Browsing by Author "Madeira, Fernando Miguel"
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- eDNA metabarcoding for diet analyses of green sea turtles (Chelonia mydas)Publication . Díaz-Abad, Lucía; Bacco-Mannina, Natassia; Madeira, Fernando Miguel; Neiva, João; Aires, Tânia; Serrao, Ester A.; Regalla De Barros, Aissa; Patrício, Ana Rita; Frade, P. R.Understanding sea turtle diets can help conservation planning, but their trophic ecology is complex due to life history characteristics such as ontogenetic shifts and large foraging ranges. Studying sea turtle diet is challenging, particularly where ecological foraging observations are not possible. Here, we test a new minimally invasive method for the identifcation of diet items in sea turtles. We fngerprinted diet content using DNA from esophageal and cloacal swab samples by metabarcoding the 18S rRNA gene. This approach was tested on samples collected from green turtles (Chelonia mydas) from a juvenile foraging aggregation in the Bijagós archipelago in Guinea-Bissau. Esophagus samples (n=6) exhibited a higher dietary richness (11±5 amplicon sequence variants (ASVs) per sample; average±SD) than cloacal ones (n=5; 8±2 ASVs). Overall, the diet was dominated by red macroalgae (Rhodophyta; 48.2±16.3% of all ASVs), with the main food item in the esophagus and cloaca being a red alga belonging to the Rhodymeniophycidae subclass (35.1±27.2%), followed by diatoms (Bacillariophyceae; 7.5±7.3%), which were presumably consumed incidentally. Seagrass and some invertebrates were also present. Feeding on red algae was corroborated by feld observations and barcoding of food items available in the benthic habitat, validating the approach for identifying diet content. We conclude that identifcation of food items using metabarcoding of esophageal swabs is useful for a better understanding of the relationships between the feeding behavior of sea turtles and their environment.
- Fine-scale foraging segregation in a green turtle (Chelonia mydas) feeding ground in the Bijagós archipelago, Guinea BissauPublication . Madeira, Fernando Miguel; Rebelo, Rui; Catry, Paulo; Neiva, João Guilherme; Barbosa, Castro; Regalla De Barros, Aissa; Patrício, Ana RitaGreen turtles (Chelonia mydas) are highly dependent on neritic foraging areas throughout much of their life. Still, knowledge of recruitment dynamics, foraging habits, and habitat use in these areas is limited. Here, we evaluated how the distribution and food preferences of green sea turtles from different life stages varied within a foraging aggregation. We focused on two islands in Guinea-Bissau, Unhocomo and Unhocomozinho, using water captures and survey dives to record habitat use and characteristics, and stable isotopes to infer diet. Additionally, we used stable isotopes to infer their diet. Two habitat types were sampled: deeper (2.26 ± 0.4 m) rocky sites fringed by mangrove with macroalgae, and sandy shallows (1.37 ± 0.12 m) surrounded by rocky reefs with macroalgae and seagrass. The two benthic communities were similar isotopically and in terms of species composition, except for the presence or absence of seagrass, which had unique signatures. We captured 89 turtles ranging from 35 cm to 97 cm in curved carapace length (i.e., juvenile to adult stages). Size distribution was habitat-dependent, with most smaller turtles present in sandy shallows and larger turtles favoring slightly deeper rocky sites. Turtle isotopic signatures differed between the habitat of capture, regardless of size, revealing a marked dichotomy in foraging preference. All turtles fed primarily on macroalgae, mostly rhodophytes. However, individuals captured in sandy habitats had evident seagrass skewed isotopic signatures. Larger turtles may be unable to use the more diverse shallower foraging sites due to increased vulnerability to predation. Despite the proximity of the sampled foraging sites (2.7 km apart), the two foraging subgroups seem to maintain consistently different feeding habits. Our study highlights how heterogeneous green turtle foraging habits can be within populations, even at small geographic scales.
- Red, gold and green: Microbial contribution of Rhodophyta and other algae to green turtle (Chelonia mydas) Gut MicrobiomePublication . Díaz-Abad, Lucía; Bacco-Mannina, Natassia; Madeira, Fernando Miguel; EA, Serrao; Regalla, Aissa; Patrício, Ana R.; Frade, Pedro R.The fitness of the endangered green sea turtle (Chelonia mydas) may be strongly affected by its gut microbiome, as microbes play important roles in host nutrition and health. This study aimed at establishing environmental microbial baselines that can be used to assess turtle health under altered future conditions. We characterized the microbiome associated with the gastrointestinal tract of green turtles from Guinea Bissau in different life stages and associated with their food items, using 16S rRNA metabarcoding. We found that the most abundant (% relative abundance) bacterial phyla across the gastrointestinal sections were Proteobacteria (68.1 ± 13.9% “amplicon sequence variants”, ASVs), Bacteroidetes (15.1 ± 10.1%) and Firmicutes (14.7 ± 21.7%). Additionally, we found the presence of two red algae bacterial indicator ASVs (the Alphaproteobacteria Brucella pinnipedialis with 75 ± 0% and a Gammaproteobacteria identified as methanotrophic endosymbiont of Bathymodiolus, with <1%) in cloacal compartments, along with six bacterial ASVs shared only between cloacal and local environmental red algae samples. We corroborate previous results demonstrating that green turtles fed on red algae (but, to a lower extent, also seagrass and brown algae), thus, acquiring microbial components that potentially aid them digest these food items. This study is a foundation for better understanding the microbial composition of sea turtle digestive tracts.