Abstract
Biogenic reefs form biodiversity hotspots and are key components of marine ecosystems, making them priority habitats for nature conservation. However, the conservation status of biogenic reefs generally depends on their size and stability. Dynamic, patchy reefs may therefore be excluded from protection. Here, we studied epibenthos and epifauna density, richness, and community composition of patchy, dynamic Sabellaria spinulosa (ross worm) reefs in the North Sea. This study was conducted by comparing boxcore (endobenthos) and video transect (epifauna) data from two research campaigns in 2017 and 2019 to the Brown Bank area on the Dutch Continental Shelf, where S. spinulosa reefs were first discovered in 2017. The Brown Bank area is characterized by dynamic, migratory bedforms at multiple scales which potentially affect biogenic reef stability. We showed that S. spinulosa habitats had a patchy distribution and alternated with habitats comprised of plain sand. Average S. spinulosa habitat patch size was 5.57 ± 0.99 m and 3.94 ± 0.22 m in 2017 and 2019, respectively (mean ± SE), which especially in 2019 closely resembled the small-scale megaripple bedforms. Contrary to the endobenthos communities that were unaffected by S. spinulosa, epifauna density and species richness were at least two times higher in S. spinulosa habitats compared to sandy habitats, resulting in different community compositions between the two habitat types. We showed that S. spinulosa persisted in the area for almost 2 years. Although the stability of individual patches remained unclear, we demonstrated that even patchy biogenic reefs may promote density and local biodiversity of mobile, epibenthic species, very likely as a result of increased habitat heterogeneity provided by reef habitat patches. This indicates that patchy biogenic reefs that occur in dynamic environments may also have high ecological value and their conservation status should be (re)considered to ensure their protection.
Highlights
Biogenic reefs are physical benthic structures formed by ecosystem engineering species
We here studied the effects of S. spinulosa habitat patches on associated endo- and epibenthic communities in the dynamic Brown Bank area in the North Sea
We showed that within this area, S. spinulosa reef habitats have a highly patchy distribution that may be linked to seafloor megaripple morphology
Summary
Biogenic reefs are physical benthic structures formed by ecosystem engineering species. Biogenic reefs modify their surroundings to such an extent that resource availability for other species is positively altered (Jones et al, 1994) They engineer a new habitat that can provide suitable settlement substrate (Coolen et al, 2015), increase refuge possibilities (Ryer et al, 2004) and food sources (van der Zee et al, 2012) for associated species, and decrease turbidity due to attenuation of waves and currents (Lenihan, 1999; van der Heide et al, 2011). The more stable reefs with persistent associated communities are generally favored for conservation (Hendrick and Foster-Smith, 2006)
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