Abstract
There is limited information on the intra-annual variability of mesophotic coral ecosystems (MCEs), worldwide. The benthic communities, measured as % cover, of two geomorphologically different mesophotic sites (El Hoyo and Hole-in-the-Wall) were examined during 2009–2010 in southwest Puerto Rico. Depths sampled were 50 and 70 m. At each site/depth combination, two permanent transects, measuring 10-m long by 40-cm wide, were surveyed by successive photoquadrants, 0.24 m2 in area. Scleractinian corals, octocorals, macroalgae, crustose coralline algae (CCA), sponges and unconsolidated sediment were the main components along the transects. Significant community differences were observed both among sites and among depths. Differences among sites were greater at 50 m than at 70 m. The El Hoyo site at 50 m was the most divergent, and this was due to a lower coral and sponge cover and a higher algal cover (Amphiroa spp., Peyssonnelia iridescens, turf) relative to the other site/depth combinations. As a consequence, the differences in community structure with depth were larger at El Hoyo than at Hole-in-the-Wall. The communities at 70 m were distinguished from those at 50 m by the greater proportion of the corals Agaricia undata, Madracis pharensis and CCA, and a reduced cover of the cyanobacterium Schizothrix. Temporal variation in the benthic assemblages was documented throughout the year. For both mesophotic sites, the magnitude of change at 50 m was significantly greater than at 70 m. For both depths, the magnitude of change at El Hoyo was significantly greater than at Hole-in-the-Wall. All assemblages experienced almost the same temporal patterns, despite the differences in species composition across sites and depths. Changes in temporal patterns are driven by an increase in the percent cover of the macroalgae Dictyota spp., and a decrease in the percent cover of non-colonized substrata (sand, pavement or rubble). Relatively rapid, intra-annual changes are dictated by the negative correlation between cyclic Dictyota spp. cover and open substrata cover. Other observed mechanisms for rapid community changes in the photoquadrants were diseases and collapses of substrata along with their associated fauna indicating that small-scale disturbance processes may play an important role within MCEs.
Highlights
Mesophotic coral ecosystems (MCEs) occur in tropical waters where light levels are reduced but where benthic photosynthesis is still important for community development
With shallow reefs under stress (Hoegh-Guldberg, 1999; Gardner et al, 2003; Carpenter et al, 2008; Jackson et al, 2014), it was initially thought that MCEs may act as a refuge for some species (Bongaerts et al, 2010), but more recent work suggests that role, if verified, is limited only to upper MCEs (Rocha et al, 2018; Slattery et al, 2018)
While there has been a dramatic increase in our knowledge of MCEs these questions largely remain unresolved
Summary
Mesophotic coral ecosystems (MCEs) occur in tropical waters where light levels are reduced but where benthic photosynthesis is still important for community development. They were initially defined operationally to start at a depth of 30 m, that was based more on the technical limits of conventional scuba diving, and to extend to approximately 150 m (Hinderstein et al, 2010) depending on the degree of light penetration. While there has been a dramatic increase in our knowledge of MCEs (see Hinderstein et al, 2010; Loya et al, 2016, 2019) these questions largely remain unresolved
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
