WWU scientists awarded $638K grant to study forage fish survival in Salish Sea

A food web is only as strong as its weakest link, a fact not lost on a multidisciplinary team of Western Washington University Marine and Coastal Science (MACS) faculty that were recently awarded a three-year, $638,000 grant from the National Science Foundation. 

The goal of the new grant is to better understand the impact of polyunsaturated aldehydes (PUAs) – a type of toxic fatty acid, or lipid – on a group close to the bottom of the food pyramid that impacts everything above it: forage fish. 

“Forage fish are a foundational functional group in the Salish Sea. Every part of their life history, from embryos in the egg to adults, are food for something else,” said WWU Associate Professor of Biology Brady Olson, who, along with Assistant Professor of Chemistry Karin Lemkau and Associate Professor of Biology Jim Cooper, are the principal investigators on the grant. Also assisting them will be Jamie Pierson, a zooplankton ecologist from the University of Maryland. 

As Olson said, forage fish such as herring and surf smelt are important because they are, as their name suggests, eaten by so many things. Less forage fish means less food for bigger fish and marine mammals. 

What are PUAs and how do they impact forage fish? 

At the very bottom of the marine food web sits the tiny diatom, a microscopic algae invisible to the naked eye. Diatoms are incredibly important not just as a food source but because they produce about 20 percent of the world’s oxygen each year and make up a sizeable portion of the organic material found in the world’s oceans. 

When diatoms become stressed – either from environmental factors such as nutrient loss or by being grazed on by predators, they produce PUAs which are ingested by those predators – and in this case, very commonly, those predators are a type of local zooplankton called copepods. Copepods ingest the diatoms and then store the diatoms’ PUAs in a process called bioaccumulation. Eventually the copepods are eaten by the juvenile forage fish in question, which brings the researchers back to their main question: how do these PUAs impact the forage fish? 

“We know PUAs negatively impact the copepods, in particular their reproductive success. Female copepods that eat diatoms produce fewer eggs, and the larvae that hatch from the eggs are often dead or deformed. Research shows that PUAs disrupt normal embryo development. So how does that transfer to these young forage fish that are themselves still developing? That’s what we are hoping to find out,” said Olson. 

Cooper said a large portion of his part of the project will be to examine how young fish that are in the process of transitioning from feeding from the yolk sac they were born with to becoming free-feeding juveniles - subsisting initially on zooplankton such as copepods -  may face mutations from ingesting PUAs during this critical life stage that could impact them as adults. These mutations could be anything from swimming issues to mutated jaws that don’t allow the fish to feed as well, and Cooper and his lab will explore measuring these potential changes on forage fish reared at WWU. 

“Fish that can’t swim as well as they should or feed as well as they should will have lower survivability. We need to better understand how the PUAs are impacting these fish at this point in their lifecycle, and from that point on,” he said. “The larval-to-juvenile stage is just so critical.” 

Lemkau, the analytical chemist in the group, will work to better understand the concentration, composition and distribution of PUAs in the Salish Sea . 

“Measuring PUAs has been a challenge, but we now have a solid method in place to do that and will be expanding our techniques from laboratory cultures into the field,” Lemkau said. 

According to Olson, nailing down this methodology was not only a case of the right person in the right place at the right time, but it proved to be vital to getting the grant approved. 

“We recruited WWU recent Biology graduate Jeremy Johnson to come to WWU as a graduate student and be co-advised by Karin and I. Jeremy worked with Karin and WWU chemistry undergrads to develop a method in Karin’s lab to measure PUAs, and afterward, he surveyed benthic (bottom-dwelling) diatom populations for production of PUAs,” Olson said. “Before his work, the PUA/benthic diatom association was mostly unknown in the Salish Sea. Of the eight most common bottom-dwelling diatoms Jeremy isolated, all produced PUAs. So now we have proven that we can measure PUAs at WWU, and just as importantly, have gathered data that shows that benthic diatoms produce PUAs.” 

Lemkau said Johnson’s work will allow her lab to measure both dissolved and particulate PUAs in the field at known forage fish spawning areas as well as from cultured populations in the lab. 

Laying the foundation 

Olson said this wasn’t the kind of study done with the goal of “fixing” an issue; rather it is to gain a better understanding of the processes impacting the survivability of such an important marine food group. 

“We can’t stop PUAs from occurring, but as of now their impact is not at all well known. We have theorized on that impact but this will provide some definitive early answers,” Olson said. “And as this diatom-to-forage-fish relationship isn’t unique to the Salish Sea, it could be the basis or jumping-off-point for other studies elsewhere for sure.” 

Cooper noted that the grant will provide paid research stipends for two grad students and a number of undergraduate researchers. 

“This will be another incredible research opportunity for Western’s undergrads to take advantage of,” he said. 

For more information on this grant or its research, contact Brady Olson at brady.olson@wwu.edu; for more information on Western’s Marine and Coastal Science program, see its website here or go to https://marine.wwu.edu/.