Epizoic diatoms have been described from diverse hosts (from invertebrates to vertebrates) and diverse environments (from freshwater to marine; see i.e. Wuchter et al. 2003; Wetzel et al. 2010; Riaux-Gobin & Witkowski 2012; Romagnoli et al. 2014; Frankovich et al. 2016; Riaux-Gobin et al. 2017 and references therein). Several genera have been described as presumably obligately epizoic (or potentially commensal, even if no specific study on real relationships between the host and the diatom has ever been published), including
In 2014–2018, a total of 142 sea turtles from the Equatorial West Atlantic, the Caribbean Basin and the South Pacific were sampled. In the course of these studies, presumably an exclusively epizoic species of
The study is part of FEDER Martinique (Fonds Européen de Développement Régional), ANTIDOT (Association of News Tools to Improve the understanding of the Dynamic Of Threatened marine turtles, Mission pour l’Interdisciplinarité), DEAL Martinique (Conventions 2012/DEAL/0010/4-4/31882 and 2014/DEAL/0008/4-4/32947), the ODE Martinique (Convention 014-03-2015) and CNRS/IPHC (Centre National de la Recherche Scientifique/Institut Pluridisciplinaire Hubert Curien) programs for Martinique (Caribbean Basin) and French Guiana (Equatorial West Atlantic), and part of several projects concerning turtles in the Society Archipelago (South Pacific) coordinated by Te Mana O Te Moana (Observatoire des Tortues marines en Polynésie française). Details of sampling sites are presented in Table 1.
Sampled turtles and geographical location
oceanic basin | location | species | nesting or subadult | juvenile | latitude | longitude |
---|---|---|---|---|---|---|
Caribbean Sea | Grande Anse d'Arlet | CM | 8 | 14°30ʹ10.95ʹʹN | 61°05ʹ13.01ʹʹW | |
Anse du Bourg d’Arlet | CM | 22 | 14°29ʹ13.43ʹʹN | 61°04ʹ58.89ʹʹW | ||
EI | 1 | |||||
Macabou | DC | 1 | 14°29ʹ55.06ʹ'N | 60°49ʹ25.42ʹʹW | ||
Les Sâlines | EI | 1 | 14°23ʹ45.55ʹʹN | 60°52ʹ14.74ʹʹW | ||
Anse Noire | EI | 1 | 14°31ʹ42.47ʹʹN | 61°5ʹ20.36ʹʹW | ||
CM | 1 | |||||
Prêcheur | EI | 1 | 14°49ʹ60ʹʹN | 61°12ʹ0ʹʹW | ||
CM | 1 | |||||
Carbet | CM | 4 | 14°42ʹ0ʹʹN | 61°10ʹ60ʹʹW | ||
Saint Pierre | CM | 2 | 14°43ʹ60ʹʹN | 61°10ʹ60ʹʹW | ||
EI | 1 | |||||
Petite Anse d’Arlet | CM | 1 | nd | nd | ||
Equatorial Atlantic Ocean | Yalimapo | DC | 16 | 5°44ʹ47.96ʹʹN | 53°56ʹ37.36ʹʹW | |
CM | 13 | |||||
Aztèque | CM | 4 | 5°41ʹ12.57ʹʹN | 53°43ʹ49.07ʹʹW | ||
DC | 1 | |||||
Cayenne | DC | 3 | 4°55ʹ10.54ʹʹN | 52°16ʹ5.31ʹʹW | ||
LO | 6 | |||||
South Pacific Ocean | Te Mana O Te Moana (Moorea) | CM | 2 | 17°29ʹ39.639ʹʹS | 149°52ʹ13.527ʹʹW | |
Tiaraunu (Tetiaroa) | CM | 7 | 16°59ʹ21.5ʹʹS | 149°34ʹ48.1ʹʹW | ||
Oroatera (Tetiaroa) | CM | 1 | 16°59ʹ37.4ʹʹS | 149°32ʹ24.0ʹʹW | ||
Onetahi (Tetiaroa) | CM | 9 | 17°01ʹ17.9ʹʹS | 149°35ʹ45.2ʹʹW | ||
Tahiti | EI | 1 | nd | nd | ||
Afareaitu (Moorea) | EI | 2 | 17°33ʹS | 149°48ʹW | ||
Nu’uroa (Moorea) | CM | 1 | 17°32ʹ5.793ʹʹS | 149°54ʹ10.325ʹʹW | ||
Haapiti (Moorea) | CM | 1 | 17°33ʹ56.2ʹʹS | 149°52ʹ09.9ʹʹW | ||
Atiha (Moorea) | CM | 1 | 17°35ʹ09.7ʹʹS | 149°50ʹ26.8ʹʹW | ||
Tetiaroa | EI | 2 | nd | nd | ||
LO | 1 | nd | nd | |||
Tikehau | CM | 1 | 15°S | 148° 10'W | ||
Moorea Lagoon | EI | 1 | nd | nd | ||
Maatea (Moorea) | EI | 1 | 17°35ʹ13.92ʹʹS | 149°48ʹ20.7036ʹʹW | ||
Opunohu (Moorea) | CM | 1 | 17°30ʹ28.7352ʹʹS | 149°51ʹ23.9328ʹʹW | ||
Temae (Moorea) | CM | 1 | nd | nd | ||
Moorea | EI | 1 | nd | nd | ||
Papetoai (Moorea) | CM | 1 | nd | nd | ||
Horoatera (Teti aroa) | CM | 1 | nd | Nd |
CM =
The protocols applied in Martinique and French Guiana were approved by Conseil National de la Protection de la Nature (CNPN,
Epizoic taxa associated to the turtle carapace or soft shell were superficially scraped (sampling period 2014–2018) from small surfaces with a blade. One hundred and forty-two samples from four turtle species [
Figure 1a–e (LM)

Figure 2a–g (SEM)

Figure 3a–d (SEM)

Figure 4a–c (SEM)

Features of
n | 21 | nd | nd | nd | nd |
Valve shape | linear elliptic with capitate apices | linear to linear-lanceolate, strongly capitate, narrow ends | lanceolate, protracted and rostrate apices | elliptical-lanceolate, rostrate apices | lanceolate, rostratecapitate |
Length | 15–25 (19 ± 3.0) | 32–50 | 35–40 | 30–40 | 12–22 |
Stria density | 24.5–30 (28 ± 1.6) | 11–14 (15) | 12–13 | 14–16 | 20–24; 24–28 on apices |
Areolae on the valve face | radiate to arched striae, apically elongate areolae | striae bent and radiate around the center, apically elongate areolae | radiate to arched striae, apically elongate areolae | striae arched, parallel near apices | striae radiate to arched |
Striae around the central area | alternatively short and long | all of the same length | alternatively short and long | alternatively short and long | of irregular length |
Central area | distinct, bow-tie/butterfly like, expanded, not really asymmetrical | expanded and asymmetrical | relatively restricted | relatively large, symmetrical | small |
Ethology | epizoic, marine | freshwater, cosmopolitan | freshwater | brackish | marine, in the mucilage of the apical slit of |
Reference | present study | Kützing 1844 Lange-Bertalot 2001 Potapova & Kociolek 2011 | Germain 1981 Rushforth & Spaulding 2010 | Grunow in Cleve & Grunow 1880 Patrick & Reimer 1966 Germain 1981 Kociolek 2011 | Taassen 1975 |
nd - no data; Morphometrics expressed as indicated in the original description or in later compilations. Morphometrics of
The central area in
Behavioral studies of marine turtles have not reported any deaths or diseases due to macro- and micro-flora associated with their carapace and skin, while deaths due to accidental fishing (Finkbeiner et al. 2011 and references therein) or following the ingestion of plastics (Nelms et al. 2015; Wilcox et al. 2018; Yaghmour et al. 2018) are confirmed and listed. Furthermore, studies describing cleaning stations for sea turtles (Sazima et al. 2010) tend to prove that turtles come there to restrict the proliferation of algal epibiont material on their bodies and are not that much inconvenienced by them. We can therefore hypothesize that diatoms (such as
On the other hand, diatoms as well as macroalgae need light to grow, even if epizoic
Nevertheless, 33% of the DC individuals examined in this study host a specific diatom (
As a result of the present survey of sea turtles from tropical sectors of the Atlantic and Pacific oceans, a new benthic diatom taxon is reported, which so far has never been found in another environment.
Figure 1a–e (LM)

Figure 2a–g (SEM)

Figure 3a–d (SEM)

Figure 4a–c (SEM)

Features of Navicula dermochelycola sp. nov. (French Guiana, Yalimapo, DC). Comparison with several other Navicula taxa (see text)
n |
21 | nd | nd | nd | nd |
Valve shape | linear elliptic with capitate apices | linear to linear-lanceolate, strongly capitate, narrow ends | lanceolate, protracted and rostrate apices | elliptical-lanceolate, rostrate apices | lanceolate, rostratecapitate |
Length |
15–25 (19 ± 3.0) |
32–50 |
35–40 |
30–40 |
12–22 |
Stria density | 24.5–30 (28 ± 1.6) | 11–14 (15) | 12–13 | 14–16 | 20–24; 24–28 on apices |
Areolae on the valve face | radiate to arched striae, apically elongate areolae | striae bent and radiate around the center, apically elongate areolae | radiate to arched striae, apically elongate areolae | striae arched, parallel near apices | striae radiate to arched |
Striae around the central area | alternatively short and long | all of the same length | alternatively short and long | alternatively short and long | of irregular length |
Central area | distinct, bow-tie/butterfly like, expanded, not really asymmetrical | expanded and asymmetrical | relatively restricted | relatively large, symmetrical | small |
Ethology | epizoic, marine | freshwater, cosmopolitan | freshwater | brackish | marine, in the mucilage of the apical slit of |
Reference | present study | Grunow in |
Taassen 1975 |
Sampled turtles and geographical location
oceanic basin | location | species | nesting or subadult | juvenile | latitude | longitude |
---|---|---|---|---|---|---|
Caribbean Sea |
Grande Anse d'Arlet | CM | 8 | 14°30ʹ10.95ʹʹN | 61°05ʹ13.01ʹʹW | |
Anse du Bourg d’Arlet | CM | 22 | 14°29ʹ13.43ʹʹN | 61°04ʹ58.89ʹʹW | ||
EI | 1 | |||||
Macabou | DC | 1 | 14°29ʹ55.06ʹ'N | 60°49ʹ25.42ʹʹW | ||
Les Sâlines | EI | 1 | 14°23ʹ45.55ʹʹN | 60°52ʹ14.74ʹʹW | ||
Anse Noire | EI | 1 | 14°31ʹ42.47ʹʹN | 61°5ʹ20.36ʹʹW | ||
CM | 1 | |||||
Prêcheur | EI | 1 | 14°49ʹ60ʹʹN | 61°12ʹ0ʹʹW | ||
CM | 1 | |||||
Carbet | CM | 4 | 14°42ʹ0ʹʹN | 61°10ʹ60ʹʹW | ||
Saint Pierre | CM | 2 | 14°43ʹ60ʹʹN | 61°10ʹ60ʹʹW | ||
EI | 1 | |||||
Petite Anse d’Arlet | CM | 1 | nd | nd | ||
Equatorial Atlantic Ocean |
Yalimapo | DC | 16 | 5°44ʹ47.96ʹʹN | 53°56ʹ37.36ʹʹW | |
CM | 13 | |||||
Aztèque | CM | 4 | 5°41ʹ12.57ʹʹN | 53°43ʹ49.07ʹʹW | ||
DC | 1 | |||||
Cayenne | DC | 3 | 4°55ʹ10.54ʹʹN | 52°16ʹ5.31ʹʹW | ||
LO | 6 | |||||
South Pacific Ocean |
Te Mana O Te Moana (Moorea) | CM | 2 | 17°29ʹ39.639ʹʹS | 149°52ʹ13.527ʹʹW | |
Tiaraunu (Tetiaroa) | CM | 7 | 16°59ʹ21.5ʹʹS | 149°34ʹ48.1ʹʹW | ||
Oroatera (Tetiaroa) | CM | 1 | 16°59ʹ37.4ʹʹS | 149°32ʹ24.0ʹʹW | ||
Onetahi (Tetiaroa) | CM | 9 | 17°01ʹ17.9ʹʹS | 149°35ʹ45.2ʹʹW | ||
Tahiti | EI | 1 | nd | nd | ||
Afareaitu (Moorea) | EI | 2 | 17°33ʹS | 149°48ʹW | ||
Nu’uroa (Moorea) | CM | 1 | 17°32ʹ5.793ʹʹS | 149°54ʹ10.325ʹʹW | ||
Haapiti (Moorea) | CM | 1 | 17°33ʹ56.2ʹʹS | 149°52ʹ09.9ʹʹW | ||
Atiha (Moorea) | CM | 1 | 17°35ʹ09.7ʹʹS | 149°50ʹ26.8ʹʹW | ||
Tetiaroa | EI | 2 | nd | nd | ||
LO | 1 | nd | nd | |||
Tikehau | CM | 1 | 15°S | 148° 10'W | ||
Moorea Lagoon | EI | 1 | nd | nd | ||
Maatea (Moorea) | EI | 1 | 17°35ʹ13.92ʹʹS | 149°48ʹ20.7036ʹʹW | ||
Opunohu (Moorea) | CM | 1 | 17°30ʹ28.7352ʹʹS | 149°51ʹ23.9328ʹʹW | ||
Temae (Moorea) | CM | 1 | nd | nd | ||
Moorea | EI | 1 | nd | nd | ||
Papetoai (Moorea) | CM | 1 | nd | nd | ||
Horoatera (Teti aroa) | CM | 1 | nd | Nd |
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