CZScience - Coduim Up, Eelgrass Down: Invasives Impact Buzzards Bay
By Dr. Joe Costa, Buzzards Bay Program

During the winter and spring of 2006, Wareham town officials and residents noticed an alarming accumulation of the green algae commonly called dead man’s fingers at Little Harbor Beach on Great Neck. The alga, whose scientific name is Codium fragile, is an introduced species that was first reported on the eastern coast of the United States in New York in 1957. By 1961, it had spread to Buzzards Bays, Massachusetts (scientists believe it is primarily transported from site to site on the hulls of ships) and has been found in abundance offshore of the Little Harbor Beach area for at least the past 20 years.

Codium fragile is anything but fragile. This robust, sponge-like alga, often grows in bushy shapes about two-feet wide and can crowd out and shade other plants and algae. The disruption to native plant life is bad enough on its own, but worse yet, at least to those who rely on shellfish for their livelihood, Codium kills shellfish. By growing on shells, Codium causes the shellfish to be smothered (it is sometimes nicknamed the oyster thief) or pulled from the bottom and washed ashore. Whelks, slipper shells, and bay scallops attached to Codium are commonly found along the shore of Buzzards Bay. The accumulation of dead shellfish in Codium wrack (i.e., the piles of seaweed and other vegetation brought ashore by waves and tides) is one of the main reasons why this beach wrack smells stronger and attracts more flies than the native eelgrass beach wrack.

The Wareham Codium problem persisted through the spring and summer of 2006. Wareham Department of Public Works (DPW) Director, Mark Gifford, reported that the dense wrack was a nuisance to both beachgoers and the DPW, which has had to haul away truckload after truckload of the odious decomposing Codium. One resident complained that after a 10-day hiatus of the DPW cleaning the beach in July, the Codium wrack had accumulated up to two feet in thickness, and beachgoers had to clear paths through the stranded Codium to access the water.

The accumulation of Codium on Little Harbor Beach was really just the tip of the iceberg of some broader problems facing upper Buzzards Bay. While there was a dramatic accumulation of Codium in 2006, the continued loss of eelgrass in northern Buzzards Bay began nearly 20 years ago.

Eelgrass beds are an important habitat and nursery for fish, crustaceans, shellfish, and birds. Between the 1960s to mid-1980s, eelgrass was abundant and widespread in Wareham's waters. (Buzzards Bay was the site of the first systematic survey of eelgrass distribution in Massachusetts; and you can view these maps at www.buzzardsbay.org/eelgrass.htm). In fact, the amount of eelgrass washing ashore in the 1980s prompted the town of Wareham to purchase a vehicle to clean beach wrack off Little Harbor Beach during the summer beach season. This south-facing beach sits in a funnel of land facing the prevailing southwest summer winds, and is a place where beach wrack naturally gravitates.

However, within a decade, the town hardly needed to clean eelgrass wrack off the beach. At the time, the change seemed a mystery. But looking back, the reason for this change is now clear—most of the eelgrass in Wareham’s water had died off. The Massachusetts Department of Environmental Protection (MassDEP) later documented this loss when they began a statewide survey of eelgrass cover using aerial photographs taken in 1996.

Eelgrass Loss and Coastal Eutrophication
It is well documented that excessive nitrogen loading (i.e., large amounts of nitrogen introduced into the environment primarily through fertilizers and fossil-fuel burning) is one of the most common causes of eelgrass loss in coastal waters. Inorganic nitrogen promotes excessive algal growth in the water and on the seafloor, decreasing water transparency in a process called eutrophication, which shades out eelgrass. In some areas, declines may be exacerbated when sediment is resuspended from boat activity, or from localized outbreaks of disease.

The initial observations of eelgrass loss off Great Neck in the 1990s was perplexing because this was an area of supposedly cleaner “offshore” waters where eutrophication losses were generally not observed. However, the scope of the pollution problem in Wareham’s waters became evident when the Buzzards Bay National Estuary Program (NEP) began nitrogen-loading assessments and the citizen group, The Coalition for Buzzards Bay, documented fair-to-poor water quality throughout Wareham’s three large river systems (the Weweantic, Wankinko, and Agawam). These river watersheds are impacted by many sources of nitrogen including the Wareham sewage treatment facility, numerous septic systems, and extensive cranberry bogs. It was then that researchers began to realize a possible cause for the widespread water quality decline offshore.

In February 2006, MassDEP released its eelgrass maps for Buzzards Bay based on mid-June 2001 aerial photographs and additional field surveys. These surveys, and other aerial images that the Buzzards Bay NEP has examined, confirm the persistent loss of eelgrass in Wareham. What likely occurred is that eelgrass was growing close to the maximum depth that it could grow off Great Neck, given existing water clarity. In such a situation, even small declines in water quality and transparency can cause large losses of eelgrass.

These events, however, do not explain why Codium was so abundant in 2006. The waters off Great Neck were a good habitat for both Codium and eelgrass. Codium needs less light than eelgrass to grow. It also grows well in nutrient-enriched waters, but, unlike eelgrass, it must attach to a hard substrate. It happens that the shoals off Great Neck have few large rocks, but they do have many gravels, stacks of slipper shell snails, and other shellfish. Codium attaches to all of these, but when it grows too large for these lightweight supports, it pulls off the bottom and washes ashore.

In the summer of 2005, because of heavy summer rains, The Coalition for Buzzards Bay recorded some of the worst water quality in their program’s 14-year history. It is possible that the heavy rains increased nutrient levels in the waters of Great Neck, which may have boosted Codium production and contributed to the massive accumulation washing ashore. Heavy spring and summer rains during 2006 may have further exacerbated the problem.

Silver Lining, and More Questions
In 1998, based in part on the Buzzards Bay NEP nitrogen loading findings and recommendations, the U.S. Environmental Protection Agency (EPA) required tertiary treatment to remove nitrogen at the Wareham wastewater facility. While treating this discharge alone would not fully restore water quality in the estuary, the upgrade of the facility was expected to result in measurable improvements in water quality in the Wareham River. The Town of Wareham completed the facility upgrade in late 2005 and it came online in the spring of 2006. The EPA permit requires that the facility discharge no more than four parts per million (ppm) total nitrogen during marine algae's fastest growing season of March to October (down from an estimated 15 to 20 ppm total nitrogen). For the 2006 season, the facility discharged an average of 3.2 ppm.

This sewage facility upgrade, together with the ongoing expansion of sewering in Wareham villages, such as Rose Point and Swifts Beach, are expected to improve water quality in the next few years. Improvements could continue as another 800 coastal homes are tied in over the next two or three years. Experiences elsewhere give reason to be optimistic. When the City of New Bedford upgraded its wastewater facility in the 1990s and fixed failing Combined Sewer Overflows, within five years there was a great expansion of eelgrass in the outer harbor and in Clarks Cove. Elsewhere in the United States, wastewater facility upgrades have often been associated with recovery of seagrasses. If the summer of 2007 has an average rainfall, it is possible that eelgrass populations may begin recovering in Wareham's waters. Codium, on the other hand, is here to stay—although the unanswered scientific question remains as to whether recovered eelgrass beds would help exclude Codium from Wareham’s subtidal real estate.

Photograph by Dr. Joe Costa