Macroalgae: Beneficial and Beautiful 

Macroalgae comprise a large and rather diverse group of relatively complex, multicellular algal species. Macroalgae are represented in all three major algae groups: brown algae (Phaeophyta), red algae (Rhodophyta) and green algae (Chlorophyta). Macroalgae are also not an individually separate phyllogenetic assemblage (i.e. they are not very closely related), since each subgroup formed independently of the other two into their multicellular forms.

Ecologically, macroalgae can also be known as 'seaweeds', as they are all very plant-like in their physical structure (at least superficially) with stem-like, leaf-like and root-like structures. Their larger size and complexity (like plants) creates a microhabitat of their own, especially when grown in dense, expansive beds. The shelter they provide is an important haven for small invertebrates, such as copopods.

The Benefits Of Macroalgae

Macroalgae is a broad type of algae that is generally beneficial and mostly used to regulate nutrient levels and microalgae growth. It is most typically found in refugiums in the sump area of the tank. Unlike Granular Ferric Oxide (GFO) or protein skimming, the use of microalgae to tackle algae growth and nutrient outputs is completely natural and inexpensive. Macroalgae are also easy to use and take care of, making them very convenient. It is no coincidence that tanks with minimal algae growth also use macroalgae. If you are looking for a cost-effective, simple, and effective solution to algae growth and high nutrient levels, you should highly consider using macroalgae!  Read more here to learn the easy to follow steps in setting up a refugium.

Saltwater aquarists are increasingly cultivating macroalgae. Typically, this is for practical reasons, while macros are commonly grown purely for fun (marine gardening, if you will). Macroalgae are also grown in a refugium to enhance the quality, meaning you don't need to change your water as often. The key reason for this is that marcoalgae absorbs excess nutrients (particularly nitrates and phosphates) from the environment. These trapped nutrients are then "extracted" from the system as portions of the algal mat is removed from your system and thrown away.  

The harvested material can also be fed to herbivorous aquarium livestock. Algal species like Sea Lettuce and Ogo are fleshier so are particularly favored across most aquarium species. Macroalgae also serves a nutritious food source for fish species including tangs, angelfish and rabbit, as well as lots of invertebrate species (e.g., sea urchins, crabs, nudibranchs). Adding macroalgae creates a beautiful and dynamic habitat for many species, especially pistol shrimp, pipefish, clownfish, gobies and seahorses. The large surface area and denser areas also allow your small crustaceans (e.g., copepods, amphipods and isopods) to be able to hide, breed and gives a place for them to lay eggs. The ornamental aspect of adding macroalgae really does enhance a saltwater tank and can help your tank inhabitants feel more confident. Even the macroalgae themselves are so beautiful and colorful that many aquarists collect them.

Beautiful Macroalgae Species

Mangrove Shoots

Mangroves (Rhizophora mangle) are widely distributed across tropical and subtropical coastal regions. Mangroves are found within estuaries and salt marshes as they prefer fairly well protected, brackish environments. Assemblages of mangrove trees, called mangals, are extremely important both for holding sediments in coastal environments and for sheltering innumerable fish and invertebrate species. Saltwater Mangroves can grow on or on almost any kind of substrate. When the root system grows, the habitat of the refugium becomes enriched.  This plant can tolerate low water quality and weak flow of water. However, it is accustomed to living in complete tropical sunshine and thus needs strong artificial illumination when kept indoors. Any natural sunshine (from a window every day) can greatly help this magnificent and gorgeous plant.

Red Ogo

Gracilaria parvispora is also often known as Birds Nest or Red Ogo. This species of marine macroalgae is a beautiful looking red macroalgae species, which looks really striking in a reef display tank. As this macroalgae species grows quicker than other Gracilaria algae species, it makes a particularly great habitat for herbivorous fish and seahorses. Not only does Red Ogo provide a stunning look, structure and pop of color, it is also a great food source for tang and foxface fish.

Mermaid Fan

Commonly known as the Mermaid's Fan plant (Udotea sp.) is a real eye catcher for the planted reef display tank. It is a stunning green calcareous macroalgae with a dark green fan shaped top at the end of the stems. Using its rhizoids, it clings to the substrate, going down to a few inches deep.


Water Conditions For Macroalgae

In the right water conditions, you can find it very easy to grow macroalgae successfully in your own marine aquarium display tank or refugium/sump and enjoy seeing them grow and turn your marine aquarium into a stunning reef aquarium with soft and hard corals.  Wondering what is a refugium?  We answer refugium questions and much more on our Saltwater Aquarium Blog

While macroalgae are not plants, they do require almost the same basic elements as plants and, of course, a very critical component is light and the macroalgae will also need the right water parameters, especially of major and minor minerals, to thrive and remain healthy. In comparison to plants, macroalgae do not grow with roots and thus the nutrients must be supplied through the water and not through the substrate.

Of course, the amount of nutrients you need for your macroalgae to grow well will vary with the macroalgae you have in your marine aquarium, how much you make adjustments in saltwater and what kind of livestock you keep in the aquarium.

Optimal marine aquarium water parameters for an improved macroalgae growth:

Temperature: min 23 °C / max 29 °C

pH: 8.0 - 8.4

Alkalinity: 8-11 dkh

Salinity: 1.024 - 1.026

Nitrate: Between 3-10 ppm, not below 2 ppm

Phosphate: 0.03 ppm  to 0.07 ppm, not below 0.02 ppm

Magnesium:~ 1300 ppm - 1450 ppm

Calcium: ~ 380 ppm - 450 ppm

Potassium: 380 – 420 ppm

Boron: 4 – 6 ppm

Iron: ~ 0.01 ppm

Iodine: ~ 0.06 ppm


In summary, macroalgae are beautiful and functional additions to any saltwater aquarium and are only growing in popularity. Macroalgae serve as a cost-effective and efficient way of purifying your system to reduce the need for additional maintenance of your water parameters.