The Power of Phytoplankton: Unseen Heroes of the Sea and Your Aquarium

In our pursuit of understanding the complex relationships in marine ecosystems, it is critical to focus our lens on an ever-present, yet often overlooked member of the marine world: the humble phytoplankton. As the driving force behind the majority of primary production in our oceans, these microscopic algae play an essential role in sustaining the tapestry of marine life - and contribute to the balance of our global climate.Akin to bacteria in size, growth rate, and rapid response to nutrient enrichment, these algae are, interestingly, also involved in water "cycling." This process, similar to nitrifying bacteria that convert ammonia into nitrite on land, may be an area where phytoplankton have a more significant role than we previously understood. The emergence of algal blooms and diatoms in newly established tanks could suggest that phytoplankton are equally - if not more - involved in this water purification process, absorbing ammonia directly from the water column before the nitrification cycle even begins.While phytoplankton may not be the most efficient primary producers on an individual level, they take center stage on a global scale, accounting for their vast spread over the Earth's surface. The upper 200m of oceanic waters are teeming with these tiny photosynthesizers, which cover over 70% of our planet.So, what feeds on these microscopic life forms? Predominantly zooplankton, including ciliates, copepods, amphipods, and tintinnids. Protozoans and some invertebrate larvae primarily consume nanoplankton, whereas copepods and amphipods prefer the relatively larger phytoplankton. On coral reefs, bivalves, tunicates, sponges, polychaetes, gastropods, crinoids, foraminiferans, and soft corals are significant phytoplankton consumers, filter-feeding the microflora as part of a vibrant and healthy reef ecosystem. With phytoplankton as a crucial food source for many organisms, especially in these nutrient-limited reef environments, it should come as no surprise that their communities can reduce phytoplankton levels significantly if an ecological balance is not established.

In reef aquaria, there is a looming question of phytoplankton's role in stony coral nutrition. While some studies suggest that specific stony corals can clear phytoplankton from the water, it's unclear to what extent they contribute to their nutrition as there has not been enough research on this. Most stony corals are better adapted to capture zooplankton prey, with phytoplankton potentially playing a minimal role in their energy needs.

As a reef hobbyist, one might question how much phytoplankton to introduce to an aquarium. The answer, however, is not straightforward, as it depends on a multitude of factors. These include the types, sizes, and quantities of potential phytoplankton consumers within a given aquarium and the differences in biomass between a tank and the same volume of ocean water in a reef environment.

While the use of phytoplankton in aquariums is often a topic of discussion, several considerations apply. Aquarium algae blooms are quite natural, following seasonal patterns similar to their wild counterparts. These blooms are largely made up of diatoms, dinoflagellates, and cyanobacteria, which, although not traditionally deemed desirable, play an essential role in aquarium ecosystems, just as they do in the wild. Caution is advised, however, since some species produce toxins that could harm tank inhabitants. If you want to optimally benefit the largest number of potential tank inhabitants that consume phytoplankton, it is recommended to allow similar ratios of various size classes as found in the wild.

While there is much more to say about the capacities of phytoplankton, what is most important to consider is the impact of phytoplankton both within and beyond our tanks. Seeing how they work within the world of an aquarium serves as a reminder of our role in preserving and understanding intricate marine ecosystems. Good aquariums are microcosms of the ocean, a testament to its beauty and resilience.

Whether you're a beginner or a seasoned veteran in aquarium keeping, your actions can contribute to the wider cause of marine conservation. We invite you to get to know IMARCS and join us in our mission to pioneer innovative mariculture solutions to conserve and restore marine ecosystems.

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References:

Borneman, E. (n.d). The Food of Reefs, Part 3:  Phytoplankton by Eric Borneman -  Reefkeeping.com. (n.d.). Retrieved from http://reefkeeping.com/issues/2002-10/eb/index.php

Kault, Jacob, & Detournay. (2022, February 21). Carbon Balance In Corals. Coral Guardian. Retrieved July 8, 2023, from https://www.coralguardian.org/en/carbon-balance-in-corals/#:~:text=To%20sum%20up%2C%20according%20to,3%20accumulation%20in%20their%20skeleton.