Sugar kelp (Saccharina latissima ) is an emerging mariculture crop in the United States that has generated interest over the past decade for its commercial value and environmental benefits . For oyster farmers, sugar kelp provides a compelling opportunity for crop diversification as it has an opposite growing season from oysters, can be vertically integrated with oysters to provide additive revenue streams, and allows for diversification into non-food markets. Many oyster farms, however, are in near-shore, shallow waters where conventional kelp farming methods cannot be employed, and kelp blades cannot be suspended off the bottom . In this study, we developed and tested methods for shallow-water kelp farming over three kelp growing seasons (2018-2019, 2019-2020, and 2020-2021) at oyster farms located in Moriches Bay (MB; 0.6 m MLW) and Great South Bay (GSB ; 1.0-3.0 m MLW ) in Long Island, NY, and compared kelp growth and quality in these shallow bays to that obtained at deeper oyster farm s in Long Island Sound (LIS ; 6.0 m MLW) and the Peconic Estuary (PE; 6.0 m MLW) where water depths were more typical for kelp farming.
Kelp was cultivated along horizontal longlines at all sites from December to May/June, with lines at shallow sites (i.e. <1.2 m MLW) ‘staked’ a fixed distance (0.3 m) above the bay bottom, and lines at deeper water sites ‘suspended’ a fixed distance (0.9- 1.5 m) below the surface using conventional mooring and buoy systems . The highest crop yields were obtained at the shallowest site in MB using the staked line system, with average line yields of 5.9, 13.4 , and 5.6 kg m-1 obtained in 2019, 2020, and 2021, respectively (Fig. 1). High yields (5.1 kg m-1 ) were also obtained in shallow waters in GSB in 2020 using both staked and suspended lines , but ice impacted kelp lines in 2019 and 2021 in GSB highlighting a potential peril of shallow-water kelp farming. Compared to deeper locations , kelp grew faster in the shallow bays , reached a harvestable size one to two months sooner, and cost substantially less to grow in terms of gear and labor. Kelp quality, however, declined earlier in the shallow bays due to fouling, grazing, and blade senescence as water temperatures warmed above ~12 ° C, with interannual variability in spring water temperatures impacting the duration of the growing season and crop yields.
Overall, sugar kelp farming along staked lines in shallow waters was found to produce higher crop yields, shorter times to harvest, and have substantially lower costs than suspended line methods in deeper water. This demonstration of shallow water kelp farming reveals opportunities for farmers previously thought implausible and may provide oyster farmers with a means to diversify crops.