Drift algae comes in many different forms

You’re scalloping, either wading or snorkeling along looking at all the sea life in and around the grass flats. You encounter tan or brown tumbleweed-sized mounds that you push away.  The mounds feel rough.  If snorkeling, take a break from hunting scallops and closely investigate some of the brown mounds. You’ll find a world of life in or under those mounds that you may never have seen before.

Those tan mounds are mostly species of Laurencia, a genus of red algae. The red algae are a diverse group found from polar seas to the tropics. Many red algae have been used by humans for centuries. Nori, a red algae, is used in sushi. Irish moss (Chondrus crispus), was made into a pudding on both sides of the Atlantic.  And carrageenan, a thickening agent, is an additive in many of our processed foods and in cosmetics. Some species of red algae are calcareous and help cement coral reefs together.

If you look closely at a piece of Laurencia, you’ll see that it is somewhat knobby, which accounts for the rough feel. Another red algae species often found in the bay is Gracilaria, which is often dark red and feels slippery.  It is easy to tell these two algae apart by feel. But these are only two species. Eight to sixty-five different species of drift algae have been found in the sea grass beds of the Gulf coast of Florida. Drift algae are found where water currents are slow and the algae can get caught on the blades of turtle grass. The relative shelter of St. Joseph Bay makes for ideal Laurencia habitat – plenty of shallow areas for light penetration, clear water, and slow currents.

The drift algae also account for the complexity and abundance of sea life in the bay. Those mounds of drift algae are either a food source or a habitat, a temporary place of refuge, or a substrate to grow on depending on the organism. Many small invertebrates are found in the drift algae. Tiny hermit crabs can be seen feeding along the fronds of algae picking off bits of smaller algae and debris. Snails, tiny crabs, and hydroids can be spotted with a little patience.  As the algae are carried by the currents, the invertebrates are transported from place to place and often distributed to new habitats. Vertebrates that take refuge in the algae are sea horses, pipefish, sea robins, blennies, and gobies, and many a tiny fish can be observed darting into the shelter of the algae when chased by a larger predator. Schools of Pinfish are easily observed grazing on bits of debris and organic matter on the surface of the algae lobes.

Many larger organisms hide beneath the mounds of algae. Gently lift part of an algae clump aside and you may be rewarded by the sight of a bottom-dwelling fish like a toadfish or possibly a blue crab hiding.

While drift algae adds to the diversity of the bay, it can also have an adverse effect on the turtle grass. If currents aren’t sufficient to move the algae along, the turtle grass does not get sufficient sunlight to grow and occasionally bare areas will be formed. In shallow areas the cellular respiration of the algae can reduce the oxygen content of the water and decaying algae will further reduce oxygen levels.

There is a delicate balancing act between grazers, algae and the sea grass. Herbivores are vital to sea grass growth because they feed on the drift algae and keep it in check. However, the balance can be easily thrown off by the simple addition of too many nutrients into the water. Algae are simple plants and they respond to fertilizers the same way your garden does. Fertilizer run-off from lawns and farms gets into the bay either by direct run-off from lawns on the bay or washed downstream from a distance. Even if your lawn is not directly on the bay, drainage ditches next to roadways carry fertilizer runoff to the bay. Nutrients from septic systems leach into the bay. Human activities have a huge effect on near-shore aquatic systems, and once the system is out of balance there is a cascade effect of overgrowth, algal die-off, depleted oxygen in the water from decomposition, cloudy water that hampers sea grass growth and so on. It takes a long time for the system to get back in balance.

Take a moment to explore the algae clumps while you snorkel.  You’ll be rewarded by some interesting sights, and gain some insight into the diversity of life in St. Joseph Bay.

Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.


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