Ocean Sprawl

Ocean sprawl is the proliferation of engineered artificial structures in coastal and offshore marine environments. These include ship hulls; infrastructure associated with land reclamation and urbanization (e.g., seawalls, bridges, floating docks); fisheries (artificial reefs, aquaculture installations); coastal defence structures (e.g., breakwaters, groynes); resource extraction (oil and gas rigs, renewable energy devices); and shipwrecks. Only fixed permanent and semipermanent structures are considered here and ship hulls are not included. Single structures can scale up with dramatic consequences for the local environment. Extreme examples of this include: the “New Great Wall” of China—seawalls enclosing coastal wetlands covering 60 percent of the total length of the Chinese coastline; “The World”, Dubai—an archipelago of over three hundred artificial islands constructed in the shape of a world map; and the “Steel Archipelago,” which describes more than four thousand oil and gas structures in the Gulf of Mexico. The placement of these fixed artificial structures modifies the local physical and chemical environment with cascading impacts on the composition, functioning, and service provision of surrounding species, habitats, and ecosystems. These structures also provide novel habitat which can offer surface for attachment, food, and protection for myriad marine species. They can act as fish aggregating devices, attracting fishing and other human activities. These structures may also have wide-reaching impacts through acting as barriers or conduits to ecological connectivity—the movement of organisms, materials, and energy between habitat units within seascapes. An improved understanding of the biological communities associated with artificial structures, coupled with the global drive for sustainable development, is driving an explosion of research into the design of multifunctional structures with built-in secondary ecological or socioeconomic benefits. Results to date have been promising but greater integration of the fields of ecology, engineering, and social sciences is necessary to better connect theory and practice in this emerging discipline.

Coastal road mortality of land crab during spawning migration

Land crabs are threatened by ocean sprawl even though they act as keystone consumers in coastal forest. Female land crabs must migrate to the sea annually to release larvae. However, they face the risk of road mortality which reduces ecological connectivity. We investigated the spawning migration rhythm and the roadkill of land crab. Migrating crabs and roadkilled crabs were recorded on coastal roads in South Korea from July 28 to August 27 in 2018. Female land crabs mainly released zoeae during spring tide. The number of roadkilled crabs also synchronized with migration peak. A majority (95%) of 739 roadkilled carcasses were female crabs. As a result, the female crabs accounted only 29.6% of the population which can lead to a population decline. The roadkill density was the highest in a residential area without cement guardrails. These results suggest the mitigation actions for land crab roadkill. Among them, prohibiting vehicular traffic between sunset and midnight during spring tides in the breeding season should increase the viability of the population.

Design catalogue for eco-engineering of coastal artificial structures: a multifunctional approach for stakeholders and end-users

Coastal urbanisation, energy extraction, food production, shipping and transportation have led to the global proliferation of artificial structures within the coastal and marine environments (sensu “ocean sprawl”), with subsequent loss of natural habitats and biodiversity. To mitigate and compensate impacts of ocean sprawl, the practice of eco-engineering of artificial structures has been developed over the past decade. Eco-engineering aims to create sustainable ecosystems that integrate human society with the natural environment for the benefit of both. The science of eco-engineering has grown markedly, yet synthesis of research into a user-friendly and practitioner-focused format is lacking. Feedback from stakeholders has repeatedly stated that a “photo user guide” or “manual” covering the range of eco-engineering options available for artificial structures would be beneficial. However, a detailed and structured “user guide” for eco-engineering in coastal and marine environments is not yet possible; therefore we present an accessible review and catalogue of trialled eco-engineering options and a summary of guidance for a range of different structures tailored for stakeholders and end-users as the first step towards a structured manual. This work can thus serve as a potential template for future eco-engineering guides. Here we provide suggestions for potential eco-engineering designs to enhance biodiversity and ecosystem functioning and services of coastal artificial structures with the following structures covered: (1) rock revetment, breakwaters and groynes composed of armour stones or concrete units; (2) vertical and sloping seawalls; (3) over-water structures (i.e., piers) and associated support structures; and (4) tidal river walls.