Showing papers in "Marine and Freshwater Research in 1999"
TL;DR: The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades, and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale.
Abstract: Sea temperatures in many tropical regions have increased by almost 1 degrees C over the past 100 years, and are currently increasing at similar to 1-2 degrees C per century. Coral bleaching occurs when the thermal tolerance of corals and their photosynthetic symbionts (zooxanthellae) is exceeded. Mass coral bleaching has occurred in association with episodes of elevated sea temperatures over the past 20 years and involves the loss of the zooxanthellae following chronic photoinhibition. Mass bleaching has resulted in significant losses of live coral in many parts of the world. This paper considers the biochemical, physiological and ecological perspectives of coral bleaching. It also uses the outputs of four runs from three models of global climate change which simulate changes in sea temperature and hence how the frequency and intensity of bleaching events will change over the next 100 years. The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades. Events as severe as the 1998 event, the worst on record, are likely to become commonplace within 20 years. Most information suggests that the capacity for acclimation by corals has already been exceeded, and that adaptation will be too slow to avert a decline in the quality of the world's reefs. The rapidity of the changes that are predicted indicates a major problem for tropical marine ecosystems and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale.
3,627 citations
TL;DR: The short-term prognosis is indeed grim, with major reductions almost certain in the extent and biodiversity of coral reefs, and severe disruptions to cultures and economies dependent on reef resources, but the long-term prospects are more encouraging because coral reefs have remarkable resilience to severe disruption and will probably show this resilience in the future when climate changes either stabilize or reverse.
Abstract: Factors causing global degradation of coral reefs are examined briefly as a basis for predicting the likely consequences of increases in these factors. The earlier consensus was that widespread but localized damage from natural factors such as storms, and direct anthropogenic effects such as increased sedimentation, pollution and exploitation, posed the largest immediate threat to coral reefs. Now truly global factors associated with accelerating Global Climate Change are either damaging coral reefs or have the potential to inflict greater damage in the immediate future: e.g. increases in coral bleaching and mortality, and reductions in coral calcification due to changes in sea-water chemistry with increasing carbon dioxide concentrations. Rises in sea level will probably disrupt human communities and their cultures by making coral cays uninhabitable, whereas coral reefs will sustain minimal damage from the rise in sea level. The short-term (decades) prognosis is indeed grim, with major reductions almost certain in the extent and biodiversity of coral reefs, and severe disruptions to cultures and economies dependent on reef resources. The long-term (centuries to millennia) prognosis is more encouraging because coral reefs have remarkable resilience to severe disruption and will probably show this resilience in the future when climate changes either stabilize or reverse.
273 citations
TL;DR: Research on fluxes of carbon in Australian floodplain rivers finds decreased inputs of floodplain carbon, following river regulation and physical disturbances to catchments and floodplains, may have resulted in many Australian rivers being dominated by algal production.
Abstract: This paper reviews research on fluxes of carbon in Australian floodplain rivers. Except where cover is absent, and in-stream gross primary production is >1 gC m–2 day–1 and ratios of production to respiration are >1, riparian sources dominate carbon pools in catchment streams. On floodplains, primary production by river red gum (Eucalyptus camaldulensis) forests is ~600 gC m–2 year–1. Total primary production by aquatic macrophytes and biofilms in floodplain wetlands is >2500 gC m–2 year–1 and >620 gC m–2 year–1, respectively. Large pools of particulate organic carbon (POC) exist on floodplains as litter (>500 gC m–2) and coarse woody debris (~6 kgC m–2). Floods may release 50 gDOC m–2 from leaf litter. Export of this DOC (dissolved organic carbon) may be substantial relative to autochthonous production in river channels. Sediments deposited on floodplains during large floods represent a substantial sink of riverine POC (up to 280 gC m–2). Bacteria are responsible for rapid decomposition of DOC and POC in floodplain wetlands (sediment respiration and methanogenesis, both ~1 gC m–2 day–1). Flow and its interaction with geomorphology control carbon fluxes in rivers. Decreased inputs of floodplain carbon, following river regulation and physical disturbances to catchments and floodplains, may have resulted in many Australian rivers being dominated by algal production.
242 citations
TL;DR: It was not possible to make reliable overall estimates of the size of the wetland resource globally or regionally, but present analyses now suggest a tentative minimum of 12.8 km2.
Abstract: This assessment is based on reviews of the extent of wetland inventory in seven regions of the world. A key conclusion is that little is still known about the extent and condition of the global wetland resource. It was not possible to make reliable overall estimates of the size of the wetland resource globally or regionally. Previous estimates range from 5.3 to 9.7 million km2 but present analyses now suggest a tentative minimum of 12.8 km2. Recommendations focus on the need for national inventory programmes and the inclusion of basic information on the location and extent of each wetland and its major ecological features as a forerunner to collecting further management-oriented information. Thus, the following core data should be collected: area and boundary, location, geomorphic setting, general description, soil characteristics, water regime, water quality, and biotic characteristics. Further, the development of standardized methods for data collection, collation and storage are called for. These should address the use of remotely sensed data and storage of information in electronic formats, including Geographic Information Systems and recording key information in a meta-database. Habitats of priority for future inventory are seagrasses, coral reefs, salt marshes and coastal flats, mangroves, arid-zone wetlands, peatlands, rivers and streams, and artificial wetlands.
227 citations
TL;DR: This paper reviews studies of relationships between riverine fish and woody debris at micro- and meso-habitat scales, and discusses the potential functions of instream structure for lowland river fish.
Abstract: This paper reviews studies of relationships between riverine fish and woody debris at micro- and meso-habitat scales, and discusses the potential functions of instream structure for lowland river fish. Experimental research, mainly in North America, has identified three main functions of woody debris as microhabitat for fish in upland streams: overhead cover that decreases predation risk both vertically and horizontally; horizontal visual isolation that reduces contact between fish; and velocity refuge which minimizes energetic costs. As with habitat features in other aquatic environments, increasing spatial complexity of woody debris may modify predator–prey interactions and provide greater surface areas for the growth of prey items. Woody debris may also provide spatial reference points for riverine fish to assist them in orienting within their surroundings. Lowland rivers differ from upland streams in terms of a number of physical variables, including turbidity, depth and water turbulence. Relationships between fish and woody debris in lowland rivers are likely to rely on mechanisms different to those in upland streams. Recent initiatives involving the reintroduction of woody debris into previously cleared lowland rivers to replace lost fish habitat are a positive development for lowland river restoration. However, if woody debris reintroduction is to maximally benefit lowland river fisheries, there is a requirement for better understanding of the ecological functions of woody debris in lowland rivers.
222 citations
TL;DR: The reef-building capacities of the coral communities and the extent of Holocene reef development were inconsistent at L2 and L3, which is interpreted as a sign of anthropogenic effects.
Abstract: Benthic communities were assessed and 22 environmental variables were monitored at seven leeward localities (L1ŒL7) in the Whitsunday Islands, Queensland, Australia. L1 was near the Proserpine and O’Connell river mouths and L7 ~80 km north of the river mouths. Distinct physico Œchemical and biological gradients were evident. Sparse scleractinian coral communities, dominated by faviids, Montipora spp. and encrusting Porites colonies, were present at L1, L2 and L3, whereas diverse reef-building communities, dominated by Acropora spp., were more common at and beyond L4. The number of coral recruits (age <6 months) did not differ significantly among localities, suggesting that coral recruitment was near random and that the environment shapes the adult community from those recruits. The study demonstrates strong negative relationships between chlorophyll a and the following: percentage coral cover, coral species richness and coral abundance. The reef-building capacities of the coral communities and the extent of Holocene reef development were inconsistent at L2 and L3, which is interpreted as a sign of anthropogenic effects.
169 citations
TL;DR: A two-year study of the relationship between water chemistry, hydrology and climatology in areas of acid sulfate soils has demonstrated that discharge of sulfuric acid to estuaries is not dependent solely on the magnitude of a rainfall event.
Abstract: A two-year study of the relationships between water chemistry, hydrology and climatology in areas of acid sulfate soils has demonstrated that discharge of sulfuric acid to estuaries is not dependent solely on the magnitude of a rainfall event. Large rain events did not always produce significant changes to water chemistry, and small rain events could produce large changes if the prevailing conditions were suitable. The magnitude of changes to estuarine waters was found to be dependent on the position of the watertable, and therefore the available soil pore space, and the store of acidic water in floodgated drains at the time of rainfall. These results have significance for predicting the discharge of acid drainage to estuarine environments and the possible impacts on aquatic organisms. A water balance equation, which estimated acid discharge to surface waters as high as 317 t of H2SO4 in one month, can be used to predict monthly discharges for rain events of varying magnitude if prevailing weather conditions are known.
126 citations
TL;DR: This paper summarizes milestones in the development of methods of pigment analysis, and shows the use of HPLC technology in their verification, and the taxonomic value of pigments and pigment suites is examined.
Abstract: Analysis of phytoplankton pigments is central to studies of marine ecology and climate research. This paper summarizes milestones in the development of methods of pigment analysis, and shows the use of HPLC technology in their verification. New advances in HPLC methods are discussed, with key developments being the use of polymeric C18 and monomeric C8 columns and pyridine as solvent modifier. These have allowed the resolution of divinyl chlorophylls a and b, and the discovery of new chlorophyll c pigments (both polar and non-polar) and new 4-keto fucoxanthin derivatives. The taxonomic value of pigments and pigment suites is examined. Methods of interpreting the percentage of algal types from field measurements of pigment ratios through the use of computer algorithms are discussed. Finally, prospects for future development are suggested.
121 citations
TL;DR: Predictions are made about how variability in sources, hydrology and biotic removal interact to generate temporal and spatial patterns in DOM from a stream’s headwaters to a large river.
Abstract: Dissolved organic matter (DOM) constitutes a large proportion of the organic carbon in all aquatic ecosystems and is often a significant carbon resource for heterotrophic microorganisms. Diverse sources, compositional complexity and multiple transformation pathways have made it difficult to generalize about the bioavailability of this material. Recently, there has been dramatic progress in identifying sources of DOM, describing its composition and tracing its movement through microbial food webs. A number of conceptual, mechanistic and empirical approaches have been proposed to synthesize this rapidly expanding body of knowledge. This paper reviews these approaches, and some general hypotheses for focusing future research are proposed. As a first step in synthesizing the available information, predictions are made about how variability in sources, hydrology and biotic removal interact to generate temporal and spatial patterns in DOM from a stream’s headwaters to a large river.
106 citations
TL;DR: The model provides a picture of nitrogen cycling through the water and sediments on bay-wide annual scales, which emphasizes the role of denitrification, and provides insights into the factors controlling regional phytoplankton blooms, including the interaction of nitrogen and silica in the western bay.
Abstract: This paper overviews the ecosystem model developed for the Port Phillip Bay Environmental Study. The model simulates the cycling of N, P and Si in the water-column, epibenthos and sediments, and is driven by a physical transport model. The integrated model is forced by exchanges with Bass Strait and by nutrient inputs from the Western Treatment Plant, rivers, and the atmosphere. The model has been calibrated and tested by using data from process studies, flux measurements and spatial surveys at a range of scales. It provides a picture of nitrogen cycling through the water and sediments on bay-wide annual scales, which emphasizes the role of denitrification. It also reproduces well the observed spatial and temporal variation under varying nutrient load regimes, and provides insights into the factors controlling regional phytoplankton blooms, including the interaction of nitrogen and silica in the western bay. The model is used to investigate the bay’s responses to changed nutrient loads, changes in sediment biogeochemistry, and marine pest invasion. The bay’s assimilative capacity for nitrogen is largely controlled by its sediment denitrification capacity. If nitrogen loads approach the limits of this capacity, a rapid onset of eutrophication is predicted.
104 citations
TL;DR: Elevated water temperature (>30°C) along with low discharge and high irradiance were major factors contributing to the Microcystis spp.
Abstract: A cyanobacterial bloom in the lower part of the Nakdong River was investigated during the dry summer of 1994. High levels of phytoplankton biomass, mainly Microcystis aeruginosa, in the surface waters (chl. α 193 ± 436 µg L-1, mean ± s.d.; >105 cells mL-1 , n = 15) were maintained for three months from mid July to mid October. After the last major rainfall in mid June, water temperature increased sharply within three weeks (18 June, 24°C; 9 July, 33°C). The highest cell density (5 × 106 cells mL-1) and highest concentration of chl. α (>500 µg L-1) in the surface water were recorded in the early phase of the bloom (21–26 July) as the drought persisted. Concentrations of dissolved inorganic nitrogen (DIN) and total phosphorus (TP) during the bloom were high (DIN 2.5 ± 0.9 mg L-1 ; TP 155 ± 98 mg L-1 ; n = 23). pH was low (~7) until the initial stage but was high (pH >9) as the bloom formed. Elevated water temperature (>30°C) along with low discharge and high irradiance were major factors contributing to the Microcystis spp. bloom in this river–reservoir system.
TL;DR: The highly non-linear responses of aquatic ecosystems to changing catchment loads of major and minor elements are explained by the interactions of the major functional groups and by competition between the pelagic and the benthos for nutrients and light.
Abstract: This paper reviews the biogeochemistry of carbon, nitrogen, phosphorus and their associated minor elements (iron and sulfur) in rivers, lakes and estuaries. The biogeochemistry of these elements can be explained by the physiology and stoichiometry of the major functional groups of micro- and macro-biota in these ecosystems. Furthermore, the global patterns of nitrogen and phosphorus limitation in freshwater and marine systems are explicable in terms of evolutionary differences between the major functional groups in freshwater and marine ecosystems, and their physiology and stoichiometry, as well as the interactions of carbon, iron, water residence times and ionic strength as the water flows from catchments to the sea. The highly non-linear responses of aquatic ecosystems to changing catchment loads of major and minor elements are explained by the interactions of the major functional groups and by competition between the pelagic and the benthos for nutrients and light.
TL;DR: Size-specific growth rates of Jasus edwardsii were estimated from 16 000 recaptures of tagged lobsters during a 3-year marknrecapture study and the von Bertalanffy growth model was fitted to observed increases in carapace length.
Abstract: Size-specific growth rates of Jasus edwardsii were estimated from 16 000 recaptures of tagged lobsters during a 3-year marknrecapture study. The von Bertalanffy growth model was fitted to observed increases in carapace length. A normal likelihood of predicted length increment as a function of starting length and time-at-large was maximized. Estimated standard deviation of the likelihood, taken as an allometric function of predicted length increment, quantified individual growth variation. The distri- butions of residuals indicated satisfactory fits. von Bertalanffy parameters of growth were estimated at three levels of spatial resolution: 18 statistical reporting blocks, 6 growth subregions, and 2 fishery management zones. Among blocks, the mean annual growth of lobsters of 100 mm carapace length was 7n20 mm for males and 5n15 mm for females. Females grew more slowly after reaching sexual maturity. Growth rates declined by approximately 1 mm year n1 per 20 m increase in depth of habitat, at depths of 20 m and deeper. Density-dependent growth was indicated by spatial anti-correlation between male growth rates at 100 mm and fishery catches by number per unit effort. Regression implied that a 10% decrease in catch rate corresponded to increased growth by weight of 2n5%.
TL;DR: Sardines have been a major contributor to the pelagic fishery off southern Africa for several decades, and seasonal hydrology, in conjunction with age-related behaviour, produces the observed size-distribution patterns.
Abstract: Sardines have been a major contributor to the pelagic fishery off southern Africa for several decades. The South African and Namibian stocks are separate, and seasonal hydrology, in conjunction with age-related behaviour, produces the observed size-distribution patterns. Sardines are relatively fast-growing and spawn repeatedly over the spring and summer months. Eggs and larvae are transported from the Agulhas Bank to the west coast by the north-flowing jet current at the shelf edge. Sardines are omnivorous, microphagist filter-feeders and are important prey for many piscivorous fishes, birds and mammals. There have been major fluctuations in sardine population biomass in southern Africa which have been associated with environment, regime shifts, recruitment and fishing, South African and Namibian sardine catches peaked in the 1960s, declining dramatically thereafter, and the pelagic fishing industry switched to anchovy. During the 1990s, sardine biomass increased but, although South African catches rose, the Namibian stock collapsed again. The annual South African total allowable catch is set through an operational management procedure that takes into account biomass estimates from comprehensive hydroacoustic surveys and the sardine by-catch in the anchovy fishery.
TL;DR: Mechanisms of copper accumulation and detoxification, and of haemocyanin biosynthesis and catabolism, in aquatic arthropods and molluscs are reviewed and the physiological significance of high concentrations of quasi-crystalline haemOCyanin within vascular spaces of the prosobranch left kidney, opisthobranch blood gland and cephalopod branchial heart appendage is discussed.
Abstract: Mechanisms of copper accumulation and detoxification, and of haemocyanin biosynthesis and catabolism, in aquatic arthropods and molluscs are reviewed. Crustacean haemocyanin transports copper in the blood by sequestering additional copper outside the oxygen-binding centre. Large changes in haemocyanin concentration in crustacean blood during moulting and hyposaline exposure generally reflect extracellular volume adjustments rather than biosynthesis and catabolism. Haemocyanin synthesis in decapod crustaceans is stimulated by hypoxia and, in an amphipod, by parasitization. Starvation causes breakdown of haemocyanin. Haemocyanin synthesis occurs principally in the midgut gland of crustaceans and in fixed blood cells (cyanocytes) that are located in certain tissues. It is hypothesized that cyanocytes provide a local oxygen reserve during circulatory arrest. Haemocyanin synthesis occurs primarily in the branchial glands of dibranchiate cephalopods but in the midgut gland of tetrabranchiates. Connective tissue pore cells are proposed as the site of haemocyanin synthesis in gastropods, although similar cells in cephalopod branchial hearts probably catabolize haemocyanin. Crustacean midgut glands contain copper-metallothioneins and glutathione, which donate Cu(I) to apohaemocyanin and function in detoxification and mineralization of excess copper. The physiological significance of high concentrations of quasi-crystalline haemocyanin within vascular spaces of the prosobranch left kidney, opisthobranch blood gland and cephalopod branchial heart appendage is discussed.
TL;DR: The present results show that a large estuary may also provide the opportunity for successful spawning of pelagic eggs, and that a gran estuario tambien puede proveer the oportunidad for the desove exitoso of huevos planctonicos.
Abstract: Most fishes that take advantage of the high productivity of estuaries exhibit offshore spawning, produce great numbers of small pelagic eggs and recruit to estuaries as larvae or juveniles. The reproductive pattern of Micropogonias furnieri (a planktonic egg spawner) in the Rio de la Plata estuary (36°S,56°W) differs from this. Biological sampling and oceanographic data showed that the spawning area covers a narrow band across the river between Montevideo (34°50´8S,56°10´W) and Punta Piedras (35°25´S,57°10´W) at depths ranging from 6 to 8 m. This area is characterized by strong haloclines, reaching 21.5 units m-1. M. furnieri eggs were present only below the halocline, in salinities of 9.7–27.3, and at 18.5–20.2°C. Spawning occurred in the innermost part of the estuary, near the upstream edge of the salinity wedge and coinciding with the turbidity maximum (up to 150 mg L-1). The regular spawning of pelagic eggs has been reported in estuaries of southern Africa and Australia characterized by intermittent landlocking. The present results show that a large estuary may also provide the opportunity for successful spawning of pelagic eggs. Resumen. La mayoria de los peces que aprovechan la alta productividad de los estuarios efectuan sus desoves en el oceano, producen gran cantidad de pequenos huevos pelagicos, y se reclutan a los estuarios como larvas o juveniles. El patron reproductivo de Micropogonias furnieri (un desovante de huevos planctonicos) en el Rio de la Plata (36°S,56°W), resulta diferente. Muestreos biologicos y datos oceanograficos demuestran que su area de desove cubre una estrecha franja a traves del rio, entre Montevideo (34°50´S,56°10´W) y Punta Piedras (35°25´S,57°10´W), en profundidades de 6 a 8 m. Esta area se caracteriza por fuertes haloclinas, de hasta 21.5 unidades m-1. Los huevos de M. furnieri se encuentran solo debajo de la haloclina, en salinidades de 9.7 a 27.3, y temperaturas de 18.5° a 20.2°C. El desove tiene lugar en la parte mas interna del estuario, cerca del limite rio arriba de la cuna salina, y en coincidencia con el maximo de turbidez (hasta 150 mg L-1). En estuarios del sur de Africa y Australia, caracterizados por el cierre intermitente de su boca, ha sido reportado el desove regular de huevos planctonicos. Nuestros resultados demuestran que un gran estuario tambien puede proveer la oportunidad para el desove exitoso de huevos planctonicos.
TL;DR: There is no process-response model in place, in any country, equivalent to those produced in response to eutrophication of the Great Lakes or acid rain, and reasons include, but are not limited to, dominance by one field of science, biology; lack of competent scientific managers; and emphasis on monitoring programmes, with no clear idea how the results will be used.
Abstract: The response of the coral reef scientific community to the present global crisis in coral reefs is here compared with response times and response patterns of scientists in two previous international environmental crises: eutrophication of the Great Lakes and acid rain in the Northen Hemisphere. In both these previous crises, less than a decade passed from first appreciation of the problem to development of identification/evaluation/mitigation frameworks that were useful in a policy context. Key elements were avoidance of arguments over methods, genuinely multidisciplinary teams, and the presence of respected, technically trained managers. By contrast, twenty years after identification of the major stresses on reefs and description of the major monitoring strategies, there is no process-response model in place, in any country, equivalent to those produced in response to eutrophication of the Great Lakes or acid rain. Reasons for this failure include, but are not limited to: dominance by one field of science, biology; lack of competent scientific managers; and emphasis on monitoring programmes, with no clear idea how the results will be used.
TL;DR: The offshore wave climate of Perth (Western Australia) was analysed by using 2.5 years of non-directional 20-min wave data collected from March 1994 to August 1996 to indicate that, on average, 30 storms are experienced annually and the storms are most frequent and intense during July.
Abstract: The offshore wave climate of Perth (Western Australia) was analysed by using 2.5 years of non-directional 20-min wave data collected from March 1994 to August 1996. The mean wave conditions are characterized by a significant wave height (Hs) of 2.0 m and a spectral mean wave period (Tm) of 8.8 s. However, considerable annual variation in the wave conditions is experienced because of a distinct seasonality in the regional wind regime. During summer, daily sea breezes generate moderate seas (ambient Hs 1 to 2 m; Tm 8 s). A low-amplitude background swell (Hs ~0.5 m), generated distantly in the Indian and Southern Oceans, is present all year round. Analysis of extreme wave conditions (Hs >4 m) indicates that, on average, 30 storms are experienced annually, and the storms are most frequent and intense during July. Estimates of extreme Hs, based on all available offshore wave data (12 years, 1975–96), for 1- and 100-year return periods, are 6.7 m and 9.8 m, respectively.
TL;DR: Evidence is added of the plasticity of S. mitsukurii in size at maturity among the SW Atlantic squalid sharks as well as the length–weight relationship, which did not differ between sexes in the SWAtlantic population, whereas it differed in one population from the NW Pacific.
Abstract: Size at maturity is analysed for Squalus mitsukurii from the SW Atlantic. Males mature between 51 and 55 cm total length and females between 52 and 60 cm total length. Hence, S. mitsukurii appears to be intermediate in size at maturity among the SW Atlantic squalid sharks. This analysis adds evidence of the plasticity of S. mitsukurii in size at maturity. The length–weight relationship did not differ between sexes in the SW Atlantic population, whereas it differed in one population from the NW Pacific. Intersexual differences in size at maturity in the present study were lower than those reported for other regions.
TL;DR: The optimum management strategy is to identify areas that consistently support large numbers of dugongs and to set these aside as dugong sanctuaries in which dugong mortality is minimized and their habitat protected.
Abstract: The dugong (Dugong dugon) is listed as vulnerable to extinction at a global scale. It has a large range that spans some forty countries and includes tropical and subtropical coastal and island waters from east Africa to Vanuatu. A significant proportion of the world's dugongs is found in northern Australian waters where most modern dugong research has been conducted. Dugongs are long-lived animals with a low repro- ductive rate, long generation time, and a high investment in each offspring. Population simulations indicate that even with the most optimistic combinations of life-history parameters (e.g. low natural mortality and no human-induced mortality) a dugong population is unlikely to increase by more than 5% per year. Dugongs are vulnerable to anthropogenic impacts because of their life history and their dependence on seagrasses that are restricted to coastal habitats. Even a slight reduction in adult survivorship as a result of habitat loss, disease, hunting or incidental drowning in nets can cause a chronic decline in a dugong population. The optimum management strategy is to identify areas that consistently support large numbers of dugongs and to set these aside as dugong sanctuaries in which dugong mortality is minimized and their habitat protected.
TL;DR: Evidence for population migration to exploit separation of light and nutrient availability is tenuous, with most field observations of the vertical distribution of phytoplankton populations showing no evidence of vertical migration to sufficient depth to reach nutrients in stratified systems.
Abstract: Fogg and Walsby’s (1971) hypothesis that buoyancy regulation in cyanobacteria might be an adaptation to exploit the separation of light and nutrients has since become a paradigm The evidence of its veracity is examined within observations of algal abundance and chlorophyll distributions in several Australian freshwater systems and is also reviewed from the literature It is clear from both laboratory experiments and field measurements that filamentous genera such as Anabaena and colony-forming genera such as Microcystis are capable of changing their buoyancy within a diurnal cycle However, evidence for population migration to exploit separation of light and nutrient availability is tenuous, with most field observations of the vertical distribution of phytoplankton populations showing no evidence of vertical migration to sufficient depth to reach nutrients in stratified systems Instead, changes in the vertical distribution of phytoplankton suggest a response either to the dynamics of the surface mixed layer or to lateral advection In natural systems, algal buoyancy appears to be dependent much more on light than on nutrients, this being consistent with the carbohydrate ballast mechanism Physical mechanisms can provide sufficient replenishment of epilimnetic nutrients to explain the observed net growth rates of phytoplankton populations in situ
TL;DR: The findings emphasize the important role of burrowing macrofauna in the transport of dissolved substances between the sediment and water bodies and the dependence of various biogeochemical processes, including nutrient release, on the benthic Macrofauna of Port Phillip Bay.
Abstract: The effect of burrowing activities of ghost shrimp (Neocallichirus limosus and Biffarius arenosus) and heart urchin (Echinocardium cordatum) on the flux of dissolved substances across the water–sediment interface was examined by comparing the transport of the tracer deuterium oxide (D2O) between sediments and overlying water in experimental laboratory tanks with and without fauna. This experiment was complemented by measurements of the diffusive flux of naturally occurring isotopes of radium (224Ra and 223Ra) from the sediments into the water column. Despite different burrowing habits, all three species enhanced flux of D2O and the Ra isotopes by similar amounts. In sandy sediments, both shrimps and urchins enhanced flux of D2O across the water–sediment interface 2.5 fold. In muddy sediments, however, results were inconclusive. There was little difference in flux of 224Ra and 223Ra between muddy and sandy sediments; flux was 2.3–3.9 times higher in the presence of the burrowing species than in their absence. These findings emphasize (i) the important role of burrowing macrofauna in the transport of dissolved substances between the sediment and water bodies and (ii) the dependence of various biogeochemical processes, including nutrient release, on the benthic macrofauna of Port Phillip Bay.
TL;DR: These techniques, extending to 12 h the post-feeding interval in which fishes may be found and differentiated among Gambusia gut contents, were tested on 631 wild-caught Gambusiusia collected in eastern Australia; an ingested native fish could be identified in the gut of 18 GambusIA, and a cannibalized fish in the Gut of three.
Abstract: Clearing and staining of Gambusia holbrooki facilitated identification of juvenile fishes among the gut contents, and a feeding trial with captive Gambusia allowed assessment of gut transit time and degradation of melanotaeniid larvae. Regurgitated fishes and eggs in fixative solutions were also investigated. These techniques, extending to 12 h the post-feeding interval in which fishes may be found and differentiated among Gambusia gut contents, were tested on 631 wild-caught Gambusia collected in eastern Australia; an ingested native fish could be identified in the gut of 18 Gambusia, and a cannibalized fish in the gut of three.
TL;DR: Offshore aggregations were found over 7 months of the year, but the size and sex ratio of aggregating lobsters varied considerably between seasons, and seasonal peaks in the proportion of male lobsters within the aggregations coincided with peak feeding rates in captive males.
Abstract: The behaviour and characteristics of J. edwardsii within offshore aggregations in northern New Zealand are described. Groups of up to 200 lobsters were found aggregating beyond the coastal reefs by day, on open sand, amongst beds of the emergent bivalve Atrina zelandica, and around low-lying patch reefs which had little topographical relief. Lobsters within the aggregations displayed behaviour consistent with the use of mutual defence. In areas of open sand, aggregations were circular, with individuals on the perimeter always facing outwards. These lobsters held their stout, spiny antennae upright and used them to fend off potential threats. On patch reefs and around Atrina beds, aggregations were less uniform in shape, and lobsters increased their level of physical protection by clustering against irregularities in the substratum. Offshore aggregations were found over 7 months of the year, but the size and sex ratio of aggregating lobsters varied considerably between seasons. Seasonal peaks in the proportion of male lobsters within the aggregations coincided with peak feeding rates in captive males. The presence of females was not as clearly related to their feeding patterns and probably also reflected behavioural adaptations associated with the carrying of eggs and release of larvae.
TL;DR: These surveys report the first quantitative information on the shallow- water, rocky-reef communities in the region, which is a vital step in assessing their ecological significance.
Abstract: The subtropical rocky reefs of Cook Island, Julian Rocks and the South West Rocks area form part of a chain of islands and reefs with significant coral cover from the Queensland border (28˚S) to the southern extent of extensive coral communities in coastal Australia (31˚S). Benthic communities at 18 subtidal sites at the three localities were surveyed quantitatively by video-transects, and coral species lists were compiled. Twenty-eight coral species previously unrecorded for these localities were identified, increasing the species richness of hermatypic corals reported for the northern NSW region (excluding the Solitary Islands) from 14 to 43. Coral species richness declined with latitude. Benthic communities were generally dominated by turfing and macroalgal species, with Pyura, sponges, and barnacles locally abundant. Scleractinian coral cover ranged from 0% to 42.6% per site, with highest coral cover at the most southern site. Julian Rocks is a designated Aquatic Reserve, and Marine Parks have been suggested for all three localities. Selection of Marine Protected Areas requires information on their ecological significance. These surveys report the first quantitative information on the shallow- water, rocky-reef communities in the region, which is a vital step in assessing their ecological significance.
TL;DR: High-precision measurements of N2 in benthic chamber waters indicated that denitrification occurs within the major sedimentary facies in Port Phillip Bay, and the sedimentary microbial processes of ammonification, nitrification and Denitrification are tightly coupled.
Abstract: High-precision measurements of N2 in benthic chamber waters indicated that denitrification occurs within the major sedimentary facies in Port Phillip Bay. The integrated fluxes of biogenic N2 , ammonia, nitrate and nitrite showed that the stoichiometric relationship between organic C and N in the muddy sediments, occupying about 70% of the seafloor, was 5.7, this being similar to the Redfield ratio of 6.6. High denitrifying efficiencies (75–85%; denitrification rates ~1.3 mmol N2 m–2 day–1) at organic carbon loadings of ~15–25 mmol m–2 day–1 indicate that most N processed through the sediments was returned to the overlying waters as biologically (generally) unavailable N2. At sites of high organic carbon loadings to the sediments (>100 mmol m–2 day–1) denitrification rates and denitrifying efficiencies were near zero and most N is returned to the Bay waters as biologically available ammonium. In chambers ‘spiked’ with 15NO3 , denitrifyers used nitrate produced in the sediments in situ, rather than the exogenous nitrate in overlying waters. The sedimentary microbial processes of ammonification, nitrification and denitrification are therefore tightly coupled.
TL;DR: Coupled hydrodynamic and transport models of Port Phillip Bay provided physical forcing for ecological simulations and identified a systematic bias in the known freshwater budget for the bay.
Abstract: Coupled hydrodynamic and transport models of Port Phillip Bay were developed as part of the Port Phillip Bay Environmental Study. Model coupling was achieved via a particle tracking method, giving great flexibility in both geometry and time step for the transport model. This technique allowed ecological (water quality) modules to be included efficiently, so that long-term management scenarios could be adequately addressed. Validation of the hydrodynamic model was done primarily against observed sea-level and current meter data. For the transport model, comparisons were made with data on salinity in the bay observed over five years. Despite some disagreement between the hydrodynamic model and observations of longer-term (non-tidal) currents, the transport model provided good simulations of salinity throughout the bay. Transport-model flushing time for the bay was about 270 days (similar to estimates obtained from salinity and radionuclide measurements), varying with model geometry and with position inside the bay. As well as providing physical forcing for ecological simulations (described elsewhere in this issue), the models identified a systematic bias in the known freshwater budget for the bay.
TL;DR: The apparent germination of akinetes early in summer and immediately following sporulation in mid summer indicated a strategy for both initiation and maintenance of populations, providing a potentially significant inoculum for cyanobacterial growth.
Abstract: Planktonic populations and benthic resting stages (akinetes) of the common bloom-forming cyanobacteria Anabaena circinalis Rabenhorst and Anabaena flos-aquae f. flos-aquae (Lyngb.) Komarek were monitored in the Murray River near Nildottie and in adjacent floodplain wetlands (lagoons) from 1995 to 1997, to determine the extent of sporulation and the contribution of recruitment from the sediments to seasonal development of blooms. Physical and chemical characteristics of the water in the river and the lagoons were examined in relation to the succession of key life-cycle stages and growth. The warm, shallow lagoons supported considerably higher populations of Anabaena in the summer than did the river, with correspondingly higher incidence of sporulation. Viable akinetes were abundant in the sediments of both the river channel and the lagoons, providing a potentially significant inoculum for cyanobacterial growth. The apparent germination of akinetes early in summer and immediately following sporulation in mid summer indicated a strategy for both initiation and maintenance of populations. A. circinalis also persisted as a planktonic population throughout winter. Germination is considered more likely to occur in the shallow lagoons than in the main channel, principally because of frequent resuspension of sediments containing resting stages to the euphotic zone or because of direct penetration of light to the sediments.
TL;DR: Differences in the ratio of maximum uptake rate to half-saturation rate between surge and assimilation uptake phases suggest a propensity for some species to take up ammonium at low concentrations.
Abstract: The uptake rates of ammonium were determined for three species of native macroalgae and an exotic macroalga from Port Phillip Bay. All species exhibited rate-saturated mechanisms of uptake described by Michaelis–Menten uptake kinetics. At the highest concentration examined (28.6 µmol NH4-N) Hincksia sordida had a higher rate of uptake (435 µmol NH4 -N g dry wt–1 h–1) than Ulva sp. (108 µmol NH4-N g dry wt–1 h–1) or Polysiphonia decipiens (53 µmol NH4 -N g dry wt–1 h–1). Maximum surge uptake rate was highest for H. sordida and lowest for P. decipiens (802 and 57 µmol NH4 -N g dry wt–1 h–1 respectively). The introduced phaeophyte Undaria pinnatifida had an intermediate capacity for ammonium uptake which was dependent on blade maturity. Differences in the ratio of maximum uptake rate to half-saturation rate between surge and assimilation uptake phases suggest a propensity for some species to take up ammonium at low concentrations. The relationships between nutrient uptake and growth among species would afford mature U. pinnatifida, H. sordida and Ulva sp. a competitive advantage for ammonium uptake in winter during high N availability, whereas P. decipiens would be able to exploit low N concentrations in spring and summer.
TL;DR: Patterns of recruitment and succession on ceramic settlement panels were examined in a subtidal marine community in eastern Australia to determine whether competition for settlement space with temperate biota was a factor potentially limiting the development of coral communities in a tropical location.
Abstract: Patterns of recruitment and succession on ceramic settlement panels were examined in a subtidal marine community in eastern Australia to determine whether competition for settlement space with temperate biota was a factor potentially limiting the development of coral communities in a subtropical location. Replicate settlement panels were installed at Split Solitary Island (30˚S) in November 1992 and were destructively sampled after 1, 3, 5, 7, 10, 12, 16 and 29 months. Species richness and community structure data were analysed by non-parametric multivariate analysis. Space on panel surfaces was rapidly occupied; the upper surfaces by algae and the lower surfaces by bryozoans, ascidians and sponges, with a divergence of community structure over time. Of the 228 coral recruits identified on the panels, 98% were recorded on the upper surface of panels, in contrast to studies at most tropical sites where corals recruit predominantly to lower surfaces. Owing to the rapid settlement of other biota, free space for coral settlement was limited and this may account for the low coral recruitment rate recorded. High post-settlement mortality (>94%) of coral recruits over a 3-month period indicated the significance of post-settlement factors in accounting for low recruitment in settlement-panel studies.