Sorting Through the Green Stuff

Christine Quigley - Public Outreach Assistant

This past week, the four Florida National Estuary Programs, along with local and regional partners, convened a 3-day workshop around the topic of macroalgae. Macroalgae refers to larger species of algae, whose individuals you can see without a microscope. Seaweed is another name commonly used. If you’ve been out in Sarasota Bay or the Gulf, chances are, you’ve probably stumbled across this “green or brown stuff” floating in the water or hanging out along the seafloor. However, it is important to note that not all the green/brown stuff you may see is algae. It could be cyanobacteria or marine plants. So what exactly is the difference between the three?

Cyanobacteria

Cyanobacteria are photosynthesizing organisms that live in fresh or saltwater. Some species live as single cells and others are filamentous, or grow in colonies that form long threads/chains. They are also one of the oldest fossils, dating back more than 3.5 billion years and are considered responsible for what’s known as the Great Oxidation Event. About 2.45 billion years ago, the Earth’s atmosphere started showing increasing levels of oxygen from photosynthesis by cyanobacteria. This transformation is said to have enabled the evolution of many species, including us. There are about 2,000 species of cyanobacteria. Common ones you might have seen or heard about are Lyngbya species. One thing that makes cyanobacteria unique is that some organisms, like Trichodesmium, can convert atmospheric nitrogen into an available form that aquatic plants and algae can use to grow.

Lyngbya
Lyngbya, Credit: Charles Cichra, University of Florida

Fun Fact

Although cyanobacteria are often called "blue-green algae", they are actually NOT algae, nor are they always blue-green. In fact, the Red Sea occasionally has cyanobacteria blooms that are reddish-pink.

Algae 

Algae cover a broad category of organisms that photosynthesize (although some may also feed on other organisms)They can range from single-celled to giant kelp and are found in freshwater, saltwater, and on landSome species of algae live inside other organisms like corals or jellyfish, forming symbiotic relationships. Overall, you get quite the variety pack when it comes to algae. Although categorizing algae is an ongoing science with new discoveries changing organization and much debate surrounding classification at higher levels, some of the general categories are 

Euglena Single Cell Flagellate Microorganism Seen Under Microscope Credit LebendkulturendeShutterstock.com
Euglena Single Cell Flagellate Microorganism Seen Under Microscope Credit Lebendkulturen.de/Shutterstock.com

1. Euglenophyta (Euglenoids) - fresh and saltwater, photosynthesize but may also feed on other unicellular organisms

Diatoms Under A Scanning Electron Microscope Credit Tescan
Diatoms, Credit: Tescan
Floating Sargassum at Biscayne National Park Credit SBEP
Sargassum at Biscayne National Park, Credit: SBEP

2. Chromophyta - this group includes many different kinds of algae that live in fresh or saltwater:

  • golden-brown algae and diatoms - they are the most abundant unicellular algae with over 100,000 different species
  • yellow green algae - unicellular, fewer species, mostly freshwater but can be found in saltwater and wet soils
  • brown algae (i.e. Sargassum, kelp) - this group contains the largest algal species
Karenia brevis Credit Ian C Robbins And Jeff Sevadjian
Karenia brevis dinoflagellate, Credit Ian C Robbins And Jeff Sevadjian

3. Dinoflagellata/Pyrrophyta (Fire algae) - mostly marine, unicellular, some species are bioluminescent hence the term “fire”. Dinoflagellates, like Karenia brevis (red tide), fall into this category.

Cryptophytes under a scanning electron microscope, Credit Wikipedia
Cryptophytes, Credit Wikipedia

4. Cryptophyta - single-celled flagellates. Flagellates are organisms with one or more "tails" or whip-like appendages called flagella. They can be found in marine or freshwater.

Caulerpa racemosa Algae Credit Wikipedia
Caulerpa racemosa algae, Credit: Wikipedia

5. Chlorophyta (Green algae) - mostly freshwater with some marine species, can be unicellular or multicellular, these algal species are most closely related to plants. Examples include: Caulerpa, Halimeda, and Ulva, or sea lettuce.

Gracilaria tikvahiae on Cayo Costa Island Credit James St. John
Gracilaria tikvahiae on Cayo Costa Island, Credit: James St. John

6. Rhodophyta (Red algae) - mostly marine, often seen as larger floating mats, important in coral reef ecosystems. Examples include Gracilaria, Hypnea, and Acanthophora.

Plants

Plants are also organisms that photosynthesize, but they are different from cyanobacteria and algae because they have a vascular system and produce seeds or flowers during reproduction. One of SBEP’s favorite marine plants, seagrass, has an interesting evolutionary history. It first evolved from algae in the sea. Then came on land as a plant, and then went back to the sea again. This pathway is similar to that of marine mammals returning back to the sea. If you are lucky enough to catch seagrasses at the right time, you may be able to see their small flowers, which are pollinated by tiny marine crustaceans.

Turtle Grass Flower Credit Abigail Cannon
Turtle Grass Flower, Credit: Abigail Cannon
Manatee Grass Flower Credit Ben Jones
Manatee Grass Flower, Credit: Ben Jones

Evolutionary History

Six Kingdoms Of Life Credit University Of Helsinki

You can see in the diagram above the separate evolutionary history of cyanobacteria, different kinds of algae, and plants. If we travel through this pathway in our grouping of the three, you'll see part of the reason why there is so much debate around what goes where.

The story still starts with photosynthesizing cyanobacteria, which evolved before either of the others. The next grouping would be those that acquired the ability to photosynthesize by engulfing cyanobacteria into their cells in a process known as endosymbiosis. This group is referred to as Archaeplastida and includes red algae, green algae, seagrasses, land plants, and a group of freshwater single-celled algae called glaucophytes. It is thought that this group only engulfed cyanobacteria once, although the science is still out. The final group consists of all of the other photosynthesizing organisms that acquired their ability to photosynthesize by engulfing, at least once, red or green algae (which already engulfed cyanobacteria). This final group includes brown algae, diatoms, dinoflagellates, golden brown algae, yellow green algae, and euglenoids.

Cyanobacteria

"We got here first and are the photosynthesizing masters! You're welcome."

Your humble servants,

  • Cyanobacteria

Archaeplastida

"We engulfed those braggy cyanobacteria & now we can photosynthesize too!"

Sincerely yours,

  • Red algae
  • Green algae
  • Glaucophytes
  • Land & marine plants

The Others

"We wanted in too, so we engulfed some of those red and green algae, maybe more than once..."

Regards,

  • Brown algae
  • Golden brown algae
  • Yellow green algae
  • Euglenoids
  • Diatoms
  • Dinoflagellates

Nom Nom

Evolution works in interesting ways. Engulfing cyanobacteria or algae is how organisms, like plants or kelp, got their chloroplasts, which is the organelle that allows them to photosynthesize. This process of endosymbiosis is the same way we got mitochondria, the “powerhouses” of our cells responsible for converting food into energy.

Endosymbiosis diagram

What Do Scientists Mean When They Say...

  • Macro – larger algae with individuals that can be seen without a microscope
  • Micro – smaller algae with individuals that can only be seen with a microscope
  • Filamentous – algae or cyanobacteria cells or colonies that form long threads, chains, or mesh-like filaments
  • Drift – algae large enough to see with the naked eye that often grow unattached along the sea seafloor, float up into the surface, and wash up onshore
  • Epiphytic – organisms that grow on other marine organisms. For example, seagrasses can have epiphytic algae
  • Macrophyte – generally refers to aquatic plants, like seagrasses, but can also refer to macroalgae
  • Phytoplankton - small marine organisms, mostly algae and diatoms, that photosynthesize
  • Seaweed – usually refers to larger types of algae
  • Submerged Aquatic Vegetation (SAV) - refers to underwater grasses and any attached macroalgae

Which Bacteria, Plants, & Algae Tend to Occur in Florida?

Organism(s)

What is it?

Water Type

Interesting to Note

cyanobacteria

marine to brackish

Some strains are toxic and some are not. The toxic strains can cause skin or eye irritation depending on the concentration.

Microsystis

cyanobacteria

fresh, can survive in low salinity

These bacteria are commonly associated with algal blooms in Lake Okeechobee.

cyanobacteria

marine

These guys can convert atmospheric nitrogen into an available form that aquatic plants and algae can use to grow.

Red Tide Karenia brevis

fire algae:
dinoflagellate

marine

FL red tides are caused by Karenia brevis. At least 2 other dinoflagellate species and 1 other diatom species cause red tide in other areas.

Caulerpa, Halimeda,
& Ulva

green algae

marine to brackish

Most species of green algae live in freshwater. Only about 10% are marine.

Gracilaria, Hypnea, & Acanthophora

red algae

marine to brackish

In contrast to green algae, about 90% of red algae species are marine.

Brown Tide
Aureoumbra lagunensis

brown algae

marine to brackish

This species was first isolated in Texas in 1990 during a 7 yr bloom in Laguna Madre & remained only in that bay system for 20 years. The first brown tides in FL happened in 2012 in Indian River Lagoon and Mosquito Lagoon.

Sargassum

brown algae

marine to brackish

The sargassum fish, Histrio histrio, lives beneath floating masses of Sargassum. It can change color and will jump out of the water onto the seaweed and stay there for some time to escape predators.

Seagrass

plant

marine to brackish

About 70% of the fish caught or eaten in Florida rely on seagrasses during all or a portion of their lives.

Benefits of Algae and Cyanobacteria

Although we tend to hear about cyanobacteria and algae in in the context of nuisance or harmful blooms, these organisms have important roles to play in the ecosystem and in our lives as well.

Oxygen - Photosynthesizing organisms in the ocean are responsible for much of the oxygen we breathe. About 50% - 80% of the total oxygen produced on Earth comes from these algae and bacteria (and marine plants too). In fact, the smallest photosynthesizing organism is a cyanobacterium called Prochlorococcus that is responsible for producing up to 20% of the oxygen in the entire atmosphere!

Primary production – These organisms also make up the basis of the food web in aquatic environments. We wouldn’t have grilled mahi dinners, weekend fishing trips, sea turtle nesting delights, and stable human life if our planet didn’t find a way to convert energy from the sun into something edible through primary producers like algae, plants, and cyanobacteria.

Weather and UV protection – Marine algae also play a large role in cloud formation, which affects how much sunlight the Earth absorbs and therefore, is important in the larger climate picture. Scientists found that when phytoplankton (algae and diatoms) are exposed to intense sunlight, they release chemicals that get broken down and eventually become particles suspended in the air. Water droplets then condense around these suspended particles and create clouds. When the sun is stronger, phytoplankton release more of these chemicals, increasing cloud cover and cooling the area.

Pretty cool, right?!