Impact of marine hitchhiker load on host energy intake

Kale, Nupur 1 ; Quinn, Lu1; Fouad, Ahmed2; Hays, Graeme 3 ; Stokes, Kimberley 1 ; Esteban, Nicole 1

Published Oct 17, 2025 on Dryad. https://doi.org/10.5061/dryad.ns1rn8q5t

Data files

Oct 17, 2025 version files 8.01 KB

Data_Marine_hitchhiker_impact.csv

5.66 KB
README.md

2.35 KB

Abstract

Determining the energetic and fitness trade-offs associated with symbiotic relationships (mutualism, commensalism, or parasitism) can reveal the implications of symbiosis for species and ecosystem health. To identify hitchhiker impact on sea turtles, this study reviewed global literature and examined the association between remoras (Echeneis naucrates) and green turtles (Chelonia mydas) at a high-density foraging site in the Red Sea using SCUBA and video (n = 71 observations) in October 2023. Previous evidence of remora-sea turtle association is limited to qualitative observations from the Atlantic and Pacific Oceans. The results show that depth significantly impacted the number of remoras per turtle (p < 0.05). Turtle grazing rate was affected by remora load (p < 0.05), decreasing by ~30% across the load range from a mean of 22.8 bites min^-1 (0 remoras) to 15.6 bites min^-1 (3 remoras). There was little evidence of benefit to turtles, with only one observation of a remora cleaning a turtle's carapace. The observed reduction in grazing effort suggests potential impacts on green turtle body condition over time, which may affect growth, reproduction, and population health, warranting long-term investigation. These findings present the first quantitative evidence that the remora-sea turtle relationship shifts from commensalism to parasitism as remora load increases, demonstrating the potential costs of hitchhikers for sea turtles.

Dataset DOI: 10.5061/dryad.ns1rn8q5t

Description of the data and file structure

This repository contains data used in Kale et al. (2025) to examine the costs and benefits associated with remoras (Echeneis naucrates) hitchhiking on green turtles (Chelonia mydas) in the Egyptian Red Sea. The file includes data collected during SCUBA surveys.

Study overview

To improve our understanding of the remora-sea turtle relationship, we explored the following relationships:

1) Remora presence/absence vs turtle size

2) Mean number of remoras per turtle (hereafter remora load) vs depth

3) Mean grazing rate per turtle vs turtle size, mean remora load per individual, and depth

Files and variables

File: Data_Marine_hitchhiker_impact.csv

Description: This file contains data collected during SCUBA surveys to examine the remora-green turtle relationship using logistic and multiple-stepwise linear regressions.

Number of variables: 15

Number of header rows: 1

Number of rows: 71

Variables

site: (character) name of site where data were collected
date: (numeric) date when data were collected
start_time: (numeric) time when the dive survey started
session: (character) time of day (morning/afternoon)
interval.h: (numeric) time elapsed between repeated observations in hours (<1, <12, >12, >24, NA)
id: (character) turtle ID
depth.m: (numeric) position of turtle underwater (in meters)
scl.cm: (numeric) visually estimated straight carapace length SCL_max of the turtle (in centimeters)
diff: (numeric) change in estimated SCL_max of turtles between repeated observations (in centimeters)
stage: (character) life stage of observed turtle (immature/mature)
tail: (character) sex based on presence/absence or length of tail (juvenile/male/female)
p.a: (numeric) presence/absence of remora (1/0)
remora: (numeric) number of remoras per turtle
rem.diff: (numeric) change in remoras per turtle between repeated observations
grazing.rate: (numeric) bites per minute for each turtle

Note: NAs indicate where data were not applicable.

Data type: character, numeric

Code/software

All analyses were performed in R v4.2.3 (R Core Team 2024).