The core of all production in the sea is phytoplankton, which multiplies rapidly, subject to presence of mineral nutrients and light. From there on, a short trophic relationship with an organism, which has a good conversion efficiency, would be the most effective and healthiest way to produce anything.

Sessile filter feeders like mussels are good candidates, because they belong to the second marine trophic level, don’t spend any energy to swim and cannot escape. The very short trophic relationship between primary production of phytoplankton and production of mussels assimilating it, combined with the very pure AAIW quality, are the unquestionable guarantee of the lowest level of anthropogenic pollutants at the end of the production process.

Mussel aquaculture has been practiced for centuries, even millennia, because it is rather an easy culture. They multiply profusely, attach themselves on any surface or created device, and feed on any organic matter they find. Several techniques are used nowadays.

• Bouchot culture: pilings, known in French as bouchots, are planted at sea; ropes, on which the mussels grow, are tied in a spiral on the pilings; some mesh netting prevents the mussels from falling away. This method needs an extended tidal zone to be able to work on it at low tide.
• On-bottom culture is based on the principle of transferring mussel ‘seed’ (spat) from areas where they have settled naturally to areas where they can be placed in lower densities to increase growth rates, facilitate harvest, and control predation.
• Raft culture is a commonly used method throughout the world. Lines of rope mesh socks are seeded with young mussels and suspended vertically from a raft. The specific length of the socks depends on depth and food availability.
• Longline culture (rope culture) is the most recent development for mussel culture and is often used as an alternative to raft culture in areas that are more exposed to high wave energy. A long-line is suspended by a series of small anchored floats and ropes or socks of mussels are then suspended vertically from the line.

Using long lines is the most productive technique for mussel aquaculture, because it takes advantage of the volume in the water column, instead of a surface. However, this production method, intended for human consumption, is too expensive, and needs to be adapted to fit aquafeed production. Several sorting and cleaning stages essential for harvests intended as human food can for instance be abandoned, freeing a lot of time and money. The long lines themselves are too expensive in their present form, and also need to be re-designed.

 

Despite the reservations just expressed, long lines mussel farming is by far the world’s most productive breeding method, currently yielding 150 to 300 tonnes, per hectare per year. To put these figures into perspective, beef production is only around 0,340 tonne per hectare per year, almost a thousand times less! With mussels on long lines, we can reasonably forecast (if the carrying capacity is given) a production between 3 to 6 million tonnes of mussel flesh (50 to 75% is shell) in a square of 90.000 ha, like the flat top of Davis Bank. This figure for the potential yield can also be compared to the 5.5 million tonnes of Peruvian anchovies caught in 2018, which is the world’s largest fishery dedicated to the production of fishmeal and fish oil. These were their highest landings since 2011 and unlikely to be heavily surpassed, due to government conservation policies that limit the Total Allowable Catches (TACs). Moreover, 2018 did not experience the famous El Niño event, which periodically occurs and results in a temporary collapse in yield of this reduction fishery.

However, as a consequence of the relative ease of culture, some aspects of the biology of mussels, such as their most efficient diet, have only been poorly documented. We know that mussels filter and ingest plankton and other organic particles from 5 to 15 microns. Diatoms, the main intake, provide DHA (good for our brain) and flagellates provide EPA (good for our heart), both important LC-PUFA omega 3. Control of mussels’ diet, neglected until now, is all important here, especially if it can be easely managed.

Each mussel filters nearly 100 liter water a day. Retaining all the particles present in the water, its food conversion factor can fluctuate, between 30 and 80%. That means mussels produce between 20 and 70% faeces (which pass through the digestive system), or pseudofaeces (materials which are immediately rejected). These sink and pollute the seabed below, because the organic content is not enough degraded by aerobic bacteria during sedimentation, especially when the sea floor is not very deep, which is the case in most coastal areas where mussels are farmed. When the faeces accumulate on the sea bottom, digestion depends on anaerobic bacteria which have a negative impact on ecosystem health. That’s why knowledge of the most efficient diet for mussels is so important. Especially if we are able to influence this food conversion factor and the nature of the metabolised substances, by using the appropriate phytoplankton mix to feed the mussels. In our plans, the most favourable phytoplankton species could be injected into the rising nutrient-rich AAIW passing through the salt fountain pipes, to let them multiply on their way up, thanks to strings of blue LEDs inside the pipes. In this way it should be possible to control the diet of the cultivated mussels, in order to minimize faecal output and maximize LC-PUFA omega-3 production.

Now we have the framework. But it will not work as described so far because of the environmental footprint of such a huge mussel farm. To avoid contamination, it still needs either to be distributed between several places, or at least trophically compartmentalized in some way, by cultivation of macroalgae for example. Anyhow, it needs also to be associated with other cultures to establish greater biodiversity among the species so that the mussel farm becomes a self-sufficient biotope. This approach is called Integrated Multi Trophic Aquaculture (IMTA) where the waste products of one species are recycled as feed for another.

 

Mussel faeces cause pollution problems in most of today’s monoculture areas. To avoid this, the soluble faeces can be assimilated by kelp or another macroalgae, and the solid ones can be assimilated by scavengers on bottom like sea cucumbers. These will also strongly contribute to the project’s viability, because of their value for Asiatic people, who appreciate them a lot as food and medicine. You can read more about it on the website of the IMTA Research Laboratory.

However, despite IMTA technics, such a mussel farm will lead to a huge threat for the existing biodiversity of this rhodolith covered seamount, which counts several species of algae, corals, crustaceans, sponges, fishes, some of which are endemic. In short, Davis Bank is a rich reef biotope as shown in this video below entitled “Fish biodiversity of the Vitoria-Trindade Seamount Chain – Pinheiro et al 2015”.

Since this filming in 2005, carbonates mining to provide fertilizers for Brazilian sugar-cane plantations has occurred on seamount summit, together with mining trials of cobalt-rich crusts on slopes. Moreover, for several years now, fleets of fishing vessels from China, South Korea, Portugal and Spain commonly work there, as we can observe on Global Fishing Watch.

 

 

If this fleets use bottom trawls, the reef might already be in pretty bad shape. I don’t know how this paradise looks like today, but if it is still pristine despite these damaging attacks, we may perhaps choose a less space requiring marine organism than bivalve molluscs farms for our purpose.

Copepods are also good candidates. From 13 000 species of known copepods, 10 000 are marine and 5 000 of them are nonparasitic and free living zooplankter, like calanus. Populations of these 1-2 mm crustaceans are so large that they represent a considerable marine biomass and are, in nature, a crucial link between energy-producing phytoplankton and fish. Like mussels, they belong to the second marine trophic level. In spring, they aggregate together in huge swarms near the surface, until seawater becomes like a syrup that the baleen whales scoop in big mouthfuls.

A single copepod can catch and consume a few hundred thousand phytoplankton cells per day, clearing about a million times their own body volume of water. They feed at the surface at night to avoid visual predators and eventual toxic emanations from phytoplankton. At daytime, they sink several hundred meters down to stay protected. In Polar Regions, they sink even to a thousand meters depth to hibernate during the cold season and live on their reserves,accumulated during the summer.
This is why their metabolism allows them to build up a very high protein and LC-PUFA content. To be able to sink, they change their oils into denser fats, wax esters. They also accumulate astaxanthin, a lipid soluble carotenoid, well known for its anti-oxidant properties, which enables them to hibernate with preserved stocks of nutriments. Astaxanthin is also the substance that gives the orange-red color to wild salmon flesh. Fish feed is currently supplemented with synthetic astaxanthin to avoid rancidness and give the right color to farmed salmon flesh.

With a view to breeding calanus spp. for fish feed, some very interesting properties can be highlighted:

• They are already natural wholesome fish feed, a not transformed whole feed for aquaculture.
• They aggregate together naturally and can thus be easily harvested.
• They have a very high protein and LC-PUFA content, naturally well balanced with all needed micronutrients.
• Bound as wax esters, the LC-PUFA are much better assimilated as those of fish oil and lead to very pronounced positive effects on important metabolic parameters.
• Thanks to their astaxanthin content which acts as a self-preservative, they may not need to be processed into meal and oil to be stored at room temperature.

My expectation is that we should be able to breed swarms of Calanus spp. inside the Perpetual Salt Fountain pipes, harvesting them on the top outflow to avoid threat to the environment.

All these conclusions of mine are written without reference to all the sources I have used, because I do not claim to have done a scientific work. The latter has finally been accomplished with the precious assistance of Dr. David Moore and has been published on January 1st, 2021 in the Mexican Journal of Biotechnology under the title Saving the Planet with Appropriate Biotechnology: 3. The High Seas Solution, as part of a complementary project aimed at rehabilitating the benefits brought by marine calcifiers in terms of climate change remediation, coastal conservation and food sufficiency.

Obviously, a great deal more research needs to be done but this logical frame of pragmatic ecology and oceanology suggest my project has a solid base to counteract the challenges of fish farming sustainability and preservation of the biological productivity of the open oceans.. We must start these efforts by installing a pilot station of perpetual salt fountain pipes on Davis Bank.

Follow me on My vision.