You scratched my seagrass!

September 2014
Steven Katona Managing Director, Ocean Health Index
Anchors effect on carbon storage

Those who sail come to know the ocean intimately; buoyed by its beauty and the rich life it nourishes, but also saddened by damage from pollution, over-exploitation, climate change or other problems.

Are there things boaters can do to lessen such problems and improve ocean health? What is the current status of the ocean's health, anyhow?

Starfish crawl across the shallow bottom of a Cape Cod bay in Massachusetts.
Starfish crawl across the shallow bottom of a Cape Cod bay in Massachusetts searching for food. These animals prey on creatures that make their homes in seagrass such as mussels, oysters, or quahogs.

The Ocean Health Index is based on the premise that a healthy ocean provides a range of benefits to people now and in the future.  This recognizes that people and the ocean must coexist, because human presence and activities affect nearly all aspects of the ocean and marine life and vice versa. In short, people need nature to thrive; and fostering a resilient, productive ocean will promote healthy sustainable societies.

The Ocean Health Index evaluates the world's oceans according to 10 public goals that represent key benefits of healthy marine ecosystems. Each goal is scored from 0 to 100 signifying how well it is doing in achieving those benefits. The scores can be looked at by country and goal, and be averaged to produce a regions overall score.

Boaters have unique opportunities to help with these goals, particularly protecting sea grass and coral reef habitats, both of which provide a remarkable suite of benefits to people and marine life, benefits valued at nearly $12,000 per acre every year. 

Grass of the Sea

Impact of an anchor dragging through a seagrass bed.

Sea grasses form shallow meadow-like expanses throughout the world’s warm and temperate waters.  Just like grass on land, as the grass grows, it takes up carbon dioxide and releases oxygen to the water and sediments. Additionally, a sea grass meadow’s extensive root system both stabilizes the sediments and stores very large amounts of carbon, keeping it buried for decades or even centuries if not disturbed, reducing the rate of carbon dioxide in the ocean and atmosphere, slowing the rate of global warming and ocean acidification. Amazingly, seagrasses sequester about as much carbon per square meter as any habitat on earth, including rainforests. Meanwhile, the leaf fronds waving gracefully above form a miniature forest that shelters larvae and young of many commercially important fish and shellfish, as well as beautiful nudibranchs, jellies, worms and crustaceans. Such habitats are also the most important habitats for seahorses. As a further benefit, the flexible fronds are also surprisingly effective at absorbing wave energy and slowing the flow of water, thereby helping to protect coastlines from storm surges.

Seagrasses are globally and regionally threatened by many things. Broad threats include land erosion and consequent sedimentation that clouds the water, reduces photosynthesis and smothers the grasses; and run-off from land of excessive amounts of nitrogen and phosphorus pollution (often from cleaning products and fertilizers) that promote growth of seaweeds or phytoplankton at the expense of seagrasses.  

Boaters can play a direct role in reducing a very specific threat, by not anchoring on seagrass beds. Anchors disturb or destroy the root systems, not only does this kill the plants, the sequestered carbon is released into the atmosphere as heat-trapping carbon dioxide. Since most seagrass beds occur in relatively clear and shallow water, boaters should anchor elsewhere and not disrupt the remarkable benefits they offer.   

Carbon storage is natural in coastal ecosystems such as seagrasses, tidal marshes and mangroves. The score of 74 is relative to their condition in the early 1980’s. A score of 100 would indicate that these habitats are all still intact today.

 Government of Bermuda.
Anchors and moorings placed in seagrass beds can cause lasting damage. Mooring chains that sweep the bottom as the boat swings around are particularly destructive and have created ‘halos’ of bare sand in many of Bermuda’s bays. Photo source: Government of Bermuda.

Coral Protection

Boaters can also make extraordinary contributions to ocean health through thoughtful anchoring when in the vicinity of coral reefs. 

Coral reefs are among our planet’s most valuable and vulnerable ecosystems. Though they cover less than 1% of Earth’s surface, their range of services and benefits is remarkable. Although they don’t sequester carbon, they provide many of the same services and benefits as seagrasses---and more.  Where they really shine is in biodiversity and productivity: they support more species per unit area than any other habitat and harbor about 25% of all marine species, serving as nurseries for about one-fourth of all marine fish including food for people in many island nations and elsewhere.  Drawn by the dazzling array of animals, plants, shapes and colors, tourists flock to reefs for diving or snorkeling, boosting jobs and revenues for coastal residents and businesses - an important benefit since coastal (mostly reef-related) tourism generates more than 50% of total GDP in small island states such as Aruba, Antigua and Barbuda, the U.S. Virgin Islands, Anguilla, the Seychelles and Vanuatu as well as Saba (the highest scoring location with a population greater than 1,000 in the 2013 Ocean Health Index; and Bonaire (the highest scoring location with a population greater than 10,000). 

All told, the total annual economic value of the ecological services and benefits provided by coral reefs is more than $140,000 per acre, yet pollution, rising sea temperatures and ocean acidification caused by increasing concentrations of atmospheric carbon dioxide, erosion and sedimentation caused by poor land use, and fishing with dynamite and cyanide have made them among Earth’s most threatened habitats.  But boaters can help prevent one other kind of damage that often occurs in the most attractive locations: reef damage from anchors, divers and snorkelers. Anchoring boats on reefs breaks the fragile corals, often killing them. The damage is magnified if the boat swings or there is difficulty in retrieving the anchor. When many boats anchor near the same spot, damage over time can be substantial. Many reef dive sites provide mooring balls so that boats need not deploy their own anchors. When moorings are not available, every effort should be made to anchor where corals are not present.    

Coastal protection measures the condition and extent of habitats that protect the coasts against storm waves and flooding. Storm protection by coastal habitats is worth billions of dollars each year – and coral reefs are an essential part of this protection to many nations. This score is judged relative to condition of coastal protection in the 1980’s.

An anchor resting on an area with coral and sponges at Finger Reef, a popular reef within Apra Harbor, Guam. Photo by Dave Burdick.
​An anchor resting on an area with coral and sponges at Finger Reef, a popular reef within Apra Harbor, Guam. Photo by Dave Burdick.  

The Ocean Health Index team salutes Sailors for the Sea for its worldwide efforts to protect the oceans, including helping seagrass beds and coral reefs provide their valuable benefits to the ocean and us. 

Take Action

You can make a difference. Follow these steps to create a positive future for the ocean.

Take Action
  • Look before you throw! Make sure you anchor in mud or sand and avoid seagrass, corals and other visible habitats. Click here for more anchoring tips.
  • Anchor in bright sunlight and read the bottom by color. Darker blue means deeper water and usually a sandier bottom. Light brown patches could mean seagrass, dark brown or black is often coral, depending on your location.
  • If possible, place your anchor by hand in the sand to minimize drag and avoid seagrass or coral. More tips on how to do this from Cruising World's Confessions of a Coral Crusher.
  • If your anchor gets caught, make sure you free it by hand whenever possible. 
  • Learn more about the Ocean Health Index and check out your favorite country's score. It can give you a great idea of how you can help when visiting.
  • The ocean (thanks in large part to seagrass) absorbs 48% of the carbon dioxide released into the atmosphere. Make its job easier by reducing your carbon footprint.