Introduction

Nannochloropsis sp. is one of the most prolific and powerful tools to the modern reef aquarist, fish breeder, coral farmer and research aquaculturist alike. Nannochloropsis is survivalist algae, one which persists in fresh, salt and brackish water. This extreme elastic ability to adapt can be attributed to the many novel biochemical compounds this algae can produce, many of which offer profound nutritional benefits to the organisms which consume them. Nannochloropsis has been widely utilized in the realm of human nutraceuticals and it has true potential as a sustainable alternative to fish oil. The benefits of this algae go beyond direct consumption, as it has been successfully applied as both a biofiltration agent as well as a live feed in greenwater culture. There is also rising evidence that certain strains of Nannochloropsis exhibit novel antimicrobial and antiviral behaviors. With its many abilities combined with its ease of care, Nannochloropsis has infinite applications in all realms of aquatic husbandry.

 

Plant Power at the NanoScale

Nannochloropsis is a green algae and a member of the Chlorophyta. This means that they share some of the powers and attributes of plants. Like plants, their green coloration reflects a large dependence on the photosynthetic pigment chlorophyll a. This pigment specializes in the capture of bluish violet (465nm) and red light (665nm). As a result of this, Nannochloropsis thrive under full spectrum ‘white’ lighting but also under many grow lights designed for terrestrial crops. This algae also has the potential to produce a wide range of accessory pigments including lycopene, beta-carotene, zeaxanthin, canthaxanthin and astaxanthin. These pigments are highly valuable and promote the long term health and coloration of corals, fish, marine invertebrates and humans alike. Nannochloropsis cells are dense with microbial proteins and have been used as feed substitutes in animals such as carp, penaeid shrimp, sturgeon, rats, rabbits and goats. Also like plants, they are capable of synthesizing precious Golden Fats such as eicosapentaenoic acid (EPA). Even more useful, is the ability of some Nannochloropsis strains to store large amounts of these lipids within vacuoles–making them essentially a glorious fat ball complete with probiotics, proenzymes and a dash of pigment!

 

Nannochloropsis has evolved an additional power from plants—the ability to construct cell walls making  them resistant to foraging from ciliates and other small, contaminating microorganisms. Larger zooplankton, such as rotifers and copepods, are fully capable of annihilating this cell wall and therefore can be grown and gut-loaded on Nannochloropsis diets.

 

A Green Gift Ever-Giving to the World of Aquaculture 

Many filter feeding and larval organisms require daily feeding with a live microalgae diet. This can be a daunting task to provide, as many microalgae species easily crash without a dedicated sterile setup and experienced technique. Nannochloropsis is especially useful in that it is relatively resilient to abrupt crashes and can be sustained for weeks without any specialized equipment. This resilience makes it a far more accessible phytoplankton to the average aquarium hobbyist.  Ease of culture has made Nannochloropsis one of the most widely embraced phytoplankton genus in both marine and freshwater aquaculture. Various Nannochloropsis species have been utilized as an easy-to-grow feed for rotifers, copepods, artemia, moina and other live feeds.

 

One of the most popular applications of Nannochloropsis is Green Water Aquaculture. With this technique, microalgae is not treated as a direct feed but as the base of a controlled ecosystem. Live Nannochloropsis cells act as the ecosystem base, absorbing ammonia and phosphates, while acting as a food source for rotifers, copepods and other live feeds in the system. These secondary grazers act as constantly available algae-loaded forage for whatever larvae is being reared. The fact that the algae tints the water green helps shade sensitive larvae from over illumination as well. The Green Water Aquaculture technique allowed for the first commercial production of clownfish (Amphiprion sp.), and since then has been applied to the larviculture of anthias, groupers, butterflyfish, damselfish, rabbitfish, seahorses, cobia, porgies, snook, sablefish and countless other marine species.   

 

Why Nannochloropsis Wears its Best Suit in The Reef Tank

Complex and bioactive nutrition is essential to success with filter-feeding marine organisms such as aphotosynthetic corals (Tubastraea, Homphyton etc.), giant clams (Tridacna), electric scallops (Ctenoides), thorny oysters (Spondylus), porcelain crabs (Neopetrolisthes), feather duster worms (​​Sabellastarte) and various reef building sponges. Nannochloropsis is an invaluable tool for successful husbandry of many species which cannot solely rely on photosynthesis and which have a limited capacity to consume dead cell material (dead algae pastes, macerated oyster gonads, formulated microfeeds etc.). Even in photosynthetic corals, periodically feeding phytoplankton can offer a considerable boost in growth and overall vibrancy. For example, Ding et al. 2021 observed increased protein and lipid utilization among colonies of Gonipora columna fed a diet of live Nannochloropsis. There is even rising evidence that live Nannochloropsis cells are capable of boosting the immune competency of other organisms and suppressing the growth of certain pathogenic Vibrio strains. 

 

Many Nannochloropsis species can survive under a wide range of salinities, temperatures and light intensities. These conditions in a reef aquarium (i.e. high illumination, high salinity, low nutrients) exponentially enhance the nutritional profile of Nannochloropsis cells. For example, Abidin et al 2021 demonstrated that Nannochloropsis oculata produced elevated levels of accessory pigments (astaxanthin, canthaxanthin, beta carotene etc.) at salinities greater than 30 ppt. Pal et al 2011 observed that Nannochloropsis oculata produced the most triglycerides and proteins at high light intensities (500-700 PAR^[1]). Su et al 2011 demonstrated that Nannochloropsis salina produced more lipids (and higher quality lipids) when nitrate and phosphate levels were below 1ppm.   

 

Conclusion 

In many nations, large ponds of Nannochloropsis are used to strip nitrate and phosphate from agricultural effluent. In the Reef Aquarium, the same cleansing occurs. Nannochloropsis soaks up all the nutrients around it and converts them into microalgal proteins, pigments and Golden Fats. This nutrition is then delivered, in a perfect single-celled package, into the mouths of hungry corals, clams and other finicky filter feeders. This versatile algae can be fed directly to the reef or used to accelerate a culture of zooplankton such as rotifers, copepods or artemia. Green and gut-loaded live feeds open an awesome Pandora's Box! Algae allows the research aquaculturist, the commercial farmer and home hobbyist alike to engage with an ever-expanding array of species–allowing them to keep the unkeepable–breed the unbreedable–and bring the worlds of the Reef Aquarium and Aquaculture to ever-greater heights!               

 

Literature Consulted

 

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1 1 PAR= μmol photon m-2s-1 of photosynthetically active light