ZAC7 Abstracts – Session 3

More than one third of all shark and ray species are threatened with extinction, with giant guitarfishes among the most endangered taxa. Their rapid decline is driven by the high value of their fins, habitat loss, and slow reproductive rates. The blackchin guitarfish (Glaucostegus cemiculus) occurs around the Cabo Verde archipelago, a marine biodiversity hotspot identified as a global conservation priority. Despite its relevance, basic biological information required for effective management of this species remains scarce, including data on population structure and genetic diversity. In this study, we developed and applied genetic tools to support conservation efforts for G. cemiculus. Using a high-quality reference genome previously generated by our working group, we identified a panel of 15 highly variable microsatellite markers suitable for DNA profiling. These markers enable the unique identification of individuals and the assessment of genetic diversity at the population level. All sequencing was conducted in-house at the ZMT using the Oxford Nanopore Technologies MinION platform, a portable and cost-effective sequencer that provides full control over data generation and analysis. We obtained genetic fingerprints for 47 individuals sampled in Cabo Verde and compared them with profiles of 20 individuals from the Mediterranean. The Cabo Verde population exhibits extremely low genetic diversity relative to the Mediterranean samples, a pattern that may reflect a recent genetic bottleneck caused by steep population decline, or recent colonization of the archipelago by a small number of founders. Ongoing analyses are expected to clarify population history, effective population size, and connectivity with mainland populations. Overall, this work represents a significant advance in the genetic characterization of G. cemiculus. It establishes DNA profiling capacity at the ZMT and provides essential data to inform conservation management, including the development of a coordinated breeding strategy for European aquariums led by the Nausicaá Centre National de la Mer.

Madagascar is a data-poor tropical bioregion increasingly exposed to severe tropical storms. Yet, the ecological effects of cyclone-driven disturbance, such as sedimentation, on estuarine ecosystems remain unstudied. We used multiple evidence base approach, and multi-disciplinary lenses framework to integrate local ecological knowledge (LEK) on seagrass bed responses to sediment deposition. Semi-structured interviews were conducted in four estuaries using convenience sampling to document regional baseline information on estuarine seagrass beds. Data were structured to capture (a) knowledge of seagrass ecology, (b) perceived disturbances related to sedimentation, and (c) short- and long-term ecosystem responses. Respondents described distinct species–sediment associations along estuarine gradients: fine-leaved, thin-rhizome species dominate muddy-sand zones near freshwater inflows, while robust, broad-leaved morphotypes occur in coarser seaward sediments. Seasonal flooding and wind-driven resuspension were consistently identified as major stressors causing burial on short timescales. Participants noted that thin-leaved species often act as early colonizers after short-term disturbance. For moderate to long-term change, seascape successional patterns were linked to sediment texture shifts related to sedimentation in some areas. Regional variations in perception of seagrass stressors further emphasized the need for site-specific management approaches. These insights provide a rare, process-based understanding of seagrass bed resilience in turbid estuarine systems and demonstrate the potential of LEK to complement conventional science for conservation and restoration of tropical coastal ecosystems under increasing climatic pressure.