We conducted visual fish surveys in coexisting mangrove-coral (CMC) habitats in Panama to analyze the effect of coral presence in mangrove habitats on the fish assemblage. Our study revealed that CMC habitats harbor distinct fish assemblages compared to mangrove habitats without coral, with greater species richness and increased herbivore abundance.

This study took place from March 13 to 27, 2019 in Bocas del Toro, Panama. Visual surveys were conducted in two types of mangrove habitat (six sites per habitat): CMC and non-CMC habitats. Each site was surveyed five times; six sites were sampled per day (CMC sites were sampled one day, then non-CMC the next) for a total of 10 days over the sampling period. To study the fish assemblage, we used the visual “belt-transect” method, snorkeling a 30 m-long transect parallel to the mangrove fringe while looking 2 m landward from the submerged prop root edge and recording species, number, and estimated size (total length, cm) of the fish taxa encountered. The entire fish assemblage was surveyed except cryptic species (Clinidae, Gobiidae). Small, silvery, fork-tailed fishes that tend to inhabit the water column in large schools (e.g., Atherinidae, Clupeidae, Engraulidae) were placed into a single group (“small pelagic forage fishes”), and these fishes were analyzed separately due to sporadic sightings in high densities. All surveys were conducted and standardized between 1000 and 1600 h to reduce possible diel rhythm effects, and transect locations were chosen at nonfixed points. At each site, we measured water temperature, salinity, dissolved oxygen, pH, and total chlorophyll using a YSI EXO2 multiparameter sonde and light intensity using a HOBO MX2202 data logger. We also measured depth, prop root density, and epibiont prop root diameter within 1-m2 quadrats (10 quadrats per site evenly spaced along a 30-m transect). Depth was measured to the mean low tide line using a 1-m long polyvinyl chloride pole marked every 5 cm. Prop root density was measured by counting the number of prop roots within each quadrat. Epibiont prop root diameter was measured by using a tape to measure the maximum diameter of the attached organism assemblage on each root within the quadrat (one maximum diameter per root). Prior to data analysis, we pooled fish species abundances for each site. To distinguish between juveniles and adults, we considered fishes to be juveniles when they were smaller than one third of the maximum species length obtained from FishBase.