Distribution and biomass assessment of macroalgae from Moroccan Strait of Gibraltar.

Abstract

The taxonomic richness, population structure, biomass assessment, and geographic distribution of macroalgae were studied between May 2017 and July 2018 from the Moroccan strait of Gibraltar. The study was based on the economic, ecological and environmental interests of macroalgae on a national scale. Samples were harvested by Scuba diving. Sixty-seven species, including one recently introduced in the Strait, have been identified. They were distributed over four classes: Bangiophyceae (2 species), Florideophyceae (36 species), Phaeophyceae (17 species), and Ulvophyceae (12 species). The distribution map of the most abundant agarophytes, Gelidium attenuatum and Pterocladia capillacea, was constructed from GPS and field data using System Information Geographic software. G. attenuatum stands extended from 1 to 7 m depth, with maximum biomass at 1 m. The population analysis revealed thalli up to 15.8 cm long, with the length class 11–13 cm mostly represented. As for the population of P. capillacea, it was located from 0 to 1.50 m depth, with highest biomass at 0–0.50 m depth. Unlike Gelidium, P. capillacea stands were distributed from 5 to 12 cm, with 85% measuring between 7 and 11 cm long. The estimated total biomass of G. attenuatum and P. capillacea was 7.77 ± 3.57 t of fresh weight and distributed on two sectors: Mrisat (66.66%) and Oued-Alian (33.34%). This Finding indicates a relatively low biomass in the strait.