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Macro algae turning into a major problem - September 19, 2013

If you have ever pulled up a crab pot or reeled in a fishing line during the summer months in the coastal bays, there is always one thing everyone notices: algae. Whether it is growing in huge green clumps or thin spreading filaments, visitors and locals cannot help but notice the sheer explosion of algae growth that seems to grip the coastal bays and its tributaries every spring, summer and fall.

Algae in the coastal bays is often seen as nothing more than a nuisance. However, the continued accelerated growth of algae that covers our benthic communities has become a real and ongoing problem with multiple causes.

There are two types of algae: micro algae, which is phytoplankton, and macro algae, which is larger and visible to the naked eye.

Macro algae is what most people have had experiences with, whether it is on their crab pot, fishing line, boat anchor or even on their legs when they go swimming in the bays. Macro algae is a wide and diverse group of photosynthetic aquatic organisms that are not true plants. Plants are multi-cellular organisms that have roots, leaves, stems, etc., while algae are organisms that can be as simple as a single cell or as complex as a multi-celled organism.

Algae lacks the roots that true plants have, however they have a multitude of different ways to get around this; some algae have holdfasts that act as anchors, some have air bladders that force their leaves to the surface and allow them to float if need be and some algae are actively mobile. However, these algae are often single-celled micro algae such as dinoflagellates. Unlike plants, algae is not vascular which means that each cell in the organism is responsible for the uptake of its own water, nutrients and sunlight.

Macro algae, for all their annoyances, are a vital part of the coastal bays ecosystem. Most of the macro algae that we find in our coastal bays are native to this area, and some of the most common macro algae in this area include:

» Ulva, which is a vibrant green algae that looks like a lettuce leaf, hence the common name sea lettuce.

» Agardhiela tenera, which is a dull red bushy algae that can grow up to a foot tall.

» Cladophora, which is a thin green filamentous algae that can create vast free-floating mats.

Macro algae can provide habitat for many creatures, food for herbivores, add dissolved oxygen to the water though photosynthesis, absorb and retain excess nutrients and even help hold onto sediments so they do not become suspended in the water column. However, as the saying goes, too much of a good thing can be taxing. While we need macro algae in the bays, we do not want too much of it.

As we have seen throughout the past few years, as the macro algae starts to grow in the warmer months, it can rapidly take over whole areas of the bays, severely limiting the amount of habitat available for Submerged Aquatic Vegetation (SAV), and benthic animals such as flounder, clams, oysters and others.­

When macro algae starts to grow rapidly during the spring and summer months, it starts to outcompete and outproduce other aquatic organisms. The macro algae can encrust and outcompete native submerged aquatic vegetation like eel grass, which is another vital player in our coastal bays, and block the sunlight needed for growth effectively killing off huge swaths of SAV beds.

Macro algae blooms can also cause major problems for boaters as it can clog up propellers and intake pipes, which then need to be cleaned and fixed. Animals such as blue crabs, lined sea horses, dusky pipe fish and many more rely on SAV beds for protection, camouflage, a nursery for their young and even as food.

Macro algae blooms have been occurring more frequently in recent years due to excess nutrients being added to our coastal bays. Macro algae can uptake nutrients at a faster rate than SAVs, and therefore can flourish in areas where excess nitrogen, phosphorous and otherwise limiting nutrients are found in high concentrations. While recently we have taken many steps toward reducing our nutrient loading into the coastal bays, because of the excess nutrients in our groundwater being added into our waterways, we will continue to experience a higher concentration of nutrients in the coastal bays for years to come.

Luckily, there has been research that shows macro algae in the coastal bays can be controlled and kept in check, provided we keep making progress in our goals to reduce the nutrient loading going into the bays.

The macro algae in our bays are native species, which means that local aquatic herbivores can and will graze on the algae.

This grazing can significantly hinder the ability of macro algae to reproduce quickly, as it can put major stress on the algae.

If we can diminish the amount of excess nutrients in our bays and increase our water clarity, then macro algae coverage in our benthic communities should diminish as they continue to be grazed upon by local herbivores and hopefully get replaced by more native SAV beds.

Harrison Jackson is the Coastal Stewards coordinator for the Maryland Coastal Bays Program.

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