Biological, chemical and physical observations in inshore waters of the Great Barrier Reef (1975-1978)

Brief description

A routine sampling program was run over three consecutive years (1975-78) at fixed field stations on a transect from the Townsville Harbour to Keeper Reef, an inner reef in the Great Barrier Reef complex. From December 1975 to December 1976, bi-weekly sampling was conducted at three stations as part of a phytoplankton productivity program, which initially included a further 7 stations. Parameters measured were temperature, salinity, transparency, phytoplankton pigments and net zooplankton.From January to December 1977 the sampling program continued at approximately weekly intervals, adding new measurements for microzooplankton, nutrients (nitrate, nitrite, ammonia, phosphate and SiO3) and particle size distribution in seawater. The sampling program up to the end of 1977 was aimed at evaluating the horizontal gradient of various biological, chemical and physical properties, so that only surface samples were consistently taken. From January to December 1978, the detailed vertical structure of the water column was investigated at Station 2. Dissolved oxygen, particulate organic carbon, dissolved organic nitrogen and phosphate (the last two items from August) were added to the items previously measured. This research was undertaken to extend the limited knowledge of the biological, chemical and physical properties of inshore waters of the Great Barrier Reef. The purpose of the initial study, which commenced in 1975, was to establish the general patterns of phytoplankton ecology in the GBR environment and to evaluate the presence or absence of a seasonal cycle.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: 1. TransparencyA standard white Secchi Disc of 300mm diameter was slowly lowered through the water column on a rope marked in metres to the point at which it completely disappeared from view. This point was checked by slightly raising and lowering the disc.2. Water samplingWater samples were collected using 5 litre Niskin bottles (General Oceanics). In 1976 and 1977, surface samples were collected with an acid washed bucket, though this practice was replaced by the use of a Niskin bottle in the second half of 1977. All glassware and sample bottles used for these samples were previously acid washed by soaking in 3N HCl overnight and rinsing 3 times with distilled water.3. TemperatureTemperature measurement was made immediately the sample was brought on board using a full immersion thermometer (accuracy ±0.1°C).4. SalinityWater samples for salinity determinations were taken into 500ml polyethylene bottles, which had been rinsed with the same sample water, and tightly closed with sealing screw caps. The samples were kept refrigerated at 5°C during storage. Preceding salinity measurements, samples were allowed to equilibrate to room temperature over a 24-hour period in the laboratory. Salinity was measured with a Plessey, Model 6230N Laboratory Salinometer, standardized with lAPSO standard seawater. The measurement is accurate to ± 0.003 0/00.5. Dissolved oxygenThe sample for dissolved oxygen analysis was drawn into a glass stoppered, 250ml reagent bottle via plastic tubing placed at the bottom of the Niskin bottle. Manganese sulphate and alkaline iodine reagents were immediately added. The bottle was vigorously shaken until the precipitate was evenly dispersed, and stored underwater until analysis at the laboratory, usually within 3 to 5 hours. The method of Strickland and Parsons (1972) was used for the determination of dissolved oxygen (see "Strickland, J.D.H. and T.R. Parsons, 1972. A practical handbook of seawater analysis. Bull. Fish. Res. Bd. Canada, 167: 1-310.1972"). Oxygen saturation was calculated from Fox's equation as a function of the temperature and salinity (see "Fox, C.J.J. 1907. On the coefficients of absorption of the atmospheric gasses in distilled water and sea water. Conseil Perm. Internat. p. l'Explor. de la Mer. Pub. de Circonstance, No. 41, 27 p.").6. NutrientsNutrients analyzed in this sampling program included ammonia, nitrate, nitrite, phosphate and silicate. Samples for ammonia were drawn directly into sample bottles without filtration, since the filtration process appeared to contaminate these samples. For the remaining nutrients, sample water was filtered through a 0.45um millipore filter at a vacuum pressure not exceeding 180mm Hg. Thus, filtered sea water was used for measurements of nitrate, nitrite, phosphate and silicate and these samples were preserved with 0.6% chloroform following the recommendation of Gilmartin (1967) for phosphate (see "Gilmartin, M. 1967. Changes in organic phosphate concentration occurring during seawater sample storage. Limnol. Oceanogr., 12:325-328"). All sample bottles (plastic, 100 ml capacity) for nutrients were rinsed 3 times with a small amount of the sample water before filling. All nutrient samples were immediately frozen on dry ice on board and kept in a deep-freezer at the laboratory until analysis. A CHEM-LAB Autoanalyzer system was used, in which the chemical methods had been slightly modified for the generally low levels of each nutrient in these samples. Dissolved organic nitrogen and phosphate were determined by the Ultra-violet photo-oxidation method, with a Photo-oxidation unit (La Jolla Scientific Co., Model PO-14). The organic fractions of total nitrogen and phosphate were calculated as the difference in concentrations before and after oxidation.7. Phytoplankton pigmentsDuplicate 500ml samples were filtered onto 47mm diameter GF/C glassfibre filters at a vacuum pressure not exceeding 180mm Hg. One of the samples was prefiltered through 20um netting to separate net plankton (>20um) from the nanoplankton (8. Particulate organic carbonDuplicate particulate organic carbon samples were taken as for phytoplankton pigment samples. The samples were filtered onto double layered GF/C glassfibre filters, which had been burned at 450°C for 30 minutes. The filters were folded, placed into acid washed containers and quick frozen on dry ice. These samples were stored in a deep freezer at the laboratory. Measurements of organic carbon were made by Dr K Iseki, Institute of Ocean Sciences, Canada, by means of an infrared carbon analyzer.9. Particle countingTwenty litre water samples were transferred to acid washed plastic buckets with tight sealing lids, and transported back to the laboratory. Particle counting was carried out within 4 hours by means of a Coulter Counter, model TAII.Two aperture tubes, 140um and 400um, were used to cover the range of particles from 2.25 to 128.0 um sphere equivalent diameter. The 140µm aperture tube measures the particles from 2.25 to 50.8µm, and the 400µm aperture tube from 6.35 to 128.0µm. Samples to be measured with the 140µm aperture tube were gently prefiltered through a 125µm mesh screen to eliminate larger particles. The results were expressed as total numbers (No/ml) and total volume (103.µm3/ml) of particles in the size range of 2.25um to 128.0um per unit volume of seawater.10. MicrozooplanktonA 4-litre sample was taken into a wide mouth plastic container and preserved with buffered formalin (sodium tetraborate) to a final concentration of 1%. The microzooplankton were concentrated for counting by the following procedures recommended by Dr A Taniguchi, Tohoku University, Japan (personal communication).The samples were allowed to stand without disturbance for at least 24 hours. Following this, the supernatant seawater was slowly siphoned off with glass tubing, leaving the settled organisms on the bottom of the container in about 500ml of water. This volume was rinsed into a 500 ml measuring cylinder, again allowed to settle over 24 hours, and siphoned off to leave about 50ml. The procedure was repeated with a smaller measuring cylinder which finally concentrated the sample down to 12ml. About 2ml of this volume was allowed to evaporate to increase salinity and prevent fungal growth. A subsample of 1ml was taken from the mixed contents of this concentrated sample and counted on a Zeiss plate chamber with a Nikon inverted microscope (Model MS). The animals were identified to Class or lower taxonomic level. The category "Others" includes radiolarians, foraminiferans, flagellates, and various larval forms of bivalves, larvaceans and chaetognaths.11. Net zooplanktonZooplankton samples were collected with a conical net of 205um mesh, the dimensions of which were 0.45m diameter and 1.5m length. The actual water volume passing through the net was estimated by means of a flow meter (Rigosha) mounted on the mouth ring. The net was towed by a winch vertically from the bottom to the surface at a constant speed of 1m/sec. The samples were preserved with buffered formalin (sodium tetraborate) to 10% concentration for biomass measurement and counting. In 1978, an additional two samples were taken and these were gently filtered onto 60um netting discs, placed into plastic petri dishes and quick frozen on dry ice for subsequent dry weight determinations.Biomass was measured in the following way before counting. The sample was decanted first into a wide petri dish from which large animals, such as medusae, fish larvae and salps were removed. The sample was then gently filtered onto a 60um preweighed mesh disc and rinsed with filtered sea water. The mesh disc containing the zooplankton was very gently blotted onto Whatman No. 1 filter paper until no further moisture was observed to come through. The sample was then immediately weighed on a Sartorius 1205 MP top-pan balance with a sensitivity of 0.005g. After weighing, the zooplankton sample was returned to fresh 10% buffered formalin-sea water solution. Dried zooplankton material was calculated to be 15.2% (± 0.9, n = 41) of the "wet" biomass as measured above.Zooplankton was counted using Bogorov trays under a dissecting microscope. Initially, all of the large and rare animals were removed and counted separately. Counts of other animals were made on a subsample containing between 500 and 1500 animals, usually a split of the original sample of 1 in 16. Zooplankton were mostly identified to Class taxonomic level and to the level of Order with crustaceans. The category 'Others' includes radiolarians, ciliates, insects, cumaceans, cephalopods, ascidian larvae, phyllosoma larvae, coelenterate larvae, salp buds and unidentified forms.

Notes

Credit
Ikeda, Tsutomu, Dr (Principal Investigator)