Restoring habitat for one of the most fascinating fish species in the Chesapeake Bay…the lined seahorse
Beneath the shallow waters of the Chesapeake Bay, a lined seahorse conceals itself in a dense bed of underwater grasses. Although the seahorse’s choice of habitat may not seem significant, it is critical to its survival. Lined seahorses are highly dependent on underwater grasses, also known as submerged aquatic vegetation (SAV). In fact, SAV, particularly eelgrass, is the preferred habitat of seahorses. Not only does SAV provide home to tiny crustaceans that seahorses eat, but it also offers seahorses shelter from predators, camouflage for ambushing prey, and breeding grounds.
Although lined seahorses prefer eelgrass, which used to be the dominant species of SAV in the lower Bay, it is not their exclusive habitat. They live in other species of underwater grasses as well as in oyster beds. Seahorses have also been found clinging to crab pots, pilings, or ropes.
Forty-six species of seahorses are recognized within the genus Hippocampus, but only one, the lined seahorse (Hippocampus erectus), is native to the Chesapeake Bay. It is not known exactly how many lined seahorses are found in the Bay, and they are not common. However, scientists typically find them during yearly trawls.
According to the International Union for Conservation of Nature (IUCN), lined seahorses are listed as vulnerable primarily due to habitat loss. Since seahorses rely on SAV, declines in underwater grass beds can impact their survival. So, it’s critical to continue efforts to monitor and restore SAV in the Bay.
“Lined seahorses are dependent on the structured habitat that SAV provides,” says Brooke Landry, SAV program chief for the Maryland Department of Natural Resources (DNR) and chair of the Chesapeake Bay Program SAV Workgroup. “They are poor swimmers, so they don’t have a lot of control over their movement. They use their tiny fins to move through the water and hold onto SAV with their prehensile tail. Although there are no concentrated studies on lined seahorses, we can infer that the loss of SAV is a threat, and protecting the species is tied to SAV restoration.”
Lined seahorses’ preferred habitat is eelgrass, a common SAV in the Chesapeake Bay watershed. They use their tiny fins to move through the water and hold onto SAV with their prehensile tail. Photo by Erin Shields, CBNERRVA.
Range in the Chesapeake Bay
Lined seahorses live year-round in the middle and lower Chesapeake Bay within higher salinity areas. They have been documented in Hampton Roads, Virginia’s lower Eastern Shore, Tangier Sound, Maryland’s Eastern Shore, and Calvert County waters.
According to the Virginia Institute of Marine Science (VIMS), the Chesapeake Bay provides habitat for more than 200 species of fish. Since 1955, VIMS has conducted its Juvenile Finfish Trawl Survey to monitor fish populations and track trends in seasonal distribution and abundance. Although the trawl surveys target juvenile fish species, lined seahorses are among the fish caught.
“The VIMS Juvenile Finfish Trawl Survey conducts 1,224 tows each year, and our team is on the water every month,” says Troy Tuckey, Ph.D., senior research scientist, VIMS. “We use a bottom trawl and tow the net for five minutes. Samples are taken in Virginia’s portion of the Chesapeake Bay and the Rappahannock, York, and James rivers—from the mouth of each river to approximately 40 miles upstream to where the freshwater-saltwater interface occurs. Water temperature, dissolved oxygen, salinity, and pH are measured at every station. We identify, count, and measure all fish species before releasing them back into the water. We also count and measure blue crabs and shrimp.
“Although lined seahorses are not common in the Bay, we still catch them every year. And we would be surprised if we didn’t catch them. Our team gets really excited when we see lined seahorses. They are such amazing fish with a truly unique lifestyle. Seahorses definitely bring a smile to your face every time you see them.”
Lined seahorses are also caught during the Maryland Blue Crab Trawl Survey, a sampling program that is conducted by the DNR every year. Samples are collected once a month from May through October from sites in the Chester River, Patuxent River, Choptank River, Eastern Bay, Tangier Sound, Pocomoke Sound, Little Choptank River, Fishing Bay, Nanticoke River, and Little Annemessex River. The trawl survey, which began in 1977, provides information about trends in blue crab abundance.
“The trawl survey focuses on blue crabs, but juvenile finfish and other marine life that live on or near the bottom are also caught,” says Chris Walstrum, natural resource biologist, fishing and boating service, DNR. “In this case, lined seahorses are not the targeted species, but they are caught when the conditions are favorable, and they are present in the right place at the wrong time.”
A Unique Fish
Lined seahorses are just one of the 500 animals and 70 species on display at Calvert Marine Museum, which focuses on the culture and natural history of Southern Maryland.
Known for their unique—almost magical—appearance, seahorses captivate aquatic enthusiasts of all ages. With its horse-like head, tubular snout with a small, toothless mouth at the end, bony plates covering its body instead of scales, and prehensile tail for grasping, the lined seahorse, or northern seahorse, doesn’t look like other fish. In fact, its closest relative is the pipefish, a small, skinny fish with a long snout.
Deriving their name from the white lines that can often be seen on their bodies, lined seahorses are approximately five to six inches long and vary in color from yellow to nearly black. Masters of camouflage, they change colors to match their environment and conceal themselves in underwater grass beds. Not only does this ability protect seahorses from predators, such as striped bass, tuna, and dolphinfish, it also helps them catch prey.
“Seahorses are ambush predators,” Tuckey says. “They hide among SAV structure, using their tail to hold tightly to the grasses, and wait for currents to wash food, mostly zooplankton and tiny crustaceans, towards them. They remain undetected and then ambush, sucking the prey into their tubular snouts.”
In addition to their iconic appearance, seahorses are perhaps most well-known for a unique trait in the animal kingdom. In a rare case of reproductive role reversal, the males become pregnant and give birth. After an elaborate courtship ritual, the female deposits her eggs into the male’s brood pouch. The eggs are fertilized and incubate for about two weeks before they hatch. The male then releases 100 to 300 fully formed baby seahorses into the water. Juveniles are less than one-quarter of an inch long.
According to National Oceanic and Atmospheric Administration (NOAA) Fisheries, seahorses, pipefish (native to the Bay), and sea dragons (native to the Western Pacific Ocean) are the only organisms in the animal kingdom in which the males get pregnant and give birth.
Protecting the Habitat of Lined Seahorses
SAV plays a critical role in the Chesapeake Bay ecosystem. It absorbs nutrients, produces oxygen during photosynthesis, improves water clarity, settles suspended sediments, stabilizes bottom sediments, absorbs wave energy, and reduces shoreline erosion. But although underwater grasses provide several benefits, they also face threats that impact their survival and abundance.
Perhaps the primary source of concern is poor water quality. Pollutants, including nutrient and sediment runoff, fuel algae blooms and cloud the water. These algae blooms prevent sunlight from reaching the plants, causing SAV beds to die. In addition, weather conditions, changes in salinity levels due to heavy rains, and climate change also impact the ability of underwater grasses to survive.
“We know that lined seahorses are present in the Bay, but we don’t know much about them,” Landry says. “By collecting more detailed information about SAV, how it’s being used by fish and invertebrates, and how it’s responding to climate change and warming temperatures, we will be able to make more informed management decisions and take more timely action to protect it, and, therefore, the species that rely on it, such as lined seahorses.”
With its horse-like head, tubular snout with a small, toothless mouth at the end, bony plates covering its body instead of scales, and prehensile tail for grasping, the lined seahorse is one of the most unique creatures inhabiting Bay waters.
“Lined seahorses are sensitive to their environment,” adds Matt Neff, curator of estuarine biology at the Calvert Marine Museum (CMM). “They depend on SAV, and since losses of underwater grasses can impact this already-vulnerable species, we need to take actions to protect its habitat in the Bay.”
In order to protect underwater grasses, SAV monitoring efforts are critical. The Chesapeake Bay Program’s SAV Monitoring Program utilizes a three-tiered approach to gather data to help manage and restore underwater grasses.
The first tier involves working with VIMS and its partners each year to map the SAV beds of the entire Bay using aerial photography and satellite imagery. The surveys, which are typically conducted between May and October, estimate the acreage of SAV. The data collected are used to track progress and identify trends over time.
According to data reported by Chesapeake Progress (chesapeakeprogress.com), an estimated 83,419 acres of underwater grasses were distributed throughout the Chesapeake Bay and its tidal tributaries in 2023—an 8 percent increase over 2022 acreage. This data reflects the most recent survey results. At the time of writing, the acreage for 2024 is not yet available for release.
“An 8 percent increase is really good,” Landry says. “When things are trending up, we typically see about a 3 percent increase, so this was good news. SAV is recovering—not only on a bay-wide scale but also in local areas. I’m especially excited to see the expansion in recent years of species in the mid-Bay, and I’m confident that we will continue to make progress.”
To restore and maintain the health of underwater grasses, the Chesapeake Bay Program and its partners focus on improving water clarity, planting underwater grasses, protecting existing grass beds, and promoting SAV-related education and outreach. The Chesapeake Bay SAV Watchers program, which is the second tier of the SAV Monitoring Program, is an integral part of these efforts. SAV Watchers is the Chesapeake Bay Program’s first official SAV monitoring program for volunteers.
The third tier of the SAV Monitoring Program is the SAV Sentinel Site Program. Sentinel sites are located in each of the Bay’s four salinity zones and are monitored using a standardized, in-depth data collection protocol in which scientists track changes in SAV habitat. The program is coordinated by the SAV Workgroup.
In an effort to enhance their understanding of shallow water habitats where lined seahorses live, the Chesapeake Bay Program is working to expand on the idea of the SAV Sentinel Site Program by developing a more comprehensive Shallow Water Habitat Sentinel Site Program. Once developed and implemented, the program will help improve understanding of the ecological functionality of shallow water habitats throughout the Bay and allow scientists and resource managers to address issues in these habitats more efficiently. The SAV Workgroup will lead the effort to develop the program. (Although program development has been funded, funding for program implementation has not been obtained at the time of writing.)
According to Landry, rather than concentrating solely on SAV, the comprehensive effort will monitor multiple living resources and water quality measures as well as climate impacts on the functional value of shallow water habitats in the Bay and its watershed. The data collected at the sites will help track changes, assess conditions, and provide early warning signs of potential issues.
“Since we don’t systematically collect data on lined seahorses, we know very little about their habits in the Bay ecosystem,” Landry says. “This new program may help us learn more about their preferences and habitat requirements, such as which SAV species they cling to, if they have dietary preferences or are purely opportunistic, how far up the Bay they will venture before salinity becomes limiting, and water temperatures at which they thrive. The more we learn about seahorses and their habitat, the more we’ll be able to protect both.”
Observing Lined Seahorses
Although seeing a lined seahorse in its native habitat may be unlikely for people who do not work on the Bay and its tributaries, such as scientists or watermen, everyone can observe this captivating fish at CMM. The museum, which has about 30 lined seahorses on exhibit, allows visitors of all ages to experience their magic.
Lined seahorses are just one of the 500 animals and 70 species on display at CMM, which focuses on the culture and natural history of Southern Maryland. All of the exhibits feature species found in Southern Maryland and the Bay. Lined seahorses are part of the Hippocampus Haven exhibit and represent CMM’s dedication to the estuarine life of the tidal Patuxent River and adjacent Chesapeake Bay. The seahorses were born at the museum by parents who were captive bred.
“Our lined seahorses are a wonderful attraction, and visitors love them,” Neff says. “I especially enjoy seeing their excitement as they observe our exhibits. I remember a little girl’s reaction after seeing the lined seahorses. She didn’t realize that they were real animals, and she was amazed by them. We hope that CMM can help raise awareness about lined seahorses and the importance of protecting their habitat. Seeing them here at the museum fosters a sense of stewardship and a realization that these charming fish—which are found right here in our backyard—deserve to be protected for future generations.”
Special thanks to the Calvert Marine Museum, Chesapeake Bay Program, and Virginia Institute of Marine Science for providing the photography illustrating this article.
