Helminth Fauna of Juvenile Green Sea Turtles (Chelonia mydas) from Rio de Janeiro State, Brazil

The green sea turtle (Chelonia mydas) is considered the largest among the hard-shell sea turtles (Márquez, 1990). It has a global distribution, with most nesting and feeding sites located in the tropics, being considered a highly migratory species (Miller, 1997). The diet of green sea turtles is closely associated with the spatial and temporal use of the habitat and the ontogenic changes experienced during the life cycle (Bjorndal, 1997), being in the early stage of their life omnivores and later become herbivores.

The green sea turtle is the most prevalent species on the Brazilian coast (Reis et al., 2009; ICMBio, 2011), with juvenile individuals being the prevalent life stage along the coast of the Rio de Janeiro state, where they forage in shallow-water seagrass beds (Marcovaldi & Marcovaldi, 1999; Tagliolatto et al., 2020).

In Brazil, there are still few studies detailing on the parasite fauna of juvenile stages of sea turtles. Only recently, Werneck and Silva (2015) in the state of São Paulo and south of Rio de Janeiro, and Binoti et al. (2016) and Gomes et al. (2017) in the state of Espírito Santo investigated the parasite fauna of juvenile green sea turtles. Aiming the fulfillment of knowledge gaps in the field, we report the gastrointestinal parasite fauna of juvenile green sea turtles from the coast of Rio de Janeiro, Brazil.

From September to December 2020, 28 juvenile green sea turtles were found dead, stranded on the beach during monitoring activities (Werneck et al., 2018). The sea turtles were obtained from the municipalities of São Francisco de Itabapoana (21° 26′ 3.5874″ S 41° 6′ 54.9354″ W), Búzios (22° 44′ 53.1276″ S 41° 52′ 52.644″ W), Casemiro de Abreu (22° 35′ 36.708″S 41° 59′ 39.084″W), Macaé (22° 22′ 18″ S 41° 47′ 9″ W), Rio das Ostras (22° 31′ 36.8364″ S 41° 56′ 34.872″ W) and Unamar (22° 38′ 34.08″ S 41° 59′ 55.7874″ W). All sites are located on the north coast of Rio de Janeiro, Brazil.

Before necropsy, all sea turtles were weighed and the curved carapace length notch-to-tip (CCL) was measured to the nearest cm. Visual assessment of the body condition for each turtle was measured according to Thomson et al. (2009). In brief, turtle condition was classified as good when the plastron was convex, fair when it was flat, and poor when it was concave.

At post mortem examination, the esophagus, stomach, small and large intestines were studied for helminth parasites following the methods described by Greiner et al. (1980). Briefly, the viscera were opened and surfaces grossly examined, then they were washed through a 60 μm mesh screen. The remaining washed material from each organ was examined under a dissecting microscope and parasites were collected, counted, washed in physiological saline solution, and preserved in 70 % ethanol. For morphological identification trematodes were stained with carmine and cleared with eugenol, then were mounted on glass slide using Canada balsam, and studied using an optical microscope equipped with the S-EYE software program.

Prevalence, mean intensity of infection and mean abundance followed Bush et al. (1997) using Quantitative Parasitology Program (QP 3.0; Reiczigel et al., 2013). The 95 % confidence intervals (CI) of prevalence were calculated using Sterne's exact method and those for mean intensity of infection and mean abundance were calculated using bootstrapping with 2,000 replications.

Species richness, mean abundance and mean intensity of infection were compared among turtle body condition classes and between turtles from different geographical areas using the non-parametric Mann-Whitney U test. The significance level adopted in the statistical tests was 5 %. Statistical analyzes were calculated using SigmaStat 3.1 (Jandel Scientific Corporation, San Jose, California).

Representative samples of the helminths collected during this study were deposited in the Helminthological Collection of the Instituto Oswaldo Cruz (CHIOC – numbers requested) in the state of Rio de Janeiro, Brazil.

Out of 28 green sea turtles, 21 were females, 4 were males and 3 were of undetermined sex. All were juveniles (CCL: 36.9 ± 5.6 ranging from 27.9 to 51.2 cm; weight: 4.5 ± 1.2 ranging from 2.6 to 6.4 kg). All green sea turtles were positive for helminths. A total of 14802 trematodes belonging to 30 species and 5 families, including Microscaphidiidae (9 species), Plagiorchiidae (3 species), Pronocephalidae (15 species), Hapalotrematidae (2 species) and Telorchiidae (1 species), were recovered (Table 1). In addition, an unidentified nematode larva was found in two turtles. The mean intensity was 536 (95% CI = 362 – 853) (range: 1 – 2831), the mean abundance was 536 (95% CI = 364 – 850), and the species richness was 7.86 (95% CI = 6.46 – 9.21) (range: 1 – 17).

The present study reports the highest prevalence, mean intensity of infection and species richness when compared to other studies on juvenile green sea turtles in Brazil (Werneck & Silva, 2015; Binoti et al., 2016; Gomes et al. 2017). The present results were also similar to those found in adult females of green sea turtles studied in Costa Rica (Santoro et al., 2006).

This finding together to different component community than previous studies (Werneck & Silva, 2015; Binoti et al., 2016; Gomes et al. 2017) suggest that the northern region of the state of Rio de Janeiro could have different environmental conditions that make richer the parasite fauna of the juvenile green sea turtles. That in the study area there is the coastal upwelling system with the highest intensity of the Brazilian coast (Coelho-Souza et al., 2012). This region represents important sources of marine productivity, generating high levels of primary productivity that propagate through the food chain. Consequently, the concentration of organisms at this site is high, possibly also including the concentration of parasitic species (Costa & Fernandes, 1993; Valentin, 2001; Coelho-Souza et al., 2012; Reis et al., 2017). Therefore, the present study supports the idea that in addition to host ontogenic factors and age, some abiotic conditions related to the specific geographical area can also directly influence the parasite fauna in these hosts (Santoro et al., 2006; Valente et al., 2009; Santoro et al., 2010; Gracan et al., 2012; Werneck & Silva, 2015; Werneck et al., 2015).

Trematodes were the predominant class of parasites in the juvenile green turtles, as expected. All species identified have been previously reported in the same host. However, Angiodictyum posterovitellatum Chattopadhyaya, 1972, Microscaphidium aberrans Looss, 1902, Microscaphidium warui Blair, 1986, Octangium hyphalum Blair, 1987, Octangium sagitta (Looss, 1899) Looss, 1902, Enodiotrema reductum Looss, 1901 and Pleurogonius laterouterus Fischthal & Acholonu, 1976 have not been previously reported in Brazil, representing new locality records. In fact, A. posterovitellatum and P. laterouterus had not yet been identified in this host from the Neotropical region (Central and South America), according to Werneck and Silva (2016).

Only 4 species of parasites were found in more than 50 % of the animals analyzed: Cricocephalus albus (Kuhl & van Hasselt, 1822) Looss, 1899, Metacetabulum invaginatum Teixeira de Freitas & Lent, 1938, Pronocephalus obliquus Looss, 1899, and Ruicephalus minutus (Ruiz, 1946) Skrjabin, 1955. Cricocephalus albus was the most prevalent species (89.3 %), followed by M. invaginatum (82.1 %), P. obliquus (82.1 %), and R. uterocrescens (53.6 %). Similar results were observed from the coast of the state of Espírito Santo (northernmost state) (Binoti et al., 2016; Gomes et al., 2017), and from São Paulo (southernmost state) and the south of the state of Rio de Janeiro (Werneck & Silva, 2015).

Sixteen (57 %) carcasses were in poor body condition; the remaining turtles were in good or fair condition. In this latter group the cause of death was drowning. This data confirms that accidental capture remains one of the main threats for this species in the coast of Rio de Janeiro state, as described in a recent study (Tagliolatto et al., 2020).

Out of 16 carcasses in poor condition, five had gross esophageal pathological changes characterized by diffuse ulcers with yellowish necrotic caseous exudate obstructing the esophageal lumen. These lesions were associated with massive infection by R. uterocrescens. The present results confirm that this trematode species may be responsible of severe disease as previously reported (Santoro et al., 2007; Ribeiro et al., 2017; Jerdy et al., 2019).

No significant statistical differences were found for species richness, abundance, and mean intensity of infection among carcasses of different body condition classes. The present results also suggest that all green sea turtles here studied belonged to the same population, as there were no differences in composition of parasite fauna or statistical values.