Polychaetes (Annelida) of the inner sector of Escollera Norte (Northern Breakwater), Port of Mar del Plata

Ports are affected by anthropogenic activities that cause irreversible damages. Mar del Plata's port (-38.036°, -57.524°) is an area of monitoring for Hippocampus patagonicus (Syngnathidae) and invertebrates. Polychaetes (Annelida) are the most diverse and abundant groups of marine benthic macrofauna. They are one of the fundamental taxa in the food chain and ecological health of the area. The aim is to study the diversity and ecology of polychaetes present in subtidal environments in different substrates (rocky and soft-bottom) of the internal sector of the Escollera Norte (breakwaters) of the Port of Mar del Plata. In this location, three samples were taken in each bottom in winter and summer, using autonomous diving. For samples on a rocky substrate, a 196 cm² square sampler with a collection bag was used, and the rock surface was scraped with a spatula. For samples on soft bottom, a 78.54 cm² cylindrical sampler was used and buried 10–15 cm deep. The depth and the temperature of the water where the samples were collected were also recorded. The collected material was fixed in 4% formaldehyde and then sieved with a stack of 1000 and 500 µm sieves. The retained organisms were preserved in 70% ethanol. They were counted and identified down to the lowest possible taxonomic level. The abundance of each taxon (δ = ind. m⁻²) was calculated. The abundance was higher in the rocky bottom sample in summer. In autumn, the highest abundance was found in soft-bottom samples. A total of 12 families were registered, the most abundant being Nereididae, Cirratulidae, and Syllidae on the rocky bottom in summer. In autumn, Maldanidae and Spionidae were found to be more abundant on the soft bottom. The families with the highest number of species are the Syllidae, found on rocky bottoms, and the Cirratulidae, present on both types of bottoms. Variations were observed in the families of the polychaete communities in the different types of bottoms. It is also found in greater abundance in summer than in autumn.