Twenty years of transects show recovery is not a return

Five years after a marine heatwave reorganized the shore at Prentice Coastal Field Station, two of the four permanent transects have returned to something close to their previous community composition. The other two have not, and show no trend toward doing so.

The finding, published this month by Aisha Tanaka and colleagues, draws on a monthly survey that has run without a gap since 2004 — the longest continuous dataset the university holds.

"Recovery is doing more work in the literature than the evidence supports," Tanaka said. "The assumption is that a disturbed shore heads back toward what was there before. Sometimes it does. Two of my four sites are now something else, and they have been stable as something else for three years."

The distinction matters for management. Restoration targets and monitoring endpoints are commonly defined against a historical baseline, and a system that has settled into an alternative state will fail against that standard indefinitely while being neither degraded nor recovering.

Tanaka is careful about the limits. Twenty years is long by the standards of the field and short by the standards of the question, and four sites on one shore cannot settle it. The value of the record is that it is continuous: the two divergent sites were watched through the transition rather than compared before and after.

The survey continues. Undergraduate researchers in marine biology are recruited from the transect walks, which remain, in Tanaka's description, cold, wet and consistently oversubscribed.