A new global database of submarine canyon geomorphic metrics has been produced based on the analysis of the SRTM30_PLUS bathymetric grid1. “Large” canyons2 were mapped, including 2,076 shelf-incising and 7,401 blind canyons. Measurements were taken of canyon area, length, depth of incision and percentage area of steep-slope (escarpments), exceeding 5o (methods described in Harris et al., 2014). The 9,477 individual canyons cover a total area of 4,393,650 km2 (i.e. 1.2% of the total ocean area). This database allows estimates to be made of the area of canyons within each country’s EEZ (the area of canyon habitat in each country) as well as the area of canyon that is currently protected within MPAs.
In order to estimate the area of canyons within national EEZs (that is, canyons that it is possible to protect within the jurisdiction of countries, as opposed to those located in areas beyond national jurisdiction, or the “high seas”), global EEZ boundaries were downloaded from the VLIZ database3 and used to calculate the areas of canyons within EEZ’s. In addition, a summary of global MPA boundaries was downloaded from the IUCN and UNEP-WCMC database4 and used to calculate the areas of canyons within MPA’s. It was found that, of the 4,037,764.35 km2 (91.9% of canyon area) of submarine canyon area in EEZs, about 5.0% is protected in MPAs (218,960 km2).
Canyon habitat that is most productive and contains the greatest biodiversity is undoubtedly the steepest (often rocky and cliff-like) section that commonly occurs towards the canyon head, in water depths of <1,000 m, found particularly in the case of shelf-incising canyons just below the shelf break. The steepest areas of seafloor, comprising a category termed “escarpments” (a seafloor gradient exceeding 5o over an area >100 km2), were also mapped by Harris et al. (2014) in their global assessment of seafloor geomorphic features. Overall it is found that 820,960 km2 of canyon area (i.e. about 18.7%) is escarpment. When we ask how much of that area is found inside existing MPAs we see that only 8,760 km2 of canyon area protected in MPA’s is escarpment located above 1,000 m. That is to say, of the most potentially ecologically valuable area of canyons, only about 0.22% is protected within MPAs.
This analysis demonstrates that, on a global basis, the design of MPA’s is biased against selection of canyon habitats most likely to be the most productive and biologically diverse. In fact, most MPA’s that overlap with canyons (and presumably are intended to protect them) protect those parts of canyon habitats that are likely to be less productive and contain less biodiversity.
1 Harris, P.T., MacMillan-Lawler, M., Rupp, J., Baker, E.K., 2014. Geomorphology of the oceans. Marine Geology 352, 4-24.
2 Harris, P.T., Whiteway, T., 2011. Global distribution of large submarine canyons: geomorphic differences between active and passive continental margins. Marine Geology 285, 69–86.
3 VLIZ. Maritime Boundaries Geodatabase, version 7. Available online at http://www.marineregions.org/.
4 IUCN and UNEP-WCMC, The World Database on Protected Areas (WDPA). Cambridge, UK: UNEP- WCMC. Available online at: www.protectedplanet.net.