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- Inter-island nesting dynamics and clutch survival of green turtles Chelonia mydas within a marine protected area in the Bijagós Archipelago, West AfricaPublication . Raposo, Cheila; R., Rebelo; Catry, Paulo; Ferreira-Airaud, Betania; Barbosa, Castro; Garcia, Tumbulo Bamba; Regalla De Barros, Aissa; Sá Sampaio, Manuel; Patrício, Ana RitaUnderstanding spatial heterogeneity in reproductive success among at-risk populations facing localised threats is key for conservation. Sea turtle populations often concentrate at one nesting site, diverting conservation efforts from adjacent smaller rookeries. Poilão Island, Bijagós Archipelago, Guinea-Bissau, is a notable rookery for green turtles Chelonia mydas within the João Vieira-Poilão Marine National Park, surrounded by three islands (Cavalos, Meio and João Vieira), with lower nesting activity. Poilão’s nesting suitability may decrease due to turtle population growth and sea level rise, exacerbating already high nest density. As the potential usage of secondary sites may arise, we assessed green turtle clutch survival and related threats in Poilão and its neighbouring islands. High nest density on Poilão leads to high clutch destruction by later turtles, resulting in surplus eggs on the beach surface and consequently low clutch predation (4.0%, n = 69, 2000). Here, the overall mean hatching success estimated was 67.9 ± 36.7% (n = 631, 2015–2022), contrasting with a significantly lower value on Meio in 2019 (11.9 ± 23.6%, n = 21), where clutch predation was high (83.7%, n = 98). Moderate to high clutch predation was also observed on Cavalos (36.0%, n = 64) and João Vieira (76.0%, n = 175). Cavalos and Meio likely face higher clutch flooding compared to Poilão. These findings, alongside observations of turtle exchanges between islands, may suggest a source-sink dynamic, where low reproductive output sink habitats (neighbouring islands) are utilized by migrants from Poilão (source), which currently offers the best conditions for clutch survival.
- Nutrient input from green turtle eggs and hatchlings in a west Africa Island and its nearshore environmentPublication . Ferreira Raposo, Cheila Sofia; Patrício, Ana Rita; Catry, Paulo; Barbosa, Castro; Camará, Assana; Regalla, Aissa; Rebelo, RuiSea turtle nesting brings marine-derived nutrients into sandy beach ecosystems, potentially influencing their dynamics. We investigated nutrient input from green turtle Chelonia mydas eggs and hatchlings into coastal habitats in Guinea-Bissau, West Africa. We assessed two islands within the João Vieira-Poilão Marine National Park (‘JVPMNP’), with contrasting sea turtle nesting density: very low (João Vieira) and very high (Poilão). On each island, we analyzed stable isotopes of carbon and nitrogen in one pair of plant species (coinvine Dalbergia ecastaphyllum bush/baobab Adansonia digitata tree) and two pairs of predator species (tufted ghost crab Ocypode cursor/African rainbow crab Cardisoma armatum and sea catfish Carlarius spp./crevalle jack Caranx hippos). The first species in each pair is distributed closer to nesting sites, while the second is found further inland or offshore. Stomach content analysis was also conducted for fishes. Results supported nutrient input from turtle clutches benefiting the species living near nesting sites. Shoreline coinvines at Poilão had higher δ15N (5.1 ± 3.2‰) compared to João Vieira (≈0‰), suggesting assimilation of turtle-derived 15N. Shoreline tufted ghost crabs at Poilão had enriched δ15N (15.2 ± 0.7‰ vs. João Vieira’s 12.2 ± 1.1‰) and δ13C (− 13.4 ± 0.7‰ vs. João Vieira’s − 18.7 ± 1.4‰), likely reflecting predation upon eggs and hatchlings. Sea catfishes at Poilão frequently consumed unhatched turtle eggs washed into the sea (17% frequency of occurrence) and hatchlings (up to 27%). This study suggests that nutrient availability from turtle nests influences and supports shoreline plants and consumers at JVPMNP.