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Making Waves – the difficulties of hermit crab field work

Submitted by: Rebecca Trinh

In Osa, beach field work is dictated by the behavior of the waves. Here, we are used to large waves, high tides, and strong rip currents that keep us out of the water, even on the hottest of days. But this past week, our shores were bombarded by monster waves that were truly impressive in their ability to restructure the beachscape. The ocean is a formidable force here, taunting you as you awkwardly trudge through the hot sand hunting for just the right hermit crab. You want nothing more than to cool off in the water. But you know better. Here, it is too dangerous to go in the water. But these new monster swells made the typical Osa waves look like puddle splashes. Fallen palm trees and logs that had littered the beach have since been completely washed away. The cliff along the tree line that distinctly marks the high tide line of the highest high tides in the area has been replaced by a gentle slope of sand. Where there once was a flowing river is now a small lagoon as the waves brought up more and more sand to fill in the beach. And where there once were hundreds of hermit crabs roaming the beach, there are now a few brave souls that venture out in the night.

These monster waves were not isolated to just Osa Peninsula or Costa Rica, but stretched from North to South America, causing damage to shorelines, coastal ecosystems, and beach front properties. But they also brought a bit of fun to some daring surfers who braved the large swells and strong rip currents for a chance to catch these ridiculously large waves. And though some found joy in surfing these uniquely large swells, the unexpected intrusion of churning water brought many complications for the local terrestrial hermit crab populations here in Osa.

National weather services all along the Pacific coast issued safety warnings concerning the impending sea state. The high surf was the result of long-period swells generated by a storm brewing southeast of New Zealand earlier in the week. The increased sea state also brought along strong rip currents. The swells raced across the Pacific at about 50 kilometers an hour, covering about 1,200 kilometers a day, finally stopping only when they broke along our shoreline.

In California, waves averaged about 3 meters, delighting local surfers, but brought dismay to property owners whose homes experienced minor flooding. At least 16 people were rescued due to the high waves. Cruise ships had to emergency dock and cut their voyages short to steer clear of dangerous waters. In Mexico, waves up to 4 meters were also recorded, leading to flooding and one fatality.   Two more fatalities were reported in Panama and Chile and one person remains missing in El Salvador due to the stormy seas.

In Costa Rica, the dangerous swells also caused an environmental catastrophe as a barge capsized within the Nicoya Gulf, spilling 180 tons of fertilizer into the coastal waters. Environmental workers and local law enforcement agencies have been working to quantify the effects of the spill and have warned the public to stay out of the water. Dead fish have been floating to the surface in association with the spill. Officials are concerned that the fertilizer could not only be toxic to some organisms, but could stimulate a harmful phytoplankton bloom, further altering the ecosystem.

Here in Osa, the swells brought the tides up into the jungle, washing over trails. They also washed away several of my field experiments for the hermit crabs. I arrived in Osa about two and a half months ago to study these hermit crabs in their native habitat. These terrestrial hermit crabs are unique in their ability to actively carve out the inside of the snail shells they use as their homes. To determine how, why, and the costs and benefits of such a laborious behavior, we devised several field and manipulative experiments to be carried out. Unfortunately, three of these field experiments have now been claimed by the sea and its monstrous waves. Nightly transects during low tides after the monster waves subsided showed how barren they left the beach. Hermit crabs that once littered the beach foraging for fallen coconuts, washed up detritus, and anything else they could find, were completely absent. A few large individual could be found deep in the mangroves and up above the water line in the trees. The waves not only washed away the existing experiments, but washed away and displaced full populations. But as frustrating as it is, having your experiments and organisms washed away, it was really interesting to be able to witness this anomalous event and be able to document its impact on the local ecosystem.