Phytoplankton, Macroalgae, or BOTH?

As marine aquarists, we might think of algae as being divided into three (maybe four) distinct categories: the benthic (i.e. bottom-dwelling) microalgae, the open-water microalgae and the macroalgae. The first group consists of the film/turf-formers, the second group consists of the phytoplankton and the third group consists of the larger, plant-like seaweeds. The first group is generally regarded as “bad” algae whereas the second two are generally considered to be desirable. Oh, and that questionable fourth group? Maybe we could list an additional, relatively small number of “bad” seaweed species here, specifically those (for example, some Caulerpa) that can in rare situations become invasive in the aquarium. Of course, this broad classification is just a practical construct; there is hardly any phylogenetic basis for the arrangement. Tetraselmis (a green planktonic microalga), for example, is more closely related to Ulva (a green macroalga) than it is to Thalassiosira (a brown planktonic microalga).

But, practical this classification certainly is. In just about every conceivable circumstance, film and turf algae really are bad! For one thing, they are rather ugly. They are also unnatural, as they do not grow to form particularly expansive films/turfs in healthy coral reef habitats. So they’re both ugly and unnatural… Pretty bad, right? For reef aquarists, that’s not even the worst of it. At their very worst, these forms can rapidly blanket entire sections of an aquascape, eventually covering and potentially killing sessile invertebrate life (e.g. corals). In aquarium systems where dissolved nutrient levels are chronically high, the negative influence of bad algae can be truly devastating.

One big thing that phytoplankton and macroalgae have in common is that they can be effectively used to control film/turf algae. The reason that they both “work” for this purpose is that they compete aggressively with bad algae for nutrients. Once the nutrients are sequestered by the “phyto” and “macro,” they are eventually exported from the system respectively via water changes and harvesting. To some notable extent, nutrients will also be recycled as algal biomass is consumed by different aquarium animals. Starved out, the benthic microalgae are ultimately beaten down or even eliminated from the system altogether.


A Tale of Two Algae: The Same but Different

Some aquarists wonder if using both phytoplankton and macroalgae in the same system is enjoying too much of a good thing. Not at all! Here, you could even say that multiple species of macro with multiple species of phyto wouldn’t be overkill. Indeed, because every species (desirable or otherwise) has its own preference with respect to nutrient availability, light intensity, etc., a combination of phytos and macros can be quite complementary in their fight against bad algae. But that’s not all; there are many other good reasons to use these beneficial algae. But, some of these uses are exclusive to one type or to the other.

Let’s start with one major difference here. Sure, both types can be utilized as a food source by various aquarium inhabitants. However, each of these will only be consumed by certain sorts of animals. To the point, your corals are probably not going to graze on your Gracilaria. Nor will you ever catch your tang sifting phytoplankton from the water column. If you have both corals and herbivorous fishes (and you probably do), your tank will likely profit from the addition of phyto as well as macros.

A typical reef tank will house all sorts of invertebrates, including corals, clams, sea cucumbers, sponges and so on. Many of these creatures are phytoplanktivores. For these, good health and coloration (if not survival) depends upon a proper density of phyto. Each species might even prefer a phytoplankton of a specific size or nutritional profile. Therefore, a diverse collection of inverts will usually benefit most from a mixed-species feed. Yet, purchasing, storing and administering a whole fridgeful of different live phyto products would surely be a real pain. Luckily, AlgaeBarn has introduced a convenient multi-species product for all reef aquaria. As it contains a carefully formulated blend of four species—Nannochloropsis, Tetraselmis, Thalassiosira and Isochrysis—the ever popular live phyto product OceanMagik is ideal for general use.

But we said a typical reef tank will be home to all sorts of inverts. This will almost certainly include herbivorous types such as many crabs, sea urchins etc. These critters, just like herbivorous fishes such as many tangs, angelfish, butterflyfish, blennies, boxfish, etc. will greatly appreciate the addition of fresh, live seaweed to their diet. Live macros usually provide considerably more vitamins, antioxidants, pigments etc. than “prepared” fare. They may be purchased on a regular basis for feed, though one can also use material harvested from a planted refugium.

That brings us to yet another consideration. Sometimes, live phytoplankton and live macroalgae can be used together, for different purposes, to serve the same species of animal! Various types of macroalgae are commonly used in the refugium for nutrient export. While they’re there, they carry out another important task: creating prime habitat for copepods!

Many copepod species that are available to aquarists are benthic as adults and planktonic as larvae. As adults, these forms of course thrive in a refugium packed with seaweed. But their young? You guessed it! They require a rich source of phytoplankton for proper growth and development. This culminates in a three-punch knockout for bad algae. The macros and phyto compete against them, plus they are consumed by the hungry pods! This also serves a three-course meal to your tank. You’ll have macro and phyto as a live food, plus the pods will constantly be available to zooplanktivores and small fishes such as mandarins.

Getting it Together

Does it seem as though your corals are lacking in vitality? Are you struggling with nuisance algae? It certainly might help to start adding live phytoplankton to the system. And if you add phyto, can you still add a little Chaetomorpha for your pods to live on? Absolutely. In fact, the presence of one of the major groups of good algae can actually increase the effectiveness of the other. Remember that each type fills its own ecological niche. Using macros and phyto in tandem can, in many cases, complete your ecosystem and create the healthiest possible environment for all of your animals!

124 thoughts on “Phytoplankton, Macroalgae, or BOTH?”

  1. Macros are my favorite since there’s ways have them in your display for presentation and functional. Phyto is great to supplement alongside it so both!

  2. I was having cyano and hair algae issues. I added a fuge giving the algae a new place to populate and started adding phytoplankton and the nuisance algae in my tank has all disappeared!! 👍🏻👍🏻

  3. Victoria Brewer

    I always noticed my pod population went up when dosing phyto. I’d love to try out algae barns blend.

  4. I bought the 5280 combo pack a few weeks for my refugium and now waiting to see if they take hold.Keeping my fingers crossed.

    1. I had been stocking my reef with pods for about 3 months before I got a Mandarin goby… She’s been in the tank for about five months now and she is very healthy. I add pods every six weeks or so now, but I could probably go longer. With all the cheto in the refugium and the every other day of phyto my pods seem to keep up with two goby’s no problem.

  5. Foster L White Jr

    Great information. I have forwarded this to others I know that have asked questions this blog addresses.

  6. Both, macro for exporting nutrients and feed the Tangs. And phytoplankton for the corals, bi valve, feather dusters, and coopods

  7. We love Algae Barn’s products. The pods and Ocean Magik helped get rid of our Dinos and saved our sanity. We will definitely continue to order pods.

  8. Set up Triton method in sump with Chaeto and Kessil H380. Added 5280 pods, phyto, and purple helix coraline algae. I have zero algae in my display tank after three two months except coraline. My display tank get direct light from a window for two hours each day and still no algae! My water test are perfect. Currently fish only and water is perfect. Only dosing to elevate pH. Zero water changes!

    You have to try Triton.

  9. I’ve recently started using phyto AND macro algae. So glad I found Algae barn with attractive alternatives to chaeto, I put my red algaes on display instead of in the refugium

  10. I like to utilize both! Algae Barn is the best! Always great information, great pods, macro algae and the cutest little urchins!
    Thank you Algae Barn!

  11. Elmer Nicomedez

    The best thing about aquariums is that, although enclosed, there is a working ecosystem. My philosophy is not to mimic nature but provide as much of a natural foundation to sustain the life within. Algaebarn, you guys helped keep my system thriving.

  12. Good info, hard to tell though, is the water filter green because it’s filtering out micro algae, should i remove the filter sock?

  13. Judi A Knight-Mitzel

    Just getting back into sw tanks after many years, and trying live phyto for the first time 🙂 I also set up a refuge with chaeto and hoping for some great pod growth. Thank you for the great info.

  14. Glad to see this article as I use both and thought maybe it was a little redundant to use both. Glad to have a leg up!

  15. Glad to see this article as I use both and thought maybe it was a little redundant to use both. Glad to have a leg up!
    Thanks to this site my vision of my tank will hopefully come to fruition.

  16. Have ordered a couple times before need to make another order soon everything has always arrived alive.

  17. I wonder if this can out compete Dino’s that have plagued me off and on for years. I can beat them into submission for a few months with adding bacteria supplements then they will return at a certain point. Worth a shot!

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