University of Maine - Wells

Restoration Project

University of Maine - Wells

Restoration Objective:

This study aimed to examine feedback mechanisms and alternate stable states in kelp ecosystems in Maine, USA. Specifically, it looked at the effect of urchin fisheries on levels of herbivory and kelp cover, and whether this shift constituted an alternate stable state.

Cause Of Decline:

While sea urchins consume kelp and can remove kelp from large areas, sea urchin fisheries can impact this process. This study suggests that the sea urchin fishery in Maine, USA provided a large scale removal of herbivores over a short period of time and changed ecosystem function fundamentally to an alternative stable state.

Key Reasons For Decline:

Predator loss

Scientific Paper

Ecosystem Flips, Locks, and Feedbacks: the Lasting Effects of Fisheries on Maine's Kelp Forest Ecosystem

R.S. Steneck, A. Leland, D.C. McNaught, J. Vavrinec
Bulletin of Marine Science, 1, Vol. 89, 2013, p.31.


Site Observations:

Observation Date

1st Jan 1986 – 1st Jan 1998

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.

Key Reasons For Decline:

Predator loss

Indicator Data:


Ending Value:

Starting Value:

Kelp Cover