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Fresh Perspectives on Freshwater

Blog Post by Avery Kaplan, Rios Saludables Intern

One sunny day this summer, the Ríos Saludables team was wading through the rivers Agujas, La Palma, Montarey, and Sabalo, collecting shrimp traps number 122 through number 132. It was the third time in three months that we had set and collected traps all along these rivers, and we were back the second time that week to check on the traps that we had set the day before. In other words, sometimes even the best field work gets repetitive.

The Ríos Saludables team in Río Agujas, from left to right: Hilary Brumberg, Keje Nagel, and Avery Kaplan.

Out of the ordinary though, we started off the day at a sustainable farm in La Palma to pick up Alex, the coordinator of the Osa palm farmers’ cooperative and one of Ríos Saludables’ local river monitoring partners, and Brian, the Peace Corps volunteer working with him. Alex has participated in many Ríos Saludables expeditions before, and was excited to see the new multiparameter probe we were using to take water quality measurements.

Avery, an Osa Conservation intern, and Brian, a Peace Corps volunteer, using the multiparameter probe to get conductivity, salinity, dissolved oxygen, and temperature measurements at a trapping site.

As we walked through the straight rows of palm plantation down to the first collection site in Río Agujas, we explained to the new volunteer why we were trapping shrimp: Osa Conservation is conducting the first ever study of giant freshwater shrimp in the Osa Peninsula to understand whether diversity is affected by the type of land-use adjacent to the river. Shrimp are a good indicator species because they migrate throughout rivers, making their abundance a reliable measure of river health.

Walking to a river that cuts through palm plantation. Plantation is one of four land use types we are studying. The others are grassland, old growth forest, and secondary forest.

After arriving at the first site and taking water quality and canopy measurements, we pulled the shrimp trap from the river to see what we would find. As we took shrimp out of the trap, being careful to avoid their pinchers, seeing the shock on Brian’s face at the size and variety of shrimp reminded me just how extraordinary these creatures are. They range from less than a gram to more than 70 grams, can be bright blue or perfectly camouflaged, and—due to anthropogenic impacts (such as deforestation and river poisoning)—are becoming a rare sight to see.

A Macrobrachium americanum, patiently waiting to be identified. Similar to the design of a minnow trap, this homemade shrimp trap is made from upcycled wood, bottles found on the beach, and mesh.

On the walk to the next trapping site, Alex spotted a boa in a palm tree. A little later, he disappeared into the brush and returned with a cacao fruit for us to snack on. Between Alex’s keen experienced eyes, and Brian’s fresh ones, I saw more that day in the field than I ever would have expected.  Every day in the Osa is an adventure, with much to learn.

The boa hidden in a palm tree. Can you spot it?

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Animal behavior: Osa’s ‘magic well’

Blog Post by Dr. Mark Laidre, Assistant Professor of Biological Sciences at Dartmouth College

Few things are more fascinating to layperson and scientist alike than animal behavior. For some, this simple fascination can ultimately fuel a lifelong passion for discovering why animals do what they do. Perhaps no better example is the Nobel Prize-winning biologist Karl von Frisch, who, as one of the founding fathers of animal behavior, spent decades studying the social behavior of bees. It may at first seem puzzling how someone could devote such prolonged study to just one critter, but von Frisch explained it quite easily, remarking: “The bee’s life is like a magic well: the more you draw from it, the more it fills with water.” And so too for countless creatures: the more we learn about their behavior, the more new and exciting questions it raises, which keeps us coming back for more.

The tropics is an unsurpassed place for such intellectual seeds to flourish. In 2008, I first stepped foot in Osa, just as Osa Conservation was opening its field station. And I’ve been coming back to the Osa nearly every year since, first as a graduate student, then a postdoc, and later a professor, with 2018 now marking a full decade of studies in the Osa (hopefully with many more visits to Osa still to come during the ensuing decades!). Each year I return to the Osa, I fall in love with its amazing wildlife once again. Most of my time is spent studying social animals, ranging from ants to birds to primates. But it is Osa’s most abundant and dominant beach denizens—the terrestrial hermit crabs (Coenobita compressus)—which have been the object of my scientific obsession since 2008.

Laidre lab at Osa Conservation’s Biological Station. From left to right: Dr. Louise Roberts (postdoc), Leah Valdes (honors thesis undergrad), Clare Doherty (PhD student), Mark Laidre (PI), Elliott Steele (PhD student), and Dr. Jakob Krieger (visiting scholar).

These ‘social hermits’ have an especially complex social life, one which revolves around a housing market of architecturally remodeled homes, passed down across generations as an extra-genetic inheritance. In contrast to social insects (e.g., the bees von Frisch studied), which mostly live among close genetic kin, social hermits live together in what is effectively a vast city of non-kin. Among these unrelated individuals, there is a constant tension between conflict and cooperation, which permeates the very core of their societies. This social drama, combined with these animals’ unusually rich behavioral repertoire and amenability to field experiments, provides a fascinating system reflecting the evolution of social life. Indeed, social hermit crabs never cease to reward curiosity and persistence with further exciting scientific discoveries.

Social group of terrestrial hermit crabs (Coenobita compressus) on Osa beach.

This past field season was no exception. From January to March 2018, myself and five members of my lab from Dartmouth continued to dig deeper into the social lives of these amazing animals. Our experiments over several months spanned the intellectual gamut from the architectural foundations of social privacy; to the evolutionary loss of displays; to ecological constraints on vision; to massive chemically-mediated funeral celebrations; to coded messages sent via substrate-borne vibration through the beach sand. During August 2018, at the International Society for Behavioral Ecology, we presented scientific talks on these studies, including:

  • ‘Scent of death: how and why is conspecific death attractive?’ (Leah Valdes)
  • ‘Evolutionary loss of a threat display: from antisocial to social living’ (Clare Doherty)
  • ‘Leaf me alone: visual constraints on the ecology of social grouping’ (Elliott Steele)
  • ‘Get off my back: vibrational assessment of resource holding potential and ownership’ (Louise Roberts)
  • ‘Exclusive social circles: the construction of privacy’ (Mark Laidre)

The many fascinating questions that can be addressed with social hermit crabs reinforces von Frisch’s important point about the ‘magic well’: the magic arises through continued focused study of a particular organism, ultimately enabling deep insights into a topic of fundamental interest. In our humble opinion, the best recipe for science is therefore simply letting an inherent pleasure in discovering new things about nature drive ever deeper exploration of one’s favorite magic well. And Osa is perhaps the most magical well one can imagine for discovering new things about nature. Hope we’ll bump into you there during our next field season.

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Conserving the last populations of the Golfito Robber Frog

Blog Post by Hector Zumbado-Ulate, Alvaro Ugalde Scholarship Awardee

My name is Hector Zumbado-Ulate and I’m one of the awardees of Osa Conservation’s Alvaro Ugalde Scholarship. Currently, I am pursuing a PhD in ecology and evolutionary biology at Purdue University. Since I started my studies in biology, I felt very attached to amphibian conservation projects, especially those helping species which are currently endangered by anthropogenic causes. For that reason, I wanted to work with the critically endangered Golfito robber frog. Specifically, I want to examine why this species persists in remnant populations after going extinct in much of their historical home range. Such information is valuable to develop adequate conservation policies that can be implemented to protect these populations and encourage their expansion back into their historical habitat range throughout Costa Rica. In particular, I am studying host-parasite interactions between endangered frog populations and the fungal parasite Batrachochytrium dendrobatidis (Bd), which causes chytridiomycosis, a potentially deadly disease that threatens many amphibian communities. At least 90% of the 34 species of robber frogs have catastrophically declined or have become completely extinct since the 1980s, likely due to this taxa’s high susceptibility to this disease. I am also quantifying how environmental stress caused by climate change affects reproduction, population dynamics, and susceptibility to chytridiomycosis in remnant populations of critically endangered robber frogs.

 

The critically endangered Golfito robber frog (Craugastor taurus) in Punta Banco, Golfito.

In the last decade, some populations of the Golfito robber frog have been rediscovered in the peripheral areas of their historic home range. This suggests that 1) peripheral populations may have survived environmental threats that affected core populations, 2) the slow recovery has made these declined species almost undetectable across their range, and 3) there might be more cases of remnant populations that still thrive but remain undetected. Remarkably, rediscovered remnant robber frog populations coexist with B. dendrobatidis without experiencing chytridiomycosis and the proposed project aims to identify the mechanisms that allow these susceptible frog species to coexist with this lethal parasite.

With the help of volunteer field assistants, I am conducting habitat monitoring and parasite detection to evaluate the risk of extinction of remnant populations three times every dry season. Specifically, I am sampling fast-flowing stream networks in Punta Banco, which are the only known streams that sustain stable populations of the Golfito robber frog. I am also monitoring and continuously looking for the Golfito robber frog in streams in the localities of Uvita, Golfito, and Rincon de Osa (this latter location historical represents the most abundant populations of the Golfito robber frog before its decline during the 1980s and 1990s).

In every stream, we are conducting multiple linear transects. On every trip to the field, we characterize every transect by measuring several environmental variables such as air temperature, humidity, stream width and depth, and canopy cover, among others. We catch individuals of all occurring frog species and measure the snout-vent-length and body mass. We also swab the frog’s skin to collect Bd zoospores. Moreover, we analyze water samples to determine if the concentration of Bd zoospores varies across stream location.

Stream monitoring in Rincon de Osa

 

Stream monitoring in Uvita.

 

Filtering of water samples from Quebrada Agua Buena in Rincon de Osa, with the aim of detecting Bd zoospores.

I am combining my research with education and outreach activities in order to share our findings with the public and policy-makers, with the goal to create optimal conservation policies for these species. In the long term, I aim to:

  1. Propose and implement in-situ strategies to increase the survival of adult frogs and recruitment of juveniles in remnant populations.
  2. Expand the range of declined robber frogs across their original home range.
  3. Establish a long-term monitoring project in collaboration with volunteer local groups, students, and professionals.

Invited speaker at Universidad de Costa Rica, recinto de Paraiso in June, 2018. Here I presented this project to ecotourism students.

 

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