The N-15 natural abundance (delta N-15) of ecosystem samples reflects measures of water availability

We assembled a globally-derived data set for site-averaged foliar delta(15)N, the delta(15)N of whole surface mineral soil and corresponding site factors (mean annual rainfall and temperature, latitude, altitude and soil pH). The delta(15)N of whole soil was related to all of the site variables (including foliar delta(15)N) except altitude and, when regressed on latitude and rainfall, provided the best model of these data, accounting for 49% of the variation in whole soil delta(15)N. As single linear regressions, site-averaged foliar delta(15)N was more strongly related to rainfall than was whole soil delta(15)N. A smaller data set showed similar, negative correlations between whole soil delta(15)N, site-averaged foliar delta(15)N and soil moisture variations during a single growing season. The negative correlation between water availability (measured here by rainfall and temperature) and soil or plant delta(15)N fails at the landscape scale, where wet spots are delta(15)N-enriched relative to their drier surroundings. Here we present global and seasonal data, postulate a proximate mechanism for the overall relationship between water availability and ecosystem delta(15)N and, newly, a mechanism accounting for the highly delta(15)N-depleted values found in the foliage and soils of many wet/cold ecosystems. These hypotheses are complemented by documentation of the present gaps in knowledge, suggesting lines of research which will provide new insights into terrestrial N-cycling. Our conclusions are consistent with those of Austin and Vitousek (1998) that foliar (and soil) delta(15)N appear to be related to the residence time of whole ecosystem N.

Climate change, coral bleaching and the future of the world's coral reefs

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.

Marine bioprospecting - Trawling for treasure and pleasure

This Microreview seeks to highlight the molecular diversity present in marine organisms, and illustrate by example some of the challenges encountered in exploring this resource. Marine natural products exhibit an impressive array of structural motifs, many of which are derived from biosynthetic pathways that are uniquely marine, Most importantly some marine metabolites possess noteworthy biological activities, activities that have potential application outside marine ecosystems, such as antibiotics, antiparasitics, anticancer agents etc... The isolation, spectroscopic characterisation and assignment of stereostructures to these unusual metabolites is both challenging and rewarding. Examples featured in this Microreview follow a common theme in that they are all recent accounts of the isolation of natural products from Australian marine sponges, carried out in the laboratories of the author. In addition to presenting brief comments on specific structure elucidation strategies, an effort is made to emphasize techniques for solving stereochemical issues, as well as to speculate on the biosynthetic origins of some of these exotic marine natural products.

Spatial and temporal variation in distribution of mangroves in Moreton Bay, subtropical Australia: a comparison of pattern metrics and change detection analyses based on aerial photographs

An assessment of the changes in the distribution and extent of mangroves within Moreton Bay, southeast Queensland, Australia, was carried out. Two assessment methods were evaluated: spatial and temporal pattern metrics analysis, and change detection analysis. Currently, about 15,000 ha of mangroves are present in Moreton Bay. These mangroves are important ecosystems, but are subject to disturbance from a number of sources. Over the past 25 years, there has been a loss of more than 3800 ha, as a result of natural losses and mangrove clearing (e.g. for urban and industrial development, agriculture and aquaculture). However, areas of new mangroves have become established over the same time period, offsetting these losses to create a net loss of about 200 ha. These new mangroves have mainly appeared in the southern bay region and the bay islands, particularly on the landward edge of existing mangroves. In addition, spatial patterns and species composition of mangrove patches have changed. The pattern metrics analysis provided an overview of mangrove distribution and change in the form of single metric values, while the change detection analysis gave a more detailed and spatially explicit description of change. An analysis of the effects of spatial scales on the pattern metrics indicated that they were relatively insensitive to scale at spatial resolutions less than 50 m, but that most metrics became sensitive at coarser resolutions, a finding which has implications for mapping of mangroves based on remotely sensed data. (C) 2003 Elsevier Science B.V. All rights reserved.

Ecosystem process models at multiple scales for mapping tropical forest productivity

Quantifying mass and energy exchanges within tropical forests is essential for understanding their role in the global carbon budget and how they will respond to perturbations in climate. This study reviews ecosystem process models designed to predict the growth and productivity of temperate and tropical forest ecosystems. Temperate forest models were included because of the minimal number of tropical forest models. The review provides a multiscale assessment enabling potential users to select a model suited to the scale and type of information they require in tropical forests. Process models are reviewed in relation to their input and output parameters, minimum spatial and temporal units of operation, maximum spatial extent and time period of application for each organization level of modelling. Organizational levels included leaf-tree, plot-stand, regional and ecosystem levels, with model complexity decreasing as the time-step and spatial extent of model operation increases. All ecosystem models are simplified versions of reality and are typically aspatial. Remotely sensed data sets and derived products may be used to initialize, drive and validate ecosystem process models. At the simplest level, remotely sensed data are used to delimit location, extent and changes over time of vegetation communities. At a more advanced level, remotely sensed data products have been used to estimate key structural and biophysical properties associated with ecosystem processes in tropical and temperate forests. Combining ecological models and image data enables the development of carbon accounting systems that will contribute to understanding greenhouse gas budgets at biome and global scales.

Implications of current ecological thinking for biodiversity conservation: A review of the salient issues

Given escalating concern worldwide about the loss of biodiversity, and given biodiversity's centrality to quality of life, it is imperative that current ecological knowledge fully informs societal decision making. Over the past two decades, ecological science has undergone many significant shifts in emphasis and perspective, which have important implications for how we manage ecosystems and species. In particular, a shift has occurred from the equilibrium paradigm to one that recognizes the dynamic, non-equilibrium nature of ecosystems. Revised thinking about the spatial and temporal dynamics of ecological systems has important implications for management. Thus, it is of growing concern to ecologists and others that these recent developments have not been translated into information useful to managers and policy makers. Many conservation policies and plans are still based on equilibrium assumptions. A fundamental difficulty with integrating current ecological thinking into biodiversity policy and management planning is that field observations have yet to provide compelling evidence for many of the relationships suggested by non-equilibrium ecology. Yet despite this scientific uncertainty, management and policy decisions must still be made. This paper was motivated by the need for considered scientific debate on the significance of current ideas in theoretical ecology for biodiversity conservation. This paper aims to provide a platform for such discussion by presenting a critical synthesis of recent ecological literature that (1) identifies core issues in ecological theory, and (2) explores the implications of current ecological thinking for biodiversity conservation.

The toxins of Lyngbya majuscula and their human and ecological health effects

Lyngbya majuscula is a benthic filamentous marine cyanobacterium, which in recent years appears to have been increasing in frequency and size of blooms in Moreton Bay, Queensland. It has a worldwide distribution throughout the tropics and subtropics in water to 30m. It has been found to contain a variety of chemicals that exert a range of biological effects, including skin, eye and respiratory irritation. The toxins lyngbyatoxin A and debromoaplysiatoxin appear to give the most widely witnessed biological effects in relation to humans, and experiments involving these two toxins show the formation of acute dermal lesions. Studies into the epidemiology of the dermatitic, respiratory and eye effects of the toxins of this organism are reviewed and show that Lyngbya induced dermatitis has occurred in a number of locations. The effects of aerosolised Lyngbya in relation to health outcomes were also reported. Differential effects of bathing behaviour after Lyngbya exposure were examined in relation to the severity of health outcomes. The potential for Lyngbya to exhibit differential toxicologies due to the presence of varying proportions of a range of toxins is also examined. This paper reviews the present state of knowledge on the effects of Lyngbya majuscula on human health, ecosystems and human populations during a toxic cyanobacterial bloom. The potential exists for toxins from Lyngbya majuscula affecting ecological health and in particular marine reptiles. (C) 2001 Elsevier Science Ltd. All rights reserved.

Managing the Brisbane River and Moreton Bay: an integrated research/management program to reduce impacts on an Australian estuary

The Brisbane River and Moreton Bay Study, an interdisciplinary study of Moreton Bay and its major tributaries, was initiated to address water quality issues which link sewage and diffuse loading with environmental degradation. Runoff and deposition of fine-grained sediments into Moreton Bay, followed by resuspension, have been linked with increased turbidity and significant loss of seagrass habitat. Sewage-derived nutrient enrichment, particularly nitrogen (N), has been linked to algal blooms by sewage plume maps. Blooms of a marine cyanobacterium, Lyngbya majuscula, in Moreton Bay have resulted in significant impacts on human health (e.g., contact dermatitis) and ecological health (e.g., seagrass loss), and the availability of dissolved iron from acid sulfate soil runoff has been hypothesised. The impacts of catchment activities resulting in runoff of sediments, nutrients and dissolved iron on the health of the Moreton Bay waterways are addressed. The Study, established by 6 local councils in association with two state departments in 1994, forms a regional component of a national and state program to achieve ecologically sustainable use of the waterways by protecting and enhancing their health, while maintaining economic and social development. The Study framework illustrates a unique integrated approach to water quality management whereby scientific research, community participation and the strategy development were done in parallel with each other. This collaborative effort resulted in a water quality management strategy which focuses on the integration of socioeconomic and ecological values of the waterways. This work has led to significant cost savings in infrastructure by providing a clear focus on initiatives towards achieving healthy waterways. The Study's Stage 2 initiatives form the basis for this paper.

Assessing ecological impacts of shrimp and sewage effluent: Biological indicators with standard water quality analyses

Despite evidence linking shrimp farming to several cases of environmental degradation, there remains a lack of ecologically meaningful information about the impacts of effluent on receiving waters. The aim of this study was to determine the biological impact of shrimp farm effluent, and to compare and distinguish its impacts from treated sewage effluent. Analyses included standard water quality/sediment parameters, as well as biological indicators including tissue nitrogen (N) content, stable isotope ratio of nitrogen (delta N-15) and amino acid composition of inhabitant seagrasses, mangroves and macroalgae. The study area consisted of two tidal creeks, one receiving effluent from a sewage treatment plant and the other from an intensive shrimp farm. The creeks discharged into the western side of Moreton Bay, a sub-tropical coastal embayment on the east coast of Australia. Characterization of water quality revealed significant differences between the creeks, and with unimpacted eastern Moreton Bay. The sewage creek had higher concentrations of dissolved nutrients (predominantly NO3-/NO2- and PO43-, compared to NH4+ in the shrimp creek). In contrast, the shrimp creek was more turbid and had higher phytoplankton productivity. Beyond 750 m from the creek mouths, water quality parameters were indistinguishable from eastern Moreton Bay values. Biological indicators detected significant impacts up to 4 km beyond the creek mouths (reference site). Elevated plant delta N-15 values ranged from 10.4-19.6 parts per thousand at the site of sewage discharge to 2.9-4.5 parts per thousand at the reference site. The free amino acid concentration and composition of seagrass and macroalgae was used to distinguish between the uptake of sewage and shrimp derived N. Proline (seagrass) and serine (macroalgae) were high in sewage impacted plants and glutamine (seagrass) and alanine (macroalgae) were high in plants impacted by shrimp effluent. The delta N-15 isotopic signatures and free amino acid composition of inhabitant flora indicated that sewage N extended further from the creek mouths than shrimp N. The combination of physical/chemical and biological indicators used in this study was effective in distinguishing the composition and subsequent impacts of aquaculture and sewage effluent on the receiving waters. (C) 2001 Academic Press.

ENCORE: The effect of nutrient enrichment on coral reefs. Synthesis of results and conclusions

Coral reef degradation resulting from nutrient enrichment of coastal waters is of increasing global concern. Although effects of nutrients on coral reef organisms have been demonstrated in the laboratory, there is little direct evidence of nutrient effects on coral reef biota in situ. The ENCORE experiment investigated responses of coral reef organisms and processes to controlled additions of dissolved inorganic nitrogen (N) and/or phosphorus (P) on an offshore reef(One Tree Island) at the southern end of the Great Barrier Reef, Australia. A multi-disciplinary team assessed a variety of factors focusing on nutrient dynamics and biotic responses. A controlled and replicated experiment was conducted over two years using twelve small patch reefs ponded at low tide by a coral rim. Treatments included three control reefs (no nutrient addition) and three + N reefs (NH4Cl added), three + P reefs (KH2PO4 added), and three + N + P reefs. Nutrients were added as pulses at each low tide (ca twice per day) by remotely operated units. There were two phases of nutrient additions. During the initial, low-loading phase of the experiment nutrient pulses (mean dose = 11.5 muM NH4+; 2.3 muM PO4-3) rapidly declined, reaching near-background levels (mean = 0.9 muM NH4+; 0.5 muM PO4-3) within 2-3 h. A variety of biotic processes, assessed over a year during this initial nutrient loading phase, were not significantly affected, with the exception of coral reproduction, which was affected in all nutrient treatments. In Acropora longicyathus and A. aspera, fewer successfully developed embryos were formed, and in A. longicyathus fertilization rates and lipid levels decreased. In the second, high-loading, phase of ENCORE an increased nutrient dosage (mean dose = 36.2 muM NH4+; 5.1 muM PO4-3 declining to means of 11.3 muM NH4+ and 2.4 muM PO4-3 at the end of low tide) was used for a further year, and a variety of significant biotic responses occurred. Encrusting algae incorporated virtually none of the added nutrients. Organisms containing endosymbiotic zooxanthellae (corals and giant clams) assimilated dissolved nutrients rapidly and were responsive to added nutrients. Coral mortality, not detected during the initial low-loading phase, became evident with increased nutrient dosage, particularly in Pocillopora damicornis. Nitrogen additions stunted coral growth, and phosphorus additions had a variable effect. Coral calcification rate and linear extension increased in the presence of added phosphorus but skeletal density was reduced, making corals more susceptible to breakage. Settlement of all coral larvae was reduced in nitrogen treatments, yet settlement of larvae from brooded species was enhanced in phosphorus treatments. Recruitment of stomatopods, benthic crustaceans living in coral rubble, was reduced in nitrogen and nitrogen plus phosphorus treatments. Grazing rates and reproductive effort of various fish species were not affected by the nutrient treatments. Microbial nitrogen transformations in sediments,were responsive to nutrient loading with nitrogen fixation significantly increased in phosphorus treatments and denitrification increased in all treatments to which nitrogen had been added. Rates of bioerosion and grazing showed no significant effects of added nutrients, ENCORE has shown that reef organisms and processes investigated ill situ were impacted by elevated nutrients. Impacts mere dependent on dose level, whether nitrogen and/or phosphorus mere elevated and were often species-specific. The impacts were generally sub-lethal and subtle and the treated reefs at the end of the experiment mere visually similar to control reefs. Rapid nutrient uptake indicates that nutrient concentrations alone are not adequate to assess nutrient condition of reefs. Sensitive and quantifiable biological indicators need to be developed for coral reef ecosystems. The potential bioindicators identified in ENCORE should be tested in future research on coral reef/nutrient interactions. Synergistic and cumulative effects of elevated nutrients and other environmental parameters, comparative studies of intact vs. disturbed reefs, offshore vs, inshore reefs, or the ability of a nutrient-stressed reef to respond to natural disturbances require elucidation. An expanded understanding of coral reef responses to anthropogenic impacts is necessary, particularly regarding the subtle, sub-lethal effects detected in the ENCORE studies. (C) 2001 Published by Elsevier Science Ltd.