Competing demand for land is driving biofuel and bioenergy research in various directions including macro-algae (seaweed). This paper reviews the main issues for the marine environment of cultivating and harvesting UK and Irish seaweed for biofuels/bioenergy, informed by stakeholder interviews. These showed stakeholders were sceptical of an offshore cultivation industry developing but generally considered inshore cultivation possible, while noting various practical obstacles and conditions. Views on expansion of seaweed harvesting were more divided, with research scientists being relatively cautious.