Thomas A. Schlacher

Estuarine and Coastal Structures: Environmental Effects, A Focus on Shore and Nearshore Structures

Rapidly growing populations and expanding development are intensifying pressures on coastal ecosystems. Sea-level rise and other predicted effects of climate change are expected to exert even greater pressures on coastal ecosystems, exacerbating erosion, degrading habitat, and accelerating shoreline retreat. Historically, society’s responses to threats from erosion and shoreline retreat have relied on armoring and other engineered coastal defenses. Despite widespread use on all types of shorelines, information about the ecological impacts of shoreline armoring is quite limited. Here we summarize existing knowledge on the effects of armoring structures on the biodiversity, productivity, structure, and function of coastal ecoystems.

Fish track wastewater pollution to estuaries

Excess nitrogen is a forceful agent of ecological change in coastal waters, and wastewater is a prominent source of nitrogen. In catchments where multiple sources of nitrogen pollution co-exist, biological indicators are needed to gauge the degree to which wastewater-N can propagate through the receiving food webs. The purpose of this study was to test whether estuarine fish are suitable as indicators of sewage-N pollution. Fish were analysed from three estuaries within a 100-km strip on the Australian East Coast. The estuaries differ substantially in wastewater loading: (1) the Maroochy Estuary receives a large fraction of the local shire’s treated sewage, (2) the Mooloolah Estuary has no licensed treated wastewater outfalls but marinas/harbours and stormwater may contribute nitrogen, and (3) the Noosa Estuary which neither receives licensed discharges nor has suspected wastewater loads. Sampling for fish included both high rainfall (‘wet’ season) and low rainfall (‘dry’ season) periods. Muscle-δ15N was the variable predicted to respond to treated wastewater loading, reflecting the relative enrichment in 15N resulting from the treatment process and distinguishing it from alternative N sources such as fertiliser and natural nitrogen inputs (both 15N-depleted). Of the 19 fish species occurring in all three estuaries, those from the Maroochy Estuary had significantly elevated δ15N values (up to 9.9‰), and inter-estuarine differences in fish-δ15N were consistent across seasons. Furthermore, not only did all fish from the estuary receiving treated wastewater carry a very distinctive sewage-N tissue signal, but enriched muscle-δ15N was also evident in all species sampled from the one estuary in which sewage contamination was previously only suspected (i.e. the Mooloolah Estuary: 0.2–4.8‰ enrichment over fish from reference system). Thus, fish-δ15N is a suitable indicator of wastewater-N not only in systems that receive large loads, but also for the detection of more subtle nitrogen inputs. Arguably, fish may be preferred indicators of sewage-N contamination because they: (1) integrate nitrogen inputs over long time periods, (2) have an element of ‘ecological relevance’ because fish muscle-δ15N reflect movement of sewage-N through the food chain, and (3) pollution assessments can usually be based on evidence from multiple species.

Give Beach Ecosystems Their Day in the Sun

The Intergovernmental Panel on Climate Change Fourth Assessment Report ([ 1 ][1]) largely overlooked the impacts of climate change on marine ecosystems ([ 2 ][2]). In their Review (“The impact of climate change on the worlds marine ecosystems,” 18 June, p. [1523][3]), O. Hoegh-Guldberg and J. F

Physical Impacts Caused by Off-Road Vehicles to Sandy Beaches: Spatial Quantification of Car Tracks on an Australian Barrier Island

Abstract Beach traffic can substantially modify the physical environment on sandy beaches. Vehicle impacts on beaches were quantified on North Stradbroke Island, a barrier island on the east coast of Australia where large volumes of recreational off-road vehicle (ORV) traffic are concentrated on two beaches (Flinders Beach and Main Beach). The distribution, density, and depth of vehicle ruts on these beaches were quantified during the peak holiday period around late December and early January 2005–06. The density of tyre tracks per meter of beach face ranged from 2.69 to 6.35 on Flinders Beach and from 2.38 to 8.06 on Main Beach, and substantial areas (54–61%) of each beach were covered withy tyre tracks up to a maximum of 90% in some areas. ORVs corrugated the sand as deep as 28 cm (mean depth: 5.86 ± 4.72 cm), with the deepest rutting occurring between the foredunes and the drift line. On a volume basis, vehicles disrupted 5.8% (Main Beach) and 9.4% (Flinders Beach) of the available faunal habitat matrix (top 30 cm of the sand) in a single day. Traffic density was higher on the lower shore, but ruts were significantly deeper in the soft sand of the upper shore. Thus, half of all sand displaced by vehicles on Flinders Beach originated from the upper shore, although this section represents only 36% of beach width. Similarly, the narrow (13% of beach width) upper shore on Main Beach contributed 55% of the total volume of sand dislodged by ORVs. Beach traffic overlapped to a large extent with the distribution of the invertebrate infauna, and vehicles routinely disturbed the drift line and the base of the foredunes. This study emphasizes the need to develop multifaceted management strategies for recreational ORV use on beaches that balance ecological requirements with sociocultural and economic demands.

Impacts of Off-Road Vehicles (ORVs) on Macrobenthic Assemblages on Sandy Beaches

Sandy beaches are the prime sites for human recreation and underpin many coastal economies and developments. In many coastal areas worldwide, beach recreation relies on the use of off-road vehicles (ORVs) driven on the shore. Yet, the use of ORVs is not universally embraced due to social conflicts with other beach user groups and putative environmental consequences of vehicle traffic on sandy shores. Such ecological impacts of ORVs are, however, poorly understood for endobenthic invertebrates of the intertidal zone seawards of the dunes. Consequently, this study quantified the degree to which assemblages of intertidal beach invertebrates are affected by traffic. The study design comprised a series of temporally replicated spatial contrasts between two reference sites (no ORVs) and two beaches with heavy ORV traffic (in excess of 250,000 vehicles per year) located in South-East Queensland, Australia. Macrobenthic assemblages on ORV-impacted beaches had significantly fewer species at substantially reduced densities, resulting in marked shifts in community composition and structure. These shifts were particularly strong on the middle and upper shore where vehicle traffic was concentrated. Strong effects of ORVs were detectable in all seasons, but increased towards the summer months as a result of heavier traffic volumes. This study provides clear evidence that ORVs can have substantial impacts on sandy beach invertebrates that are manifested throughout the whole community. Demonstrating such an ecological impact caused by a single type of human use poses a formidable challenge to management, which needs to develop multi-faceted approaches to balance environmental, social, cultural, and economic arguments in the use of sandy shores, including management of “beach traffic.”

Sewage impacts coral reefs at multiple levels of ecological organization

Against a backdrop of rising sea temperatures and ocean acidification which pose global threats to coral reefs, excess nutrients and turbidity continue to be significant stressors at regional and local scales. Because interventions usually require local data on pollution impacts, we measured ecological responses to sewage discharges in Surin Marine Park, Thailand. Wastewater disposal significantly increased inorganic nutrients and turbidity levels, and this degradation in water quality resulted in substantial ecological shifts in the form of (i) increased macroalgal density and species richness, (ii) lower cover of hard corals, and (iii) significant declines in fish abundance. Thus, the effects of nutrient pollution and turbidity can cascade across several levels of ecological organization to change key properties of the benthos and fish on coral reefs. Maintenance or restoration of ecological reef health requires improved wastewater management and run-off control for reefs to deliver their valuable ecosystems services.

Science priorities for seamounts: research links to conservation and management.

Seamounts shape the topography of all ocean basins and can be hotspots of biological activity in the deep sea. The Census of Marine Life on Seamounts (CenSeam) was a field program that examined seamounts as part of the global Census of Marine Life (CoML) initiative from 2005 to 2010. CenSeam progressed seamount science by collating historical data, collecting new data, undertaking regional and global analyses of seamount biodiversity, mapping species and habitat distributions, challenging established paradigms of seamount ecology, developing new hypotheses, and documenting the impacts of human activities on seamounts. However, because of the large number of seamounts globally, much about the structure, function and connectivity of seamount ecosystems remains unexplored and unknown. Continual, and potentially increasing, threats to seamount resources from fishing and seabed mining are creating a pressing demand for research to inform conservation and management strategies. To meet this need, intensive science effort in the following areas will be needed: 1) Improved physical and biological data; of particular importance is information on seamount location, physical characteristics (e.g. habitat heterogeneity and complexity), more complete and intensive biodiversity inventories, and increased understanding of seamount connectivity and faunal dispersal; 2) New human impact data; these shall encompass better studies on the effects of human activities on seamount ecosystems, as well as monitoring long-term changes in seamount assemblages following impacts (e.g. recovery); 3) Global data repositories; there is a pressing need for more comprehensive fisheries catch and effort data, especially on the high seas, and compilation or maintenance of geological and biodiversity databases that underpin regional and global analyses; 4) Application of support tools in a data-poor environment; conservation and management will have to increasingly rely on predictive modelling techniques, critical evaluation of environmental surrogates as faunal “proxies”, and ecological risk assessment.

Land–Ocean Coupling of Carbon and Nitrogen Fluxes on Sandy Beaches

Rivers link oceans with the land, creating global hot spots of carbon processing in coastal seas. Coastlines around the world are dominated by sandy beaches, but beaches are unusual in that they are thought to rely almost exclusively on marine imports for food. No significant connections to terrestrial production having been demonstrated. By contrast, we isotopically traced carbon and nitrogen pathways leading to clams (Donax deltoides) on beaches. Clams from areas influenced by river plumes had significantly different isotope signatures (δ13C: −18.5 to −20.2‰; δ15N: 8.3–10.0‰) compared with clams remote from plumes (δ13C: −17.5 to −19.5‰; δ15N: 7.6–8.7‰), showing that terrestrial carbon and sewage, both delivered in river plumes, penetrate beach food webs. This is a novel mechanism of trophic subsidy in marine intertidal systems, linking the world’s largest shore ecosystem to continental watersheds. The same clams also carry pollution signatures of sewage discharged into rivers, demonstrating that coastal rivers connect ecosystems in unexpected ways and transfer contaminants across the land–ocean boundary. The links we demonstrate between terrigenous matter and the largest of all marine intertidal ecosystems are significant given the immense social, cultural, and economic values of beaches to humans and the predicted consequences of altered river discharge to coastal seas caused by global climate change.

Monitoring human impacts on sandy shore ecosystems: a test of ghost crabs (Ocypode spp.) as biological indicators on an urban beach

Sandy beaches comprise one of the most important coastal resources worldwide, providing habitats to threatened vertebrates, supporting underappreciated invertebrate biodiversity, and delivering crucial ecosystem services and economic benefits to mankind. Monitoring of the natural resource condition of sandy beaches and assessments of the ecological impacts of human disturbance are, however, rare on sandy shores. Because a crucial step in developing beach monitoring is to identify and test biological indicators, we evaluated the utility of using population densities of ghost crabs (genus Ocypode) to measure how beach biota respond to human pressures. Densities of crabs—estimated via burrow counts—were quantified at two sites exposed to high and low levels of human disturbance on an urban beach in eastern Australia. Human disturbance consisted of pedestrian trampling and shoreline armouring which led to the loss of dune habitat. Overall, crab numbers were halved in disturbed areas, but contrasts between impact and control sites were not necessarily consistent over time and varied between different levels of the shore: stronger and more consistent effect sizes were recorded on the upper shore than further seawards. In addition to lowering crab densities, human disturbance also caused shifts in intertidal distributions, with a greater proportion of individuals occurring lower on the shore in the impacted beach sections. The number of visible burrow openings also changed in response to weather conditions (temperature and wind). We demonstrate that spatial contrasts of burrow counts are broadly useful to indicate the existence of a human-induced disturbance effect on urban beaches; we also highlight a number of critical, hitherto unknown, issues in the application of this monitoring technique; these encompass three broad dimensions: (1) a need for standardised protocols; (2) unresolved causal links between observed patterns and putative pressures; and (3) uncertainties of how organisms responds specifically to both natural and human changes of environmental conditions on sandy shores.

Metrics to assess ecological condition, change, and impacts in sandy beach ecosystems.

Complexity is increasingly the hallmark in environmental management practices of sandy shorelines. This arises primarily from meeting growing public demands (e.g., real estate, recreation) whilst reconciling economic demands with expectations of coastal users who have modern conservation ethics. Ideally, shoreline management is underpinned by empirical data, but selecting ecologically-meaningful metrics to accurately measure the condition of systems, and the ecological effects of human activities, is a complex task. Here we construct a framework for metric selection, considering six categories of issues that authorities commonly address: erosion; habitat loss; recreation; fishing; pollution (litter and chemical contaminants); and wildlife conservation. Possible metrics were scored in terms of their ability to reflect environmental change, and against criteria that are widely used for judging the performance of ecological indicators (i.e., sensitivity, practicability, costs, and public appeal). From this analysis, four types of broadly applicable metrics that also performed very well against the indicator criteria emerged: 1.) traits of bird populations and assemblages (e.g., abundance, diversity, distributions, habitat use); 2.) breeding/reproductive performance sensu lato (especially relevant for birds and turtles nesting on beaches and in dunes, but equally applicable to invertebrates and plants); 3.) population parameters and distributions of vertebrates associated primarily with dunes and the supralittoral beach zone (traditionally focused on birds and turtles, but expandable to mammals); 4.) compound measurements of the abundance/cover/biomass of biota (plants, invertebrates, vertebrates) at both the population and assemblage level. Local constraints (i.e., the absence of birds in highly degraded urban settings or lack of dunes on bluff-backed beaches) and particular issues may require alternatives. Metrics - if selected and applied correctly - provide empirical evidence of environmental condition and change, but often do not reflect deeper environmental values per se. Yet, values remain poorly articulated for many beach systems; this calls for a comprehensive identification of environmental values and the development of targeted programs to conserve these values on sandy shorelines globally.