Feeding your Reef Aquarium

Certain sea stars, such as this Nardoa spp. in the author's aquarium, are excellent scavengers

I often hear the phrases “In the wild, reefs are nutrient poor” and “a reef aquarium should have a low nutrient level”. Seeming in contrast to these statements is the necessity of feeding the coral and other inhabitants of the reef aquarium. What do these phrases really mean, especially to the hobbyist?

These terms are somewhat confusing, and lead many reef aquarists to believe that they should feed their reef aquariums sparingly, and avoid a “high bio-load” of fish and other animals. This is a misinterpretation, and aquarists should be encouraged to feed heavily and should not be overly concerned about stocking fish in a reef aquarium to reasonable levels. As a marine biologist and hobbyist, I'd like to shed some light on what originated as a scientific statement that is now often (mis)used in the hobby.

“Nutrients” commonly refers to all Dissolved Organic Compounds (DOC's) measurable in a given sample and a given location, but for the purposes of this article will refer to dissolved organic compounds that can be easily measured and are familiar to aquarists, mainly ions such as nitrates (NO3-) and organic phosphates (PO4-). Both of these organic compounds are absolutely essential to life, and coral and other reef invertebrates are no exception. Minute readings of nitrates and phosphates are vastly preferably to zero in terms of coral health and growth!

The phrase “reefs are nutrient poor” refers specifically to the low amount of dissolved nutrients in the water column, and how available nutrients are usually confined to living animals. However, there is a very large difference between dissolved nutrients and available food source(s). Plankton, (phytoplankton and zooplankton), is incredibly abundant on a reef, and is a vital and constantly available food source to a myriad of corals and other animals. Corals live in a literal soup of food (plankton and suspended biomatter), yet also technically they are in a “nutrient poor” water (water with little dissolved nutrients). The fact that this statement causes confusion amongst aquarists should come as no surprise!

In the past, aquarists have an unfortunate tendency to associate foodstuffs with nutrient levels in the reef aquarium, a habit that leads to slower growth rates, and a lower level of success with some species. As there is no animal known that can create a full organic nutrient profile solely via photosynthesis, every coral requires some form of foodstuffs in order to survive and thrive. Luckily, this trend is beginning to change.

'LPS' coral like this Blastmussa merletii require frequent feedings to survive & prosper

Feeding a reef aquarium undeniably increases the dissolved nutrient level in the water column. However, this is most definitely not a reason to avoid feeding, or to feed sparingly, and in fact, can be a good thing. Today's modern reef aquarium, possessing a healthy anoxic sand bend and an efficient protein skimmer, is more than capable of preventing the accumulation of nutrients to harmful levels in between weekly water changes. I feed my reef aquariums heavily, every day, and from one who has fed both heavily and sparingly, I can tell you honestly that the growth and vigor of well-fed corals is astounding! I am not alone in my feeding method: any coral propagation facility that is raising coral for commercial sales feeds their corals an incredible amount when compared to the average hobbyist: often enough to completely cloud the system two or three times a day! Low nutrient levels are maintained in these facilities via massive protein skimmers, ozonizers, and very large (often daily) water changes.

Seachem makes several great 'wet-packed' foods

Although regular feeding has been commonplace commercially for many years, feeding has only recently begun to gain serious recognition in the hobby. Over the last two or so years, many excellent products have appeared on the market for reef aquarists who now understand the importance of daily feedings. Three excellent products that I've used for years and highly recommend are Cyclops-eeze (especially the frozen version), Coral Frenzy, Seachem’s NutriDiet, and Formula One. The first three are designed to mimic zooplankton in the aquarium, and elicit an obvious feeding response in corals. The last is marketed as a fish food, and is essentially a finely blended mix of several ingredients. Other excellent foods are frozen mysid shrimp, and shredded or blended raw seafood from your local grocery store.

Contrary to popular belief, phytoplankton supplements are generally of little use in the aquarium, with the possible exception of a soft coral or bivalve dominated display. The largest consumers of phytoplankton are living zooplankton, bivalves, fan worms, and other filter feeding invertebrates. Most coral species commonly kept by aquarists will not consume phytoplankton, and it is not necessary to feed phytoplankton to Tridacnids assuming there are measurable levels nitrates and phosphates in the aquarium. Unless you are interested in culturing plankton, keeping non-photosynthetic soft corals, or keeping oysters, phytoplankton supplements are virtually useless.

I list the commercial brands first because of their ease of use and convenience. However, more natural methods produce more natural, healthier, and more effective food sources if the aquarist has the time and inclination. Culturing of Artemia, Dapnia, and Gammarus is possible and fairly easy to do, if somewhat time consuming. Another excellent natural method for producing plankton for the home aquarium would be a refugium, preferably a refugium with a deep sand or mud bed, and stocked with plenty of macroalgae. The biodiversity revealed in a refugium that is stock with live sand, macroalgae, and a small amount of quality live rock is astounding. Refugiums have the added advantage of reducing your tanks’ dissolved nutrient level: nutrients are both filtered and stored biologically by the diverse invertebrate fauna that can be found in a refugium, or are removed directly by pruning and removing excess macroalgae growth. Bigger is definitely better in the case of refugiums: build or buy the largest one you can fit and/or afford because they are well worth the investment.

Feeding corals can be a challenge, but here are a few general guidelines to help you in your quest to provide better nutrition:

Soft corals such as ricordea mushrooms and zooanthids (button polyps) are greedy eaters of all small foodstuffs: while mysids are usually too large, Cyclops-eeze and Coral Frenzy are greedily consumed, as are Artemia nauplii. My Ricordea yuma population almost doubles in size every month on a diet of Coral Frenzy alone! A few soft corals will feed upon phytoplankton, such as Nepthea spp and other (usually non-photosynthetic) soft corals.

'LPS', or large polyp stony corals are voracious eaters, especially of meaty food items, such as mysids, mashed Formula One, Gammarus or Daphnia, and shredded raw shrimp and other seafood. LPS corals should be target fed at least three times a week to ensure adequate nutrition and to increase growth rate.

SPS, or small polyp stony corals often have an unknown food requirement. However, oyster eggs, finely blended meaty seafoods, and Artemia nauplii are often consumed.

Although brief, I hope that this article touching upon the importance of feeding the reef aquarium will benefit hobbyists, as well as dispel a few misunderstandings that tend to crop up again and again in this hobby. Please keep in mind virtually all reef inverts can slowly starve over a period of months/years. A "mystery death" after a few months to eighteen months can usually be attributed to slow attrition, of which the hobbyist was unaware. I have a saying; “if it’s not growing, it’s starving!”, so feed, feed, feed!

All images © 2009 by Mike Maddox. All aquarium photos are from the authors' aquariums.

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