Macrobenthic Communities Associated to Mussel Beds in a Southern Patagonia Estuary, Argentina

Abstract

Macrobenthic communities associated to the ecosystem engineer Mytilus platensis were examined across four intertidal shores in the Río Gallegos estuary (southern Patagonia, 51°35’S), a high-latitude macrotidal system (8 m range). We compared spatial (sites S, C, A, E) and seasonal (summer, autumn, winter, spring) variation in assemblage structure. Samples were collected seasonally using a 0.20 × 0.20 m quadrat (5 replicates per site/season). A total of 39 species were recorded (20–30 per site). Species richness and diversity were lowest in summer (S´: 3–5 spp.; H´: 1.4) and highest in winter (S´:4–8 spp.; H´: 2.0). Density remained stable year-round at sites S and C (350–670 ind/m²), while sites A and E peaked in winter and winter-spring (ca. 1000 ind/m²). Assemblage composition differed spatially in summer-autumn (sites S/C, A,and E forming distinct groups) but homogenized in winter-spring, except for the persistent isolation of site S in winter. Beta-diversity partitioning revealed that species turnover (80%) dominated over nestedness, indicating species replacement along environmental gradients. Redundancy analysis identified desiccation stress (driven by seasonal variation in air/water temperature, wind speed, and humidity) as the primary environmental filter structuring assemblages. Trophic structure was consistently dominated by predator/scavengers across all sites and seasons. We suggest that harsh summer conditions (prolonged air exposure, strong winds, high temperatures, and increased predation) reduce biodiversity and amplify spatial patchiness, whereas cooler, wetter winter conditions enhance recruitment, increasing diversity and leading to more homogeneous assemblages. Together, these findings demonstrate that seasonal fluctuations in environmental stress drive spatial and temporal patterns in macrobenthic assemblages, underscoring the fundamental role of mussel beds as reservoirs of biodiversity in high-latitude estuarine systems.