ocean acidification

Long Island Sound Shell Day 2023

Shell Day logo, credit: Austin Pugh, NECAN

On 24 August, 2023, 10 community science organizations, the Connecticut Department of Energy and Environmental Protection (CT-DEEP) and the University of Connecticut collaborated to simultaneously sample total alkalinity in the embayments and rivers bordering Long Island Sound (LIS). Led by DMS PhD Candidate Lauren Barrett, the event was a regional repeat of the 2019 effort led across New England by the Northeast Coastal Acidification Network (NECAN, http://necan.org/ShellDay).

The participating groups sampled for total alkalinity (TA) and hydrographic variables such as salinity and temperature during low, mid-, and high tides, meaning the spatial variation in alkalinity across the Sound. Seawater alkalinity requires high precision, expensive instrumentation and a skilled analyst, and thus typical observations of TA in LIS conducted by a single or a few researchers require that spatially separate samples also have a temporal difference. However, TA varies across diel and tidal cycles, so the spatial and temporal difference is important to parse. The collaborative effort of Shell Day allowed for a spatial identification of TA trends in LIS without the confounding temporal variation.

Shell Day 2023 was a successful event. Despite some mild rain in the afternoon, community scientists weathered the storm and still provided high-quality samples, which are currently undergoing TA analysis at UConn. The results of this work will be interpreted in the context of open LIS data (available through the Vlahos lab at UConn) and the data collected during Shell Day 2019. This work will be presented to the LIS Science Technical and Advisory Committee (STAC) this fall as well as to the participating organizations at a meeting which is to be determined.

Surveying ocean acidification on the Northwest Atlantic shelf

By Ewaldo Leitao.

In August of 2022, Prof. Samantha Siedlecki and Prof. Craig Tobias, along with students Halle Berger and Alex Frenzel, went on the East Coast Ocean Acidification Cruise (ECOA-3). The cruise was led by scientists at the University of New Hampshire, joined through transdisciplinary partnerships with other universities, aboard the NOAA Ship Ronald H. Brown. The UConn Avery Point members joined the cruise to investigate the contribution of sediments to carbon chemistry and how that ultimately impacts ocean acidification.

“Core team” on the deck of NOAA Ship Ronald H. Brown with multi-core sampler. Left to right: Halle Berger, Samantha Siedlecki, Craig Tobias, Alex Frenzel

Sam, Craig, Halle and Alex were the sediment coring team. The cores go all the way down to the bottom of the ocean and collect both the upper part of the sediment and the layer of water above it. This way, it is possible to understand chemical reactions in this zone between the sediments and the water above it. “The idea here is to understand how sediments control the chemistry of bottom water. There are sediment reactions that could help buffer acidity. But it's unclear how sediments talk to the water above it or how that communication might change in the future” says Craig. You can learn more on the Facebook page of research vessel Ronald H. Brown.

These measurements are valuable information because they are not only timestamps of what is happening at the moment of collection. Increasing the number of observations and fine-tuning the measurements of these chemical processes in bottom waters helps the research of modelers, like Sam. Models are important to test our understanding of ocean processes. We need more measurements like this to more accurately predict marine climate change. Part of Sam’s work is to use this information into regional ocean models to better constrain the role of sediments in the chemistry of the ocean.

Graduate student Halle uses modeling to understand how ocean acidification and warming impacts marine animals like Atlantic sea scallops. “I learned a lot about how all the different carbonate system parameters are measured, and it was great to meet other students and scientists working on ocean acidification. We got to see some whales and dolphins, amazing sunsets and starry nights, and ate a lot of delicious food. My favorite memory was at one station where all the multi-corer brought up was a single hermit crab (no sediment at all). We named him Fred.”, said Halle.

Sediment sample with overlying seawater and a white brittle star attached to the side of the tube

Alex Frenzel (left) and Halle Berger (right) collecting a subsample of the core on the deck

This was the third ECOA survey, which only happens every four years. The cruise starts in Newport, RI, travels to Portland, ME and then continues on to Nova Scotia. Traveling the Gulf of Maine, Georges Bank, Long Island Sound, Mid-Atlantic Bight, Chesapeake Bay, and the South Atlantic Bight. Each of these regions has their own physical processes that affect ocean acidification in each region, such as the Gulf of Maine receiving cold waters from the northern Labrador current and freshwater from rivers. In each of these regions, ocean acidification will likely have different effects. In the South Atlantic Bight, coral reefs, soft bottom corals, and therefore fish abundance may decline with ocean acidification. To better understand and accurately predict the impact of ocean acidification in different ecosystems, it is important to continuously do these measurements in order to understand how processes are changing over time in such dynamic environments.

Under Ocean Acidification, Embryos of a Key Forage Fish Struggle to Hatch

A potential ripple effect from carbon in the atmosphere could have severe impacts throughout the ocean ecosystem

This photo shows sand lance embryos that have and have not hatched. Sand lance have trouble hatching at future ocean CO2 levels (photo courtesy of Emma Cross).

By Elaina Hancock. Reposted from UConn Today, 7 April 2022

When carbon is emitted into the atmosphere, about a quarter of it is absorbed by the earth’s oceans. As the oceans serve as a massive ‘sink’ for carbon, there are changes to the water’s pH – a measure of how acidic or basic water is. As oceans absorb carbon, their water becomes more acidic, a process called ocean acidification (OA). For years, researchers have worked to understand what effect this could have on marine life.

While most research so far shows that fish are fairly resilient to OA, new research from UConn, the University of Washington, the National Oceanic and Atmospheric Administration (NOAA), and Southern Connecticut State University, shows that an important forage fish for the Northwest Atlantic called sand lance is very sensitive to OA, and that this could have considerable ecosystem impacts by 2100. The team’s findings have just been published in Marine Ecology Progress Series 687.

Sand lance spawn in the winter months in offshore environments that tend to have stable, low levels of CO2, explains UConn Department of Marine Sciences researcher and lead author Hannes Baumann.

“Marine organisms are not living in a uniform ocean,” Baumann says. “In near shore environments, large CO2 fluctuations between day and night and between seasons are the norm, and the fish and other organisms are adapted to this variability. When we stumbled upon sand lances we suspected they are different. We thought that a fish that lives in a more open-ocean offshore environment might be more sensitive than the near-shore fish because there’s just much less variability.”

The project was a collaboration with physical oceanographers, including Assistant Professor of Marine Sciences Samantha Siedlecki and Michael Alexander from NOAA’s Physical Sciences Laboratory in Boulder, Colorado, who modeled CO2 levels in 2050 and 2100 for a specific part of the Gulf of Maine where sand lance spawn. Then Baumann and his team reared sand lance embryos in the lab under experimentally higher CO2 levels matching the projected levels.

There are instances of direct fish mortality as result of elevated CO2, but they are rare, says Baumann. However, sand lance embryos proved to be exceptionally sensitive, and fewer embryos hatched under future oceanic CO2 conditions. The researchers repeated the experiments three more times to avoid jumping to conclusions but each time they observed the same result.

“We found that embryo survival-to-hatch decreased sharply with increasing CO2 levels in the water, concluding that this is one of the most CO2-sensitive fish species studied thus far,” Baumann says.

Sand lances are surely one of the most important forage fish here on the Northwest Atlantic shelf… The humpback whales, sharks, tuna, cod, shearwaters, terns — you name it — they are all relying on sand lance.

With this interdisciplinary approach combining model forecasts and serial experimentation the researchers arrived at a picture that is much more specific.

“We consequently applied principles of serial experimentation, which is a most timely and important topic in ocean acidification research right now,” Baumann says. “Because our findings are backed up by repeated independent evidence, they are more robust than many published ocean acidification studies to date.”

In addition to preventing many sand lance embryos from developing normally, the researchers document a second negative, and novel, response to elevated CO2. Higher CO2 levels appear to make it harder for embryos to hatch.

Baumann explains the lowered pH likely renders enzymes needed for successful hatching less effective, leaving the embryos unable to break through their eggshell (chorion) to hatch.

The results show that by 2100, due to acidification, sand lance hatching success could be reduced to 71% of today’s levels. Since sand lance are such a critical component of the food web of the Northwest Atlantic, this marked decrease in sand lance would have profound impacts throughout the ecosystem.

“Sand lances are surely one of the most important forage fish here on the Northwest Atlantic shelf,” Baumann says. “Their range spans from the Mid Atlantic Bight all the way to Greenland. Where we studied them, on Stellwagen Bank, they are called the backbone of the ecosystem. The humpback whales, sharks, tuna, cod, shearwaters, terns — you name it — they are all relying on sand lance, and if sand lance productivity goes down, we will see ripple effects to all these higher trophic animals. Even though we humans don’t fish for sand lance, we need to take care of the species because it has such a huge effect on everything else.”

Baumann says this study supports the hypothesis that offshore, high latitude marine organisms like the sand lance may be among the most vulnerable to OA. As a result, these organisms and food webs will likely be impacted first and soon, and we must act now.

Previous research has focused on opportunistically chosen species when testing their sensitivity for ocean acidification, says Baumann, but this should change.

“We need strategic thinking about what species we are testing next, because we cannot test every marine fish species, that’s an impossible task. We should concentrate on fish species that are likely the most vulnerable, and therefore the ones that are probably being affected first and this research makes a compelling argument that those are the fish species at higher latitudes and in more offshore than nearshore environments.”