UConn Cookie Information

Silversides are a group of small, inconspicuous looking forage (or 'bait') fishes of the Americas (family: Atherinopsidae). Over past decades, ecologists and evolutionary biologists have used them as models and discovered important new patterns of adaptation and climate sensitivity in the aquatic realm. Among them, the Atlantic silverside is arguably the most famous.

Over the years, our lab and collaborators have contributed to an already rich eco-evolutionary literature by (1) thoroughly investigating how silversides may cope with rising temperatures, rising CO2-levels and reduced oxygen conditions in potential future oceans, and (2) discovering in great detail the genomic architecture that allows Atlantic silversides to adapt so efficiently to environmental gradients in temperature or to size-selective fishing pressure.

Atlantic silversides are abundant in our local waters and readily accessible with a beach seine. We have often begun experiments by first collecting spawning ripe adults (May-July) to then produce fertilized embryos for rearing treatments.

Publications:

This iconic resident of North-American Pacific coasts has been the second Pacific silverside species after topsmelt that we studied experimentally. We looked for potential latitudinal patterns in larval growth rate and vertebral number, among other traits. In 2009/2010, we headed west to collect spawning ripe adults from places like Malibu Beach (CA) to produce and then transport fertilized embryos back to Stony Brook University. Fish were reared until late larval stages under different temperature conditions.

The species is beloved among naturalists, and scientists treasure them as a model organism, because grunion embryos are accessible with relative ease - you don't even have to get your feet wet (or just a little). During so called grunion runs, the fish beach themselves at night king tides, spawn and return to the ocean, while the larvae develop in the warm moist sand for about half a moon.

Interestingly enough, over the small latitudinal range that were able to sample and assess, we did not find population differences in temperature-dependent larval growth rates. On the other hand, we discovered that California grunion that are among the few fish species that have environmental sex determination. During a certain time window of the larval stage, warmer temperatures usually make more male-biased sex ratios. In addition, we discovered that photoperiod, too, changes sex ratios in California grunion. A very novel find!

Publications:
(1) Brown et al. Marine Ecology Progress Series 2012
(2) Brown et al. Journal of Experimental Marine Biology and Ecology 2014

In 2012, a team of Stony Brook researchers traveled to the Florida Keys to sample a type of silverside species that only occurs there in hypersaline ponds, which are lagoons surrounded by mangroves that often have salinities over 40 psu. We then used morphometrics and genetic tools to answer the question whether this is truly a different species or simply an ecotype of the Tidewater silverside, which occurs abundantly in coastal waters of Florida and the Gulf of Mexico.

Publications:
(1) O'Leary et al. Bulletin of Marine Science 2016

In 2012, this silverside species became the first documented case of direct, CO₂-induced effects on growth and survival in a fish. We reared offspring from fertilization to approximately one week post hatch under various levels of elevated CO₂, which may occur in future open ocean waters due to ocean acidification; mankinds other CO₂ problem.

As ocean acidification-relevant CO₂ levels increased, survival declined.

Publications:

(1) Baumann et al. Nature Climate Change 2012

(2) Depasquale et al. Marine Ecology Progress Series 2015

The sea silverside (or Chilean silverside) is the most recent addition of a silverside species investigated in our lab. It is - like all silversides - a small, ecologically important forage fish, but there's something new: It turns out that it recently became the first documented case of countergradient growth adaptation in a Southern hemisphere fish!

The study was possible, because Hannes spent the best part of his sabbatical in 2023/24 in a Marine Station in Chile, constructing and conducting a common-garden rearing experiment on different populations from different latitudes along the Chilean coast.

Learn more about the whole sabbatical project called 'Expanding the silverside system'.

Publications:
(1) Baumann et al. Ecology and Evolution 2026

Topsmelt are the taxonomically and ecologically best equivalent to silverside species on thee North-American Atlantic coast. In 2008-2009, we formally set out to measure latitudinal patterns of local adaptation in topsmelt to then compare the strength of these evolutionary patterns between ocean gradients. This was Hannes' first project after coming to the US as a post-doc. We ventured along the Pacific coast to places from Orgeon to Baja California, strip-spawned ripe adults, and then transported the embryos via airplane to Stony Brook.

Ultimately, these experiments revealed that co- and countergradient adaptation patterns have clearly evolved between topsmelt populations from different latitudes - but, the strength of these patterns is weaker than in Atlantic silversides. This likely reflects the weak vs. strong latitudinal temperature gradients along Pacific vs. Atlantic coasts.

Publications:
(1) Baumann et al. Proceedings of the Royal Society B 2011
(2) Baumann et al. Copeia 2012

Apart from silversides, sandlances are another major research focus of our lab. On the northwest Atlantic shelf, two closely related species exist, and more than 70 different fish, bird, and mammalian predators rely on them as prey. Sandlances are really special; not only do they occur in large schools in midwaters to feed on zooplankton, but at night or during resting periods they also bury themselves into sand to hide from predators.

Northern sandlance live on offshore sandbanks, and a good decade ago we hypothesized that their embryos might be adapted to more stable open ocean CO2 conditions and may therefore perhaps be less tolerant to manmade ocean acidification. Since our initial discovery of the unusual CO2-sensitivity of sand lance embryos we have continuously built on this research using comparative and molecular tools.

More recently, the evolutionary question what keeps the the closely related congeners (Northern vs. American sand lance) separated and whether sandlance may be vulnerable to magnetic fields from undersea cables have become important new research angles.

Publications:
(1) Murray et al. Conservation Physiology 2019
(2) Silva et al. Conservation Science and Practice 2020
(3) Staudinger et al. Fish and Fisheries 2020
(4) Suca et al. ICES Journal of Marine Sciences 2021
(5) Suca et al. Fisheries Oceanography 2022
(6) Baumann et al. Marine Ecology Progress Series 2023
(3) Jones et al. ICES Journal of Marine Science 2023
(7) Jones et al. Environmental Biology of Fishes

This particular sandlance species occurs on suitable sandy areas all across the North-eastern Pacific shelf, where it is a similarly important forage fish for a diverse guild of predators than its North-Atlantic congeners. We have not yet worked experimentally with Pacific sandlance, but in 2019 obtained a modest sample of specimens from beaches at the Salish Sea just south of the US-Canadian border. DNA extracted from fin-clips of these samples was sequenced and then used as an outgroup in a large population-genetic study of North-Atlantic sandlances.

Publications:
(1) Jones et al. ICES Journal of Marine Science 2023

Following the discovery of the unusually high CO₂-sensitivity of Northern sandlance embryos, we have recently begun to ask the question whether closely related sandlance species might be similarly vulnerable to mankind's other CO₂-problem, ocean acidification.

In winter of 2025/26, we conducted experimental work on Lesser sandeel embryos, a species that occurs on North-eastern Atlantic shelf habitats. Together with Norwegian collaborators at the Austevoll Marine Research Station, we again subjected newly fertilized embryos to a range of CO₂ levels as they may occur in future oceans. The experiments were successful, and hopefully the results will be published soon.

Publications:

The American sandlance is the other sandlance species in coastal waters of the North-west Atlantic shelf. It is both morphologically and genetically so similar to Northern sandlance that the two species have undoubtedly been confounded in the literature over past decades. Scientists often assume that what is separating the two species is simple habitat preference: the American sandlance is assumed to occur only in nearshore waters, whereas the Northern sandlance are said occur exclusively over offshore sandbanks.

Our research has taken an increasing interest in testing this assumption, using novel genetic markers to look at large numbers of samples throughout the species distributions.
In addition, we have also begun to work experimentally with American sandlance, again asking the question whether embryos of this species are similarly sensitive to increasing CO2-levels in their waters.

Publications:
(1) Staudinger et al. Fish and Fisheries 2020
(2) Jones et al. ICES Journal of Marine Science 2023

This small benthic dweller occurs abundantly in North-west Atlantic coastal waters. It is of no commercial interest but it has been repeatedly used as a model to understand how fishes grow and survive during their early and most vulnerable larval stages. It was among the first fish species our lab worked on (back when H.Baumann was himself still a student); in 2001/02 we studied daily increments in the otoliths (earbones) of shanny larvae sampled from a large bay in Newfoundland.
This showed that faster growing larvae (having wider daily increments) are more likely to survive the first weeks and months of their life - confirming the so-called "Bigger-is-Better Hypothesis" that is among the central paradigms in marine ecology.

Publications:
(1) Baumann et al. ICES Journal of Marine Sciences 2003

These two exotic damselfishes are common inhabitants of Australias Great Barrier Reef. In December 2007, Hannes worked for a few weeks with Australian collaborators on the fabled Lizard Island Research Station, where he became enamored with the juveniles of these fishes settling in large recruitment pulses onto the reefs.
We analyzed the otoliths of these little guys and discovered that in these cases otolith growth only begins to approximate the growth of the actual fish (somatic growth) after juveniles had successfully transitioned from their pelagic larval to their benthic coral reef life.

Publications:
(1) Baumann and Gagliano Helgoland Marine Research 2011

Sprat are herring-like forage fish (family Clupeidae) that occur abundantly in the Baltic and North Sea. Interest in this species increased in the late 1990s, when it became apparent that the Baltic Sea had experienced a regime shift from a formerly cod-dominated to a now sprat/herring dominated ecosystem. The largest national research project at that time - GLOBEC Germany - ran from 2002-2008 to thoroughly investigate the causes and consequences of this regime shift, using field, experimental, and modelling methods.
Hannes contributed as a PhD student, by trying to better understand what generates the high variability in sprat year classes and therefore stock biomass. Otolith microstructure analysis, i.e., the analysis of daily growth increments in a fish's earbones, was a central tool - showing temperature- and region-specific growth patterns, selective survival of fast over slower growing young-of-the-year, along with basic research into the fundamentals of otolith:somatic growth coupling.

Publications:
(1) Baumann et al. Journal of Marine and Freshwater Research 2005
(2) Hinrichsen et al. Journal of Marine Systems 2005
(3) Voss et al. Marine Ecology Progress Series 2006
(4) Baumann et al. Canadian Journal of Fisheries and Aquatic Sciences 2006
(5) Baumann et al. Marine Ecology Progress Series 2006
(6) Baumann et al. Fisheries Oceanography 2006
(7) Baumann et al. Journal of Fish Biology 2007
(8) Baumann et al. Fisheries Research 2008
(9) Baumann et al. Journal of Sea Research 2009
(10) Guenther et al. Canadian Journal of Fisheries and Aquatic Sciences 2012
(11) Peck et al. Progress in Oceanography 2012
(12) Voss et al. Progress in Oceanography 2012
(13) Peck et al. Journal of Experimental Marine Biology and Ecology 2015

Alewife are iconic inhabitants of the North-American Atlantic coast, famous for swimming up rivers to spawn and emigrating back out to the ocean to feed and grow. The phenomenon is called anadromy, and it comprises and important link between marine and freshwater habitats that is being imperiled by human activities. We have just began working experimentally with alewife, rearing fish at different - and changing - salinities to better understand the physiology behind their remarkable abilities to switch between fresh and ocean waters.

Haddock are close relatives of cod, and they are of equally large economic importance due to their tasty white meat. Detailed records of fishery-independent surveys of haddock abundance and year-class strength go back almost 100 years - among the longest time-series in fisheries and thus a valuable source of scientific information.
To estimate a fish's age - to then understand how many are out there from each year class - scientists began taking a few scales from each individual caught, counting the number of rings to estimate the age in years. Later, the method changed, and otoliths were used for the same purpose, because they yield more reliable estimates for older fish.

We compared how haddock otolith and scales grow, discovering that they yield different estimates of back-calculated growth.Publications:
(1) Baumann et al. Transactions of the American Fisheries Society 2013

Atlantic cod is arguably the most famous commercial fish species in the North-Atlantic; it's exploitation goes back centuries. However, while all the same species, many discernible cod stocks exist with different growth patterns, feeding habits, even different colorations. In 2006/07, a team from Germany met with Norwegian collaborators in Tromso, Norway - to figure out a way to use the shape of the otoliths to distinguish a local cod stock called Norwegian coastal cod from a more northern, and temporarily transient cod stock called Northeast Arctic cod.

Publications:
(1) Stransky et al. Fisheries Research 2007

Pacific bluefin tuna are record-holders in many ways; from the enormous size of adults to the astronomic amounts of money they fetch on fish markets around the world. But did you know that they are also performing one of the longest transoceanic migrations known in the marine world? As juveniles, all Pacific bluefins decide at some point to travel more than 8000 km west across the Pacific Ocean to reach the California Current Large Marine Ecosystem; where upwelling produces plentiful phytoplankton, zooplankton, and zooplanktivorous fish (like anchovies, sardines) that the tuna eat.

We used different tools, from isotopic markers to trace elements in otoliths, to better understand how long tuna juveniles travel and when exactly they arrive in California after their transatlantic journey.

Publications:
(1) Baumann et al. ICES Journal of Marine Science 2015
(2) Madigan et al. Environmental Science & Technology 2018
(3) Rooker et al. Scientific Reports 2021

Black sea bass are the northernmost grouper (family Serranidae) species in the Atlantic - and of late they have become something like Exhibit A for marine species reacting to climate climate change via poleward range expansions. For black sea bass, this is technically true for the northern stock, which indeed increased considerably in abundance and now occurs in places where the fish were previously rare or absent.
In Long Island Sound, black sea bass increased by one order of magnitude in abundance since 2010!
Our lab has become ever more interested in this species, studying its COoverwinter growth and mortality, and more recently its broad diet that makes it a likely competitor to many other fishes in our waters. Our experiments coupled with model projections suggested that black sea bass may change their overwinter migration and could someday soon overwinter right here in Long Island Sound.

Publications:
(1) Zavell et al. Transactions of the American Fisheries Society 2024
(2) Zavell and Baumann Environmental Biology of Fishes 2024
(3) Batta-Lona et al. Fishery Bulletin 2025
(4) Zavell et al. Marine and Coastal Fisheries 2025
(5) Zavell et al. Marine Ecology Progress Series 2026

Sturgeon are evolutionary ancient bony fish, and even though they have survived for millions of years they are now endangered species due to human fishing and habitat degradation.

Atlantic sturgeon require rivers to travel up for spawning, but spawning populations have vanished from many of the rivers flowing into the Atlantic Ocean. Our research looked at a seasonal aggregation of Atlantic sturgeon using the Connecticut River; we determined ages from sections of their pectoral fin spines and we analyzed telemetry data, i.e., records from acoustic tags implanted into some individuals which can then be 'listened' to by receivers in the river.

We did not find conclusive evidence that Atlantic sturgeon have begun to spawn again in the Connecticut River, but they sure travel far up into freshwater for reasons unrelated to reproduction.

Publications:
(1) Mosca et al. Fishery Bulletin 2025

Early experimental work had suggested that ocean acidification may be particularly problematic for corals or shell-forming invertebrates like mussels, clams, or snails. In 2013-14, we looked at early juvenile stages of two local bivalve species - hard clams and bay scallops - conducting exposure experiments that showed that hypoxia and acidification have additive and synergistic negative effects on their growth, survival, and metamorphosis.

Publications:
(1) Gobler et al. PLOS One 2014