[Coral-List] Are mesophotic coral ecosystems distinct communities and can they serve as refugia?

[Marjorie L. Reaka]

We are pleased to announce the publication of our article “Are mesophotic
coral ecosystems distinct communities and can they serve as refugia for
shallow reefs?” online in *Coral Reefs.  *The online citation is:  Semmler,
Hoot and Reaka, Coral Reefs, 2016, DOI 10.1007/s00338-016-1530-0.  The
full-text article is now legally and publicly available for viewing by
anyone, and can be downloaded and printed by those with personal or
institutional subscriptions at http://rdcu.be/oa4Z.   In addition, the
article is fully accessible at ‘Online First’:
http://link.springer.com/article/10.1007/s00338-106-1530-0 to all users at
libraries and institutions that have a Springerlink license.

*Abstract*

We analyzed an extensive dataset of over 9000 benthic and suprabenthic
species found throughout the Gulf of Mexico (GoMx) to assess whether
mesophotic coral ecosystems represent distinct assemblages and evaluate
their potential to serve as refugia for shallow reef communities. We
assessed community structure of the overall benthic community from 0 to
300 m via non-metric multidimensional scaling (NMDS) of species presence
across depth bands. We used the Jaccard index of similarity to calculate
the proportion of shared species between adjacent depth bands, measure
species turnover with depth, and assess taxonomic overlap between shallow
reefs versus progressively deeper depth bands. NMDS ordinations showed that
the traditionally defined mesophotic range (30–150 m) as a whole is not a
distinct community. In contrast, taxonomically distinct communities,
determined by hierarchical clustering, were found at 0–70, 60–120, 110–200,
and 190–300 m. Clustering highlighted an important separation in the
benthic community at ~60 m, which was especially important for
actinopterygian fishes. Species turnover between adjacent depths decreased
with depth for all taxa combined and individual taxa, with peaks at ~60,
90–120, and 190–200 m. Fishes showed lower turnover from shallow to upper
mesophotic depths (0–50 m) than all taxa combined, a substantial peak at
60 m, followed by a precipitous and continued decline in turnover
thereafter. Taxonomic overlap between shallow (0–20 m) and progressively
deeper zones declined steadily with depth in all taxa and individual taxa,
suggesting that mid- and lower mesophotic habitats have less (but not
inconsequential) potential to serve as refugia (60–150 m, 15–25% overlap
with shallow habitats) than upper mesophotic zones (30–60 m, 30–45% overlap
with shallow habitats) for all taxa combined. We conclude that the
traditional mesophotic zone is home to three ecological communities in the
GoMx, one that is confluent with shallow reefs, a distinct mesophotic
assemblage spanning 60–120 m, and a third that extends onto the outer
continental shelf.

*Keywords*

Mesophotic coral ecosystems, Gulf of Mexico, Depth refugia, Coral reef
biodiversity, Benthic community structure, Deep reef refugia hypothesis



Dr. Marjorie L. Reaka
Professor
Department of Biology
The University of Maryland
College Park, Maryland 20742