The introduction of coastal infrastructure as a driver of change in marine environments

Abstract

Summary1. Coastal landscapes are being transformed as a consequence of the increasing demand for urban infrastructure to sustain commercial, residential and tourist activities. A variety of man-made structures, such as breakwaters, jetties and seawalls have thus become ubiquitous features of intertidal and shallow subtidal habitats. This transformation will accelerate in response to the exponential growth of human populations and to global changes, such as sea-level rise and increased frequency of extreme meteorological events (e.g. storms). Here, we provide a critical overview of the major ecological effects of increasing infrastructure to marine habitats, we identify future research directions for advancing our understanding of marine urban ecosystems and we highlight how alternative management options might mitigate their impacts. 2. Urban infrastructure supports different epibiota and associated assemblages and does not function as surrogate of natural rocky habitats. Its introduction in the intertidal zone or in nearshore waters can cause fragmentation and loss of natural habitats. Furthermore, the provision of novel habitat (hard substrata) along sedimentary shores can alter local and regional biodiversity by modifying natural patterns of dispersal of species, or by facilitating the establishment and spread of exotic species. 3. Attempts to use ecological criteria to solve problems of urban infrastructure are promising. Incorporating natural elements of habitat (e.g. wetland vegetation; seagrass) into shoreline stabilization can reduce ecological impacts, without impinging on its efficacy in halting erosion. Likewise, improving the ecological value of artificial structures by adding features of habitat that are generally missing from such structures (e.g. rock-pools) can contribute to mitigation of the detrimental effects of urbanization on biodiversity. Management of anthropogenic disturbances (e.g. maintenance works; harvesting) to artificial habitat is, however, necessary if such attempts are to be successful. 4. Synthesis and applications. Increasing our understanding of the ecological functioning of marine habitats created by urban infrastructure and incorporating ecological criteria into coastal engineering are crucial for preserving biodiversity in the face of the growth of human populations in coastal areas and of forecasted global changes. Achieving this goal will need strong collaboration between engineers, managers and ecologists.

Population genomics of the introduced and cultivated Pacific kelp Undaria pinnatifida: Marinas—not farms—drive regional connectivity and establishment in natural rocky reefs

“…Marinas form dense networks along the coasts and host diverse and abundant NIS taxa (e.g., sessile NIS in marinas of the Celtic Sea, Bishop, Wood, Lévêque, Yunnie, & Viard, 2015; Minchin, 2007b). As such, they are putatively an important source of propagules for the colonization of neighbouring natural habitats (Bulleri & Chapman, 2010; Glasby, Connell, Holloway, & Hewitt, 2007). Similar spillover effects can occur from farmed NIS, as exemplified in the well‐studied Pacific oyster Crassostrea gigas (or Magallana gigas according to the World Register of Marine Species, Costello et al., 2013) in the NE Atlantic (Troost, 2010), or the Atlantic salmon Salmo salar in the NE Pacific (Fisher, Volpe, & Fisher, 2014; Glover et al., 2017).…”

Predation contributes to invasion resistance of benthic communities against the non-indigenous tunicate Ciona intestinalis

“…Although these artificial structures are now recognized as invasion hotspots (Bulleri and Chapman 2010), subsequent invasions to natural habitats are limited (Glasby et al 2007). Assessments of invasion risks around the world also report that more introduced species are found on artificial hard substrata in estuaries and bays than on open coasts (Wasson et al 2005;Ruiz et al 2009).…”

Coastal use accelerated the regional sea-level rise

“…These rises are expected to accelerate through the 21st century (Nicholls and Cazenave, 2010). For instance, geological and tide-gauge data worldwide indicate that mean sea-level rise (SLR) was 1.7 mm/yr between 1961 and 2008 and 3.26 mm/yr between 1993 and 2008, respectively, suggesting that the SLR is accelerating at a global scale (Ablain et al, 2009;Church et al, 2011). However there is high regional variability and higher rates have been recorded.…”

“…Heterogenous patterns in SLR mainly result from non-uniform driving factors (Cabanes et al, 2001). In addition to climatic events (e.g.…”

“…land subsidence due to groundwater depletion, or sediment supply reduction caused by hydraulic engineering) increasingly contribute to relative SLR (Ranasinghe and Stive, 2009;Fiedler and Conrad, 2010). Global coastlines are becoming increasingly managed and engineered as a consequence of urbanization over recent decades, and patterns of coastal use have greatly influenced the extent and intensity of human activities on coastal zones (Bulleri and Chapman, 2010).…”