Field Notes: Settling into a Field Site and Embracing my Inner Limpet

As I summit Everest, sweating from exertion with the sun glaring on my face, I turn my gaze downward and sweep the creviced ground with my eyes. The creatures I am here to study are inconspicuous, blending into the rocks with their grey, ridged shells. Their species name is Siphonaria gigas, the Greek gigas meaning “giant,” and these animals are indeed large among mollusks. Excitement at the prospect of potential discovery keeps me energized despite the hard physical work involved in this research.

Was I studying a rare, elevation-tolerant Himalayan mollusk here on Everest? Actually, I was standing 3 m above sea level at a tropical 8.9° N latitude, and I could hear waves of the Pacific Ocean lapping at the base of this “mountain” . . . I had not just climbed the indomitable 8,849 m Himalayan peak. Rather, “Everest” was our research team’s nickname for one prominent granite hill at my study site on the Pacific coast of Panama. I was here to study the behavior and reproduction of a particular species of limpet, a large marine snail with a shell shaped like a pointy hat.

A close-up view of *Siphonaria giga*s on its scar. Notice how the bottom of its shell is uneven, having grown to match the uneven rock below. This individual has numerous smaller barnacles attached to its shell. *Photo by John Christy*

You may often hear scientists refer to a “study site,” meaning the geographic area where their research is focused. My study site in Summer 2016 comprised a swath of rocky intertidal zone (i.e., the coastal area covered by water at high tide and exposed to the air at low tide) at Punta Culebra, Panama. This place was home to around 350 S. gigas. The main goal of the study was to determine how the spatial organization of these limpets—where they live, and who they live nearby—relates to their reproduction. Answering this question required me to spend nearly every day for three months watching the limpets in their natural habitat, tracking individuals’ movements, mating, and egg production over time.

The study site (Punta Culebra, Panama) at low tide. Research was conducted here in collaboration with the Smithsonian Tropical Research Institute. *Photo by John Christy.*

The location of the study site at Punta Culebra on the Pacific coast of Panama (Pacific Ocean is to the south in the large map). The inset map shows a zoomed-out view.

The first time I laid eyes on my study site, I saw little more than a bunch of undistinctive rocks. Gradually, after visiting this place daily—traversing the terrain over mornings and evenings, stormy and sunny days, high and low tides—I developed a completely different understanding of the site. Standing at the top my intertidal Everest, I could scan the expanse of grey granite boulders and recognize different mounds and ridges separated by small valleys. The rocks were crisscrossed with cracks, and the deeper valleys would fill with water and turn into channels as the tide rose later that day. Beside Everest there was a slightly lower peak we called “K2,” and just to the north was a flat expanse dubbed “Mesa.” These areas, densely populated with limpets, are where we focused our data collection. Many of the limpets clustered along larger crevices, some of which we gave names. “Main Street” was a long and centrally located crack parallel to the waterfront, and “Wall Street” was a shorter crack where the limpets squeezed together, causing us to speculate that they would compete fiercely with one another for resources. Naming these geographic features of our study site was not just for entertainment; the nicknames helped our research team form a mental map and keep track of individual limpets living in different areas.

Overhead view of one of “Mesa” with limpits lining the cracks.

Upon closer inspection of the landscape, these rocks were dotted not just with limpets but with a plethora of coastal marine creatures. There were purplish crusty barnacles, a variety of snails, quick-footed crabs, and slipper-shaped chitons (a type of mollusk, like snails and limpets, but with a flattened shell made up of multiple plates). Organisms of the intertidal are specially adapted to living in this zone straddling the land and sea. Because they are alternately submerged at high tide and exposed to the air at low tide, they must be able to cope with extreme daily fluctuations in temperature, salinity (salt concentration), and moisture.

Understanding how organisms deal with such challenges requires studying their physiology and behavior, both in the lab and in their natural habitats. As a field biologist, I love nothing more than to immerse myself in the habitat of my study organisms and watch how they behave “in the wild.” It’s important to imagine how the world looks from the animal’s perspective, as different species have different sensory abilities that cause them to perceive their world in different ways (just think of the infrasonic hearing of elephants, bat echolocation, or the ultraviolet vision of many invertebrates). Behavioral ecologists use the term Umwelt (the German word for “environment”) to describe the unique perceptual world inhabited by an animal [1]. While humans are constrained by our own sensory abilities, one way biologists can catch a glimpse of an animal’s Umwelt is through careful, prolonged observation plus some leaps of imagination.

Over time at Punta Culebra, I learned how the lives of intertidal organisms are ruled by the tides—two high and two low tides per day, shifting in timing and height as the moon waxes and wanes. My life was similarly ruled by the tides that summer. I checked the tide chart daily and timed my arrival at the study site to correspond with the falling tide, when the rocks were exposed but still damp and S. gigas are most active (also, I would have been swimming over my study site had I arrived at high tide). I observed a behavior common in limpets called homing, where each individual forms a spot on the rock, called a scar, that is like home base for that individual [2]. Siphonaria gigas grow their shells to match the contours of the rock beneath them, so they fit snuggly on their scars like 3-D puzzle pieces. They leave their scars to crawl around and graze on algae when the tide is falling, but they are only active for short periods of time, staying close to their scars and returning home before the rocks get too hot and the sun bakes them [3].

Collecting data at the site. These rocks would all be covered by water at high tide. *Photo by John Christy*.

I also came to recognize different individual limpets. There was that oddly matched pair of one tall, skinny limpet and its tiny, squat partner; a wandering limpet that kept switching its scar location so we would lose it for several days at a time; and one atop Everest that was the largest and probably one of the oldest. I wondered how limpets choose a location as their home base. Do they pick spots near another limpet, select sites based on food abundance, or aim for a particular height in the intertidal? The answer is still not completely clear. However, my research from that summer showed that limpets living in pairs produced more egg masses than solitary limpets [4]. This supports the idea that the location of scar formation and spatial organization of S. gigas are related to reproduction. Given their tide-limited movement, perhaps living near other limpets is a strategy to ensure they always have access to a mate.

The limpets in this photo are raising their shells to lower their body temperature through evaporation (analogous to sweating in humans). Notice the discoloration of the rock under the three limpets on the right side of the crack; this occurs because the dark reddish algae covering most of the rock does not grow on the limpets’ scars since the limpets are often sitting on them. *Photo by Jessica Schaefer*.

To me, getting to know a new study site involves two parallel processes. The first process is mapping the site in my head for practical, research purposes. It’s necessary to identify landmarks for orientation and data collection, learn where the animals hang out, figure out good paths around the site, and find the best rocks to sit on for a water break. The second process requires keen observation and more creativity: I must put myself in the place of my species and try to envision their Umwelt. What challenges does this terrain pose to the animal? Which sensory perceptions and natural rhythms and physical constraints are most important to them, shaping not just their behavior but the trajectory of their evolution? As I sat on the crest of Everest pondering these questions, the Umwelt of a limpet glimmering in my mind, it was not such a leap to imagine that I really had just summited a mighty mountain.

These limpets have a perfect view of cargo ships cruising toward the Panama Canal. *Photo by Jessica Schaefer.*

Jessica Schaefer is a PhD student in the Animal Behavior Graduate Group at UC Davis. She studies the behavior and mating systems of creatures from limpets to lizards to birds. Jessica loves poking around tidepools and looking at coastal animals and algae.

References:

[1] Partan, S., & Marler, P. (2002). The Umwelt and its relevance to animal communication: Introduction to special issue. Journal of Comparative Physiology 116(2), 116–119.

[2] Cook, A., Bamford, O. S., Freeman, J. D. B., & Teideman, D. J. (1969). A study of the homing habit of the limpet. Animal Behavior 17(2), 330–339.

[3] Garrity, S. D. (1984). Adaptations of gastropods to physical stress on a tropical rocky shore. Ecology, 65(2), 559–574.

[4] Schaefer, J. L. B., Christy, J. H., & Marko, P. B. (2020). Multiple and extra-pair mating in a pair-living hermaphrodite, the intertidal limpet Siphonaria gigas. Integrative Organismal Biology, 2(1), obaa013, https://doi.org/10.1093/iob/obaa013.

[Edited by Josie Hubbard and Maggie Creamer]