Subtidal biodiversity in Comau Fjord, Cahuelmó Fjord, and Lilihuapi Island, Autumn 2024.

The study was conducted in May 2024 (austral autumn) at shallow rocky reefs in Comau Fjord, Cahuelmó Fjord, and Lilihuapi Island, covering a total of 11 sampling stations distributed inside (n = 7) and outside (n = 4) the fjord. At each station, a 25-meter linear transect was established, with an effective sampling area of 50 m² (1 m on each side of the transect), totaling 22 transects. The assessment of macroalgae and megabenthic invertebrates was carried out by SCUBA divers using standardized photographs of 0.5 m² quadrats placed alternately on both sides of the transect line (n = 40 per station), at depths ranging from 5 to 15 meters. For fish surveys, a second diver swam along each transect at a constant speed of 2 m·min⁻¹, visually recording all observed species, their abundance, and estimated total length. In situ photographs were taken to support taxonomic identification. Species were assigned to trophic groups based on specialized literature. Abundance data were transformed according to the biological group: square-root transformation for benthic invertebrates, presence/absence for macroalgae, and no transformation for fish due to their low abundances. Additionally, oceanographic variables such as temperature, salinity, dissolved oxygen, and pH were recorded at each station using a multiparameter.