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Project: Effects of environmental variation on coral-reef fish

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Project title

Effects of environmental variation on coral-reef fish

Mentor name

Andrew Sellers,


Pearl Islands and Coiba, Panama

Project summary and objectives

Coral-reefs are among the most diverse ecosystems on the planet, providing important services to millions of people. Reef-building corals create three-dimensional structures that provide habitat to invertebrates and fish, which contribute to the persistence of corals by consuming their competitors and predators. Thus, consumers, like herbivores and predators, play a key role in structuring coral reefs.

Corals are generally associated with warm nutrient-poor tropical seas, however, those in the Tropical Eastern Pacific experience a changing patchwork of environmental conditions shaped by upwelling activity. Wind-driven upwelling events deliver cold nutrient-rich water from the ocean’s depths to coastlines, supporting some of the most productive ecosystems on the planet. Our research focuses on understanding how regional and seasonal variation in primary productivity and temperature shaped by upwelling affects the abundance, growth, and fitness of coral-reef fish. On one hand, high food availability in upwelling regions could support larger fish populations with fast growth rates and increased individual fitness. On the other hand, low water temperature could impose metabolic constraints on tropical reef fish, and lower their growth rates. Despite the importance of fish in structuring coral reef ecosystems, their physiological responses to the wide-ranging fluctuations in water temperature and primary productivity associated with upwelling remain understudied. The atmospheric and oceanographic processes that drive upwelling events are predicted to change in response to anthropogenic climate change. Studying how coral-reef fish respond to dramatic changes in food availability and water temperature is critical to understanding how coral-reef ecosystems will be altered by climate change.

Panama’s Pacific coast is an ideal location to study how regional and seasonal variation in oceanographic conditions influence ecological processes in coral-reefs. The Gulf of Panama is exposed to seasonal upwelling events between December and April which generate dramatic increases in primary productivity, and declines in water temperature. Meanwhile, upwelling is weak in the Gulf of Chiriqui, leading to more stable environmental conditions. We take advantage of this unique setting to answer the following questions:

  1. Are fish more abundant and/or larger in the Gulf of Panama?
    • Through visual and video surveys, and using remote cameras we quantify the abundance and size of coral-reef fish in Coiba (Gulf of Chiriqui) and the Pearl Islands (Gulf of Panama).
  2. Does upwelling support higher fish growth rates?
    • Growth bands on fish bones called otoliths allow us to study relationships between size and age within fish populations
  3. How do regional and seasonal changes in environmental conditions influence fish diet and gut microbial community?
    • Metagenomic tools and stable isotope analysis allow us to study seasonal and regional changes in fish diet and gut microbiota.  
  4. Do differences in diet across upwelling gradients generate divergence in physiological traits associated with feeding?
    • By linking our diet analysis with detailed morphometric measurements of fish jaws we examine adaptations by fish to regional differences in food availability.
  5. Do fish exhibit stress responses to cold temperature during upwelling periods?
    • We quantify cortisol levels in blood to examine stress responses to cold periods.

Mentorship goals

We look forward to working with a motivated young researcher who will participate in both field and laboratory aspects of this research. Our field work takes place in the Pearl Islands and Coiba, providing interns to unique access to rich marine environments. Interns will receive training in fish collection methods, blood extraction procedures, and fish dissection. They will also learn how to extract, prepare, and analyze fish otoliths to determine size at age relationships. Opportunities are also available for interns to learn molecular techniques and help with genetic analyses of fish stomach contents. Interns will have the opportunity to interact with a diverse research team made up by young scientists from a variety of scientific backgrounds, including physiology, molecular biology, and marine ecology.

Interns will participate in field and laboratory activities. In the field, interns will be involved in sample processing aboard a research boat. They may also join the fish collection team if they choose. In the lab, interns will dissect fish, extract and prepare fish otoliths for examination, and may assist with molecular analyses. Field trips can range from day-trips to expeditions lasting as long as two weeks. Interns will work with the rest of the team after fish collection trips dissecting fish. Fish dissections often extend into the night. When not participating in field collections or dissections, interns will work on extracting and preparing fish otoliths. By the end of their appointment, interns are expected to have extracted and catalogued the fish otoliths from one of our seasonal collections. Interns are also expected to prepare a portion of those otoliths for analysis. Travel costs to field locations and food during expeditions lasting more than one day are covered by the project.

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