Characterization of seagrasses at two new locations in the Eastern Tropical Pacific (El Jobo and Matapalito, Costa Rica)

Seagrasses in the Eastern Tropical Pacific (ETP) region are currently only found at a limited number of locations. Seagrass meadows are a threatened coastal habitat worldwide, and there is already a report of seagrass loss in the ETP. Here, we characterize seagrasses at two new locations in Costa Rica, El Jobo and Matapalito, to provide further information on spatial and temporal variability of seagrasses in the ETP. Seagrasses consisted of monospecific Halophila baillonii meadows, which is a small colonizing species with a limited global distribution. Seagrasses were present at Matapalito on all three dates between August 2017 and May 2018, while seagrasses were only found at El Jobo on the first visit. Seagrass biomass at these new locations was 8.4 ± 5.3 g DW m⁻² and shoot density 1556 ± 785 shoots m⁻². Leaf length was 0.9 ± 0.3 cm, width 0.4 ± 0.1 cm, area 1.2 ± 0.6 cm², and LAI 0.20 ± 0.15 m² m⁻². Seagrass flowers were not encountered. Biomass Cₒᵣg percentage was 30 ± 4 % and Cₒᵣg content was 0.3 ± 0.2 Mg Cₒᵣg ha⁻¹. Seagrass sediment contained 1.5 ± 0.4 % Cₒᵣg and 17.4 ± 12.1 % Cᵢₙₒᵣg. Sediment bulk density was 1.1 ± 0.2 g ml⁻¹ and Cₒᵣg content was 15.7 Mg Cₒᵣg ha⁻¹. Halophila baillonii δ¹³C was -9.4 ± 0.9‰ and δ¹⁵N was 4.0 ± 0.8 ‰; while sediment δ¹³C was -20.1 ± 1.0 ‰ and δ¹⁵N was 8.0 ± 1.0 ‰. Seagrass contribution to sediment carbon content was ∼ 50 %. Seagrass morphometrics and carbon content are within reported ranges for Halophila meadows. The reason for lack of seagrasses at El Jobo on subsequent samplings remains unclear. Continued research into seagrass spatial and temporal dynamics in the ETP, and their associated environmental conditions, is currently needed for adequate seagrass conservation and management initiatives in this region.