Functional consequences of the long-term decline of reef-building corals in the Caribbean: evidence of across-reef functional convergence

Abstract

Functional integrity on coral reefs is strongly dependent upon coral cover and coral carbonate production rate being sufficient to maintain three-dimensional reef structures. Increasing environmental and anthropogenic pressures in recent decades have reduced the cover of key reef-building species, producing a shift towards the relative dominance of more stress-tolerant taxa and leading to a reduction in the physical functional integrity. Understanding how changes in coral community composition influence the potential of reefs to maintain their physical reef functioning is a priority for their conservation and management. Here, we evaluate how coral communities have changed in the northern sector of the Mexican Caribbean between 1985 and 2016, and the implications for the maintenance of physical reef functions in the back- and fore-reef zones. We used the cover of coral species to explore changes in four morpho-functional groups, coral community composition, coral community calcification, the reef functional index and the reef carbonate budget. Over a period of 31 years, ecological homogenization occurred between the two reef zones mostly due to a reduction in the cover of framework-building branching (Acropora spp.) and foliose-digitiform (Porites porites and Agaricia tenuifolia) coral species in the back-reef, and a relative increase in non-framework species in the fore-reef (Agaricia agaricites and Porites astreoides). This resulted in a significant decrease in the physical functionality of the back-reef zone. At present, both reef zones have negative carbonate budgets, and thus limited capacity to sustain reef accretion, compromising the existing reef structure and its future capacity to provide habitat and environmental services.

The role of geomorphic zonation in long-term changes in coral-community structure on a Caribbean fringing reef

“…1B ). For example, Estrada-Saldívar et al (2019) recently reported that similar ecological changes led to functional convergence and homogenization between back-reef and fore-reef sites along the north-east Yucatan, including the one at Punta Maroma. However they considered the RF and CG zones as a single “fore-reef” zone.…”

“… (A) Location of Punta Maroma; (B) reef zonation and geomorphology showing: slope breaks and geomorphological zones (following Blanchon et al, 2017 ) and ecological seascape zones (following Jordan et al, 1981 ; Estrada-Saldívar et al, 2019 ); (C) view of the reef-front zone (or fore reef) at ~5 m; (D) view of the rock-terrace zone (or fore reef) at ~10 m; (E) view of the mid-shelf break (or fore reef) between 10 and 15 m. …”

“…Other environmental data, including depth, spatial position and distance to the mid-shelf edge, were also recorded. Scleractinian coral species were classified based on their morphology and life history following Estrada-Saldívar et al (2019) . We informed the authorities of Comision Nacional de Areas Naturales Protegidas (CONAMP) prior to conducting fieldwork as it is a requirement in order to carry out activities within MPA.…”

“…With the demise and deterioration of Caribbean reefs during the last 40 years, and the decimation of keystone Acroporids in particular ( Gardner et al, 2005 ; Jackson et al, 2014 ), this complex ecological seascape is radically changing ( Perry & Alvarez-Filip, 2019 ). Biodiversity loss and biotic homogenization are not only compromising the ecological functioning of reefs ( Olden & Poff, 2003 ; Burman, Aronson & Van Woesik, 2012 ; Alvarez-Filip et al, 2013 ; Elliff & Silva, 2017 ) and their ability to provide local and regional services ( Alvarez-Filip et al, 2009 , 2011 ), but are predicted to reduce their potential for long-term accretion ( Perry et al, 2013 ; Estrada-Saldívar et al, 2019 ). Assessing the accuracy and validity of these accretion predictions, however, is problematic for several reasons ( Lange, Perry & Alvarez-Filip, 2020 ).…”

Peer Review #2 of "The role of geomorphic zonation in long-term changes in coral-community structure on a Caribbean fringing reef (v0.1)"

“…With the demise and deterioration of Caribbean reefs during the last 40 years, and the decimation of keystone Acroporids in particular (Gardner et al, 2005;Jackson et al, 2014), this complex ecological seascape is radically changing (Perry and Alvarez-Filip, 2019). Biodiversity loss and biotic homogenization are not only compromising the ecological functioning of reefs (Olden and Poff, 2003;Burman et al, 2012;Alvarez-Filip et al, 2013;Elliff and Silva, 2017) and their ability to provide local and regional services (Alvarez-Filip et al, 2009, but are predicted to reduce their potential for long-term accretion (Perry et al, 2013;Estrada-Saldívar et al, 2019). Assessing the accuracy and validity of these accretion predictions, however, is problematic for several reasons (Lange et al, 2020).…”