Amazing life lives in seagrass

Know your islands

Seagrass

February 2 was designated World Wetlands Day and as we think about preserving national assets such as mangroves and other wetland areas, let us remember that seagrass communities are also wetlands with many important functions.

Let us try to protect and preserve these systems also!

While most of us know something about the ocean and coral reefs, we know little about seagrass beds. Moving seaward from the mangroves we typically find seagrass beds. Photograph by Frank Roulstone.

There are about 60 species of seagrass found worldwide.

These mostly range from the size of your fingernail to plants with leaves as long as seven metres.

Seagrass is the only type of flowering plant that has adapted to life in the sea. There are six species of seagrasses in the Caribbean. Species recorded in Cayman include turtle grass (Thalassia testudinum), shoal grass (Halodule wrightii and Halodule bermudensis) and manatee grass (Syringodium filiforme). The most common species in the Cayman Islands is turtle grass (Thalassia testudinum). Turtle grass gets its name from its important connection to green turtles. It is an important source of food for green turtles and is easy to identify with its broad flat green blades that make up lush meadows growing over the sea floor. The North Sound has broad areas of mud-rich sediments with shoal grass, but predominantly turtle grass.

Seagrass has a number of important functions.

They are habitats and nursery grounds for recreationally and commercially important finfish and shellfish. Juvenile finfish found in seagrass beds include snappers, croakers, grunts, groupers, and many others. Other commercial species found in these beds are queen conchs, lobsters and shrimps.

Some animal species which are not of commercial importance are also found in seagrass beds. These include sea urchins (commonly referred to as sea eggs), sea cucumbers, starfishes, brittle stars, snails such as Murex, cones and olives, octopus, anemones, and sponges. Even sea horses may be found in seagrass beds. Of course seagrass beds are also grazing grounds for turtles. There is an incredible diversity and abundance of organisms in this environment.

Mangroves, seagrass beds and coral reefs are often linked and all three habitats must remain healthy for each to thrive. Mangroves filter pollutants and trap sediments that would otherwise smother seagrass and coral. Sediment banks accumulated by seagrasses may eventually form substrate that can be colonized by mangroves. Seagrass also creates clean water for coral reef inhabitants by trapping sediment and slowing water movement, causing suspended sediment to fall out. In turn, coral reefs protect mangroves and seagrass from ocean storms by slowing the surging waves. All three communities keep nutrients from being dispersed and lost into the surrounding oceanic waters.

All species of seagrass can be affected by pollution and damage in the environment. This can cause seagrass to die from being shaded from light, covered by faster growing algae, buried by sediment from a land base source or harmful chemicals. Human impacts include physical disturbance by anchoring of boats and by propellers, complete destruction by dredging and sand mining for coastal construction, heat and oil pollution, and the release of excessive organic materials such as sewage.

Explore the seagrass areas close to our coasts and discover the amazing life in these marine meadows!

Grow Cayman Plants and encourage Cayman Wildlife! For more information, to share your knowledge or if you would like to get involved with the many activities in the National Trust’s Know Your Islands Program, please visit www.nationaltrust.org.ky, or call 949-0121.The weekly column from the National Trust is submitted by Marnie Laing, Education Programs Manager at the Trust.

Last week’s answer: Silver Thatch tree trunks provided the rollers for launching locally built schooners.

Trivia question: What is the name of a young red mangrove seedling?

Look for the answer in next week’s feature!

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