Coralline algae are a distinctive and widely distributed group of marine organisms. These unique algae possess a hard, calcified structure, setting them apart from other seaweeds. They thrive in diverse marine environments, from intertidal zones to deep-sea depths, and contribute significantly to the health and stability of marine ecosystems. Their presence often indicates a thriving underwater habitat.
Defining Coralline Algae
Coralline algae are a type of red algae, classified within the Phylum Rhodophyta and Order Corallinales. Their defining characteristic is the ability to precipitate calcium carbonate within their cell walls, giving them a stony, hard texture. This calcification process results in a skeleton primarily composed of calcium carbonate. Unlike many other algae, this internal calcification provides a rigid structure, making them feel like rock rather than typical soft seaweeds.
Types and Appearance
Coralline algae exhibit diverse visual characteristics, primarily classified into two main growth forms. Encrusting forms grow as flat, hard layers tightly adhered to surfaces like rocks, coral skeletons, and glass. Articulated forms develop branching, tree-like structures with flexible, uncalcified joints that allow them to withstand strong water movement. These algae display a wide spectrum of colors, including shades of pink, purple, red, green, yellow, white, or blue. Their vibrant colors stem from photosynthetic pigments combined with the calcification process.
How Coralline Algae Grow
The growth of coralline algae involves calcification, forming their rigid calcium carbonate skeleton. They extract calcium and carbonate ions from seawater to build their hard structure within their cell walls. This process is biologically induced, meaning the algae create the necessary chemical environment for mineral precipitation.
Environmental factors significantly influence their growth. Light is a major requirement for photosynthesis, which provides energy for calcification. Optimal water chemistry parameters, including calcium (380-450 ppm), alkalinity (8-12 dKH), and magnesium (1200-1400 ppm), are necessary for healthy calcification. Temperature also plays a role, with different species adapted to various thermal ranges.
Ecological Role in Marine Ecosystems
Coralline algae serve significant functions in marine environments, acting as primary producers that convert sunlight into energy, supporting the broader food web. Their hard, calcified structures play a substantial role in coral reef ecosystems, acting as a “cement” that binds and stabilizes the reef framework. This binding helps protect the reef structure from erosion and breakage, contributing to its integrity and growth. Coralline algae also facilitate the settlement of coral larvae; many coral species prefer to settle on surfaces covered by these algae, which release chemical cues encouraging attachment. The complex structures formed by coralline algae provide microhabitats and shelter for small marine organisms, enhancing biodiversity.
Coralline Algae in Home Aquariums
In marine home aquariums, coralline algae are often desired by hobbyists for several reasons. Their colorful encrustations, typically pink, purple, or red, add aesthetic appeal to live rock and tank surfaces. A thriving growth of coralline algae is also considered an indicator of a mature and stable aquarium environment, suggesting that water parameters are suitable for other sensitive marine life like stony corals.
For successful growth in an aquarium, coralline algae require stable water parameters similar to those for stony corals. Adequate lighting, often with a spectrum that includes blue and violet light, is also beneficial, though many species can grow in moderate to low light. Low nutrient levels, specifically low phosphates and nitrates, are also important, as high levels can encourage nuisance algae that outcompete coralline algae for space and resources.
Coralline algae can spread within an aquarium through spores released into the water, or by direct contact and growth onto adjacent surfaces. Hobbyists typically introduce it by adding live rock already encrusted with coralline algae or by placing frag plugs with existing growth into the tank. Scraping a small amount of existing coralline algae and allowing the fragments to settle can also help seed new areas. While generally desirable, coralline algae can grow on tank equipment and glass, necessitating regular scraping to maintain clear views and prevent interference with pump performance. Some herbivorous animals, such as certain sea urchins, can help control its spread by grazing on it.