Spatial Distribution of Epibionts on Olive Ridley Sea Turtles at Playa Ostional, Costa Rica

bioRxiv preprint doi: https://doi.org/10.1101/669523; this version posted June 12, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 1 1 Full Title: Spatial distribution of epibionts on olive ridley sea turtles at Playa Ostional, Costa Rica 2 3 Nathan J. Robinson1,2,*, Emily Lazo-Wasem3, Brett O. Butler4, Eric A. Lazo-Wasem5, John D. Zardus6, 4 Theodora Pinou7 5 6 1The Leatherback Trust, Goldring-Gund Marine Biology Station, Playa Grande, Guanacaste, Costa 7 Rica 8 2Cape Eleuthera Institute, The Cape Eleuthera Island School, Cape Eleuthera, Eleuthera, The 9 Bahamas 10 3Lyles School of Civil Engineering, Purdue University, West Lafayette, Indiana, U.S.A 11 4Museo de Zoología “Alfonso L. Herrera”, Facultad de Ciencias, Universidad Nacional Autónoma de 12 México, A.P. 70¬–399, Ciudad de México CP 04510, México 13 5Division of Invertebrate Zoology, Peabody Museum of Natural History, Yale University, New Haven, 14 Connecticut, U.S.A 15 6Department of Biology, The Citadel, Charleston, South Carolina, U.S.A 16 7Department of Biological and Environmental Sciences, Western Connecticut State University, 17 Danbury, Connecticut, U.S.A 18 *Corresponding author: [email protected] 19 20 Short title: Spatial distribution of epibionts on sea turtles bioRxiv preprint doi: https://doi.org/10.1101/669523; this version posted June 12, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 2 21 ABSTRACT 22 There is a wealth of published information on the epibiont communities of sea turtles, yet many of 23 these studies have exclusively sampled epibionts found only on the carapace. Considering that 24 epibionts may be found on almost all body-surfaces and that it is highly plausible to expect different 25 regions of the body to host distinct epibiont taxa, there is a need for quantitative comparative 26 studies to investigate spatial variation in the epibiont communities of turtles. To achieve this, we 27 measured how total epibiont abundance and biomass on olive ridley turtles Lepidochelys olivacea 28 varies among four body-areas of the hosts (n = 30). We show that epibiont loads on olive ridleys are 29 higher, both in terms of number and biomass, on the skin than they are on the carapace or plastron. 30 This contrasts with previous findings for other hard-shelled sea turtles, where epibionts are usually 31 more abundant on the carapace. Moreover, the arguably most ubiquitous epibiont taxon for other 32 hard-shelled sea turtles, the barnacle Chelonibia spp., only occurs in relatively low numbers on olive 33 ridleys, while the barnacles Stomatolepas elegans and Platylepas hexastylos are far more abundant. 34 We postulate that these differences between the epibiont communities of different sea turtle taxa 35 could indicate that the carapaces of olive ridley turtles provide a more challenging substratum for 36 epibionts than do the hard shells of other sea turtles. In addition, we conclude that it is important to 37 conduct full body surveys when attempting to produce a holistic qualitative or quantitative 38 characterization of the epibiont communities of sea turtles. 39 40 KEYWORDS 41 Epibiosis, Lepidochelys olivacea, East Tropical Pacific, arribada, barnacles, turtle-scape, settlement 42 substratum, site selection 43 44 INTRODUCTION 45 In the marine environment, almost any non-toxic, non-protected surface will eventually be colonized 46 by an array of microorganisms, plants, algae, or animals [1,2]. This is true for non-living substrata, bioRxiv preprint doi: https://doi.org/10.1101/669523; this version posted June 12, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 3 47 such as rocks, sand grains, or the shells of dead molluscs, as well as the bodies of living marine 48 animals. Those organisms that live on the surfaces of other organisms are referred to as epibionts 49 [3], a grouping of diverse taxa with a wide-range of life-histories, physiological tolerances, and 50 mechanisms for attaching to their host [4]. It is therefore not surprising to discover that epibiont 51 communities vary among different host species [5,6], populations [7], and even between different 52 body-areas on a single host [8,9]. Understanding the factors driving spatial variation in the 53 distribution of epibionts, be it on the scale of an ocean or a host’s body, can shed light the habitat 54 requirements of these varied associates. In turn, this information can be used to understand habitat 55 preferences or behaviour of the host [e.g. 10,11] and even epibiont-related disease transmission 56 [e.g. 12]. 57 58 Sea turtles arguably host the most abundant and diverse epibiont communities of all large marine 59 megafauna. In an effort to characterize these epibiont communities, researchers have generated 60 hundreds of species-lists reporting the presence of epibiont taxa for sea turtle populations around 61 the world [13]. As these datasets have grown, there is now an impetus to synthesise these data and 62 elucidate epibiont community spatial patterns globally and make quantitative assessments of 63 epibiont loads [14]. Yet to help draw robust conclusions about geographic differences in epibiont 64 communities, it would be beneficial to understand spatial patterns in epibiosis at a finer-scale – the 65 scale of a turtle’s body. Indeed, it is highly likely that epibionts are non-uniformly distributed over a 66 turtle host for several reasons. For example, the physical properties of certain body-parts, such as 67 the carapace, differ from those of the plastron or skin [15], which likely affects attachment or 68 settlement of different epibiont species. Different locations on the host’s body may also present 69 different opportunity for feeding. For example, some epibiont species feed preferentially on certain 70 tissues and thus will be found predominantly in those areas [16] whereas filter feeders might prefer 71 to be in areas where water flow over the host is optimal [17]. Either of these factors, as well as bioRxiv preprint doi: https://doi.org/10.1101/669523; this version posted June 12, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 4 72 attachment mode, crypsis, mating habits, and others, could lead to distinct variation in the 73 distribution of epibionts on sea turtles. 74 75 While it may be clear that epibiont distribution is likely to vary over the host’s body, many studies on 76 sea turtle epibiosis have either not provided any quantitative assessment of where on the host the 77 epibionts were found [e.g. 7,18], and/or have simply sampled epibionts from a single location on the 78 animal, commonly the carapace [e.g. 19,20]. Tellingly, even some of the most seminal studies 79 investigating the distribution patterns of epibionts on the loggerhead turtle Caretta caretta and 80 green turtle Chelonia mydas hosts have focused exclusively on the carapace [8,21]. There are only 81 two studies of which the authors are aware that have compared the abundance of epibionts from 82 over the entire body: Devin and Sadeghi (2010) [22] and Razaghian et al. (2019) [23]. Interestingly, 83 both studies, which focused on hawksbill turtles Eretmochelys imbricata nesting in Iran, identified 84 that epibiotic barnacles were actually more common on the plastron than the carapace. If this is true 85 for all sea turtle species, then this finding could have important implications for epibiont sampling. 86 Specifically, if epibionts are not uniformly distributed on the hosts’ body then the actual biodiversity 87 of epibionts might be underestimated if only sampled from a single region of the body. 88 89 To better understand spatial variation in epibiont communities on sea turtle hosts, we made a 90 quantitative assessment of the abundance and biomass of several epibiotic taxa from different 91 regions of the body of olive ridley sea turtles Lepidochelys olivacea. This species was chosen because 92 several studies have focused on characterizing the epibiont communities of this species in recent 93 years [e.g. 6,11,18,24] yet no previous studies have specifically looked at epibiont distributions for 94 this host species. Our null prediction was that there would be no variation in the abundance or total 95 biomass of the various epibiont taxa among the different body-areas. 96 97 METHODS bioRxiv preprint doi: https://doi.org/10.1101/669523; this version posted June 12, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 5 98 Study Site 99 Olive ridley turtles were sampled from Playa Ostional, which is located on the Pacific coast of the 100 Nicoya Peninsula in northwest Costa Rica (9° 59’ N, 85° 42’ W). We selected this site as it is one of a 101 few beaches worldwide that has mass-nesting assemblages or “arribadas” of olive ridley turtles , 102 thus making it feasible to sample large numbers of turtles relatively easily.

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