Costa Rica

Brooke in Golfo Dulce

This rare tropical fiord is now recognized as one of the most extraordinary marine environments in the world! In 2010 and 2011, Brooke Bessesen and research assistance/boat captain Jorge Largaespada conducted a marine sighting survey that gave rise to profound scientific discoveries. Since then, even more interesting findings have come to light. Brooke shares them below through blurbs, photos, media links, and reader-friendly personal essays like this introduction: Two Seasonal Marine Surveys. Scroll down and explore!


Bessesen established the online database GolfoDulce.org in 2015 to make peer-reviewed articles from a broad array of biologists available to Costa Rica's conservation organizations and policy makers.


In 2017, she returned to Golfo Dulce to gently catch, measure and release dozens of venomous yellow sea snakes for a morphological and behavioral study. Cumulative data allowed Bessesen and co-author Gary J. Galbreath to name the subspecies Hydrophis platurus xanthos. This taxonomic designation—which received global media coverage—is hoped to provide foundational footing for the protection of the snakes and their habitat.


"Now the days float by in blues and teals and misty greys. I feel like Margaret Wise Brown's black kitten, peering from my seaward vessel in search of life's secrets. What will we find today?"  —from Brooke's blog


Scientific Papers & Personal Essays

LEK study

Local Ecological Knowledge—meaning, information shared during interviews with experienced fishermen and tour boat guides in Golfo Dulce—helped accurately assess current population abundance of several important species, including whales, dolphins, and sea turtles. The conservation benefits were encouraging as we work together to protect biodiversity.


Bessesen BL and M González-Suárez. 2021. The value and limitations of local ecological knowledge: Longitudinal and retrospective assessment of flagship species in Golfo Dulce, Costa Rica. People and Nature 3:627–638. [link]


Read Brooke's related essay: Human knowledge can supplement vital marine studies.



Hydrophis platurus xanthos

Life is not always easy for wild animals. Even though xanthic sea snakes are venomous and have few if any natural predators, they are sometimes harassed by dolphins, who have been seen tossing them around like play toys.


Bessesen BL, M González-Suárez, D Herra-Miranda and L Oviedo. 2021. Hydrophis platurus xanthos (Golfo Dulce Yellow Seasnake): Harassment by dolphins. Natural History Note. Herpetological Review 52(2): 425–426. [link]



Hydrophis platurus xanthos

Hydrophis platurus xanthos assumes a unique sinusoidal ambush posture, which appears to make its body like a buoy in rough water. Hanging its head allows it to access fish below the surface.


Bessesen BL and GJ Galbreath. 2017. A new subspecies of sea snake, Hydrophis platurus xanthos, from Golfo Dulce, Costa Rica. ZooKeys 686: 109—123. [link]


Read articles about xanthos in Newsweek, Science News, and The Wire.



humpback mothers and calves

Golfo Dulce is a rare birthing ground for humpback whales from both the northern (top) and southern (bottom) hemispheres. In the bottom image, milk whitens the water as a young calf nurses.


Bessesen BL. 2015. Occurrence and distribution patterns of several marine vertebrates in Golfo Dulce, Costa Rica. Revista de Biología Tropical 63(Supl.1):261—272 [link]


Read Brooke's essays: "A Humpback Whale Hotspot" and "Nature is a Mother"



Bottlenose dolphin lesions

Expert examination of these strange skin lesions revealed that some of Golfo Dulce's resident bottlenose dolphins suffer a chronic disease called LLD, likely related to water degradation.


Bessesen BL L Oviedo, LB Hart, D Herra-Miranda, JD Pacheco-Polanco, L Baker, G Saborío-Rodriguez, L Bermúdez-Villapol and A Acevedo-Gutiérrez. 2014. Lacaziosis-like disease among bottlenose dolphins Tursiops truncatus photographed in Golfo Dulce, Costa Rica. Diseases of Aquatic Organisms 107:173—180 [link]


Read Brooke's related essay: "Photo-identification of Bottlenose dolphins".



mating green turtles

Several hundred green sea turtles (as well as critically endangered hawksbill, Olive Ridley's and Pacific leatherback sea turtles) depend on the waters of Golfo Dulce.


Bessesen BL and G Saborío-R. 2012. Tropical fiord habitat as a year-round resting, breeding, and feeding ground for East Pacific green sea turtles (Chelonia mydas) off Costa Rica. Herpetological Review 43:539—541 [link]


Read Brooke's essay: "So Many Sea Turtles".



2010 sightings for sea snakes

In 2010, plotted sighting points first revealed a geographical gap between typical yellow-bellied sea snakes and an all-yellow population inhabiting the inner-basin waters of Golfo Dulce.


Bessesen BL. 2012. Geospatial and behavioral observations of a unique xanthic colony of pelagic sea snakes, Pelamis platurus, residing in Golfo Dulce, Costa Rica. Herpetological Review 43:22—26 [link]


Read Brooke's essay: "Canary-colored Sea Snakes".



vesper rat

Coming upon a hungry rodent in the nighttime rainforests of the Osa Peninsula expanded our scientific understanding about the diet of vesper rats.


Bessesen BL and G Saborío-R. 2009. First report of vesper rat, Nyctomys sumicrasti (Rodentia: Muridae) feeding on palm fruits. Brenesia 71/72:73—76 [link]


Read Brooke's Blog: "Scientific Paper in Brenesia".