Multi-Year Viability of a Reef Coral Population Living on Mangrove Roots Suggests an Important Role for Mangroves in the Broader Habitat Mosaic of Corals

Abstract

Half of coral species that occur on Caribbean reefs have also been reported living in mangroves. Given the vulnerability of corals living on reefs to environmental change, populations of the same species living in mangroves may prove critical to longterm survival of these coral species and the resilience of nearby reefs. To date, few studies have addressed the health and viability of mangrove coral populations, which is necessary if we are to understand their role in the broader meta-community.Here we present the first longitudinal study of the distribution, survival, growth, and recruitment of a mangrove coral population over multiple years. From 2014 to 2018, we fully censused a population of Porites divaricata along 640 meters of a mangrovelined channel at Calabash Caye, Belize, and beginning in 2015, we tagged individual colonies for longitudinal monitoring. Year-to-year survivorship averaged 66.6% (±3.9 SE), and of the surviving colonies, on average, 72.7% (±2.5 SE) experienced net growth. The number of colonies, their spatial distribution, and population size-structure were essentially unchanged, except for an unusually high loss of larger colonies from 2016 to 2017, possibly the result of a local disturbance. However, each annual census revealed substantial turnover. For example, from 2016 to 2017, the loss or death of 72 colonies was offset by the addition of 89 recruits. Integral projection models (IPM) for two consecutive one-year intervals implicated recruitment and the persistence of large colonies as having the largest impacts on population growth. This 5-year study suggests that the P. divaricata population in the mangroves is viable, but may be routinely impacted by disturbances that cause the mortality of larger colonies. As many corals occur across a mosaic of habitat types, understanding the population dynamics and life-history variability of corals across habitats, and quantifying genetic exchange between habitats, will be critical to forecasting the fate of individual coral species and to maximizing the efficacy of coral restoration efforts.

Identifying mangrove-coral habitats in the Florida Keys

“…3 and 5 ). However, unlike Calabash Caye ( Scavo Lord et al, 2020 ), we did sometimes observe coral colonies attached on the bottom substrate of these mangrove channels. In cases where there was carbonate substratum, such as the bedrock walls of 430 Sugarloaf Key Merged Canal, we observed F. fragum and S. radians in addition to Porites porites morphs.…”

“…The prop-root-coral habitats identified in the Florida Keys during this project were most similar to those recently described in Belize (Bengtsson et al, 2019;Scavo Lord et al, 2020) and Cuba (Hernández-Fernández, 2015). Porites divaricata is consistently the numerically dominant mangrove-coral observed in all three regions indicating this coral is particularly capable of adapting to mangrove environments (Bengtsson et al, 2019).…”

“…The Tarpon Canal coral (P4) and the three prop-root corals in the Upper Keys (P1-P3) were all on the north side of channels. Calabash Caye, Belize also had higher numbers of prop-root-coral colonies on the northern side of the primary channel site (Scavo Lord et al, 2020). In 430 Sugarloaf Key Merged Canal we found corals growing on prop roots on both the eastern (P7) and western (P8-P15) sides of the channel.…”

“…As in previous studies, it was fundamental to distinguish between mangrove-coral habitat types in this study: (A) corals growing directly on prop roots ( Bengtsson et al, 2019 ; Hernández-Fernández, 2015 ; Scavo Lord et al, 2020 ; Yates et al, 2014 ), (B) corals growing on benthic substrates under the mangrove canopy (including what we refer to in this study as channel-coral habitats) ( Rogers, 2017 ; Yates et al, 2014 ), and (C) corals growing in mangrove lagoons but not under the canopy ( Camp et al, 2019 , 2017 ). In our study, we found prop-root and channel-coral habitats to have different coral species composition and in the Upper Keys to have slight but significant differences in salinity and dissolved oxygen ( Tables 1 and 2 ; Fig.…”

“…Further, ecological surveys of Florida mangroves from the 1930s to 1980s made no mention of the presence of corals when detailing associated fauna ( Davis, 1940 ; Odum, McIvor & Smith, 1982 ). However, a number of recent studies have identified several locations around the world with corals growing on or near mangrove prop roots ( Bengtsson et al, 2019 ; Camp et al, 2019 , 2017 ; Hernández-Fernández, 2015 ; Macintyre et al, 2000 ; Rogers, 2009 , 2017 ; Scavo Lord et al, 2020 ). In some of these habitats, mangroves are sheltering corals even in the face of extreme variability in pH, dissolved oxygen, and temperature, resulting in lower incidences of bleaching and high rates of recovery ( Camp et al, 2019 , 2017 ; Yates et al, 2014 ).…”