The ocean holds many curious creatures, but not many people stop to consider if flowers exist under the surface of the sea. While it’s easy to lump all sea plants into one category, there is actually a difference between algae and seagrass. Both obtain energy from the sun, but seagrass is a true plant – it anchors itself with roots and reproduces with flowers.

Most true plants prefer to live on land, but seagrass has adapted ways to transform salt water into fresh water in its fibrous tissue. Plants with such salt tolerance are called halophytes. Seagrasses rely on the process of photosynthesis to produce energy, and so they must inhabit relatively shallow waters where plenty of sunlight is available. Additionally, land provides important nutrients such as nitrogen and phosphorus for the seagrass to use, making estuaries of mud and silt (like the one right here in San Carlos Bay!) an ideal location to put down roots.

The distribution of seagrass in Florida. 

The distribution of seagrass in Florida. 

In Florida, we have 7 species of sea grass – manatee grass, turtle grass, shoal grass, paddle grass, star grass, Johnson’s seagrass, and widgeon grass. Each species is unique, preferring a specific depth and salinity range. Seagrass not only provides oxygen for the ocean, it also traps sediments – creating a cleaner ecosystem for animals to thrive in.

The relative depths at which various species of seagrass like to grow. 

The relative depths at which various species of seagrass like to grow. 

Seagrass is one of the most biologically rich ecosystems and provides a home to so many sea creatures. Every square acre can produce up to ten tons of leaves, and can provide shelter for forty thousand fish and fifty million Invertebrates. This abundance of prey attracts predatory mega fauna like dolphins and sharks. Some animals also obtain nutrition from seagrass. Manatees and some sea turtles like to munch on these fibrous plants to gain nutrients and fresh water. This constant removal of the leaves promotes growth of the meadows.

Campers at Sanibel Sea School created their own seagrass garden in the Richard C. Kennedy Building. 

Campers at Sanibel Sea School created their own seagrass garden in the Richard C. Kennedy Building. 

Seagrasses also provide humans with many services, like clean water and oxygen, but these important ecosystems are in danger around the world. Some of the direct threats to seagrass meadows include dredging, prop scars, and coastal development. According to Dr. William Dennison of the University of Maryland for Environmental Science, “Globally, we lose a seagrass meadow the size of a soccer field every 30 minutes.” Right here on Sanibel, influxes from the Caloosahatchee are indirectly killing sea grass in two ways. Tannins produced by mangroves upriver are washed into the bay, limiting the amount of light that can penetrate to the leaves. This freshwater also reduces the salinity of the water, which these species depend on.  

A Sanibel Sea School camper monitors seagrass health near Andros Island in the Bahamas. 

A Sanibel Sea School camper monitors seagrass health near Andros Island in the Bahamas. 

No matter where you live, it’s important to let your elected officials know that you care about protecting important marine habitats like seagrass, and to support organizations that are working to make this happen. It can be as easy as a letter or a phone call, and a Google search will deliver plenty of ideas for how to get involved. We’d love to hear about your efforts! 

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