Spatially congruent sites of importance for global shark and ray biodiversity

[22]. Our study is one of the first to demonstrate a relatively high degree of spatial congruence between hotspots of ED species richness and total species richness of all shark and ray species, as compared to the overlap of endemic species and total species. The areas of spatial congruence for total and threatened shark and ray species cluster around coastal waters, while endemic species are primarily found at the convergent boundaries of tropical and temperate ecosystems. These warm reef environments at the convergent boundaries have been known to serve as hotspots for species evolution due to their high pro- ductivity and habitat complexity [52,53]. In most cases, these areas of overlap are also found within the bounds of a country’s exclusive economic zone (EEZ), which have also been flagged as hotspots of functional diversity in sharks [5]. The species richness measures examined in this paper only represent a small aspect of biodiversity and do not take into account other mea- sures, such as functional diversity. Functional diversity is known to be crucial in maintaining the structure and function of marine ecosystems [54] and would likely also yield similarly incongruent hotspots. Ultimately, a future study could expand on our findings by exploring the extent of spatial congruency between other biodiversity metrics, such as functional diver- sity in all sharks and rays. Studies that consider different levels of spatial resolutions have considered only one level of resolution that are either smaller (e.g. � 1˚) [5,23,55] or larger (e.g. � 8˚) [4] than those

assessed in our study, missing the potential differences that could occur between the two. Our findings demonstrate that there are differences between these two levels of spatial resolution. We found that a reduction in resolution (i.e. larger sampling units, such as grid cells here) influenced global patterns of species richness hotspots for all sharks and rays. For example, at a coarse resolution (here, 8˚ cells), if an individual species’ range slightly crossed the boundary of an 8˚ grid cell, its distribution would now be considered to encompass the entirety of that 8˚ cell as opposed to its true smaller fraction. The coarsening of hotspots and shifting of congru- ency locations resulting from coarser resolutions causes congruency locations to disappear where they were otherwise present at finer resolutions (i.e. Brazil and Uruguay; Fig 6). Previ- ous work on riparian weeds also found that coarser resolutions were unable to model fine- scale distributions successfully and were also poor predictors of national species’ distributions [56]. Overall, our results support the well-known finding that changes in spatial resolution can influence results in spatial analyses. Different areas of congruency identified at various spatial resolutions can make it difficult for conservation management to direct focus to any particular area but demonstrates the importance of explicitly considering spatial resolution when deter- mining important areas to further investigate for conservation priority. Furthermore, there are

now numerous studies that examine how to integrate conservation planning across multiple levels of resolution [57–59]. It is important to note the caveats of the distributional dataset used for this study. The IUCN species distribution map database was created from peer-reviewed, expert-generated maps around known locations of species distributions [25]. Experts from the IUCN Shark Spe- cialist Group (SSG) created a shapefile of the geographic distribution for each chondrichthyan species based on the original maps provided to the Food and Agriculture Organisation of the United Nations, using the standard mapping protocol for marine species devised by the IUCN Global Marne Species Assessment team (https://sites.wp.odu.edu/GMSA/). The maps show the Extent of Occurrence of the species cut to one of several standardized basemaps depending on the ecology of the species (i.e. coastal and continental shelf, pelagic, and deepwater). The original maps were updated, corrected, or verified by experts at the Red List workshops or by out-of-session assessors and SSG staff [25]. These maps are likely to contain commission rather than omission errors such that a species is shown to be present in an area when in fact it is not [60]. Commission errors can be problematic for hotspot identification because they risk PLOS ONE Spatially congruent sites of importance for global shark and ray biodiversity PLOS ONE | https://doi.org/10.1371/journal.pone.0235559 July 6, 2020 12 / 19