Most news is bad for sea life these days, trapped between global warming, plastics, and overfishing, but a rare glimmer of hope comes from an unexpected place. Structures we are building in the oceans, even to drill for oil, turn out to be surprisingly well suited to supporting endangered ecosystems, not just on an individual basis, but in the ways we tend to distribute them too.
Anything we build in the ocean quickly gets colonized by marine creatures. Sometimes this undermines the reason why the object was placed there in the first place, for example by blocking intake valves. At other times there are great benefits. Sunken ships make such good platforms for tropical coral reefs that tourist venues compete to have old vessels scuttled in suitable conditions to attract scuba divers.
Dr Lea-Anne Henry of the University of Edinburgh wanted to look beyond the individual effects of such structures, and see whether they combine to form highly connected networks of the sort that make ecosystems resilient.
In Scientific Reports, Henry describes modeling she did of the dispersal of Lophelia pertusa larvae between oil and gas installations in the North Sea, taking into account ocean currents, the larvae's swimming capacities, and video evidence of the depths at which corals have colonized specific rigs. She notes the region has more than 1,500 oil and gas installations, many colonized by protected species, which in turn become food for others.
Henry found the distribution of the major structures favors larvae dispersal between rigs, wrecks, and pipelines over large distances. This prevents populations from becoming inbred, while also offering resilience should disaster strike a particular sector. Many rigs are well suited to replenishing natural habitats depleted by decades of overfishing.
The corals Henry studied are relatively slow-growing cold-water species, not the gorgeous tropical varieties that make homes for such a large proportion of the world's marine biodiversity. Many cold-water corals are currently most common at great depths, but are expected to be more affected by ocean acidification there, making shallow-water structures potential sites of refuge. On the other hand, similar modeling of marine buildings in temperate waters might well show that these could become habitats for tropical corals driven out of their normal range by bleaching events.
On the downside, oil and gas rigs not only induce the climate change causing many of these problems in the first place, but often leak pollution that damages the capacity of sensitive species to make a home there. The rapid growth of North Sea offshore wind farms, however, may provide suitable networked habitats without the accompanying drawbacks, but modeling has yet to be done as to whether these sites are also suitably distributed.
