Research News

Sandlance palooza on Stellwagen Bank

Posted on November 13, 2026November 13, 2026 by Hannes Baumann

Chilean silversides become famous!

Posted on July 28, 2026July 28, 2026 by Hannes Baumann

26 July 2026. We are excited to share the great news that Ecology & Evolution just published the first findings from our experimental research on Chilean silversides! The paper describes in detail the rationale, experimental procedures, results and implications of our work in 2023 and 2025 - showing the patterns and statistical tests to support the central claim that the sea silverside Odontesthes regia is now the first documented case of countergradient growth adaptation in a southern hemisphere fish species.

After returning from Chile with samples and data in December 2025, and then combining those with the samples and data from 2023 - it became readily obvious that larvae from the more northern, lower latitude population (Iquique, 20S) grew significantly slower across all tested temperatures than their conspecifics from the more southern, higher latitude population (Dichato, 37S). This pattern of local adaptation is called countergradient variation - and it has previously only been shown in fishes from the northern hemisphere.

Figure showing the temperature dependent growth capacity of silverside larvae — Temperature-dependent growth capacity of *O. regia* larvae from northern (blue symbols/lines) vs. southern populations (red symbols/lines). Both populations have the same thermal growth maximum between 20 and 23C, but the higher latitude population grows faster at all temperatures than the lower latitude population (modified after Fig.6 in Baumann et al. 2026).

Since this form of climate adaptation appears to be so ubiquitous worldwide, it is therefore likely that it also applies to adaptation of organisms to climate change in time - which is an important and increasingly urgent question for mankind. Or as we write in a more technical synopsis of the study:

We performed common garden experiments on offspring of the sea silverside Odontesthes regia to characterize thermal growth reaction norms of different populations along the Chilean coast. This showed that the species exhibits local adaptation in the form of countergradient growth adaptation because higher-latitude southern populations grew faster at all tested temperatures than their conspecifics from lower-latitude northern populations. We also show that fish from northern populations have on average two fewer vertebrae than their southern conspecifics, which is a form of cogradient adaptation also known as Jordan's Rule in fishes.

Chilean silverside embryos on the day of hatching

NSF-REU experiment reveals surprising heat tolerance of silverside embryos

Posted on July 5, 2026July 7, 2026 by Hannes Baumann

3 July 2026. Just in time for America250 celebrations, we want to share our own small cause of joy and accomplishment. The team, NSF-REU student Gabe Redmon, graduate student Emma Siegfried, and Hannes Baumann, just finished the second and last experiment on Atlantic silverside embryo heat tolerance. The data will become part of a globally distributed experiment on fish embryo heat sensitivity (Thermal Ecology Alliance, P. Pottier), hopefully helping to reveal broader evolutionary and ecological patterns across taxa.

In the most work-intensive moments, the team could not have succeeded without the help of Hermione Lao (NSF-REU 2026), graduate students Vicky You & Hannah Roby, and Hiryu Shinand (undergrad). Thank you!

The general experimental design was straightforward to make it broadly adaptable across systems. The goal was to expose newly fertilized fish embryos to heat stress and quantify their mortality. Choose a presumed stressful range of temperatures, vary the duration of the exposure, assess it at two developmental stages (early vs. advanced). Generally, silversides make great model organisms; they have been studied for decades and repeatedly rose to fame for revealing novel eco-evoluationary patterns (e.g., Conover, Therkildsen et al., Akopyan et al., Murray et al.).

However, the thermal sensitivity of Atlantic silverside embryos had not yet been robustly quantified.

The project is a central part of Gabe Redmon's NSF-sponsored Research Experience for Undergraduates (REU, UConn-MysticAquarium, NSF #2349353). Gabe discovered early that 'straightforward' does not equal 'easy' or 'low effort'. First lesson; silversides don't particularly care about Mo-Fr schedules, they are on a moon schedule, which influences the tides. For good quality experiments, it is best to collect adults right before they spawn on full and new moons. And with all the events that than need to follow in short order; there simply is no way to avoid weekends. Luckily, Gabe was completely unflinched by any of that; his dedication and curiosity were outstanding. Together, we designed some novel rearing designs to allow tracking groups off embryos through hatching. Together, we went to Mumford Cove to collect spawning-ripe adults with a beachseine. Twice.

Together - and with the necessary portion of luck - we pulled it off.

The time to show you the data will come later, the time to show some pictures is now. The analysis, which turns numbers into patterns, which then may lead to new insights has only just begun. One thing, however, is already clear from these data; silverside embryos are surprisingly heat stress tolerant. Exposures of up to 4h to 27-34C produced no measurable increase in mortality.

But that's not the whole story. There is more to come.

For now, join me again in a big show of hands for the whole team and the many helping hands!

Emma reflects on her research stay in Norway

Posted on April 29, 2026 by Hannes Baumann

By Emma Siegfried.

In 2019, the Evolutionary Fish Ecology lab at the University of Connecticut led by Dr. Hannes Baumann published their first paper investigating the effects of ocean acidification and warming on Ammodytes dubius. They found that levels of ocean acidification predicted for the year 2300 significantly decrease hatching success of embryos. The finding has begged the question if congener species are similarly susceptible – indicating the potential evolutionary conservation of this trait.

I began my PhD with the goal of doing similar experiments to other closely related species. One location where this would be possible is at the Institute of Marine Research (IMR), where a few scientists, notably Prescilla Perrichon, the leader of the Norwegian AQUASERV programme, have been spawning and raising Ammodytes marinus for a few years now. I applied to the AQUASERV transnational access program from the European Union and was fortunate to receive funding.

I arrived at the Austevoll Research Station at IMR in December 2025 unsure of what my time in Norway would bring. I had attempted similar experiments with Ammodytes americanus the previous winter and was not successful. In mid-January, the adult A. marinus that Reidun Bjelland had gone out and caught before I arrived began spawning. The fertilized embryos were placed in a rearing system, created with the help of Helen and Sam Rastrick, which exposed them to a combination of two different temperature and four carbon dioxide levels.

So far, we have collected data on the number of individuals hatched and how many embryos were in each individual tank initially. These values will be used to analyze hatching success and compare the impacts of ocean acidification and warming on A. marinus to the effects on A. dubius. In addition, we have photos of larvae that we can use to measure length, body area, and energy reserves. Finally, videos of the larval heart beating were taken for measurements of heart rate. In time, all this data will be analyzed and published.

I’m continuously grateful for the time I was able to spend at the Austevoll research station. It was truly the experience of a lifetime. I came out of my time in Norway with more knowledge and experience than I even thought possible and some new friends to boot. I am grateful for the support of all the staff at IMR, but particularly Prescilla, Reidun, Helen and Sam, and none of this research would have been possible without the AQUASERV program. I am very grateful for the support I received and the people that I have met through this program and look forward for potential opportunities for collaboration in the future.

A grouper on its way north – MEPS publishes Black Sea Bass synthesis paper

Posted on April 16, 2026April 17, 2026 by Hannes Baumann

16 April 2026. We are excited to share that Marine Ecology Progress Series today published our synthesis paper on Black Sea Bass in Long Island Sound!

The publication combines laboratory research on juvenile and adult black sea bass with ocean and climate modeling to make the case that these fish are already or at some point soon likely to change their habit of moving offshore in winter. This is because inshore waters are warming, so the fish can stay longer in fall and return earlier in spring, but also because the whole Northwest Atlantic shelf is warming, which reduces the distance the fish need to swim to reach overwinter habitat.

In the laboratory, PhD student Max Zavell with the help of his dedicated undergraduate assistants Matt Mouland and David Barnum conducted 2 overwinter experiments on juveniles to simulate their thermal experience of migrating offshore or remaining within Long Island Sound (LIS). Surprisingly, this showed that overwintering inshore caused only minor reductions in survival (100→84%), led to no loss in lipid reserves, but incurred a growth cost in both length and weight.

Thanks to the involvement of two inhouse physical oceanography groups (James O'Donnell, Samantha Siedlecki), we were able to project how mean LIS winter temperatures will increase from 3.2°C to 4.8°C by mid-century, which reduces the average time black sea bass cannot live in LIS by 30%, from 95 to 68d per year. A separate shelf model projected the rapid northward movement of the 10°C isotherm in February bottom temperatures on the Northwest Atlantic shelf - this reduces the overwinter migration distance from ~600 to ~120 km by mid-century!

Inshore overwintering will become increasingly feasible for black sea bass, perhaps lead to partial migration that furthers the poleward range expansion of this species.

The publication results from a particularly strong interdisciplinary collaboration of no less than 5 research labs: The Baumann and Schultz lab dedicated to fisheries and evolutionary fish ecology, the Matassa Lab with expertise in benthic ecology, the O'Donnell and Siedlecki groups dealing with modeling projections for nearshore and offshore waters in the North-Atlantic. The publication is an example of inclusiveness, given that the list of authors not only includes the graduate student as the lead, but also two particularly engaged undergraduate students, in addition to two post-doctoral researchers and the 5 more senior faculty.

Ambitious Experiment Discovers ‘Flipped’ Genetic Secrets of a Small Fish

Posted on March 9, 2026March 9, 2026 by Hannes Baumann

A grueling road trip led to an extraordinary experiment at UConn’s Rankin Seawater lab that discovered how inverted chromosomal segments help Atlantic silversides adapt

When a species lives in two distinct types of habitats, individuals with traits better suited to each habitat will thrive and reproduce, naturally selecting descendants with those traits. But what about mobile, aquatic species that live across a broad range of temperatures and latitudes? How do they maintain their genetic differences if individuals are free to mix and interbreed?

New research published on 5 March 2026 in Science finds that chromosomal inversions – which occur when a chunk of chromosome containing tens to thousands of genes breaks off, flips 180 degrees and reattaches to the same chromosome – play a central role in shaping these advantageous adaptations.

Read the whole story at UConn Today (9 March 2026)

Akopyan, M., Jacobs, A., Rick, J., Wilder, A., Baumann, Z., Conover, D., Baumann, H., and Therkildsen, N. (2025)
Multiple chromosomal inversions modulate continuous local adaptation along a steep thermal cline
Science 391:1015-1021

Hannes visits Emma’s sand lance experiment in Norway

Posted on March 9, 2026March 9, 2026 by Hannes Baumann

Austevoll, the world-famous marine research station, has also been PhD student Emma Siegfried's home for the past 2 1/2 months. Emma became the first US recipient of a European Union exchange fellowship (AQUASERV program) that covered the costs of her stay and her research in Norway. The goal of her project is to rear embryos of a local sand lance species, the Lesser sandeel Ammodytes marinus, under different levels of CO2 to then compare the results to what is already known for the Northern sand lance A. dubius on the western side of the Atlantic ocean.

Emma's experiment has been a success so far, thanks in no small part to the incredible help of our Norwegian collaborators. Every one at the station has been welcoming, friendly and eager to show us the large-scale aquaculture research on cod, halibut, haddock, plaice and many other fish species that is being conducted here every day of the year.

As we gape at the impressive tanks and installations, as we chat eagerly about deepening our collaborative ties and enjoy Norwegian hospitality and nature, we feel that this may indeed be the beginning of another great chapter of sand lance science to come.

Norwegian sand lance are hatching!

Posted on February 10, 2026February 10, 2026 by Hannes Baumann

By Emma Siegfried.

Austevoll, 10 February 2026. More than two months into my research stay here in Norway, things are going pretty well. Instead of one single experiment, we actually ended up running 3 separate experiments at once because the female fish took their sweet time to get ready to spawn.

As I learned, it is quite common in the tanks here that only a few females become ready to spawn at a time, which meant that a new trial had to be started again and again.

Our first spawn was now exactly 4 weeks ago, and I'm happy to report that our first embryos in the 10˚C treatment started hatching last week! Now we’re counting the larvae that are hatching each day, taking photos of them on the day of hatch and then also taking videos of their hearts to measure heart rate.

The hatchlings are then preserved, mostly in ethanol but also in RNAlater for potential further genomic and transcriptomic analyses.

The 2nd experiment & Hannes’ time in Chile end – but the science just started

Posted on December 21, 2025December 21, 2025 by Hannes Baumann

Whole Blog

22 December 2025. Shortly before Christmas, a cloudless blue summer sky stretches endlessly over Dichato. The summer vacationers now arrive in troves in this small Chilean village. Hannes just returned again for a few short days to help end the second common garden experiment at the Marine Station, preserve all sampled specimens, and ready them for their journey to Connecticut. The days are filled with bittersweet emotions, as one chapter ends while marking the beginning of the data analysis phase of the whole project.

For more than 5 weeks, research technician Tamara Cuevas diligently attended to the experiment while Hannes finished teaching his class at UConn. Tamara successfully executed the daily husbandry, feeding, testing, the frequent sampling events, while reacting nimbly to all the unforeseeable, yet inevitable things that came her way. Tamara, you're truly the hero of this second experiment, well done!

Meanwhile, Hannes used his third journey to the southern hemisphere to make a few stops along the way. In Lima (Peru), he met with Victor Aramayo, a biologist at the Peruvian Institute of Marine Research (IMARPE), to receive silverside samples from two locations in Peru. He then traveled to Valparaiso (Chile) to meet with Prof. Mauricio Landaeta (Universidad de Valparaiso), who contributed samples from the southernmost silverside species (Odontesthes smitti) from Punta Arenas in Chile's far south. He flew for a day trip to Antofagasta (Chile) to meet Prof. Marcelo Oliva (Universidad de Antofagasta) who contributed specimens from this particular locale. All together, we now have silverside samples from 7 populations spanning 45 degrees of latitude (9-54S) for genomic analyses!

As Hannes shakes hands and emotionally says good bye to his Chilean friends and colleagues, it is the excitement for the findings to come that shines as bright as the December sun over Dichato.

Saludos y feliz navidad!

Emma arrives in Norway to start sand lance experiment

Posted on December 18, 2025December 18, 2025 by Hannes Baumann

By Emma Siegfried

16 December 2025. Hi, Emma here reporting in from the Institute of Marine Research in Storebø, Norway! After a quick stop in Amsterdam, I landed in Bergen on Saturday morning. I grabbed a quick ferry to get over to the island and settled in over the weekend in one of the on-station residences. The area is pretty rural, but the surroundings are idyllic. The islands are exactly what you would expect to see out of a movie.

Yesterday, I was able to get a tour of the station, and the facilities here are incredible. If I had to estimate it’s probably 6 or 7 times the size of Rankin lab. The facility has been doing research on the early life history stages of Cod, Haddock and Plaice on top of previous work with Lesser Sand Lance (Ammodytes marinus) larvae, and as a result has some quite large broodstock tanks.