Macroalgal diversity along an environmental gradient in a saltwork

Environmental physicochemical variation results in changes in the coastal biota. Macroalgae in saltworks have been poorly investigated regarding their distribution and the environmental factors that modulate the community. Thus, this study aimed to analyze the spatial distribution of macroalgae in a saltwork and the environmental parameters that drive them. Macroalgae were collected at 17 sampling points, where several environmental parameters were also determined. The sampling area was split into four sectors (S1, S2, S3, and S4) according to the recorded environmental gradient. An increase in salinity, temperature, and dissolved inorganic nitrogen was recorded from S1 (the sector closest to the sea) to S4 (the sector farthest from the sea), whereas depth showed an inverse pattern. A total of 31 macroalgal taxa were recorded in the saltwork. The highest number of macroalgal taxa (i.e., 27) was registered in S1. Macroalgal richness decreased in S2, S3, and S4. The most frequent genera in this study were Gracilaria sp. (Rhodophyta) and Caulerpa sp. (Chlorophyta), both with four species. Ochrophyta was only represented by Canistrocarpus cervicornis. Based on a redundancy analysis (RDA), increasing salinity, temperature, nitrite, and nitrate negatively affected the occurrence of macroalgae, whereas increasing pH positively affected the articulated calcareous macroalgae Amphiroa fragilissima and Jania sp., as well as the calcified Acetabularia sp. and the fleshy macroalgae Hypnea pseudomusciformis, Gracilaria caudata, and Ceramium sp. Increasing depth also positively affected the occurrence of macroalgae. In this study, it was possible to determine the distribution of macroalgae along an environmental gradient in a saltwork. The observed differences were driven by environmental changes, mainly in salinity, depth, and temperature.