Photograph by Marco Secchi, Getty Images
Published September 19, 2013
When Italian salvage workers propped up the Costa Concordia this week, they cleared a major hurdle in the long saga of the cruise ship that sunk off the coast of Giglio in January 2012. Over the next few weeks, crews will attempt to completely remove the ship from the area.
But beneath the ship may be a bigger problem that worries some biologists. Having run aground in the Tuscan Archipelago National Park, the largest marine conservation area in the Mediterranean Sea, the shipwreck has posed unique challenges to environmental managers.
The salvage team hired by the Costa Concordia cruise line has taken precautions for the sake of the local marine life. The company has allocated $400 million to minimize environmental damage. Since the beginning of the salvage project, workers have transplanted noble pen shells, removed heavy oil and diesel from the ship, put down pollutant-absorbent booms, and created "bubble walls" in the water to reduce noise pollution.
But one challenge remains: the reef's seagrass.
Feathery-looking Neptune grass blankets the seafloor around the ship. Sitting on the ocean floor for more than a year, the wreck has killed an unknown amount of seagrass; the cruise line has not disclosed the exact size of the area impacted.
The Benefits of Seagrass
Silent and often unseen, seagrass plays a crucial role in the marine ecosystem. In a 2009 study the Florida Department of Environmental Protection quantified the importance of seagrass, estimating that one acre has an approximate economic value of $20,500.
"Seagrass meadows function as a nursery for the ocean," says Nicole Paul, resident biologist and operations manager of Florida-based Seagrass Recovery, a company specializing in the restoration of seagrass in damaged areas. According to Paul, "one healthy acre of seagrass can produce ten tons of seagrass blades per year, providing food, habitat, and nursery areas" for marine life.
Recent studies, including one from 2006, have suggested that seagrass plays a vital role in combatting climate change, as well. Collectively, seagrass meadows around the world are estimated to remove approximately 10 percent of the world's annual carbon emissions.
While crews attempt to replant damaged Neptune seagrass beds, there's debate over whether the area will spring back.
The Challenges of Restoring Seagrass
Enric Sala, a marine ecologist and National Geographic resident explorer, is not optimistic about the team's chance of success. If divers successfully replant the seagrass beds, "it would be a first," he says, explaining that prior attempts have not been at such a large scale.
Indeed, an international study in 2006 on seagrass replanting efforts pointed out the complications. "Some species [of seagrass] are so difficult to transplant that restoration is not logistically or economically feasible," the researchers found.
Yet it may not be out of the question. Kevin Hovel, a biology professor at San Diego State University and a participant in numerous seagrass replanting projects, sees possibility at the Concordia site. "There is an element of chance to it," says Hovel, adding that "seagrasses are a pretty sensitive species."
Outside factors can play a role. While Hovel and his team attempted to replant seagrass in the San Diego Bay, a tropical storm decimated their work, tearing up the grass that wasn't fully rooted in the sediment. In the Mediterranean, Hovel says problems with invasive species like algae, which competes with seagrass, could complicate the effort.
The plant's delicacy is a result of its intricate root system. In parts of the ocean, the Mediterranean included, seagrass beds and their roots have been around for thousands of years. In one case, biologists from the University of Western Australia found a seagrass bed in the Mediterranean that was around 200,000 years old. These ancient root systems keep the seagrass hearty, but they pose challenges to workers during the replanting process.
Whether the seagrass in the area bounces back has implications for people on land. The way the plant stabilizes sand can reduce shoreline erosion from waves and storms. "With no seagrass to diminish the force of the currents along the bottom [of the ocean]," says Nicole Paul, "beaches, business, and homes can be subject to greater damage from storms."
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The comment about the seagrasses helping combat climate change by globally removing 10% of carbon dioxide emissions annually raises a mass-balance issue. (neat!, the Ctrl-U and Ctrl-B commands work). If every year, seagrasses are sequestering 10% of the carbon from carbon dioxide into new biomass, where is it going? If the quantity of active seagrasses is constant (or decreasing due to environmental degradation), then only three possibilities occur to me.
One is the release of a certain amount of biomass through the water to elsewhere (acting as nursery area), but unless this biomass is increasing in this elsewhere area, it is not causing a net removal of CO² (that's the closest I could come to the proper format, by using Alt-253 as there is no subscript option with ASCII codes. I don't know a keyboard command for subscripts). A mature ecosystem would have a stable biomass quantity (allowing for fluctuations about some constant median) because it would be full. Organisms would be growing and dying in rough equilibrium and so the carbon tied up in active biomass would not change.
The second option is to increase the carbon in the root zone, with possible further transport of non-living carbon deeper if (an important caveat) there were downward water circulation to transport it below the root zone in this part of the sea floor. This implies that as plants replace themselves (natural cycle of aging, predation, dying, replacement), the roots of the dead plants are not recycled (eaten) by burrowing animals, bacteria, and other micro-organisms. This is possible. Conditions at some depth below the sea floor surface may be inhospitable to recycling organisms while allowing roots to grow. Peat forms by this scenario. I am not a biologist and so don't know what the ecological mass balance is for this plant. There may be a net increase in storage of non-living carbon in or below the root zone by these plants. The living plant mass in the roots should be constant in a mature ecosystem if the above-ground plant mass is the same. I presume the roots functions are to retrieve nutrients from the sea-floor soils and to act as hold-fasts rather than to obtain water for the plant. The article mentions the root network is abundant.
A third option is storage of carbon by precipitation of carbonates, such as limestone muds. This is an effect of photosynthesis because it changes the the CO² concentrations of the adjacent seawater between night and day provided the saturation with CO² is sufficient and water alkalinity appropriate. If present, this mechanism would be apparent because the precipitated muds build up the sea floor and bury the older parts of the plants or other organisms. Limestone algal mats grow upward this way. It should be obvious if this is how the grasses store carbon because of this progressive rising of the sea floor. It would also leave the dead root zones behind in this case as an additional contribution to carbon sequestration.
My concern is whether it is really plausible that the mass balance is really that skewed to sequestration of carbon, as opposed to simply making new biomass that replaces an equivalent amount of biomass consumed or otherwise returned to the environment as new CO². Mature woodlands hit a point when the only new carbon being tied up is dead material in and below the root systems because the quantity of living biomass has peaked. The ecosystem is full. Peat bogs, some swamps, and anoxic zones on the sea floor are examples where dead material is not recycled back into CO². I don't know enough about marine ecology to know whether the statement that 10% of our annual human CO² production is being sequestered by these plants (globally) every year, year after year, is really happening. However, I need to see this confirmed by a professional marine biologist familiar with these plants and determining mass budgets of ecosystems. Too often people are confused by the difference between the productivity of an ecosystem in making new biomass and the net removal of carbon from the system once an ecosystem has come into balance with its conditions (it's full).
The damage from the Concordia cannot be undone, however is there a possibility of an artificial reef being created after the removal of the ship and cleanup of the area. The artificial reef would boost growth, and add beauty to the area.
Very interesting article. I've been following the Concordia disaster from the beginning, but had not given much thought to the residual damage to the essential seagrass ecosystem. One would think the seagrass would re-grow, left to its natural devices (although perhaps not in a timeframe suitable to aid the recovery of Concordia's reputation). Let us hope that the replanting does not cause further, but unpredictable, problems.
It's sea grass, it will grow back. Bubble walls for noise?
They would be batter off not wasting money on that kind of crap and instead mandate more funds be spent on keeping future accidents from happening
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