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Inorganic carbon, nitrogen and phosphorus are the main elements required by seaweeds for photosynthesis and growth. This review focusses mainly on nitrogen, but the roles of carbon and phosphorus, which may interactively affect seaweed physiological processes, are also explored. Fundamental concepts such as limiting nutrients, sources, and ratios, mechanisms of nutrient uptake, nutrient assimilation and storage, patterns of uptake and preferences for different nitrogen sources are discussed. The roles of abiotic (water motion, light, temperature, salinity and desiccation) and biotic (life stages and age class) factors in nutrient (nitrogen, phosphorous, carbon) uptake are also reviewed. Understanding species-specific nitrogen physiologies and nitrogen source preferences will enable polyculture of different seaweed species and the use of seaweeds as biofilters in integrated multitrophic aquaculture systems.

In theory Seaweed biomass production is severely hampered by a 10,000 fold slower diffusion rate of a Carbon source or Dissolved Inorganic Carbon (DIC) in the biophysical medium water in comparison to terrestrial C3 crops. Despite this inflicting property pelagic seaweeds outcompetes C3 crops for annual green biomass production which is called “the seaweed-paradox”. Here we have reported our findings and hypothesized that for four seaweed species that due to an internal acidification the abundant oceanic bicarbonate ion (HCO3–) is introduced into the cell which will in the inner acidic mitochondrial environment (matrix) rapidly be converted to CO2 which is the only C-form photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) can react with to produce with solar energy and water green biomass. We hypothesize this intracellular acidification is performed by reversal of the fifth pump of the chemi-osmotic model of Mitchell. It can be expected that in nearby future seaweeds may play a prominent role in providing the unfettered growth of the world population -estimated at around 10 billion people at the midst of the 21st century: food, fuel and other bioactive ingredients.

Modern methods of macroalgal cultivation of the large brown seaweeds commonly and collectively referred to as ‘kelp’ began in the early 1950’s in China, with research spearheaded by ‘the father of mariculture’, Prof. CK Tseng and his team. Since this time, kelp aquaculture has steadily grown in China and other Asian countries such as Japan, and the Republic of Korea. Now, almost all of the seaweed produced for human consumption, alginates and other purposes comes from aquaculture, with the extent of cultivation clearly visible on satellite images in some regions. Research in these countries has focused on brown algal species including Saccharina japonica and Undaria pinnatifida, concentrating primarily on developing a number of commercial strains that demonstrate temperature-tolerance of warmer seawater, and latterly, on improved productivity. In China, it is common practice to have centralised seaweed hatchery facilities that produce plantlets for further on-growing at a number of local sea sites.The development of centralised facilities using controlled seaweed strains most likely lends itself to a higher degree of standardised operations during the production cycle.

In direct contrast to the mass culture of seaweed in China and other Asian countries, commercial cultivation production in Europe remains on a small scale. While European research on kelp has existed at least as long as for that conducted in China, seaweed cultivation techniques have been known (generally only within research facilities) for approximately thirty years. For most of this time, cultivation has existed at a demonstration/pilot-scale only, although this is now changing in a number of countries, primarily across NW Europe. It was recognised early on that the Chinese method of growing seaweed by inserting small plantlets into ropes for on-growing at sea would not be economically efficient in Europe, given the cost of labour. Alternative cheaper seeding techniques, as described in this document, have been developed instead. Longline design is also different in Europe, where sea conditions are generally more challenging than the more sheltered areas that typically support Chinese aquaculture. This influences design and of course the cost of equipment that is used. The concurrent European research on wild strains of kelp species, partnered with a strong requirement for developing site specific cultivation systems has naturally led to some variance in production protocols and systems.

The EnAlgae project has allowed its research partners in NW Europe the opportunity to use hindsight of the expansion of global seaweed cultivation to full advantage. A theme of the project(WP1, Action 5) has been ‘the development and exchange of best practice for mass production of macroalgae’. For this action to be completed satisfactorily, demonstration/pilot sites (WP1, Action 2)were constructed at the macroalgal partner facilities. The subsequent development of a close working relationship enabled production of comparable data for identified species (Saccharina latissima and Alaria esculenta) on cultivation methodology, data collection (WP1, Action 3) and macroalgal growth results. The standardisation of all of these elements was designed to produce reliable data and share common experiences between macroalgal cultivation stakeholders in NW Europe, culminating in the production of this manual, and the accompanying Macroalgal Best Practice document.

This document is a manual of collated Standard Operating Protocols (SOPs) that were developed in the three EnAlgae macroalgal hatcheries in the National University of Ireland, Galway(NUIG), Queen’s University, Belfast (QUB) and the Centre d’Etude et de Valorisation des Algues (CEVA). It describes the set-up/requirements of each seaweed hatchery, the hatchery cultivation process, thesea on-growing process, as well as biomass and environmental parameter measurements and sampling. While some SOPs were subject to some inherent differences within each hatchery (e.g. pre-existing seawater pumping and distribution systems), an effort was made to ensure that as many elements of the SOPs were standardised across the partners. For example, the biomass sampling SOP was particularly important to enable the collection of comparable data in Ireland, Northern Ireland and France.

The SOP manual has been designed for reading with the EnAlgae Macroalgal Best Practice document. This sister document offers further advice and observations of the methods used, including elements of the processes that worked, and equally importantly, where system failures occurred, and revisions were made. It is hoped that both documents will become a valuable resource for those interested in developing European kelp cultivation in NW Europe and beyond, providing information on techniques that can further refined, leading to ever-increasingly efficient seaweed production at sea.

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