Port Hacking Research Articles

Smooth or oscillating late Holocene sea-level curve? Evidence from the palaeo-zoology of fixed biological indicators in east Australia and beyond

Abstract The nature of late Holocene sea-level change has important palaeo-environmental implications for the understanding of past and present coastal, oceanic and climatic systems. This study develops a fixed biological indicator (FBI) method based on tubeworm–barnacle assemblages in order to construct a late Holocene sea-level curve for south east Australia. It also compares changes within and between mid-latitude regions of the Southern Hemisphere using the palaeo-biology of inter-tidal sub-fossils that have provided time–elevation data covering the past 5000 years. Five sites from around the mouth of the Port Hacking estuary, 29 km south of Sydney, are described in detail. The results suggest that, rather than relative sea-level describing a stable or smoothly falling pattern from a maximum of +1.0 m above present over the last ∼5000 years on the southeast Australian coast, there have been complex movements from a maximum of over 1.5 m, with at least one marked fall between 3500 and 3400 yr BP, and the possibility of a small positive oscillation around 1900 yr BP. Furthermore, changes in the inter-tidal species at our sites suggest that there was a period between 4300 and 2800 years where ocean temperatures were warmer than present. Our Port Hacking findings are compared with other studies from the east coast of Australia, as well as the Pacific Islands and Brazil. Evidence from each location suggests a broad similarity in the timing of environmental events and marine fluctuations across an expanse of the Southern Hemisphere. Are such similarities coincidental or part of mechanisms common to mid-latitude Southern Hemisphere regions?

Spatial and temporal variation in populations and community of ectoparasites on young snapper, Pagrus auratus (Bloch & Schneider) (Sparidae), from the wild and captivity at Port Hacking, Sydney, Australia

Snapper in both the estuary (0+, 1+ age classes) and from offshore reefs (1+, 2+, 3+ age classes) at Port Hacking, NSW, were infested with the monogeneans Lamellodiscus pagrosomi, Anoplodiscus cirrusspiralis and Bivagina pagrosomi and the copepods Unicolax chrysophryerzus, Pseudoeucanthus australiensis, Hatschekia pagrosomi, Clavellopsis sargi and Lernanthropus atrox; offshore snapper also had the monogenean Choricotyle australiensis and the copepods Caligus spp. and Lepeophtheirus sekii. Most species had a higher prevalence, but not intensity, on offshore fish. Season was not a significant factor for most infrapopulations. Species richness, number of parasites and diversity were greater on offshore fish and differed among estuary samples but not offshore samples. Estuary infracommunities were dominated by L. pagrosomi (mainly 1+) and B. pagrosomi (mainly 0+); C. sargi and L. atrox dominated when richness was low. Offshore infracommunities were dominated by H. pagrosomi except in winter when L. pagrosomi was dominant, possibly owing to movement of estuary fish to offshore reefs. Captivity in experimental cages in the estuary resulted in transient increases in A. cirrusspiralis, B. pagrosomi and Benedenia sekii. Lamellodiscus pagrosomi increasingly dominated all samples and infracommunities. Neither condition factor nor stocking density had a significant influence on infestation.

Hormone induction and larval rearing of mulloway, Argyrosomus hololepidotus (Pisces: Sciaenidae)

Pond-held mulloway ( Argyrosomus hololepidotus) from Port Hacking, New South Wales, were induced to spawn by injecting human chorionic gonadotrophin (hCG) at 1000 IU/kg for females and 250 IU/kg for males. Two pairs of fish were stripped, and fertilised eggs were incubated at 23.5±1°C. Fecundity was high with an estimated 900 000 and 1 042 000 eggs collected from each female. At hatch, larvae averaged 2.25 ± 0.09 mm TL (mean ± s.d.) with a yolk sac of 0.88 ± 0.08 mm and an oil globule of 0.27±0.03 mm. Feeding and initial swim bladder inflation started between day 3 and 4 after hatch. Metamorphosis started when larvae reached 12 mm at 23 days of age, and was complete by day 34 when larvae were 15–26 mm. Larvae with functional swim bladders (>70% by day 11) grew faster than those without swim bladders. Cannibalism of smaller fish, many without swim bladders (4.2±0.06 mm), occurred from day 18. Fish were offered live food to day 68, supplemented with finely chopped pilchards and pellets from day 38. From day 106 to day 180 fish were feeding solely on pellets. Juveniles grew to a mean weight of 21.0±0.7 g and a mean length of 121.5±1.3 mm in 180 days. These results indicate that A. hololepidotus has potential for hatchery production.

Distribution and abundance of marine fish larvae in relation to effluent plumes from sewage outfalls and depth of water

Fish larvae were sampled in and below three separate sewage plumes associated with the cliff-face (shoreline) outfalls at North Head, Bondi and Malabar, and at three control (non-plume) sites located>8 km away from the sewage outfalls, at Long Reef, Port Hacking and Marley Beach, in nearshore waters off Sydney, south-eastern Australia. Samples were collected at the surface and at 20 m depth during three periods: December 1989, April/May 1990 and August/September 1990. In December 1989, a greater number of taxa were caught at both depths at the plume sites compared to the control sites, but this did not occur during the other two sampling periods. Similarly, in April/May 1990, greater numbers of the clupeid Hyperlophus vittatus but fewer anthiines were caught at both depths near the outfalls (plume sites). Myctophids were more numerous in surface samples, but not at 20 m, at the plume sites in both April/May and August/September 1990, whereas in April/May 1990, labrids and anguilliformes were less abundant at 20 m at the plume sites compared to the control sites. These differences in the numbers of fish larvae caught may have been an effect of the effluent plumes, but these results were only correlative. The results most probably reflect spatial heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney. There were striking differences, however, in the number of fish larvae caught at the surface and at 20 m, and among sampling periods, but these differences were similar across all sites. Of the 46 taxa considered common, 33 occurred in greater numbers at 20 m than at the surface, whereas only 8 taxa were caught in greater numbers at the surface. The composition of the fish larvae also differed markedly among sampling periods; few taxa were common to all three sampling periods. Greater numbers of fish larvae were caught in April/May and August/September 1990 than in December 1989, particularly at 20 m depth. The data highlight the large spatial and temporal heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney and the difficulty of identifying effects that are solely due to sewage plumes.

Growth of snapper,Pagrus auratus, from south‐eastern Australia in captivity

Abstract This study aimed to determine whether the relatively slow growth of wild Pagrus auratus in south‐eastern Australia can be increased in captivity to a rate acceptable for aquaculture. Juvenile snapper from Port Hacking, New South Wales (34°47'S) were reared at ambient water temperatures. The fish were fed on a dry, sinking pellet with 42% protein. At the start of the trial in April 1989, the snapper had a mean fork length (FL) of 121 + 11 mm SD, an average weight of 50 g, and an estimated age of 8 months. After 12.5 months their mean FL was 249 ± 15 mm and their mean weight was 403 ± 70 g. Our data indicate that, like the reproductively isolated population in Japan, growth of Pagrus auratus from Australasia can be rapid enough for aquaculture, and that there is potential to increase growth rate further.

Temporal variability in the demography of the palaemonid prawn Macrobrachium intermedium in two seagrasses

Spatial and temporal variations in the demography of the palaemonid prawn Macrobrachium intermedium were investigated in Port Hacking. New South Wales, Australia. Populations in 2 adjacent seagrass meadows. Zostera capricorni and Posidonia australis, were sampled monthly over 3 yr (1976 to 1978) using a small beam trawl. For most population variables there were no consistent differences between meadows and both meadows showed similarly variable temporal changes. Neither meadow consistently supported larger populations nor recruited more juveniles. In 1976 abundance was greater in Zostera than Poddonia, the opposite occurred in 1977, whilst there was no difference in 1978 Seasonal and annual changes in abundances were basically similar in both populations and repeated in all 3 yr. Abundances peaked between spring and autumn and were smallest in wnte r . In both meadows, abundances were greater in 1976 and 1978 than in 1977. Breeding and recruitment of juveniles occurred throughout the year, although ovigerous females were most abundant in summer/ autumn and juveniles recruited predominantly in late summer/autumn and in spring. At least 2 cohorts of juveniles were produced annually, the spring cohort being the largest. In 1976 and 1978 more juveniles recruited to the Zostera meadow whilst in 1977 more recruited to the Posldonia meadow. There were no consistent differences in the size structures of the 2 populations. During spring, juveniles predominated until summer/autumn when populations consisted of adults and only a few juveniles, after which the numbers of adults declined to virtually disappear by winter. Females grew faster and attained a larger size than males. Most individuals survived at least 15 mo, but longevity was estimated to be up to 2 yr. For most population variables, year-to-year variations within each meadow were as great as differences between the 2 meadows within each year. These variations were most likely due to factors extrinsic to the seagrasses themselves. This study stresses the need for long-term studies to verify the consistency of spatial differences between sites.

Chemical properties of a low-oxygen water column in port hacking (Australia): Arsenic, iodine and nutrients

In a study of a water column in a basin of the South West Arm of Port Hacking, changes in dissolved oxygen, temperature and salinity were determined for several weeks. When there was < 1 ml 1 −1 oxygen in the bottom water, the water column was sampled to study the vertical distribution of dissolved nutrients (ammonia, nitrate, nitrite, orthophosphate and reactive silicate) and the oxidized and reduced forms of arsenic and iodine. Results showed that changes in the water column were dominated by inputs of these elements from the anoxic sediment. Near-bottom waters were enriched in all nutrients, arsenate and iodide. The mechanisms that influence the speciation of the redox elements arsenic and iodine are discussed. Low dissolved iodate concentration is proposed as a recorder of the occurrence of oxygen-depleted conditions in isolated marine water bodies.

Seasonal variation in the copper complexing capacity of Port Hacking

The copper complexing capacity (CuCC) of waters at the entrance to Port Hacking estuary, Australia, was monitored approximately daily from February to November 1984. Biological and hydrological parameters collected from this area since 1942 provide a wealth of historical data to aid in the interpretation of the results. From May to August, the CuCC values averaged about 5 nM, with occasional high values (up to 17 nM) attributable to terrestrial runoff following heavy rainstorms. In mid-October, CuCC values up to 56 nM were attributable to a phytoplankton bloom that resulted from the intrusion of nutrient-rich slope waters onto the continental shelf. These intrusions of slope water seem to be driven onto the continental shelf by the approach of the East Australian Current and its associated eddy field. The approach of an eddy coincided with a secondary maximum in the CuCC (30 nM) that occurred in mid-April. The CuCC of Port Hacking is dominated by processes originating outside the estuary; Port Hacking cannot therefore be a significant source of organic ligands to coastal waters.

Generation and decay of hydrogen peroxide in estuarine waters

Apart from its central role in photosynthesis, one of the most dramatic effects of light in marine and freshwater systems is its ability to generate reactive chemical intermediates. Of these, hydrogen peroxide is one of the more stable and easily detected. Aspects of the generation and decay of hydrogen peroxide in the Port Hacking River estuary, New South Wales, have been investigated in a number of field and laboratory studies. Peroxide concentrations in surface waters in the early morning are relatively uniform over the estuary and typically less than 35 nM, whereas concentrations in mid-afternoon in excess of 100 nM have been observed. Variation of peroxide concentration with depth in the deep basins of Port Hacking is dependent on the extent of structure within the water column, with little mixing of surface- generated peroxide into poorly-illuminated bottom waters under stratified conditions. Laboratory studies confirmed that light induces the production of hydrogen peroxide, the initial rate of production increasing with increasing molar absorptivity of the filtered water sample. Filtration of samples had little effect on the generation of hydrogen peroxide but dramatically reduced the rate of decay of photogenerated hydrogen peroxide.

Synthesis and Modelling of Intermittent Estuaries

Port Hacking is a small subtropical estuary, relatively unpolluted despite its location only 30 km south of Sydney on Australia's Pacific coast. It was the site of a 5‐year (1973–1978) multidisciplinary ecosystem project, focusing on the flow of carbon into, within, and out of the estuarine system. The ultimate goal of the project was the formulation and implementation of a predictive model of the carbon dynamics. However, this book, which summarizes the project, reports that the scientific team failed in its effort to reach the goal of a predictive model.

Community structure and trophic relationships of the fish fauna of an estuarine Posidonia Australis seagrass habitat in port hacking, new South Wales

The fish community present in a 400-m 2 area of seagrass meadow dominated by Posidonia australis Hook f. was quantitatively sampled during two springs and two autumns by enclosure and poisoning with rotenone. Thirty-nine species were collected and these were classified into permanent residents (∼ 50% of total numbers), temporary residents (∼ 30%) and transients (∼20%). Approximately 30% of the total numbers of fish collected belonged to species of some economic importance. Species diversity indices were calculated and compared between seasons, but no obvious differences were found. Shannon's H′ (heterogeneity index) ranged from 2.11 to 2.56, Gleason's d (richness index) ranged from 3.08 to 5.05, and scaled H (eveness index) ranged from 0.59 to 0.74. Stomach contents of all fish were analysed by an estimated volumetric method. Agglomerative polythetic classification to the average diets of all species collected indicated 7 basic feeding groups within the community. Many species preferred crustaceans as food (this latter group comprising approximately 50% of the overall community diet), and several species consumed seagrass (approximately 10% of the overall community diet). Upper water column dwellers were mainly microcrustacean feeders; canopy dwellers fed primarily on crustaceans, seagrass and algae; benthic dwellers consumed mainly crustaceans and polychaetes.

THE GENUS BALLIELLA ITONO &amp; TANAKA (RHODOPHYTA: CERAMIACEAE) FROM EASTERN AUSTRALIA1

ABSTRACTThree new species of the genus Balliella Itono &amp; Tanaka are described from eastern Australia. Balliella amphiglanda from Lord Howe I. and Port Hacking, N.S.W., is distinctive in producing either abaxial or adaxial gland cells from the basal cells of lateral branches and in having tetrasporangia restricted to short branches. Balliella repens, from Tryon I., Heron I and Wistari Reef Qld., and Lord Howe I., N.S.W., is distinguished from the other species of the genus by its regularly developed prostrate systems and clustered tetrasporangia. Balliella grandis, from Wistari Reef, North West I. and One Tree I., Qld., is the largest recorded species of Balliella. It has correspondingly large gland cells and abaxial as well as adaxial tetrasporangia. Our work supports the placement of Balliella in the tribe Antithamnieae, a move which necessitates emending Wollaston's definition of the tribe to include species with procarps that form at successive levels along main axes rather than at only one or two points behind the apices.

Trophic structure and production in the macrobenthos of a temperate Australian estuary

The soft-bottom fauna of Gunnamatta Bay, Port Hacking, N.S.W., was sampled to estimate the abundance, trophic structure and net production of the macrobenthos. The samples were classified into groups from spatially distinct strata, the groups differing in species abundance and diversity and in the identity of the dominant species. The composition and community structure of the fauna was generally similar to that in other sheltered embayments on the southeastern coast of Australia. Estimated production values were low for an estuary, ranging from 10 kJ m −2 year −1 in an intertidal stratum of well sorted sand to 210–450 kJ m −2 year −1 in shallow subtidal strata with an admixture of silt. Estimated net production over all strata was 160 kJ m −2 year −1. Polychaetes dominated production, providing 45% of the total; crustaceans provided 20%, and molluscs and echinoderms 12% each. Detritus-feeders were dominant in most strata: the bivalve Theora fragilis, the polychaetes Australonereis ehlersi and Notomastus torquatus, and the urchin Echinocardium cordatum were major contributors to overall biomass and to net production. Substantial biomass and net production was also contributed by the suspension-feeding bivalve Corbula vicaria and a carnivorous crab Ceratoplax cf. glaberrimus. Overall, detritus-feeders contributed 61% of estimated net production, carnivores 32% and suspension-feeders 7%. Production estimated for carnivores was higher than could be supported by the non-carnivore populations, suggesting that some of the species considered to be carnivores have additional feeding modes. Excessive harvesting of bivalves by humans is suggested as the main reason for the low biomass of, and therefore low production by, suspension feeders.

Biomass and growth of Zostera capricorni aschers. in port hacking, N.S.W., Australia

The biomass and net productivity of the leaves of Zostera capricorni Aschers. were measured in an estuary near Sydney, New South Wales, at various times during the period 1976–1979. The mean standing crop biomass of leaves was 55 g dry wt. m −2, while mean relative growth rate ranged from 0.014 g g −1 day −1 in winter to 0.028 g g −1 day −1 over the summer months. Productivity was estimated by a leaf marking method, and showed a closer relationship to water temperature than to solar radiation. Data on leaf length composition indicate that new leaf production continues throughout the year.

Temporal patterns in the structure of macrobenthic communities of an Australian estuary

The benthic fauna of a small estuary was examined to test hypotheses about community structure and environmental stress (foreign, or natural but excessive, perturbations in the environment). Quantitative samples were collected at approximately 2-month intervals over 18 months from Cabbage Tree Basin, Port Hacking, New South Wales. The sites sampled ranged from the intertidal to a central basin subject to deoxygenation of the bottom water. The species composition of the intertidal and shallow-water sites was more stable than that of the deeper sites, due to the presence of short-lived opportunistic species at the deeper sites after periods of deoxygenation. There were no obvious changes in species composition associated with temperature minima or maxima. No changes directly associated with reduced salinity after rainfall were found, although heavy rainfall prior to the sampling period may have reduced the number of species at some sites. The stable community structure and species composition at the intertidal and shallow-water sites indicated that greater environmental harshness does not necessarily imply less faunal stability. Differences in diversity among these sites were interpreted as evidence that biological accommodation was responsible for a reduction in diversity from values predicted by the neutral model. At a deeper site, diversity was close to neutral model predictions. It is suggested that the ecotone point in a stressed community may be characterized by diversity values that are in agreement with neutral model predictions. The statistical properties of the measures of diversity and evenness were not important for their interpretation. Biomass-based measures indicated patterns that were often different from frequency-based measures.

Experimental studies on the settlement and growth of bryozoa in the natural environment

A rack of six panels of roughened black Perspex was placed in Port Hacking, Sydney, for a period of 34 weeks. Some panels were screened and the rack was examined each week for accumulation of Bryozoa. Some colonies were allowed to grow for the complete study period; some panels were scraped free of all organisms each week; some were scraped free of all organisms except Bryozoa; and some panels which had been screened were returned to the environment unscreened. Sizes of colonies were noted and are presented in tabular form. Results show that there is a marked variation in the growth of Bryozoa, even extending to the same species on the same panel. No rigorous statistical analysis of the growth is attempted. Environmental variables such as rainfall, salinity and temperature were monitored at stations close to the panel site and are discussed in relation to bryozoan growth.

Benthic communities in an estuary with periodic deoxygenation

The relationship between spatial patterns in the physical environment and patterns in community and trophic structure in the benthic fauna was investigated in an estuary with periodic deoxygenation of the near- bottom water. Six sites were sampled between intertidal mangroves and an 8 m deep basin of Port Hacking, N.S.W. A total of 163 species was collected, ranging from 11 to 94 at each site. Both frequency and biomass were least in the central basin and highest in a bed of the seagrass Zostera capricorni Aschers. The abundances at these sites encompass the range of values previously recorded for estuaries on the east coast of Australia. The dominant species differed from those reported from other New South Wales estuaries, although the same species were usually present. The distribution of common species was limited by fluctuations in dissolved oxygen levels, but not obviously so by sediment differences or short-term fluctuations in water temperature or salinity. Frequency-based diversity and evenness values were similar to those from other estuarine areas. Biomass-based values were lower at most sites than frequency-based values. Patterns of diversity and evenness could not be simply interpreted as indicators of environmental harshness in the community.

Seasonal Variations of Phytoplankton Production in an Estuary in Relation to Coastal Water Movements

Primary production and phytoplankton biomass in Port Hacking, an estuary 24 km south of Sydney, were measured at 2-4 day intervals for one year. Primary production was measured by in situ 14C uptake, and phytoplankton biomass by 14C uptake at constant irradiance and in vivo chlorophyll fluorescence. Measurements of solar irradiance and light attenuation by the water column were also obtained. Nutrient concentrations were measured both in the estuary and in the coastal waters adjacent to Port Hacking. The short-term variations of phytoplankton biomass were found to be due to both estuarine hydrological events resulting in the release of regenerated nutrients, and to coastal hydrological events, where slope water intrusions enriched the coastal waters and were introduced into the estuarine basins by tidal exchange. The annual variation of primary production in Port Hacking was related to the annual variation of solar irradiance. A minor part of the annual variation appeared to be due to temperature, but the nature of this relationship was uncertain.

A study of the role of the seagrass Posidonia australis in the carbon budget of an estuary

The budget and fate of organic carbon from the leaves of the seagrass Posidonia australis Hooker f. were studied in a small sunken river valley in Port Hacking, New South Wales. Standing stock and leaf growth were measured over 12-month periods. Estimated average relative leaf growth was 2.3 mgC g dry wt. −1 day −1. Estimated losses totalled 2.6 mgC g dry wt. −1 day −1 of which 48% was in the form of dissolved organic carbon, while grazing by herbivores (3%), leaves floating off (12%) and sinking leaves (37%) accounted for the remainder of the carbonaceous material lost from the seagrass leaves.

Description and use of an improved method for determining estuarine zooplankton grazing rates on phytoplankton

A method of rapidly determining zooplankton grazing rates on natural mixed phytoplankton populations using 14C is described. The method simplifies the design of grazing experiments as the grazing time can be kept short enough to prevent recycling of the isotope, and growth of the phytoplankton substrate. Very high specific activity, 14C-labelled phytoplankton concentrated either by centrifugation or sieving, may be used either as the sole grazing substrate, or as a tracer in natural mixed phytoplankton. Zooplankton, confined in glass jars at either ambient, or higher than ambient concentrations, are permitted to feed on the phytoplankton for periods of 30 min and 2 h, and are then separated by sieving. The zooplankton community grazing rate, or, if the samples are sorted into species, the individual species grazing rates, can be determined after scintillation counting of the zooplankton. The rate of appearance of 14C-labelled phytoplankton in the zooplankton is an estimate of the grazing rate, and the slope of the line joining the grazing rates at various phytoplankton concentrations gives an estimate of the grazing rate constant for the zooplankton population. The method provides a quick way of obtaining both zooplankton population, and individual species grazing rates on natural mixed phytoplankton. In two experiments, labelled phytoplankton was used as the sole grazing substrate in concentrations ranging between 0.4 and 5 times ambient levels. Grazing rate constants, for net-caught zooplankton concentrated to 46 times (Experiment 1) and 28 times (Experiment, 2) ambient estuarine levels were-0.14and-0.12 of the phytoplankton standing stock per day, respectively. There was a linear increase in the amount of phytoplankton grazed with an increase in phytoplankton concentration up to four times ambient phytoplankton levels. When tracer amounts of labelled phytoplankton were added to samples containing both phytoplankton and zooplankton at ambient concentrations the grazing rate constants were-0.28 and-0.42 of the phytoplankton standing stock per day. We conclude that zooplankton grazing was the major control factor of phytoplankton population size during October–November 1975 in South West Arm, Port Hacking, near Sydney, Australia.