Tides, Topography, and Seagrass Cover Controls on the Spatial Distribution of Pinna nobilis on a Coastal Lagoon Tidal Flat. Issue 3 (24th February 2022)

• Record Type: Journal Article
• Authors: Silvestri, Sonia; Capra, Veronica; Cucchiaro, Sara; Pivato, Mattia; Tarolli, Paolo
• Is Part Of: Journal of geophysical research. Volume 127:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-24
• Subjects: Pinna nobilis spatial distribution -- Cymodocea nodosa density -- ecogeomorphology -- UAV surveys for ecological applications -- P. nobilis emersion frequency and duration -- remote sensing; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2021JG006667
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: In the last two decades Pinna nobilis, the largest bivalve mollusk endemic to the Mediterranean Sea, has recolonized the tidal flats of some coastal lagoons along the Italian Adriatic coast. In this study, we investigate the influence of tides on the spatial distribution and density of a P. nobilis population developing on a tidal flat of the Venice lagoon (NE Italy) by exploiting remote sensing technologies. Our results show that there is a threshold topographic elevation (about 0.5 m below mean sea level for the studied tidal flat) above which the number and duration of emersions become limiting factors of P. nobilis abundance. Above this elevation, the population density decreases sharply. Densely populated areas tend to occur in tidal flat depressions, where the duration and frequency of emersions are low. We find, however, that the population density has large spatial variability in response to other factors, such as the seagrass percentage cover. The density of the shells increases with increasing seagrass percentage cover, and the dense P. nobilis population (0.8–2.68 N/m 2 ) grows within the Cymodocea nodosa meadow that has a high seagrass percentage cover (>85%). However, within the seagrass meadow with the highest percentage cover, the bivalve preferentially colonizes the portion closest to the main channel, a possible source of nutrients. The shift to C. nodosa —dominated meadows in the Venice lagoon occurred during the last two decades has probably facilitated the observed colonization by P. nobilis . Our findings provide management information for protection and/or restoration of P. nobilis in coastal lagoons. Plain Language Summary: Pinna nobilis is the largest mollusk of the Mediterranean Sea and strictly protected by European laws. Recently this species has been attacked by pathogens which are causing mass mortality events. In early 2021, the P. nobilis population of the Venice lagoon (Italy) was attacked and is in risk of disappearing. Thanks to a survey performed using a drone in the summer of 2020, we studied the pre‐epidemic distribution of the P. nobilis population colonizing a tidal flat. We found that exposure to limited emersions is a key factor for the bivalve survival as emersions can cause desiccation. Another key factor is the seagrass percentage cover: P. nobilis tends to colonize dense portions of the seagrass meadows, often close to the channels, which are a potential source of food. Until early 2021, when the pathogens attacked, the population growth has been likely facilitated by a constant expansion of Cymodocea nodosa, a subtropical seagrass species. The expansion of C. nodosa has probably been promoted by a small but constant increase of the water temperature during the last two decades. Our findings provide management information for the protection and/or restoration of P. nobilis in coastal lagoons. Key Points: In tidal systems, Pinna nobilis distribution is strongly affected by the bottom topography and the duration and frequency of emersion There is a significant positive correlation between the density of P. nobilis and seagrass cover Summer time monitoring of P. nobilis using unmanned aerial vehicles (UAVs) is not effective when the tidal flats are emerged and seagrass leaves obscure the shells