Impact of marine hitchhiker load on host energy intake

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.