Abstract
Extensive development and construction in marine and coastal systems is driving a phenomenon known as “ocean sprawl”. Ocean sprawl removes or transforms marine habitats through the addition of artificial structures and some of the most significant impacts are occurring in sedimentary environments. Marine sediments have substantial social, ecological, and economic value, as they are rich in biodiversity, crucial to fisheries productivity, and major sites of nutrient transformation. Yet the impact of ocean sprawl on sedimentary environments has largely been ignored. Here we review current knowledge of the impacts to sedimentary ecosystems arising from artificial structures.Artificial structures alter the composition and abundance of a wide variety of sediment-dependent taxa, including microbes, invertebrates, and benthic-feeding fishes. The effects vary by structure design and configuration, as well as the physical, chemical, and biological characteristics of the environment in which structures are placed. The mechanisms driving effects from artificial structures include placement loss, habitat degradation, modification of sound and light conditions, hydrodynamic changes, organic enrichment and material fluxes, contamination, and altered biotic interactions. Most studies have inferred mechanism based on descriptive work, comparing biological and physical processes at various distances from structures. Further experimental studies are needed to identify the relative importance of multiple mechanisms and to demonstrate causal relationships. Additionally, past studies have focused on impacts at a relatively small scale, and independently of other development that is occurring. There is need to quantify large-scale and cumulative effects on sedimentary ecosystems as artificial structures proliferate. We highlight the importance for comprehensive monitoring using robust survey designs and outline research strategies needed to understand, value, and protect marine sedimentary ecosystems in the face of a rapidly changing environment.
Highlights
The intensifying development of urban foreshores, coastlines, and offshore areas is driving a phenomenon commonly referred to as “ocean sprawl” (Duarte et al, 2012)
We focus primarily on the effects of artificial structures on un-vegetated sediments, as these habitats have been underrepresented in the literature to date, but utilize examples from vegetated sediments where relevant and informative for sedimentary ecosystems more broadly
These designs provide the advantage of controlling for temporal changes that are confounded with the introduction of an artificial structure, as well as site-specific differences that are unrelated to structure introduction
Summary
The intensifying development of urban foreshores, coastlines, and offshore areas is driving a phenomenon commonly referred to as “ocean sprawl” (Duarte et al, 2012). Meiofaunal, macrofaunal, and macrophytic assemblages (e.g. saltmarsh, mangrove, seagrass) live on and within the sediments (Adam, 1990; Coull, 1988; Lugo and Snedaker, 1974; Orth et al, 1984; Paerl and Pinckney, 1996; Snelgrove, 1998) and provide prey resources for fishes, shorebirds, and large vertebrates, such as gray whales (Eschrichtius robustus), dugongs (Dugong dugon), and green sea turtles (Chelonia mydas) (Carruthers et al, 2002; Gray and Elliott, 2009; Lopez and Levinton, 1987; Weitkamp et al, 1992) These assemblages underpin many ecosystem services of fundamental importance to humanity, including fisheries productivity, biogeochemical cycling, remediation of contaminants, and shoreline stabilization (Bolam et al, 2002; Snelgrove, 1997, 1999; Snelgrove et al, 2014; Weslawski et al, 2004). We make the case that the proliferation of artificial structures is of vital concern for sedimentary ecosystems and highlight knowledge gaps and future research that will be needed in order to protect ecosystem services provided by marine sedimentary habitats in the face of ocean and climate change
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