Macroalgae

The macroalgae include a huge and rather diverse group of relatively complex, multicellular algal species. Macroalgae are represented in all three major algal groups: The brown algae (Phaeophyta), red algae (Rhodophyta) and green algae (Chlorophyta). Hence, the macroalgae are not a distinct phyllogenetic assemblage (i.e. they are not very closely related), as each subgroup evolved into their multicellular forms independently from the other two. Ecologically, though, this concept of a “macro” algae is meaningful and useful. These “seaweeds” are all very plant-like in their physical structure (at least superficially), bearing stem-like, leaf-like and root-like structures. Their greater size and complexity (like plants) creates a microhabitat of its own, especially when they are grown in dense, expansive beds. The shelter they provide is an important haven for small invertebrates such as copepods. Increasingly, marine aquarists are cultivating macroalgae. Usually, this is for practical purposes, though macros increasingly are grown simply for enjoyment (marine gardening, if you will). Macroalgae are frequently cultured in a refugium to improve water quality and reduce the need for water changes. In practice, the seaweeds take up excess nutrients (nitrate, phosphate, etc.) from the system. These locked up nutrients are then “exported” from the system as portions of the algal bed are harvested and thrown away. Alternately, the harvested material can be fed to herbivorous aquarium animals. Fleshy types (sea lettuce, ogo, etc.) are relished as a highly palatable, nutritious food source for fishes (tangs, rabbitfish, angelfish, etc.) and invertebrate (sea urchins, certain crabs, etc.). As alluded to above, macroalgae add more biogenic “refuge” to a refugium. The enormous amount of surface area they provide can dramatically boost pod populations. Here, small, desirable microcrustaceans (copepods, amphipods, isopods, etc.) can hide from predators and breed. With so many interesting ornamental macroalgae becoming available, one might begin collecting certain types purely for their beautiful appearance. The deep reds of Gracilaria or rich blues of Hypnea might come to mind here. Healthy and flourishing specimens of slower-growing varieties look so impressive that they can quite justifiably be used in the display tank (presuming an absence of herbivores!). In this section you will learn which types of macroalgae live in which types of habitats, how they can benefit your captive ecosystem and what they need to grow lushly.