Physical, chemical and biological properties of waters over coral reefs at Lizard Island, Great Barrier Reef (LIMER II Expedition, September 1977)

Brief description

Waters associated with the main reef complex at Lizard Island, North Queensland were studied during September 1977 as a component of the second "Lizard Island Metabolic Exchange on Reefs" (LIMER II) expedition. Two approaches were taken:a) Nutrient Transects; water sampling for biological and nutrient analyses was carried out along fixed transects (one leeward reef, one windward reef) on which radar-reflecting buoys were set up marking boundaries between major benthic zones and b) Hydrology Transects; temperature, salinity and oxygen data was determined to describe water structure.
a) Nutrient Transects Sampling stations on the windward reef were Af-Gf with an offshore station (Hf) approximately 1km in front of the reef face. Station Af was approximately 50m in front of the reef crest in a water depth of about 20m. Stations Bf and Cf were not marked by buoys but were about 15m on either side of the reef crest. Station Bf was in a water depth of about 7m. The remaining stations (Df-Gf ) were marked by buoys and positioned across the 800m wide reef flat.Sampling stations on the leeward reef were Hb, Ab-Fb. Station Hb was about 60m in front of the reef margin in lagoonal waters about 2.5m deep. Station Ab was immediately in front of the reef margin in water about 1m deep. Remaining stations (Cb-Fb) were positioned across about 700m of the leeward reef flat. Depths and the typical profiles were obtained from a series of runs across the transects with a depth sounder. The tidal datum was determined from the tidal plane for Lizard Island in reference to tidal predictions for Cairns (the standard port for Lizard Island). Depth at each station was calculated from the datum point establishment for the station and the predicted tide height for Lizard Island.Water SamplingFluorescein or a curtain drogue (at night) was placed in the water at the front of a transect. For the windward reef, transects began at Station Af. Leeward reef transects began at station Hb. Samples of water were taken by 2/3 filling of nalgene plastic containers (40l) previously treated with flowing seawater to remove traces of plasticizer. The plastic bins were placed in the water alongside the boat and washed several times before being filled. A second boat ferried water samples back to the laboratory ensuring that samples were not stored for more than 2h before analysis, thus minimizing temperature variation, and chemical and biological changes. Samples were taken at station Hf, 1km offshore, at about the same time that sampling of windward reef transects commenced. On return to the laboratory, water samples were gently mixed and subsamples removed for the various analyses. The time and position of sampling was recorded on a large aerial photograph by observers on a hill above the reef complex. If water flowed away from the line of buoys, samples were taken at boundaries of the biotic zonation marked by the buoys.At night, these positions were determined by the onshore observers using the aerial photograph and radar positions of the sampling boat and marker buoys. A string of 810 crushed aluminium beer cans was found to give a better radar reflection than vertical aluminium plates at right angles because the latter did not maintain reflection orientation in strong winds (>7m/sec) or at low tide. Samples were taken alongside the centre of the patch of fluorescein during the day. Daytime deployment of the curtain drogue showed that it moved, on average, about 1.3 times faster than the fluorescein; however, night time samples were taken as the drogue reached each appropriate point. On two occasions, standing water samples were collected across the windward reef transect independent of water mass flow. On the leeward reef, two transects were carried out in which a volume of water was enclosed in a large plastic bag at station Ab, the bag was allowed to drift with the water current, and water samples were taken from the bag and the traversing seawater at each station (referred to as "Bgd" in data tables).b) Hydrology TransectsPreliminary studies of movement, horizontal and vertical mixing processes, and light transmission were made in the Lizard Island reef waters. Some study was carried out at stations on the Nutrient Transects of the windward and leeward reefs, while others were at discrete stations across the reef system; these stations being established to determine characteristics of particular hydrological events. Temperature, salinity, oxygen concentration and light transmission were determined.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Sample Analysesa) Nutrient Transects:Water samples were identified by a date/time/station code i.e. 02.10. Hf was collected on 2nd September from a transect study commenced within the hour following 1000h and sampled from Station Hf (offshore, windward reef). Each water sample was subsampled for different analyses.Dissolved inorganics and dissolved organic nitrogen (DON):Analyses were carried out on 1.5l membrane-filtered water samples (47mm diameter, 0.45u Millipore filter at 1/4-1/3 atmosphere vacuum). Nitrate, nitrite and ammonia were determined on-site (Strickland and Parsons, 1972). The remaining filtered water was frozen (0°C) in 250ml plastic containers and returned to AIMS for repeat analyses of nitrate, nitrite and ammonia and for analyses for reactive phosphorus and silicate. These analyses were carried out with a Technicon autoanalyser. Dissolved organic nitrogen (DON) was determined as nitrate from frozen samples by the method of D'Elia et al., (1977).Particulate organic carbon and nitrogen (POC, PON). Particulates were collected and analysed by two methods. First, 1l seawater was passed through a 25mm glass fibre filter (Whatman GF/C) which had been previously heated at 490°C for 4h to remove any organics. The filter was washed with 2ml Na2SO4 and analysed on-site for particulate organic carbon (POC) by the wet oxidation technique (Strickland and Parsons, 1972). Second, 2l seawater was passed through a 47mm glass fibre filter (Whatman GF/C) which had been heated as before. The filter was wrapped in aluminium foil, stored over silica gel desiccant (Sharp, 1974) and returned to AIMS for analysis. POC and PON (particulate organic nitrogen) were determined with a Perkin Elmer CHN Elemental Analyser using acetanilide as a standard. Immediately prior to combustion, samples were acidified with 0.5ml N NCl (BDH) and then dried under vacuum to remove any particles of CaCO3 (Gordon, 1969). When transects were made at night these procedures were repeated on water samples which had been prefiltered through a 145um plankton net ("+ sieve") to remove large zooplankters abundant in reef waters at night.Chlorophyll a. A 2l seawater sample was vacuum-filtered through 47mm diameter GFC glass fibre filters. Photosynthetic pigments associated with retained particles were extracted in 8ml 90% acetone in the dark at 4°C. Chlorophyll a concentration was calculated from optical density values determined (630, 647, 664, 750nm) in 5cm light-path cuvettes (Jeffrey and Humphrey, 1975).ATP.A 250ml volume of each water sample was vacuum-filtered through 25mm diameter 0.2um Millipore membrane. ATP content of retained materials was determined (Bulleid, 1977).Bacteria.Acridine orange was added to each 10ml sample of seawater before filtration through 0.2um polycarbonate membranes. Direct counts were by light microscopy techniques. In some case, 1l of seawater was analysed for muramic acid. These methods and data are described by Moriarty (1979).Heterotrophic Potential.A 50ml water sample was incubated with UL-14C reconstituted algal protein amino acid hydrolysate (equimolar in equal specific activity amino acids). The 14C-incorporation into particulate materials of each seawater sample was determined (Smith, Meyer & Horner, 1981) and results expressed as relative heterotrophic potential.Primary Productivity. Relative primary productivity was measured on 10ml seawater samples incubated with H14CO3(0.522 MBq) under constant irradiance (180uEin, m2/sec) (Smith and Wiebe, 1976).b) Hydrology Transects:Salinity and temperature of the water were measured using a portable meter and probe (Yeskal Environmental Electronics, Sydney; Model 602) calibrated daily against standardised thermometers and seawater.Oxygen concentration in the water were measured by the Winkler method (Strickland and Parsons, 1972).Attenuation of solar radiation by the water column in the 400 to 700 nm band, was measured using a quantum meter (Lambda Instrument Co.; model LI-185 with underwater quantum sensor, LI-I92S). Irradiance was measured at the surface and at 1m intervals to 10m depth, and thereafter at 2m intervals to 20m depth. The attenuation coefficient (E) has the units m-1 and is defined by Qz=Qo10-Ezwhere Qo and Qz are the downward irradiances expressed in quanta and Z is the depth in metres. Attenuation was also measured using 1m path-length transmissometer (Hydro Products, San Diego; model 912S) at a depth of 1 m. As the spectral character of the light source in the transmissometer is different to that of the sun, the attenuation coefficients from each method are slightly different.

Notes

Credit
Barnes, David J, Dr (Principal Investigator)