Hidden underneath the cerulean blue waters along the coast of Cartagena and its surrounding islands are expansive coral reefs. In the Spring of 2023, the AAUS Doctoral Scholarship gave me the opportunity to visit Cartagena to get to know these reefs personally. Swimming among these rainforests of the sea, I encountered boulder corals that towered over me and colonies of diverse corals stretching far beyond where the eyes could see. It was truly like exploring an underwater city.
 














Image 1. Diverse corals on a reef off the coast of Cartagena and its surrounding islands. Photo by Dr. Eric Crandall.

My research involves investigating the microbiomes of coral endosymbionts, photosynthetic dinoflagellate algae of the family Symbiodiniaceae. Corals are made of an animal host and a myriad of other microorganisms including algae, bacteria, viruses, fungi and protists. I am curious about how Symbiodiniaceae and bacteria work together to keep the coral holobiont alive and healthy. Most of my research involves working with lab-maintained Symbiodiniaceae cultures. However, the cultures available in our lab were isolated decades ago and have been grown under lab conditions since then. Thus, much of the microbiomes in our lab cultures likely reflect years of lab-based culture conditions rather than true eco-evolutionary relationships. It is thus important for us to collect fresh Symbiodiniaceae from the field and sample their microbiomes immediately to capture what their microbiomes look like in nature. 

In Cartagena, the team employed SCUBA to collect fragments from two reef-building coral species – Orbicella faveolata and Porites asteroides. Back on land, I extracted the endosymbionts from these coral fragments and processed them for DNA extraction and sequencing back in the lab. I employed a sequential filtration and washing method that separates Symbiodiniaceae-associated bacteria from coral-associated bacteria by retaining only bacteria cells that are closely adhered to the cell surface of Symbiodiniaceae. We will then compare the microbiomes of lab-cultured versus freshly field collected Symbiodiniaceae to identify microbiome community members that are conserved between the lab and the field, which could help us to identify bacterial taxa that perform essential functions in algal-bacterial symbiosis.
While I appreciated the opportunity to conduct field work in Cartagena, the moments I treasured even more were the conversations I got to have with the locals living in the fishing communities on Cartagena’s surrounding islands. We had the chance to speak with retired fishermen who lived off the oceans in their youth as well as younger fishermen who were currently out on the waters. The contrast between the abundance of ocean life now and just a couple of decades ago was jarring. While diverse marine resources were abundant in the past, today it is common to hear of fishermen who return from a full night of fishing with nothing in their nets.


Image 3 and 4. Fishermen in Cartagena returning at dawn from a night out at sea. Photos by Vivian Li.

Coral reefs are tremendously important ecosystems for global biodiversity and marine fisheries, supporting approximately six million fishers in approximately 100 countries around the
world and generating upwards of US$375 billion annually in goods and services. In the face of global change causing coral bleaching, disease and mass mortality, coral reefs are expected to disappear starting as early as 2030-2040. Coral mortality often results from dysbiosis between the coral host, its microalgal photosymbionts (Symbiodiniaceae), and other microorganisms that make up the coral holobiont. A better understanding of the interactions and relationships between the coral host, Symbiodiniaceae and their associated microbiomes is thus urgently needed for developing rapid and scalable nature-based solutions for coral conservation.

I am honored and grateful to have received generous support from AAUS which allowed me to meet the corals and the people who my research will directly impact. This trip has reminded me that my research is about more than just the corals themselves, it is also about the human lives they support. I hope that in the near future my research can contribute to improving the plight of coral reefs and of the communities that depend on them.