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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Palmaria palmata was integrated with Atlantic halibut Hippoglossus hippoglossus on a commercial farm for one year starting in November, with a temperature range of 0.4 to 19.1°C. The seaweed was grown in nine plastic mesh cages (each 1.25 m 3 volume) suspended in a concrete sump tank (46 m 3 ) in each of three recirculating systems. Two tanks received effluent water from tanks stocked with halibut, and the third received ambient seawater serving as a control. Thalli were tumbled by continuous aeration, and held under a constant photoperiod of 16 : 8 (L : D). Palmaria stocking density was 2.95 kg m -3 initially, increasing to 9.85 kg m -3 after a year. Specific growth rate was highest from April to June (8.0 to 9.0°C), 1.1% d -1 in the halibut effluent and 0.8% d -1 in the control, but declined to zero or less than zero above 14°C. Total tissue nitrogen of Palmaria in effluent water was 4.2 to 4.4% DW from January to October, whereas tissue N in the control system declined to 3.0-3.6% DW from April to October. Tissue carbon was independent of seawater source at 39.9% DW. Estimated tank space required by Palmaria for 50% removal of the nitrogen excreted by 100 t of halibut during winter is about 29,000 to 38,000 m 2 , ten times the area required for halibut culture. Fifty percent removal of carbon from the same system requires 7,200 to 9,800 m 2 cultivation area. Integration of P. palmata with Atlantic halibut is feasible below 10°C, but is impractical during summer months due to disintegration of thalli associated with reproductive maturation.Key Words: bioremediation; IMTA; integrated multi-trophic aquaculture; nutrient removal; Palmaria INTRODUCTIONMany aquaculture businesses are intent not only on maximizing productivity and profitability, but also accomplishing this using environmentally responsible practices. Efficient use of energy (e.g., pumping of water) and natural resources (surrounding environment, ambient water supply, and waste streams) are key elements in this approach. Land-based recirculating aquaculture systems facilitate greater control over culture water and waste discharge than flow-through systems (Blancheton et al. 2009). Though the surrounding environment may be enhanced by moderate volumes of aquaculture discharge (White et al. 2011), the trend toward larger land-based facilities (e.g., 1,000 metric tons finfish production per year) and the associated effluent waste may pose a risk of local eutrophication. Alternatively, integration of seaweed and land-based marine finfish culture can convert these nutrients to a usable product. Previous investigations into land-based seaweed integration have included Gracilaria For this study, integration of Palmaria palmata and Atlantic halibut was established within a land-based recirculating aquaculture facility for one year to evaluate the growth and nutrient uptake characteristics of the seaweed in a commercial application. This study was essential to compare the bioremediation capacity of P. palmata under both lab and small-scale applied conditions...