Researchers Sleuth Palate to Solve Lobster Mystery

There is a mystery floating amongst lobster populations in the Gulf of Maine, a missing link in the series of steps by which larvae grow and develop. The tiny, leggy larvae floating through the water column are abundant – but the number of juvenile lobsters settling on the seafloor are decreasing.

Bigelow Laboratory Senior Research Scientists David Fields and Pete Countway are searching for the root of this disconnect. They suspect that the answer may lie in the lobsters’ diets, and that a change to their food could be causing many of the larvae to starve. They are using a combination of approaches to determine exactly what lobster larvae eat, an important piece of the puzzle that is unknown.

"This work will allow us to draw the food webs that support larval lobsters for the first time, and answer basic questions like whether they eat a wide or narrow range of foods," Countway said. "We’re at the center of the lobster universe in Maine, yet these techniques have never been used here and can provide information of value to both the industry and our understanding of basic biological processes."

Countway and Fields began this work in the summer of 2019, taking a two-pronged approach to parse what a growing baby lobster eats. Alex Asher, a graduate student working with Fields and Rick Wahle at University of Maine, used a microscope to look inside the guts of larvae specimens and identify the tiny plants and animals that comprised the animals’ last meal.

However, that process is like trying to pick out the ingredients in a smoothie – sometimes you can identify a small piece, but everything is generally mixed into an unrecognizable slurry. Countway and José Orozco Juarbe, an NSF-sponsored Research Experience for Undergraduates intern, worked to get around that challenge by using genetic techniques to examine the gut contents for DNA fragments. Guided by Asher’s observations under the microscope, they were able to detect several different species of algae and the larvae of other invertebrate species, including clams and copepods, another type of small crustacean.

Though warming waters spurred Maine’s lobster boom of the last several decades, the continuation of this warming trend is taking a toll and threatening the population’s health and survival. This has already occurred in lobster populations further south, where commercial lobstering is now all but gone. The exceptionally rapid warming occurring in the Gulf of Maine makes the future of its lobster populations dubious, threatening many livelihoods that rely on this industry.

Over the last several years, Fields has worked with graduate students Jesica Waller and Maura Niemisto to conduct a series of experiments examining how climate change is affecting lobsters. They discovered that temperature has a strong impact, with warmer water triggering females to develop more quickly – resulting in smaller females that carry fewer and smaller eggs. They also found that lobsters along the East Coast are already changing in response to warming ocean temperatures. Lobsters in Rhode Island waters are smaller than they used to be, while their largest cousins thrive in cooler Canadian waters. Fields and Asher are also assessing the condition of eggs from lobsters along the coastline to see whether they are equally rich in the fat resources needed to help larvae survive.

"There are several ways that climate change can affect animals, both through direct changes to their health and also indirect changes in the environment," Fields said. "If we find that lobster larvae rely heavily on eating organisms that are threatened by climate change, it could help explain the disruption in their life cycle."

This research will take the next step in the summer of 2020, when Fields, Countway, and Wahle run an integrated lab and field program. They aim to measure lobster larvae populations living at different depths in the Gulf of Maine, assess the abundance of their potential prey, and ground-truth the relationship between what the larvae eat and what food is apparent in their gut.

This research may also both benefit from and inform the new DNA-based monitoring project that Countway and several other Bigelow Laboratory scientists are part of, which is using advanced genetic techniques to illuminate the Gulf of Maine coastal community structure. It will also provide research opportunities to several students, from undergraduate interns to doctoral scientists, to learn from this interdisciplinary effort.

"This project gives us the opportunity to answer some fundamental biological questions, and it’s a brilliant opportunity for education," Fields said. "The diverse types of expertise that each team member brings, from deep knowledge of the ecosystem to cutting-edge genetic techniques, creates a synergy that will finally answer important and longstanding questions."

This work is funded by the National Oceanic and Atmospheric Administration Sea Grant Program, the National Science Foundation, and the Established Program to Stimulate Competitive Research.

The larval lobster image is courtesy of Jesica Waller.