University of Puerto Rico Student Researches Coral Reef Bleaching in Culebra

Raisa Hernández Pacheco is working on her doctoral thesis for the Biology Department at the University of Puerto Rico-Río Piedras with specialization in coral reef ecology. Her research was featured in the scientific journal Ecosphere (January 20, 2011), of the Ecological Society of America, the most prestigious ecology society in the United States. 

The research focuses on the impact of the bleaching phenomenon of the main builder of Caribbean reefs, the coral Montastraea annularis. She analyzed corals at the Carlos Rosario Beach, located in the Luis Peña Canal on the island of Culebra (Puerto Rico). According to Hernández Pacheco, coral bleaching occurs when the symbiosis between corals and algae that live inside it (zooxanthellae) are separated physically, causing the coral to turn white. Because photosynthetic algae products are an important part of the daily diet of coral, prolonged bleaching represents a high risk for coral reefs. 

Hernández explained that in 2005, there was a massive unprecedented bleaching in the northeastern region of the Caribbean causing high mortality of several species of coral. These species include Montastraea annularis, which is one of leading reefs builders in the region. She worked with biology professor Dr. Alberto M. Sabat and affiliated researcher Dr. Edwin A. Hernandez-Delgado, “to carry out a survey to examine the demographics of this coral before, during, and after the 2005 bleaching event. [. . .] Our study revealed that the demographics of Montastraea annularis is highly sensitive to bleaching, which resulted in significant decrease of the reef population’s growth rate for two consecutive years after the event.”

According to the graduate student, the mass bleaching of 2005 was due to high temperatures of the sea associated with climate change, so if the patterns of rising surface temperatures continue as has been predicted, coral populations around the globe are highly endangered.

The full study may be accessed through

Photo (by Edwin A. Hernández-Delgado) from the cover of Ecosphere; see

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