The unit is a hectare.
Page 72: This just reports other sources, which appear to be based on what costs would have to be, rather than what costs are:
Sanderson (2006) estimated the costs of setting up a one ha seaweed farm, based on a detailed breakdown of the costs per 40 m longline (surface barrel-floats, headline, anchor rope, stainless steel swivels, thimbles for splicing, shackles and mooring blocks) of £2382.49, depreciated over 5 years, together with approximations of other annual costs. Following on from these assumptions he estimated the one ha plot would have to yield worth 130 t wet weight, worth £500 t-1 to break even.
Table 5.3 Comparative data on energy output from different feedstocks compiled by Lucy Lewis, Greenfinch Ltd; Laminaria saccharina values derived from Chynoweth et al. (1987), values in lightly shaded sections are estimates and will vary with growing conditions. Values in the darkly shaded areas are based on the unsupported assumption that the cost of L. saccharina production* will be equivalent to that of the most expensive terrestrial crop used in the comparison
The estimated costs generated by Sanderson (2006) are almost certainly over estimates, and could be considerably lower given economies of scale.