Acoustic cues of fish sounds as proxy for ecosystem health in sea grass meadows of the Mediterranean.
Supervisor: Lucia Di Iorio (Chorus Research Institute)
In the Mediterranean Sea, the seagrass Posidoniaoceanicaprovides storm protection for coasts,carbon sequestration, and habitat for countless species. It is also under increasing anthropogenicpressure from coastal development, ocean warming, and anchoring. Because of this, it isprotected by the European Water Framework Directive and the Habitats Directive, which requirecomprehensive monitoring of meadows and in service of this, many monitoring efforts have beenestablished. In France, monitoring networks focus on seagrass health at species level andsometimes at community level, and often require teams of trained divers and collection of plantsamples. One aspect of monitoring which has not currently been developed is acoustics. Not onlycan acoustics provide a non-invasive, and cost and time effective method for monitoring, butthese meadows are acoustically very rich, and support a host of sound producing species. Thisstudy focuses on one specific sound ubiquitous to Posidoniaoceanicameadows called the /kwa/call. This call is produced by Scorpaena spp. in seagrass meadows across the Mediterranean. Ourobjective was to use recordings to explore and qualify this calls natural variability andenvironmental drivers and evaluate its potential as an ecosystem health indicator. We identifiedkey influential acoustic parameters and explored their variation over time and space. We alsoquantified their relations with a variety of environmental variables and discovered that manywere strongly correlated with meadow density, recouvrement, and meadow area, indicating thatsound production is high in lush, large meadows. Finally, we computed three descriptive indicesand found that one, the index describing background noise level (the ANL index), was stronglycorrelated with established ecological health metrics. This index shows a significant potential asa health indicator and can be a powerful complementary monitoring tool.