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.

Golden opportunities: a horizon scan to expand sandy beach ecology

Robust ecological paradigms and theories should, ideally, hold across several ecosystems. Yet, limited testing of generalities has occurred in some habitats despite these habitats offering unique features to make them good model systems for experiments. We contend this is the case for the ocean-exposed sandy beaches. Beaches have several distinctive traits, including extreme malleability of habitats, strong environmental control of biota, intense cross-boundary exchanges, and food webs highly reliant on imported subsidies. Here we sketch broad topical themes and theoretical concepts of general ecology that are particularly well-suited for ecological studies on sandy shores. These span a broad range: the historical legacies and species traits that determine community assemblages; food-web architectures; novel ecosystems; landscape and spatial ecology and animal movements; invasive species dynamics; ecology of disturbances; ecological thresholds and ecosystem resilience; and habitat restoration and recovery. Collectively, these concepts have the potential to shape the outlook for beach ecology and they should also encourage marine ecologists to embrace, via cross-disciplinary ecological research, exposed sandy beach systems that link the oceans with the land.