Mar Environ Res 2025 Jun 26;210:107329. doi: 10.1016/j.marenvres.2025.107329.

Community structure of marine megafauna inhabiting the Gulf of Arauco: The role of natural and anthropogenic factors in its spatial-temporal dynamics.

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One of the challenges of ecology is to understand how natural and anthropogenic factors determine patterns of species distribution and abundance. The Gulf of Arauco, located in the central part of Chile, is a biologically highly productive area in the eastern South Pacific, with important human settlements and intensive coastal use. There is a submarine pipeline that carries effluent from wood pulp production to the coastal ocean. This study quantified the distribution and abundance of benthic megafauna in the Gulf of Arauco over a 3-year period, and evaluated the spatial dissimilarities from the submarine outfall through 13 seasonal surveys. The main results were as follows: (i) The megafauna in the Gulf of Arauco consisted of 92 taxa. The most abundant were Echinodermata: Ophiuroidea with Ophiactis sp. ; Mollusca-Gastropoda with Nassarius dentifer; and Cnidaria-Anthozoa with Renilla sp.; (ii) Species presence and abundance and community structure were highly heterogeneous at the spatial scale of the site and study Zones within the gulf; (iii) At the spatial scale of the gulf, and based on the gradient of the underwater pipeline, three significantly different areas were identified (Zones 1 and 3, close to the outfall with a signal of terrestrial organic matter, Zone 2 near to the coast, and Zones 4 and 5, far away from it), a pattern that was repeated across years, seasons of the year, and sampling periods; (iv) The areas closest to the submarine outfall were dominated by ophiuroids, probably associated with a greater load of organic matter from terrestrial plants in the sediments; (v) The areas closest to the pulp mill effluent are more influenced by the terrigenous and industrial inputs as indicated by the sediment lignin, tannin and AOXs contents; (vi) The zone closest to the submarine outfall had the highest average species richness, but beta multivariate diversity showed the opposite pattern, with the highest mean values in the zones farthest from the outfall.

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