Feature Friday: Erin Dillon

Hi, Erin Dillon! Great to have you on ReefBites. 

erinmdillon@wordpress.com ; @erinmdillon

Erin is a PhD candidate at the University of California, Santa Barbara. Her research focuses on reconstructing historical shark communities on coral reefs using dermal denticle (shark scale) assemblages preserved in sediments. Read more about her work below! 

Give an elevator pitch of what your research/project is about.

How many sharks should there be on a coral reef? Sharks play important roles as predators, cultural symbols, and ecotourism attractions, yet they are susceptible to overfishing. Many coastal shark populations have undergone dramatic declines over the last several decades, and at least a quarter of shark species and their relatives are threatened with extinction. However, the timing and extent of these declines are poorly understood. In order to effectively recover shark populations and their ecological functions, we must first document what was lost. My research aims to reconstruct reef shark communities over the last several thousand years using dermal denticles (shark scales), which are shed by sharks and accumulate in marine sediments. I use these microscopic “skin teeth” as a time machine to define pre-exploitation baselines, explore sharks’ ecological roles on intact historical reefs, and quantify change in shark communities over long ecological timescales. In turn, these paleoecological data can be leveraged to inform shark management and ecology.

Why is this research/project important and timely?

Sharks play prominent roles as predators on coral reefs — structuring food webs, affecting prey behavior, and facilitating nutrient cycling — yet they are vulnerable to anthropogenic activities, underscoring the need to effectively manage their dwindling populations. Declines as high as 80-99% have been documented in oceanic shark populations over the last several decades, but less is known about the state of reef-associated shark communities. This is particularly true in the Caribbean, where humans have had profound and widespread effects on reef ecosystems and where this research project first began. Given the antiquity of human disturbances in the Caribbean, the degradation of reefs and their predator assemblages preceded the systematic monitoring of their structure and ecology, contributing to shifted perceptions of reef baselines. Consequently, we’re missing historical context to help define what is natural, examine how and why reefs have (or have not) changed over time, disentangle human and natural drivers of change, and identify recoveries. In particular, long-term shark abundance data are limited, hindering efforts to set appropriate management targets and determine the ecological consequences of shark declines on these reefs.

What is the broader impact and implication of your findings?

Previously, dermal denticles and fish teeth accumulating in marine sediments have been used in deep time to investigate changes in fish communities over millions of years. Collaborators and I set out to explore whether denticle assemblages could be used a proxy for shark abundance over the last several thousand years – a timescale relevant to thinking about how humans have impacted sharks. Specifically, we’ve been developing an approach to recover denticles from coral reef sediments, test their ecological fidelity, and interpret this record. So far, we’ve discovered that denticle assemblages retain ecological information about past shark communities and can preserve a time-integrated signal of shark abundance in low energy reef environments. We’re now applying this technique to reconstruct patterns of change in relative shark abundance over time in the Caribbean and Pacific. This research is part of a larger project that uses the recent fossil record to reconstruct entire reef ecosystems before humans. Our work aims to leverage the past to help characterize historical ranges of variation, advance our understanding of long-term ecological shifts, and guide management targets based on local expected conditions.

How did you come to work in this field/project?

I first became interested in coral reef ecology as an undergraduate student at Stanford University, although my passion for marine biology began when I was in middle school. The summer after my freshman year in college, I had the chance to assist with a research project on Palmyra Atoll, a remote atoll located in the central Pacific Ocean about 1000 miles southwest of Hawaii. I was blown away by the reefs and the overwhelming abundance and complexity of life that inhabited them. Never before had I been in the company of a reef so full of predators! But of course, this was not true for every reef that I visited as part of my undergraduate program, and I became curious about these spatial differences, what was natural for a reef in any given location, and how this variation could help guide conservation efforts.

I still remember my first introduction to historical ecology, which was a seminar I attended at Hopkins Marine Station. Dr. Loren McClenachan was discussing her work using historical photographs from the Florida Keys to document the loss of large trophy fish since the 1950s. That was an aha moment for me, when I realized that I could combine my interests in ecology, history, and conservation.   

After graduating from college, I applied for an opportunity to work at the Smithsonian Tropical Research Institute in Panama on a coral reef paleoecology project with Dr. Aaron O’Dea. What was originally intended to be a three-month-long internship became a two-year-long stay and eventually a PhD project – and the rest was history! 

What is your top graduate school life hack or survival resource?

Stay organized, but be flexible! I’m a big fan of lists, so I keep a daily planner in addition to creating to-do lists with varying time frames. This helps me break down tasks into actionable and focused SMART goals as well as keep track of how I use my time. Also, reward yourself when you finish important tasks. 

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