Author: Schuler, Debra

DMS researchers show fish to grow slower under future oceanic CO2 conditions

By Elaina Hancock.

As humans continue to send large quantities of carbon into the atmosphere, much of that carbon is absorbed by the ocean, and UConn researchers have found high CO2 concentrations in water can make fish grow smaller.

Researchers Christopher Murray PhD ’19, now at the University of Washington, and UConn Associate Professor of Marine Sciences Hannes Baumann have published their findings in the Public Library of Science (PLoS One).

“The ocean takes up quite a bit of CO2. Estimates are that it takes up about one-third to one-half of all CO2 emissions to date,” says Murray. “It does a fantastic job of buffering the atmosphere but the consequence is ocean acidification.”

Life relies on chemical reactions and even a slight change in pH can impede the normal physiological functions of some marine organisms; therefore, the ocean’s buffering effect may be good for land-dwellers, but not so good for ocean inhabitants.

Baumann explains that in the study of ocean acidification (or OA), researchers have tended to assume fish are too mobile and tolerant of heightened CO2 levels to be adversely impacted.

“Fish are really active, robust animals with fantastic acid/base regulatory capacity,” says Murray. “So when OA was emerging as a major ocean stressor, the assumption was that fish are going to be OK, [since] they are not like bivalves or sea urchins or some of the other animals showing early sensitivities.”

The research needed for drawing such conclusions requires long-term studies that measure potential differences between test conditions. With fish, this is no easy task, says Baumann, largely due to logistical difficulties in rearing fish in laboratory settings.

“For instance, many previous experiments may not have seen the adverse effects on fish growth, because they incidentally have given fish larvae too much food. This is often done to keep these fragile little larvae alive, but the problem is that fish may eat their way out of trouble — they overcompensate – so you come away from your experiment thinking that fish growth is no different under future ocean conditions,” says Baumann.

In other words, if fish are consuming more calories because their bodies are working harder to cope with stressors like high CO2 levels, a large food ration would mask any growth deficits.

Additionally, previous studies that concluded fish are not impacted by high CO2 levels involved long-lived species of commercial interest. Baumann and Murray overcame this hurdle by using a small, shorter-lived fish called the Atlantic silverside so they could study the fish across its life cycle. They conducted several independent experiments over the course of three years. The fish were reared under controlled conditions from the moment the eggs were fertilized until they were about 4 months old to see if there were cumulative effects of living in higher CO2 conditions.

Murray explains, “We tested two CO2 levels, present-day levels and the maximum level of CO2 we would see in the ocean in 300 years under a worst-case emissions scenario. The caveat to that is that silversides spawn and develop as larvae and early juveniles in coastal systems that are prone to biochemical swings in CO2 and therefore the fish are well-adapted to these swings.”

The maximum CO2 level applied in the experiments is one aspect that makes this research novel, says Murray,

“That is another important difference between our study and other studies that focus on long-term effects; almost all studies to date have used a lower CO2 level that corresponds with predictions for the global ocean at the end of this century, while we applied this maximum level. So it is not surprising that other studies that used longer-lived animals during relatively short durations have not really found any effects. We used levels that are relevant for the environment where our experimental species actually occurs.”

Baumann and Murray hypothesized that there would be small, yet cumulative, effects to measure. They also expected fish living in sub-ideal temperatures would experience more stress related to the high CO2 concentrations and that female fish would experience the greatest growth deficits.

The researchers also used the opportunity to study if there were sex-determination impacts on the population in the varying CO2 conditions. Sex-determination in Atlantic silversides depends on temperature, but the influence of seawater pH is unknown. In some freshwater fish, low pH conditions produce more males in the population. However, they did not find any evidence of the high CO2 levels impacting sex differentiation in the population. And the growth males and females appeared to be equally affected by high CO2.

“What we found is a pretty consistent response in that if you rear these fish under ideal conditions and feed them pretty controlled amounts of food, not over-feeding them, high CO2 conditions do reduce their growth in measurable amounts,” says Murray.

They found a growth deficit of between five and ten percent, which Murray says amounts to only a few millimeters overall, but the results are consistent. The fish living at less ideal temperatures and more CO2 experienced greater reductions in growth.

Murray concludes that by addressing potential shortcomings of previous studies, the data are clear: “Previous studies have probably underestimated the effects on fish growth. What our paper is demonstrating is that indeed if you expose these fish to high CO2 for a significant part of their life cycle, there is a measurable reduction in their growth. This is the most important finding of the paper.”

This work was funded by the National Science Foundation grant number OCE #1536165. You can follow the researchers on Twitter @baumannlab1 and @CMurray187.

Prof. Ann Bucklin presented a Webinar hosted by the Marine Biodiversity Observation Network (MBON)

UConn Marine Sciences Professor Ann Bucklin presented a Webinar on July 22, 2020 hosted by the Marine Biodiversity Observation Network (MBON), as well as other international programs focused on marine biodiversity, including GOOS, OBPS, OBIS, and OceanObs RCN, as well as SCOR. The webinar focused on ongoing activities of the SCOR Working Group, MetaZooGene: Toward a new global view of marine zooplankton biodiversity based on DNA metabarcoding and reference DNA sequence databases. The presentation was followed by a Question & Answer session with three MetaZooGene-member Panelists: Katja Peijnenburg, Todd O’Brien, and Leocadio Blanco-Bercial. The Webinar was recorded and the video (and presentation PDF) can be viewed at this link: Please feel free to share the link with interested colleagues and students.

Ann Bucklin chosen to receive UConn Faculty Excellence in Research and Creativity-Sciences Award

Ann Bucklin (Professor of Marine Sciences) has been chosen to receive the Faculty Excellence in Research and Creativity-Sciences Award. This award is given by the UConn Foundation Alumni Relations Office in recognition of research excellence and highest level of creativity to enhance the University’s academic and creative reputation. The award acknowledges significant and/or creative contributions to a field of knowledge or area of inquiry.

Grad Students Enjoy #OSM20

Nine graduate students shared their research at the 2020 Ocean Sciences Meeting in San Diego, California. A total of 22 presentations were given by DMS faculty, postdocs, and students. Besides the science, folks visited the La Jolla beaches and San Diego Zoo, ate delicious Mexican food, and networked with colleagues. We’re looking forward to more conferences and sharing our science!


See the full list of presentations:


  • Palm trees and sunshine
    Palm trees and sunshine!
  • Vlahos lab group
    Vlahos Lab looking fierce (seated Penny Vlahos; standing left to right: Lauren Barrett, Emma Shipley, and Allie Staniec).
  • Mengyang Zhou OSM2020
    Graduate student Mengyang Zhou with his poster.
  • Lauren Barrett OSM2020
    Graduate student Lauren Barrett giving her oral presentation.
  • DMS booth OSM2020
    Working the DMS booth in the exhibit hall (left to right: postdoc Martina Capriotti, and graduate students Mengyang Zhou, and Kelly McGarry).
  • La Jolla sea lions
    Sea lions hanging out on the beach in La Jolla, CA.
  • Halle Berger OSM2020
    Graduate student Halle Berger (far left) presenting her research on the Dungeness Crab.
  • San Diego Convention Center
    Outside the San Diego Convention Center.
  • Poster hall OSM2020
    Poster hall at OSM20.

DMS investigators complete full comprehensive nitrogen balances of LIS

Of the nitrogen delivered to Long Island Sound (LIS) using a 20 year time series, Vlahos, Whitney, and colleagues Found 40% of it is exported as primarily organic nitrogen (70% vs 30% as nitrate). However, 60% of the nitrogen Entering the LIS is either buried in sediments and/or denitrified to nitrogen gas and N2O.

UConn DMS at Ocean Sciences 2020

The Department of Marine Sciences is excited to be well represented at Ocean Sciences 2020 in San Diego next week. With 22 presentations by faculty, students, and researchers and an exhibition booth, there are lots of ways to find out more about our research and opportunities in our department. See the full list of presentations below.

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Former Marine Sciences graduate student, Dr. Maria Rosa, named as an Emerging Scholar by Diverse: Issues In Higher Education magazine

Former Marine Sciences graduate student, Dr. Maria Rosa, named as an Emerging Scholar by Diverse: Issues In Higher Education magazine ( For the past 19 years, Diverse: Issues In Higher Education has recognized an interdisciplinary group of minority scholars who represent the very best of the U.S. academy. Emerging Scholars are selected from hundreds of nominations, and those professors selected have distinguished themselves in their various academic disciplines and are actively working to make our society more equitable and just. This year, former Marine Sciences graduate student, Maria Rosa was one of fifteen professors nation-wide selected for the honor. Maria completed her PhD degree in 2016 (major advisor: Dr. J. Evan Ward), spent two years as a NSF-funded postdoctoral scholar at Stony Brook University (mentor: Dr. Dianna Padilla), and is currently the George and Carol Milne Assistant Professor of Biology at Connecticut College.

IUCN releases comprehensive report on ocean deoxygenation

9 December 2019. During the COP25 summit in Madrid, the International Union for Conservation of Nature (IUCN) released its latest comprehensive report titled “Ocean deoxygenation: everyone’s problem” that compiles the current evidence for the ongoing, man-made decline in the oceans oxygen levels. The 588 page, 11 chapter wake-up call to these detrimental changes was produced by leading experts in the field. UConn DMS faculty Baumann is one of the co-authors in chapter 6 “Multiple stressors – forces that combine to worsen deoxygenation and its effects”.

From the executive summary:
“The equilibrium state of the ocean-atmosphere system has been perturbed these last few decades with the ocean becoming a source of oxygen for the atmosphere even though its oxygen inventory is only ~0.6% of that of the atmosphere. Different analyses conclude that the global ocean oxygen content has decreased by 1-2% since the middle of the 20th century. Global warming is expected to have contributed to this decrease, directly because the solubility of oxygen in warmer waters decreases, and indirectly through changes in the physical and biogeochemical dynamics.”

Access to the full report:

Chapter 6. Multiple stressors – forces that combine to worsen deoxygenation and its effects (5.86 MB)