A historical review of giant kelp harvesting in Tasmania

Kelps have a long history of human use and exploitation. Knowledge of past harvesting practices offers insights into environmental baselines and the contemporary management and conservation of these critically important ecosystems. In Tasmania, Australia, giant kelp (Macrocystis pyrifera) was commercially harvested for alginate production from 1964 to 1973, but those forests have since undergone precipitous declines due primarily to climate change. We reviewed a collection of archival data and sources to describe the history, methods, and scale of this understudied and largely forgotten industry. We calculated that >65,000 tonnes (wet weight) of Macrocystis were harvested from eastern Tasmania over a decade (mean annual harvest = 6531 t), making it one of the largest wild harvest industries to ever exist in the region. However, the industry had challenges finding sufficient biomass to sustain operations, ultimately driving its closure in less than a decade. Feasibility surveys prior to harvesting suggested much greater kelp availability than was ultimately realized, perhaps motivating overexpansion. Against a backdrop of climate change in this ocean warming hotspot, harvest efforts grew wider and more intensive, and during summer months when stocks were lowest, almost all exploitable biomass was harvested. It remains unclear whether harvesting contributed to the decline of Tasmanian Macrocystis forests, but it may have reduced their resilience and exacerbated other stressors, particularly in heavily harvested areas. This historical review provides a rare opportunity to examine the past scale and use of now-endangered Macrocystis forests and also to help inform the contemporary management and conservation of seaweed resources.