Article source: Schofield et al 2017. Aerial and underwater surveys reveal temporal variation in cleaning-station use by sea turtles at a temperate breeding area. https://doi.org/10.3354/meps12193
Taking a shower, washing our hands, these are daily normal activities that I at least take for granted. Could you imagine if you had to seek out cleaning stations, which would require time and effort that could be spent on other activities? Well, for many animals, getting groomed and cleaned in their natural environment is a commodity.
Many animals make a choice to participate in cleaning symbioses with other species. For example, crustaceans and small fish attach themselves to whales and sea turtles “cleaning” their body surfaces of parasites and grime. Cleaning symbioses provide an important service that removes unwanted organisms, damaged tissues, and debris from external body surfaces of so-called “clientele.” There are benefits for the “cleaners,” too, as these critters get to feed on a concentrated food source from their customer. Sure, a clean turtle sounds like a healthy turtle, and therefore appealing, right? But what about the costs of spending time being cleaned? Do turtles make a conscious choice to forgo breeding to remove gunk from their shells?
A big question and why it matters
For decades, researchers of both land and sea animals have grappled with this question: Why do species engage in cleaning symbioses? These behaviors are expected to provide benefits, such as keeping parasites at bay and even giving stress relief. But while the benefit of a squeaky-clean carapace for, say, a loggerhead turtle seems like justification enough for lining up to have fish and crustaceans scrub away the grime, there is likely a cost associated with this activity. For sea turtles, that cost is competition. Sea turtles not only compete with other turtles for available cleaners, but they also lose out on time for other critical activities, such as feeding, breeding, and being on the lookout for predators. Imagine if taking a shower put you at a disadvantage for meeting friends and finding your next meal?
The present study investigated how much time loggerhead sea turtles spent at cleaning stations during their breeding season in July 2015 and 2016. The study took place at Laganas Bay on Zakynthos Island, Greece, where the authors previously surveyed fish cleaning stations. The stations consisted of isolated rock piles in a large sandy area.
The researchers used underwater and aerial surveys to observe turtle activity at the cleaning stations throughout the breeding season. They also identified the “cleaner” fish species based on the fishes’ continuous presence at the station and whether they approached turtles on arrival or waited for the turtle to signal that it wanted a cleaning.
During underwater observations, divers used a combination of photography and video to record the number of unique turtles visiting a station over the entire study period as well as the number of times and for how long the turtles visited the station. For the aerial surveys, the researchers used an unmanned aerial vehicle (UAV; commonly called drones) that flew over the turtles’ breeding area in Laganas Bay and recorded video footage of the presence of rocks and reefs along the sandy area where the underwater surveys took place. Combining both aerial and underwater allowed the researchers to count turtles and capture any behaviors and interactions between turtles and fish.
The researchers expected that turtles would actively seek out cleaning stations, and compete with other turtles for cleaner fish. They also anticipated fewer turtles present at cleaning stations during the breeding season.
The researchers found that sheepshead bream was a major fish species that participated in cleanings in both years. During both years, the majority of turtles that visited the cleaning stations were female, and most of the turtles encountered in 2016 only visited the station once. In addition, when a turtle entered a station where another turtle was already being cleaned, several of the fish immediately switched turtles.
Interestingly, the turtles visited the cleaning stations throughout the breeding period, which is contrary to what the researchers expected: theoretically, turtles should be minimizing movement and conserving energy for raising clutches of eggs. What could explain this unexpected result?
Turtle movement into a station seemed to be intentional, as evidenced by repeated visits of unique turtles among the study years. In addition, the researchers frequently observed 2 or more turtles using the cleaning station at the same time. They observed turtles engaging in behaviors to attract fish or antagonistic behavior to displace the turtle being cleaned. If turtles are competing with one another for the attention of a cleaning fish, maybe taking the time and energy to be cleaned is beneficial to turtles.
The big picture
Cleaning symbioses occur across many groups of animals. Understanding how and when animals participate in these interactions is important, especially as human-induced changes to coastal ecosystems may threaten the persistence of these symbioses.
The researchers hypothesized that during the mating and breeding season, sea turtles actively swim in the nearshore waters each day in response to prevailing winds, so that they can reach warmer downwind waters. As turtles swim toward warmer waters in the beginning of the breeding season, early to mid-June, females locate their favorite (warmest) spots to mature their eggs. These females actively seek out breeding grounds; but in their seeking, they may incidentally happen upon rocks with fish that turn out to be cleaners. So, sea turtles may find their cleaning stations “by accident,” and then in the next year’s breeding season, they return to these stations using memory.
So, sea turtles use memory to locate breeding and cleaning stations, not worrying about energy conservation. Why is this important? If one does it, others likely do it too. We can probably appreciate that many more marine animals rely on memory and environmental cues for finding refuge from predators, breeding grounds, and foraging habitat. In this study, turtles seemed to respond to the wind-driven patterns of cold and warm water; if we think about the global climate and how ocean currents can change, then there are important potential consequences for loggerhead turtles and other marine species that not only use memory and wind cues, but for species that rely on cleaning symbioses for their survival.
Kate is a 4th year PhD candidate in the Biological Sciences Department at the University of Notre Dame, and holds a Masters in Environmental Science & Biology from SUNY Brockport. She studies the ecology of benthic (bottom) algae in the Great Salt Lake, Utah, in particular how this resource is important to the overall food. Outside of lab and field work, she enjoys running and kickboxing.