Diatom Diversity on the Skin of Frozen Historic Loggerhead Sea Turtle Specimens

Lucija Kanjer,Bojan Lazar,Bart Van De Vijver,Sunčica Bosak,Romana Gračan,Roksana Majewska

doi:10.3390/d12100383

Abstract

In recent years, biofilm-forming diatoms have received increased attention as sea turtle epibionts. However, most of the research has focused on carapace-associated taxa and communities, while less is known about diatoms growing on sea turtle skin. The current study investigated diatom diversity on the skin of loggerhead sea turtle heads detached from the carcasses found along the Adriatic coast between 1995 and 2004 and stored frozen for a prolonged period of time. By using both light and scanning electron microscopy we have found diatom frustules in 7 out of 14 analysed sea turtle samples. Altogether, 113 diatom taxa were recorded, with a minimum of seven and a maximum of 35 taxa per sample. Eight taxa, Achnanthes elongata, Berkeleya cf. fennica, Chelonicola sp., Licmophora hyalina, Nagumoea sp., Navicula sp., Nitzschia cf. lanceolata, and Poulinea lepidochelicola exceeded 5% of relative abundance in any one sample. The presumably obligately epizoic diatom taxa, A. elongata, Chelonicola sp., and P. lepidochelicola, dominated in six loggerhead samples, contributing up to 97.1% of the total diatom abundance. These observations suggest that on the sea turtle skin highly specialised taxa gain even greater ecological advantage and dominance over the co-occurring benthic forms than in the carapace biofilms. The suitability of frozen sea turtle skin specimens for diatom analysis and limitations of this approach are discussed.

Highlights

The present analysis of the historic frozen head specimens of the loggerhead sea turtles showed that the skin of the Adriatic loggerheads is colonised mainly by presumably obligately epizoic taxa such as Achnanthes elongata, Chelonicola sp. and P. lepidochelicola, reported previously from various sea turtle species from different geographic regions [5,6,7,8,9,10,13,14,16,17,18,24]
The sample size was relatively small, the above-mentioned diatom taxa constituted an important element of the Adriatic loggerhead skin biofilm dominating in six out of seven samples containing diatoms, despite the location, cause of the host death, host age, or the year or season in which the sea turtle carcasses were collected
Among the 113 diatom taxa found in the sea turtle skin samples, as many as 83 contributed less than 1%

Summary

Introduction

With the recent increased interest in diatom diversity on marine vertebrates [1,2,3,4] in general and sea turtles in particular [5,6,7,8,9,10], a considerable number of sea turtle-associated diatom taxa have been described within the last five years [11,12,13,14,15,16,17,18,19,20,21,22,23,24] and it became clear that diatoms constitute an important element of the sea turtle epi-microbiome on both juvenile and adult individuals. To date, more attention has been given to diatoms growing on sea turtle carapaces, Diversity 2020, 12, 383; doi:10.3390/d12100383 www.mdpi.com/journal/diversity. Diversity 2020, 12, 383 there is growing evidence that these may differ significantly from the skin-associated taxa and assemblages [10,11,12,16,24]. Except for leatherbacks (Dermochelys coriacea Vandelli, 1761), sea turtles possess bony carapaces covered with keratinous plates or scutes, while their skin, being both durable and flexible, is only moderately keratinised [25]. The shedding patterns of the sea turtle skin scales differ from those typical of the hard shells, in which scutes are either retained or shed periodically [26]. It is not surprising that sea turtle carapaces are usually more heavily colonised with epibiotic diatoms than their skin [10]. Immersed surfaces undergo a generally similar sequence of events leading to the development of the well-established biofilm [27]

Methods

Results

Conclusion