Temporal variability, both on short-term (within a month), and long-term (between months) time scales, was found to exist in the shallow water (10m) macrofauna communities of Oahu's south shore. The timing and magnitude of the variation was dependent upon the particular station examined. There was evidence for the existence of seasonality and lunar periodicity in certain taxa.
Examination of the results of the rain event sampling combined with the results of spatial comparisons of stations along a transect leading away from Ala Wai Canal suggests that runoff from the Ala Wai is not important with respect to density of Total Macrofauna and Total Macrofauna biomass. K-dominance curves, combined with the results of Abundance Biomass Curves do not show a pattern indicating that stations located near the mouth of the Ala Wai Canal are negatively impacted by proximity to runoff. However, the results of the abundance biomass curves were not conclusive and further work needs to be done to determine if this technique would be useful in Hawaiian benthic communities to detect human-induced and natural perturbations.
Resource Description: NODC Accession Number 9900120
Online Links:
#FILENAMES: gradient.prn gradient.wk1 Macrobenthic Data for Stations A, B and C (August 1993 and February 1994)
lunar-3.prn lunar-3.wk1 Macrobenthic Data for Station 3 25 July 1993-11October 1993 lunar-4.prn lunar-4.wk1 Macrobenthic Data for Station 4 (Lunar Periodicity) 25 July 1993-11October 1993
rain-1.prn rain-1.wk1 Macrobenthic Data for Station 1 23 July 1993-27 September 1993
rain2.prn rain2.wk1 Macrobenthic Data for Station 2 23 July 1993-27 September 1993
salinity.prn salinity.wk1 Salinity values for Stations 1, 2, 3 and 4 June 1993- May 1994
sediment.prn sediment.wk1 Sediment grain size composition for temporal variability Stations 1-4 and Gradient Stations A-C. June 1993- May 1994
temper.prn temper.wk1 Water temperature data for Stations 1, 2, 3 and 4 June 1993- May 1994
tv1-all.prn tv1-all.wk1 Macrobenthic Data for Station 1 (June 1993-May 1994)
tv2-all.prn Macrobenthic Data for Station 2 (June 1993-May 1994) tv2-all.wk1
tv3-all.prn Macrobenthic Data for Station 3 (June 1993-May 1994) tv3-all.wk1
tv4-all.prn Macrobenthic Data for Station 4 (June 1993-May 1994) tv4-all.wk1
mccarthy.txt text document of the study
Mamala Bay Study MB-9 Department of Zoology Department of Oceanography University of Hawaii
Assess macrobenthic community structure in relation to rain events
Intermediate stations: Station A: 21 16.55 N 157 50.59 W (near the mouth of the Ala Wai Canal) Station B: 21 16.41 N 157 50.38 W (near the mouth of the Ala Wai Canal) Station C: 21 16.30 N 157 50.23 W (off Waikiki Beach)
All stations were located in sand channels present between reef structures at 8- 10 m depth. A permanent 30m X 10m area was established at each station and was marked at each end of one side by cement blocks.
METHODOLOGY Salinity: =========
Samples (approximately 250 ml) of surface and bottom water were obtained from each station during each monthly sampling period. Salinity was determined using an EKTECH conductivity probe calibrated with IAPSO seawater.
Water Temperature: ================== A thermometer was used to determine the sea surface and bottom water temperatures at each station during each monthly sampling period.
Sediment Grain Size: ==================== Determination of sediment grain size was completed quarterly beginning in August 1994. The procedure used was modified slightly from that described in Folk (1965). Here are complete details: Sediment samples were obtained using SCUBA. Samples were returned to the laboratory and processed wet. Initially, the mud was separated from the sand by wet sieving. A 63 ?m sieve was placed over a clean white bucket. The wet sample was placed into the sieve. Approximately 950 ml of distilled water was slowly added to the sample. The sieve was gently puddled in the bucket for a minimum of two minutes. The sieve was lifted carefully above the surface of the water and the side of the sieve was sprayed with distilled water. Excess water was allowed to drip into the bucket. The sieve and its sedimentary contents were placed into a drying oven (80 deg C) and allowed to dry (approximately 20 minutes). This was called the sand fraction; the procedure for handling this fraction is discussed later. The distilled water and sediment mixture in the bucket were used for determination of the percent composition of mud. Water in the white bucket was swirled and carefully poured into a 1L graduated cylinder. Tubing attached to a syringe was placed into the graduated cylinder and lowered until the lower end of the tube was at the 400 ml mark (approximately 20 cm below the surface). 20 ml of the mud suspension was extracted from the graduated cylinder and squirted into a pre-weighed aluminium weigh boat. The weigh boat was placed into a drying oven (80 deg C) and dried to a constant weight. The weight of the aluminium weigh boat was subtracted from the weight of the dried mud suspension and aluminium weigh boat combination to obtain the weight of the mud. Since only 20 ml of the 1 L sample was dried, the mud weight was multiplied by a factor of 50 to arrive at a total mud weight for the sample. Dried samples were weighed and placed on a graded series of sieves (2mm, 1mm, 0.5mm, 0.25mm, 0.125mm, 0.063mm) on a mechanical sediment shaker and shaken for 10 min. The sediment retained on each sieve was weighed. Sediments which passed through the 0.063 mm sieve into the closing pan at the bottom were weighed and added to the mud fraction. Each sediment fraction (including the mud) was added together and a total weight determined. Percent composition by size class was determined by dividing the percent in each size class by the total weight. Data from each quarter reflects the mean of 5 samples for each sediment fraction (mud, fine sand and coarse sand).
Biological Parameters: ====================== A hand-held corer (diameter 10.5 cm) was inserted into the sediment to a depth of 10 cm by divers using SCUBA. Grided maps of the study areas were used to predetermine the position of each replicate for each sampling date. This random predetermination of sampling sites ensured re-sampling of a specific site did not occur. Samples were fixed in a 10% seawater -buffered formalin/rose bengal solution for a minimum of 24 hours then stored in 70% alcohol until processed. For replicates which had large amounts of coral rubble, an acid dissolution technique (Brock and Brock, 1977) was used for recovery of the endolithic and cryptic organisms present within the coral rock. To facilitate rapid extraction of non-calcified organisms each sample was elutriated six times through a 0.5 mm mesh sieve. The sediment and macrofauna retained on the sieve were stored in 70% alcohol and used for determinations of community structure and biomass (ash free dry weight). The remaining sediment fraction was sieved (0.5 mm), placed in 70% alcohol and processed with the elutriated sample. Organisms were identified to major taxa using a dissecting microscope. See below for specific methodology used for determination of ash-free dry weight. Due to the extremely small size of the majority of organisms, biomass determinations were made by pooling organisms from all replicates for each taxon. The number of individuals weighed was used to determine an average individual weight. This individual weight was used to back calculate the taxa weight per replicate. The specific sampling regime for each objective was as follows: Objective 1: Five benthic core samples were collected from Stations 1-4 monthly for examination of a seasonal signal. Samples were obtained every ten days for three months from Stations 3 and 4 for examination of lunar periodicity. All stations were located at approximately 10m depth. Objective 2: Five benthic core samples were collected from Stations 1-4 every ten days for a period of two months immediately after a significant rainfall event associated with the passage of two tropical storms south of Oahu. Objective 3: Five benthic core samples were collected from seven stations (1, 2, A, B, C, 3 and 4 ) located along a transect leading east from the Ala Wai Canal. Sampling of the seven stations occurred once in the summer (August 1993) and once in the winter (February 1994) .
Ash-Free Dry Weight Determination (Methodology) Macrofauna biomass was determined quarterly. Samples were sorted by separating infauna from sedimentary material and organisms identified to lowest possible taxon. After identification, individual organisms from the same taxa from each of the five replicates were pooled to produce one biomass value per taxon per station. Non-living portions of the organisms were mechanically removed from mollusks (shell) and polychaetes (tubes). The echinoderms were dried to constant weight, and boiled in 10% (w/v) sodium hydroxide for one hour to chemically remove the organic matter. The remaining body structure was washed with distilled water, dried to a constant weight and weighed again. The ash-free dry weight was determined by subtracting the final dry weight from the initial dry weight. Except for the echinoderms, once the non-living portions of the organisms were removed, all water was evaporated from the samples by heating in an oven (100 deg C) to a constant weight. The ash content (consisting of salts, silica, calcium, phosphate, carbonate) was determined by burning off the organic matter (4 hrs at 550 deg C).
Specific list of biological parameters: lists major macrobenthic taxa
#INSTRUMENT TYPES: Salinity: EKTECH conductivity probe Water Temperature: thermometer Biological Parameters: hand-held corer (diameter 10.5 cm)
#REFERENCES: Folk, R.L. 1968. Petrology of Sedimentary Rocks. Austin, Texas. 170 pp.
McCarthy, S.A, and Kay, E.A., 1995. Mamala Bay Study: Temporal variability in
macrobenthic community structure and the effect of freshwater runoff.
Mamala Bay Study, Project MB-9. Mamala Bay Study Commission. 1996.
Mamala Bay Study Final Report.
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