Phytoplankton and Copepod Cultivation in Reef Tanks | The Role of Microorganisms
This article covers the roles of phytoplankton and copepods in reef tanks, how to add and cultivate them, and which organisms and fish utilize them.
Key Takeaways
This article covers the roles of phytoplankton and copepods in reef tanks, how to add and cultivate them, and which organisms and fish utilize them.
Discussions about reef tanks tend to focus on the husbandry of corals themselves, but phytoplankton and copepods—minute organisms that are difficult to see—also function as part of the tank's ecosystem. While a separate article addressed the relationship between soft corals and amphipods, which are relatively large microorganisms, this article focuses on an even smaller tier of organisms: phytoplankton and copepods.
Position of Phytoplankton and Copepods in Reef Tanks
Phytoplankton are single-celled microscopic algae that perform photosynthesis and serve as primary producers in seawater. Copepods are small crustaceans that feed on phytoplankton and fragments of organic matter, and they represent a basic food resource for many marine organisms. In natural coral reefs, the food chain of "phytoplankton → copepods → larger organisms that eat them" is constantly operating on an invisible scale.
In the closed environment of an aquarium, this food chain often cannot establish itself naturally, so aquarists add phytoplankton to feed copepods or establish copepods themselves in tanks or refugiums as a means of cultivating microorganism populations.
Adding Phytoplankton | What Is It For?
Phytoplankton supplements (the so-called "culture" type products) are typically added directly to the tank. What is important to understand is that the main role of phytoplankton is to "serve as food for zooplankton such as copepods," and it is not something that can be definitively said to directly benefit corals (enhance coloration or directly promote growth). Results vary greatly depending on individual organisms and environmental conditions, and phytoplankton only become meaningful when basic conditions such as nutrient management, lighting, and water flow are in place. It is practical to view them as merely supplementary elements.
When adding phytoplankton, keeping the following points in mind will make management easier:
- Adjust the dosage gradually based on tank size and the existing population of copepods and microorganisms
- Adding too much can cause the water to turn cloudy or increase nutrient (phosphate and nitrate) loads, so manage this in conjunction with nutrient testing
- Some aquarists add small amounts via drip to refugiums or indirectly lit areas and concentrate feeding in copepod breeding areas
Increasing Copepods | Breeding and Creating Habitat
Copepods will breed naturally in a tank if they have hiding places and food. A commonly used environment to support breeding is a refugium with porous live rock and lush Chaetomorpha (macroalgae). Because the refugium has gentle water flow and is isolated from predators (fish), it functions as a refuge where copepods can increase without being consumed by predators. While the refugium's role in nutrient export is covered in a separate article, it also serves as a breeding ground for microorganisms.
Points to promote breeding are as follows:
- Arrange macroalgae and porous rock in a corner of the refugium or sump to provide hiding places
- Add small amounts of phytoplankton regularly to prevent food shortages
- Avoid overstocking fish on the main tank side and maintain population balance so copepods are not completely consumed by predators
Who Uses These Microorganisms?
Copepods and their larvae (nauplii) can be an important food resource for various organisms. For example, non-photosynthetic corals (lacking zooxanthellae or with low dependence on them) and filter-feeding organisms such as giant clams are believed to take in fine phytoplankton and copepods from the water column for nutrition. SPS and LPS polyps may also use copepod nauplii and similar particulate feeds as targets for target feeding, but this is merely one feeding option, and adding copepods alone will not ensure sufficient nutritional status for corals.
For fish, particularly species with strong predatory habits such as Picasso triggerfish that constantly seek out small living prey, whether a copepod population is maintained in the tank is often discussed as a factor affecting feeding difficulty. When acquiring such fish, it is essential to continue observing feeding behavior and not rely solely on copepod supply.
Precautions When Starting
Adding phytoplankton and copepods is a supplementary means of enriching the microorganism population in a tank and cannot replace basic conditions such as water quality management, lighting, and water flow. When starting supplementation, it is practical to begin with small amounts to assess effects on water quality, establish environmental hiding places such as a refugium, and then gradually build up the population over time.
Related Articles
- Soft Coral and Amphipod Interactions | Microecosystem Around Soft Corals
- Nutrient Export via Refugium | Managing Nitrate and Phosphate with Macroalgae
- Nitrogen Cycle in Saltwater Tanks and Beneficial Bacteria | Introduction to Microbial Ecology
- SPS Coral Feeding and Polyp Extension | Guidelines for Particulate Feed and Nutrient Balance
