats in tropical Australia. Mar. Biol. 96: 193-205.Robertson AI, Dixon P and Daniel PA (1988). Zooplankton dynamics in mangrove and other nearshore habitats in tropical Australia. Mar. Ecol. Progr. Ser. 43, 139-150.Robertson AI and Duke NC (1990) Mangrove fish-communities in tropical Queensland, Australia: spatial and temporal patterns in densities, biomass and community structure. Marine Biology 104: 369-379.

Notes

Credit
Robertson, Alistar I, Dr (Principal Investigator)