What is Algae?

Introduction

Along the rocky coasts of Maine at low tide you are likely to come across a mess of brownish green and red tendrils covering the shore. Ascophyllum nodosum (rockweed), Fucus spp. (bladderwrack), Chondrus crispus (Irish moss), Ulva lactuca (sea lettuce), and Saccharina latissima (sugar kelp) are several seaweeds that make up the base of coastal ecosystems in this region and are just a few of the roughly 22,900 species of macroalgae that can be found around the world.

A video (3:56) about the origins of algae and how algae evolved to become what know today. Video credit: Scottish Association for Marine Science

What makes something ‘algae’?

Seaweeds– also called macroalgaeMarine plant-like organisms that photosynthesize and are visible to the naked eye, also known as seaweed.– are a group of multicellular algae that are usually visible without a microscope. AlgaeA simple, non-flowering, and typically aquatic plant of a large group that includes seaweeds and many single celled organisms. are a diverse group of aquatic primary producers that include macro- and microalgae. They produce energy via photosynthesisProcess where plants use their chloroplasts to create food from water and carbon dioxide., which is the conversion of light energy into chemical energy using carbon dioxide and water. Algae are like plants in that they are autotrophsAn organism that can produce its own food using light, water, carbon dioxide, and other chemicals.: organisms that produce energy without consuming other organisms. Instead, algae and plants take up nutrients from their environment in the form of simple inorganic compoundsA chemical compound lacking carbon hydrogen bonds. (like CO2, H2O, NH3, NH4+, HPO4 2-, PO4 3-) and use these nutrients to grow, reproduce, and maintain a stable internal environment.

However, despite their similarities to plants, algae are not plants. For example, algae have a different level of biological complexityHow complicated an organism is, which is directly related to that organism's ability to survive in its environment than plants; algae can be unicellular, multicellular, or colonial and can also be classified based on cellular complexity as prokaryotic or eukaryotic while plants are always multicellular and eukaryotic. Algae also use a different method for photosynthesis than plants do. 

Biology Complexity Explained

Image credit: Smithsonian National Musseum of Natural History

What do algae do in the environment?

Algae– and by extension seaweeds– play a crucial role in creating the conditions for life on earth as we know it. Every time we breathe in, 50 percent of the oxygen filling our lungs, entering our bloodstream, and powering our cells comes from algae– specifically phytoplankton. PhytoplanktonPlankton consisting of microscopic plants. are single-celled algae that live drifting in freshwater and marine environments.

In addition to providing oxygen, algae are also important in the carbon, nitrogen, and phosphorus cycles because they absorb large amounts of these nutrients from aquatic environments. This means that they help to control excess nutrient and carbon dioxide levels in the water, contributing to local reduction of eutrophicationExcessive nutrients in the water, usually due to runoff, that causes an increase in plant growth and kills animals due to a lack of oxygen. and ocean acidificationDecrease of pH in the ocean, primarily caused by the uptake of carbon dioxide from the atmosphere..

How can algae be categorized?

One way to subdivide the massive group of organisms classified as ‘algae’ is to distinguish them by cellular structure. As we mentioned above, macroalgae are multicellular algae that are visible to humans without microscopes. (These are also commonly known as ‘seaweeds’). Most macroalgae are benthicFrom, relating to, or occuring on the bottom of a body of water., meaning they attach to the substrateA substance that an organism grows and lives on, or is supported by. in the body of water they grow in. Macroalgae that we most commonly think of are marine, living in saltwater or brackish water, although there are a few species that can live in freshwater such as filamentous green algae.

MicroalgaeMicroscopic single celled algae that are not visible to the naked eye, and typically live in fresh and salt water environments., on the other hand, can be unicellular, multicellular, or colonial and are abundant in saltwater and freshwater. Microalgae are often free floating and individual cells can only be seen with a microscope. In abundance, microalgae give rise to different coloration in the water – often greens, yellows, and browns – which can be observed to the naked eye. Both microalgae and macroalgae are primary producers in aquatic ecosystems, meaning they create chemical energy from light. However, microalgae tend to play the role of ‘food’ in these ecosystems while macroalgae are more commonly a structural element of aquatic environments and play the role of ‘habitat.’

A video (10:24) explaining the evolution of macroalgae and how algae have influenced Earth as we know it featuring phycologists Susan Brawley, P.h.D, and Jessie Mulin, P.h.D. Video Credit: Maine Aquaculture Innovation Center. Available on YouTube: https://www.youtube.com/watch?v=60DAcVHGyvQ&list=PLa6yzmcW1D9fLMWDQ4EUMRwBzCUXOyuLR&index=2

Within the categories of microalgae and macroalgae, there are many more groups of algae are further divided into based on the type of photosynthetic pigmentA pigment present in photosynthetic organisms that captures light energy needed for photosynthesis. they contain and the structure of their cells. Since this learning module focuses on farmed seaweeds, we will only cover the classification of macroalgae into three groups: brown, green, and red. These three types of macroalgae contain unique light-absorbing pigments, have distinct reproductive strategies, and evolved from separate biological lineagesA series of populations, organisms, cells, or genes connected by a continuous line of descent from parent to offspring..

Algae’s place in aquaculture

Globally, around 220 species of seaweed are farmed although nearly 95 percent of seaweed landings come from eight major species of red and brown algaes: Laminaria japonica, Eucheuma spp., Gracilaria spp., Undaria pinnatifida, Porphyra spp., Kappaphycus alvarezii, Sargassum fusiforme, and Eucheuma denticulatum.