According to a new report, in summer 2023, the Chesapeake Bay experienced cooler water temperatures, healthier oxygen levels, and higher salinity levels than average. In general, these conditions are good for striped bass, blue crabs, oysters, and other species.
The NOAA Chesapeake Bay Office develops four seasonal summary reports each year. Each report includes analysis of observations from CBIBS buoys and satellites to determine how Bay conditions compared with the average over the past 20 years. Then scientists explore how those differences may have affected species that live in the Chesapeake Bay.
Water Temperatures Were Cooler than Average
Data from CBIBS buoys and from satellites show that water temperatures in the Chesapeake Bay were cooler than average throughout summer 2023.
Data from satellites shows that water temperatures from June through August 2023 were cooler than the average from 2007–2022.
In the summer, water temperature and dissolved oxygen levels determine where striped bass live in the Bay. The Maryland Department of Natural Resources has defined what water temperatures and dissolved oxygen levels are good—and not good—for striped bass:
- Normal: temperatures up to 82.4° and dissolved oxygen levels of more than 4 milligrams/liter
- Tolerable (striped bass can live here for up to a month without affecting their growth or death rates): temperatures 82.4°–84.2° and dissolved oxygen levels of between 3 and 4 mg/L
- Marginal (striped bass can stay in these waters only briefly; otherwise, they can experience high death rates): temperatures 84.2°–86° and dissolved oxygen levels of between 2 and 3 mg/L
- Unsuitable (striped bass try to avoid these conditions): temperatures above 86° and dissolved oxygen levels below 2 mg/L
This graph shows water temperatures at the CBIBS buoy at the mouth of the Potomac River warmed to conditions considered marginal for striped bass health on only a few days.
But in summer 2023, the number of days where striped bass encountered even “marginal” conditions was very small. The striped bass population along the U.S. East Coast has been low. Overfishing is one reason. But scientists are also concerned about their habitat. Tracking information about striped bass habitat—like water temperature and dissolved oxygen levels—can help scientists learn more about what the effects of climate change could mean for this species.
Another Bay species that suffers when waters get too warm is eelgrass. Eelgrass is an underwater grass that provides habitat for many species, like blue crab. So conditions in summer 2023 may have helped eelgrass—and in turn, blue crab.
The Bay experienced healthier-than-average oxygen levels this summer. Scientists believe this may be for two reasons:
- Because spring rainfall was lower than average, less nutrients may have washed into the Bay. Excess nutrients can fuel algae blooms that lead to low dissolved oxygen.
- June was fairly windy. Windy days can help mix up the water in the Bay, helping to incorporate more oxygen into the waters.
Plants and animals in the Bay need oxygen, just like humans. When water has very low levels of dissolved oxygen (less than 2 mg/L), it is considered “hypoxic.” The volume of the Bay considered hypoxic this summer was below average. That’s likely good news for Bay species.
Estimates of hypoxic volume in the Chesapeake Bay from the Chesapeake Bay Environmental Forecast System show that summer 2023 hypoxic volume was less than in the years 2018–2022.
Freshwater Input and Salinity
Freshwater input to the Chesapeake, tracked through precipitation and streamflow levels, was also lower than usual. This led to mostly higher-than-average salinity. In general, higher salinity levels support above-average survival and growth of young oysters. But high salinity (15-20 psu) can support two oyster diseases, Dermo and MSX. These diseases can kill oysters.
Data from the Gooses Reef CBIBS location shows that salinity was higher than average in summer 2022.
Some fish prefer saltier waters. For example, bay anchovy like surface water salinities between 17 and 26 psu in the summer. But fish are complex, and while these fish like that salty water, other aspects of their habitat (like dissolved oxygen and water temperature) are important, too.
For a scientific dive into summer 2023 conditions and how they may have affected living resources in the Chesapeake Bay, as well as more graphs, see the full summer 2023 scientific seasonal summary.