Seasonal implications of the benthic ecological status assessment in a protected Mediterranean coastal lagoon: Stagno Longu of Posada (Sardinia, Italy)

Understanding how biotic indicators respond to natural variability is essential for the health state evaluation of the benthic ecosystems. This study analysed the composition and structure of the benthic communities in the coastal lagoon Stagno Longu of Posada (Sardinia) to investigate the seasonal response of the biological indicator M-AMBI. Multivariate analysis and biodiversity descriptors showed temporal (winter-summer) and spatial variability (across the three basins of the lagoon). The ecological status (ES) of Stagno Longu was assessed using M-AMBI index: results mainly showed the lagoon to be in "good'' and "moderate'' status across seasons and basins, while "poor'' status was recorded in the North basin during summer. Despite the absence of direct human pressures, sediment organic content (OC) varied seasonally and spatially and M-AMBI revealed winter to summer shifts on the ES of 3 out of 6 sampling stations. Overall, this study reveals negative significative correlation on the variations on M-AMBI with the increase of sediment OC across the studied sites, none the less discrepancies on the ES of certain stations were detected causing over/underestimation. Results suggested that natural seasonal variability is a relevant factor to be considered while performing ES assessments and implementing monitoring programmes in Mediterranean transitional ecosystems when applying indicators such as M-AMBI. (C) 2021 Elsevier B.V. All rights reserved.