Action Summary:
Ecosystem feedback mechanisms in kelp-forests were studied over 40 years, by studying the effect of urchin fishery landings on herbivory, urchin fishery landings, urchin density and kelp cover.
Lessons Learned:
The abundance of kelps supported juvenile crab populations that preyed on juvenile urchins, and reinforced the kelp-dominated stable state. Kelp cover stabilised in 1998, and has remained at a similar level as of 2010, while urchin density and herbivory stayed near zero over this time.
Project Outcomes:
This study found that herbivory by urchins drove algal deforestation, but deforestation declined after fishing for sea urchins began in 1987. As the fishery expanded north-eastward, so too did phase shifts to macroalgae dominated states. By 2000, macroalgae dominated nearly all of coastal Maine. Additionally, while many juvenile urchins were observed virtually none survived to adulthood due to predation by young crabs supported by the kelps. Experiments intended to restore herbivory by translocating 51,000 adult sea urchins resulted in complete urchin mortality both years as a result of predation by crabs. Cascading sequential processes of herbivory, recruitment and predation create reinforcing feedback, effectively locking this ecosystem into alternative stable states.
