Using bioindicator species to characterize distinct mangrove habitats on Turneffe Atoll, Belize

Abstract

Mangroves are critical to the biodiversity and productivity of tropical ecosystems, and for this reason, they are part of the foundation for Belize’s Blue Economy. Despite their ecological and economic significance, mangroves are among the most threatened marine habitats in the world. Turneffe Atoll, home to the largest and newest marine reserve in Belize, is unique among the four atolls located along the Mesoamerican barrier reef in that it is dominated by mangroves. In an effort to investigate the role of Turneffe’s mangroves in supporting marine biodiversity, we conducted longitudinal surveys of the epibionts (marine species inhabiting the submerged mangrove roots). From 2016-2017, in two low-flow ponds and two high-flow channels, we scored the presence or absence of 28 indicator species on 182 roots (a total of 5096 observations). We observed significant differences between sites in the proportion of roots occupied by several indicator species, and we documented substantial stability from year-to-year in the presence of specific indicators. We also conducted exhaustive surveys of mangrove corals, revealing that particular mangroves on Turneffe appear to be important habitat for corals. Over a 4-year period, one population of the thin finger coral (Porites divaricata) occupying a few hundred meters of shoreline at Calabash Caye exhibited gradual population growth over multiple years. While all mangrove-lined shores may appear similar to observers on passing boats, beneath the water, mangrove communities are diverse, and this diversity is critical to their wider role in the health of coastal ecosystems. The study described here revealed that mangrove epibiont diversity on Turneffe Atoll varies over fine spatial scale in a manner that may be predictable, e.g., some mangrove species are generalists, while others are specialists found in selective mangrove habitats. Of course, “natural” patterns of species distribution are a reflection of habitat quality, which is directly impacted by human activities. Continuing longitudinal studies of biodiversity in these understudied habitats will be essential to monitoring the health of Turneffe Atoll and the health of Belize’s coastal ecosystems generally.