The structures, functions, and services provided by coral reef ecosystems are deteriorating worldwide. However, not all coral reefs are affected the same way, with some showing signs of resistance and/or recovery from disturbances. Understanding the drivers and feedbacks that contribute to shifts in community structure is valuable to support resilience-based management. In this study, key community variables that influence the resilience of coral reef ecosystems were examined in 64 sites of the Mesoamerican Reef (MAR) monitored in both 2006 and 2016, as part of the Healthy Reef Initiative (HRI), using the Atlantic and Gulf Rapid Reef Assessment (AGRRA) monitoring protocol. Based on benthic cover thresholds, sites were classified into three different states: coral state (CS) with >10% live coral and <5% fleshy macroalgae; stressed coral state (SCS) with >10% live coral and >5% fleshy macroalgae and; depauperate coral state (DCS) <10% live coral. The associations between site states and the density of different fish functional groups were analyzed to determine their effects on coral reef resilience. The results highlight that territorial herbivores (algal-gardening damselfish) may play a key role in maintaining feedbacks toward macroalgae-stressed states. This supports the recommendation of reinforcing Marine Replenishment Zones (MRZ) in order to promote healthy populations of resident predator fish (like groupers and snappers), which could potentially regulate algalgardening damselfish populations and diminish negative cascade effects on coral reefs. Collaborative and resilience-based management will continue to be promoted by the HRI partners, supporting the establishment of additional MRZs along with ongoing efforts to directly protect herbivorous fish (surgeonfish and parrotfish) and to improve water quality, through better wastewater treatment, watershed management, and coastal development plans, with the purpose of continuing to build coral reef resilience in the MAR.
The genus Siderastrea exhibits high levels of morphological variability. Some of its species share similar morphological characteristics with congeners, making their identification difficult. Siderastrea stellata has been reported as an intermediary of S. siderea and S. radians in the Brazilian reef ecosystem. In an earlier study conducted in Mexico, we detected Siderastrea colonies with morphological features that were not consistent with some siderastreid species previously reported in the Gulf of Mexico. Thus, we performed a combined morphological and molecular analysis to identify Siderastrea species boundaries from the Gulf of Mexico. Some colonies presented high morphologic variability, with characteristics that corresponded to Siderastrea stellata. Molecular analysis, using the nuclear ITS and ITS2 region, corroborated the morphological results, revealing low genetic variability between S. radians and S. stellata. Since the ITS sequences did not distinguish between Siderastrea species, we used the ITS2 region to differentiate S. stellata from S. radians. This is the first report of Siderastrea stellata and its variability in the Gulf of Mexico that is supported by morphological and molecular analyses.
Mangroves are coastal ecosystems recognized by their capacity to store organic carbon, even more so than tropical and temperate forests. Therefore, they contribute to the local adaptation and mitigation of climate change. Mangroves have different characteristics that origin mangrove ecological types. There are few studies on mangroves in karstic environments, where there is spatial heterogeneity associated with topography-hydroperiod-nutrient interactions. To estimate the total carbon stock in mangroves and determine whether carbon storage differs according to the mangrove ecological type in a natural protected area in the karstic region of the Yucatan Peninsula (northern Ria Celestun Biosphere Reserve), a study was conducted following the recommendations of the IPCC Good Practice Supplement for wetlands and standardized methods used in mangroves studies around the world. According to the results, mangroves associated with springs, called “petenes” or hammock mangroves, showed higher total ecosystem carbon stock (683.7 Mg C ha–1) than fringe, basin, and dwarf mangrove ecological types (429, 385, and 214 Mg C ha–1, respectively). Above- and below-ground carbon stock was different between mangrove ecological types. Carbon stock variation was related to environmental hydrology variables (flooding level, interstitial water salinity, and redox potential). According to the δ13C analysis from the surface soil, carbon accumulated in mangrove sediments in a karstic scenario is mainly autochthonous and predominantly originates from mangrove leaves. Carbon stock in mangroves in the northern Ria Celestun Biosphere Reserve was 9.7 Tg C, of which 40.7% comes from dwarf mangroves due to their extension. These results could be used as a tool for developing specific management actions at regional or local scales for mangrove restoration and conservation.
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