Nathan Waltham

Application of management tools to integrate ecological principles with the design of marine infrastructure

Globally the coastal zone is suffering the collateral damage from continuing urban development and construction, expanding resource sectors, increasing population, regulation to river flow, and on-going land change and degradation. While protection of natural coastal habitat is recommended, balancing conservation with human services is now the challenge for managers. Marine infrastructure such as seawalls, marinas and offshore platforms is increasingly used to support and provide services, but has primarily been designed for engineering purposes without consideration of the ecological consequences. Increasingly developments are seeking alternatives to hard engineering and a range of ecological solutions has begun to replace or be incorporated into marine and coastal infrastructure. But too often, hard engineering remains the primary strategy because the tools for managers to implement ecological solutions are either lacking or not supported by policy and stakeholders. Here we outline critical research needs for marine urban development and emerging strategies that seek to mitigate the impacts of marine infrastructure. We present case studies to highlight the strategic direction necessary to support management decisions internationally.

Contaminants in water, sediment and fish biomonitor species from natural and artificial estuarine habitats along the urbanized Gold Coast, Queensland.

Metal and pesticide contaminants were measured in water, sediment and fish species in various Gold Coast waterways, Queensland. With the exception of Cu, metal concentrations in water, measured using the diffuse gradients in a thin film (DGT) technique, complied with relevant Australian guidelines. Cu concentrations in these waterways have been related to recreational vessel activities previously. All sediment metal concentrations measured were below the national guidelines, although Cu, Zn and Pb were found to vary significantly between habitat types. Evidence of spikes in sediment pesticide concentrations (some banned over 50 years ago) was observed in some artificial residential waterways. Heavy metals and pesticides were measured in the tissue (muscle, gills and liver) of three economically important species of fish, with different feeding strategies (partly herbivore Arrhamphus sclerolepis, carnivore Acanthopagrus australis, detritivore Mugil cephalus). We tested the hypothesis that fish accumulate different amounts of contaminants from wetland habitats affected by different intensities of anthropogenic activities (i.e., marinas, artificial residential canals, artificial residential lakes, estuaries and natural, vegetated waterways). Significantly higher concentrations of Cu were found in the gills of each fish species from marinas compared to fish caught in other waterways. Furthermore, fish caught in canals had the second highest Cu and natural waterways the lowest. These results support the stated hypothesis for Cu and furthermore indicate that these fish species are suitable as biomonitors in estuarine waterways. Metal and pesticide concentrations in the edible muscle tissue of all fish complied with the Australian Food Standard Code recommended limits for human consumption, apart from As which is likely to be due to bioconcentration of lower toxicity organo-As species. These results indicate a low health risk for humans consuming fish, in terms of contaminant levels. The accumulated body of evidence on contaminants within Gold Coast waterways generally suggests that there are no major threats of metal or pesticide contamination, except for marina facilities which are a major source of Cu which also accumulates in fish. Water quality threats are also highlighted in residential canals, presumably as a consequence of their hydrological design.

Use of flathead mullet (Mugil cephalus) in coastal biomonitor studies: Review and recommendations for future studies

There has been a widespread world-wide use of flathead mullet, Mugilcephalus, in fish biomonitor studies within the coastal zone. This review summarises this research field, focusing on heavy metals, and considers the implications of the accumulated data. Differences in sampling methodology, tissues analysed and units of reported data provide challenges in assessing and benchmarking these biomonitor studies. The benthic feeding strategy of M.cephalus invariably increases exposure risk relative to middle or upper water column feeders, nevertheless contaminant accumulation via direct and indirect pathways was regulated sufficiently such that toxicants were below food guidelines in most coastal regions (32 of the 49 examined). Human health issues can arise if fish are consumed from heavily industrialised regions. Recommendations are provided for future biomonitoring studies, based on the results for M. cephalus but relevant for fish species more broadly, to provide more comparable data so that managers can benchmark against local conditions.

Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web

Despite the widespread use of carbon stable isotopes to distinguish among potential energy pathways in food webs, their usefulness is limited where potential basal carbon sources are numerous and diverse. We measured carbon isotope values of the major fisheries species, the mostly carnivorous Scylla serrata (giant mud crab), and potential basal, autotrophic sources supporting the food web. Conventional mixing modelling of autotroph and crab isotope data could not differentiate contributions from different sources. Pooling of modelled contributions from sources with similar isotope values indicated a role for organic matter from seagrass meadows or saltmarshes, but still did not define contributions well. Crab isotope data from a subsequent, spatially explicit survey of 14 sites, selected to represent different distances from key habitats, were analyzed using multiple regression. Crab isotope values showed a significant relationship with distance from seagrass (R^2 = 0.87), but not with distance from mangroves or saltmarsh grass. Alongside seagrass meadows, crabs had very enriched isotope values, demonstrating their reliance on sources with enriched isotope values (seagrass and algae epiphytic on seagrass, 65–90% of their energy intake). At the site furthest from seagrass (21 km), crabs assimilated carbon primarily from depleted sources such as mangroves and terrestrial organic matter from coastal catchments (70–85%). Explicit spatial analysis of isotope data following a comprehensive survey revealed energy pathways not evident in conventional analyses.

The temperature regimes of dry-season waterholes in tropical northern Australia: potential effects on fish refugia

The ephemeral rivers in northern Australia break up into a series of waterholes during the long, dry summer season. These in-stream waterholes provide vital habitat for the survival of aquatic biota during this period. We describe how high-time-resolution (20 min) waterhole temperature measurements made in the Flinders and Gilbert Rivers in tropical northern Australia were used to derive thermal frequency curves that show how often waterhole temperature exceeded any given temperature threshold. During the summer period, temperatures near the surfaces of waterholes were often above that suitable for the optimum growth of some tropical fish (31°C). At the bottom of waterholes, this exceedance occurred less often, and in turbid waterholes that were stratified, temperatures rarely exceeded this threshold. Temperatures that could be lethal to some fish (34°C) also were exceeded at the surface of waterholes, but rarely, if ever, at the bottom of waterholes. An energy-balance model was used to estimate daily mean waterhole temperature with good accuracy (±1 K) at all but the sites where wind speed may have been >2 m/s (assumed in the model). The model also was used to predict the effects of climate change on waterhole temperature and the change in exceedance of thermal thresholds. A 2 K climate warming raised waterhole temperature by ∼1 K. However small this increase might seem, it led to a doubling of the length of time water temperatures were in excess of thresholds around 31°C.

Protecting the Green Behind the Gold: Catchment-Wide Restoration Efforts Necessary to Achieve Nutrient and Sediment Load Reduction Targets in Gold Coast City, Australia

Abstract The Gold Coast City is the tourist center of Australia and has undergone rapid and massive urban expansion over the past few decades. The Broadwater estuary, in the heart of the City, not only offers an array of ecosystems services for many important aquatic wildlife species, but also supports the livelihood and lifestyles of residents. Not surprisingly, there have been signs of imbalance between these two major services. This study combined a waterway hydraulic and pollutant transport model to simulate diffuse nutrient and sediment loads under past and future proposed land-use changes. A series of catchment restoration initiatives were modeled in an attempt to define optimal catchment scale restoration efforts necessary to protect and enhance the City’s waterways. The modeling revealed that for future proposed development, a business as usual approach to catchment management will not reduce nutrient and sediment loading sufficiently to protect the community values. Considerable restoration of upper catchment tributaries is imperative, combined with treatment of stormwater flow from intensively developed sub-catchment areas. Collectively, initiatives undertaken by regulatory authorities to date have successfully reduced nutrient and sediment loading reaching adjoining waterways, although these programs have been ad hoc without strategic systematic planning and vision. Future conservation requires integration of multidisciplinary science and proactive management driven by the high ecological, economical, and community values placed on the City’s waterways. Long-term catchment restoration and conservation planning requires an extensive budget (including political and societal support) to handle ongoing maintenance issues associated with scale of restoration determined here.

A comparison of temperature regimes in dry-season waterholes in the Flinders and Gilbert catchments in northern Australia

Dry-season waterholes in ephemeral rivers provide vital habitat for aquatic biota, whose survival is dependent on the waterholes lasting throughout the dry season with temperatures that are not lethal. To examine this in the Flinders and Gilbert Rivers, 20-min temperature measurements were taken during the 2012–2013 dry season in 10 waterholes in each catchment. These data were used to derive thermal-frequency curves that quantify how often waterhole temperature exceeds thresholds for (1) the optimum growth of tropical fish and (2) their lethal temperature. Waterholes that remained deeper than ~0.5m throughout the dry season provided thermally suitable fish refugia, especially if they were turbid, because this decreased the risk of exposure to undesirable temperatures at the bottom of the waterhole. However, surface temperatures in these waterholes often exceeded optimal and even potentially lethal temperatures, so fish may have had to move to cooler water at the bottom of these waterholes. The risk to aquatic species in waterhole refugia is, therefore, primarily determined by depth, with shallow waterholes presenting the greatest risk because they become thermally unsuitable well before (1–2 months) they fully dry out.

Freshwater crabs occupying tropical north Queensland coastal creeks

Balancing coastal urban development with species conservation and habitat protection can be challenging for managers especially where good quality ecological data is lacking. Primary freshwater crabs (Austrothelphusa species) of the family Gecarcinucidae (formerly Parathelphusidae) that occupy inland creek systems are also present in small coastal areas. In coastal regions, habitat loss in response to urbanisation and transformation of natural water channels to concrete drainage lines is a major threat to coastal crab populations. We provide data showing that one species, A. transversa, still exists in natural creek lines in Townsville, but not in engineered creek channels a little further downstream in some cases. Continued urbanisation means that populations will be under threat as the city continues to expand, transforming further natural creek lines to engineered concrete channels. Whether the absence of crabs in urban channels is due to increased predation from fish present in the permanent water (including noxious Oreochromis mossambicus), water chemistry differences, increased competition for food and shelter, or simply because this species cannot burrow in concrete channels to complete important lifecycle stages, warrants further investigation. Evidence is also provided that A. transversa coexists in natural waters with another freshwater crab species, the varunid, (Varuna litterata). The importance of management strategies for both species is discussed, particularly under continuing habitat squeeze with expanding coastal development.

Gold Coast Broadwater: Southern Moreton Bay, Southeast Queensland (Australia)

The Gold Coast Broadwater, a large shallow estuarine water body, is a central feature of the Gold Coast City in Southeast Queensland (Australia) and forms the southern part of Moreton Bay. The Broadwater has undergone dramatic changes over the past few decades, including the construction of an extensive number and network of artificial waterways that account for up to 90 % of Australias canal estates. Positioned in one of the fastest growing regions in the developed world, urbanisation surrounding the Broadwater will continue. The region has important biodiversity values that have led to areas of the Broadwater being listed as an international Ramsar site and inclusion to international migratory bird agreements. The Broadwater provides a vital function in the provision of feeding, spawning and nursery sites for recreationally and commercially important finfish species. Key to the protection of the Broadwater is a reduction of pollutant loads from urban and agricultural stormwater run-off, golf courses and industrial infrastructure/areas and replacement of natural habitats with urban development. Collectively, initiatives undertaken by regulatory authorities have been successful to date and demonstrate that future conservation requires the integration of multidisciplinary science and proactive management driven by the high ecological, economical and community values placed on the Broadwater and adjoining waterways.

Aerial Herbicide Spray to Control Invasive Water Hyacinth (Eichhornia crassipes): Water Quality Concerns Fronting Fish Occupying a Tropical Floodplain Wetland:

Water hyacinth (Eichhornia crassipes) is an aquatic weed degrading tropical floodplains everywhere. On the Burdekin floodplain, northern Australia, it is widespread and contributes to poor water quality, specifically hypoxia which contributes to voluminous wetland fish kills each summer. Removing weeds have focused on applying herbicides using aerial spraying, though restoration success is not monitored. Here, we investigated four aerial spray applications scheduled between November 2013 (Year 1, November 2013 to November 2014) and November 2015 (Year 2, November 2014 to November 2015) in Lochinvah wetland (35 ha wetland, Burdekin floodplain). Using high-frequency (20 min) loggers, dissolved oxygen (DO%) was tracked, which revealed that concentrations were similar before and several weeks after a spray application (independent t test, p > 0.01, except spray application 2, p = 0.06). More interestingly, aquatic weed coverage was low (5% of wetland) during Year 1 and DO had a typical diurnal cycle (20% to 130%). In contrast, low wetland flushing in Year 2 and high weed coverage (80% coverage) combined to increase DO hypoxia exposure risks for fish, with nearly 100% of the logging time failing acute and chronic values known for local fish. The Year 2 weed cover also increased water temperature exposure risk (twofold increase), which was unexpected and which means that fish probably could access cool, deeper, water refugia more frequently compared with Year 1. Controlling aquatic weeds using aerial spraying seems to have minimal risk for fish when cover is low; however, the proliferation of aquatic weeds and spraying has deleterious impact on available oxygen for fish.