Using Epiphytic Foraminifera to Assess the Anthropogenic Impact on Posidonia Oceanica Meadows in Mallorca Island (Balearic Islands, Spain): A 60-Year Retrospective Analysis

The increase in marine pollution has led to an urgent need to find effective, affordable, and speedy methods to detect contaminants and their sources in a global change context. The use of marine organisms as bioindicators is a highly relevant and efficient approach, particularly if it can provide quick and cost-effective data without damaging any biota. Epiphytic foraminifera provide a good example of reliable bioindicators applicable in marine ecosystems such as seagrass meadows. The study of benthic foraminifera associated with Posidonia oceanica meadows began in the Mediterranean in the early 20th century, with the Balearic Islands being one of the first scenarios for this discipline. Foraminiferal analysis, particularly the occurrence of Planorbulinatum mediterranensae assemblage, became a useful criterion for characterizing P. oceanica ecosystems in the Mediterranean and indirectly assessing their environmental quality. This work uses epiphytic foraminifera as bioindicators of P. oceanica ecosystems in the Balearic Islands. A comprehensive review of the so-called grey literature, including theses, reports, and repositories from the 1960s to 2020s on foraminiferal assemblages reported in P. oceanica meadows has been conducted. Subsequently, epiphytic foraminifera-based indices (the modified FORAM (Foraminifera in Reef Assessment and Monitoring) Index (FI′), and the “Long vs Short life span” index (ILS)) have been applied to this historical dataset to detect the anthropogenic impact of touristic development over the last 60 years. In regions with minimal human influence, such as the Cabrera Archipelago National Park, foraminiferal indices were found to be the highest. Also, a diminishing trend was recorded after the 1960s, during the beginning of tourism development, to late 1990’s and early 2000’s. The FI′ and ILS indices have been increasing and stabilizing over the last two decades, reflecting conditions over a large area and suggesting an improvement in the marine environment and P. oceanica conditions, reflecting the enforcement of legislative protection. The simplicity and ease of application of these indices make them ideal for use with a wide range of databases, allowing for powerful analysis of long-term trends in the health and environmental variability of P. oceanica meadows.