Seaweed aquaculture technologies have developed dramatically over the past 70 years mostly in Asia and more recently in Americas and Europe. However, there are still many challenges to overcome with respect to the science and to social acceptability. The challenges include the development of strains with thermo-tolerance, disease resistance, fast growth, high concentration of desired molecules, the reduction of fouling organisms and the development of more robust and cost efficient farm systems that can withstand storm events in offshore environments. It is also important to note that seaweed aquaculture provides ecosystem services, which improve conditions of the coastal waters for the benefit of other living organisms and the environment. The ecosystem services role of seaweed aquaculture and its economic value will also be quantitatively estimated in this review.

We previously demonstrated the suitability of seaweed aquaculture as a nutrient management tool, using the warm temperate rhodophyte Gracilaria tikvahiae McLachlan. The present follow-up study revealed an even higher nutrient bioextraction capacity in the cold-water species Saccharina latissima at 3 sites -the mouth of the Bronx River Estuary (Bronx, NY; BRE), western Long Island Sound (Fairfield, CT; WLIS) and central Long Island Sound (Branford, CT; CLIS), during winter and spring of the 2012−2013 growing season. These sites differ in temperature (BRE > CLIS > WIS), salinity (BRE < WLIS = CLIS) and nutrients (BRE >> WLIS = CLIS). We estimated that S. latissima could remove up to 180, 67 and 38 kg N ha −1 at BRE, WLIS and CLIS respectively, in a hypothetical kelp farm system with 1.5 m spacing between longlines. In the same hypothetical kelp farm system, the estimated carbon sequestration values are 1350 (BRE), 1800 (WLIS) and 1100 (CLIS) kg C ha −1 . The potential monetary values of N sequestration by the sugar kelp are up to $1600 (BRE), $760 (WLIS) and $430 (CLIS) ha −1 , if incorporated in the State of Connecticut Nitrogen Credit Trading Program and a carbon-pricing scheme. The potential economic values of C sequestration are $30−300 (BRE), $40−400 WLIS), and $24−240 (CLIS) ha −1 . These results suggest that seaweed aquaculture is a useful technique for nutrient bioextraction in urbanized coastal waters, such as LIS and BRE. Alternation of the warm-and cold-water species would maximize nutrient bioextraction and augment other ecosystem services, producing economic benefits for the region while helping to manage non-source eutrophication.

Porphyra is one of the world's most valued maricultured seaweeds and has been cultivated for several hundred years in Asia. The objective of this study was to produce critical information as a guide for the selection of an appropriate Porphyra species from coastal New England for the development of a land-based aquaculture system. Four Northwest Atlantic Porphyra species: P. leucosticta, P. amplissima, P. linearis and P. umbilicalis, were cultivated for 1 and 2 weeks at saturated light intensities (100-150 μmol photons m −2 s −1 ) and six combinations of ammonium (25 and 250 μmoles L −1 ) and temperature (10, 15 and 20°C). Specific growth rate (SGR) increased with decreasing temperature in P. leucosticta, P. linearis and P. umbilicalis and increased with increasing temperature in P. amplissima. The SGR of all species was greater at the higher ammonium concentration. Porphyra linearis had the highest SGR, increasing in biomass by approximately 16% day −1 . Phycoerythrin (PE) content was higher at 10°C and 250 μmoles L −1 in all species except P. amplissima. The PE content, measured as fresh weight (FW), of P. linearis (29 mg g −1 FW −1 ) and P. umbilicalis (26 mg g −1 FW −1 ) was significantly higher than the other two species. Tissue nitrogen content of all species measured in dry weight was on average 1.45% higher at 250 μmoles L −1 than at 25 μmoles L −1 ammonium concentration. Porphyra umbilicalis had the highest tissue nitrogen contents (6.76%) at 10°C and 250 μmoles L −1 ammonium. Based on these results, P. linearis and P. umbilicalis should be considered as potential candidates for bioremediation with finfish and shellfish mariculture.

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