High Human Population Numbers Guarantee Problems with the Biosphere — Obvious Concept, yet the Overwhelming Majority of People and Policy-Makers Ignore It — an Illustrative Example Provided by Dying Cape Cod Salt Marshes

12 June 2012

This essay makes two demonstrable points and a sociological observation

Indirectly relevant to the climate change debate and, more generally, environmental sustainability:

(1) Human population pressure on specific habitats has dramatic negative effects.

(2) At least occasionally, thoroughly done science can prove the specifics of these impacts beyond reasonable refutation.

(3) But human nature looks for ways to blame illusory alternative causations.

My supporting example uses a study that set out to discover the causes of dying Cape Cod (USA) salt marshes.

A (reportedly thorough) scientific analysis of dying Cape Cod salt marshes demonstrates that recreational fishing is the cause of decline

The paper, documenting a comparison between 7 dying and 7 healthy salt marshes on Cape Cod comes from Brown University.

It is scheduled to be published in the journal, Ecology. Authors are Mark Bertness, Andrew Altieri, Tyler Coverdale, Nicholas Hermann, and Christine Angelini.

Citation — to the press release

David Orenstein, Recreational fishing brings salt marsh die-off, Brown University (12 June 2012)

Cause of salt marsh die-off has been successfully traced

The research team was able to prove that Cape Cod salt marsh declines are due to:

(i) the recreational fishing of

(ii) predatory fish and blue crabs that

(iii) eat terrestrial Sesarma (genus) crabs, who

(iv) eat the salt marsh grasses that sustain the marshes.

The studies involved demonstrated that the marshes are dying because fisherman and blue crab-eaters remove the striped bass, smooth dogfish, and blue crabs that keep the grass-eating Sesarma crab populations in check.

Why dying salt marshes are “bad”

Economic studies generally rank salt marshes at or near the top of Earth’s most valuable ecosystems.

Salt marshes:

(i) act as resilient barriers between the ocean and more easily-eroded coast lines,

(ii) provide protected homes and necessary food stocks for juvenile fish and crabs,

and

(iii) filter (at least some of) humanity’s pollutants, before they enter the sea.

What is impressive about this study is its reported thoroughness

The research team anticipated backlash from the recreational fishing community. A series of companion experiments eliminated possibly alternative reasons for the marshes’ decline.

First, the basics — measuring fishing pressure

Fishing pressure was calculated by counting fishermen and using aerial photographs of the region that had been taken over the years. The photographs revealed a progressive buildup of docks and also provided an aerial record of the marshes’ disappearance.

Measuring Sesarma crab populations

Sesarma population sizes were extrapolated from sampling traps. Marsh die-offs correlated with increased Sesarma crab populations.

More crabs, less marsh

From the press release:

The story told by these measurements was clear. As recreation fishing infrastructure has developed over time, nearby marshes have increasingly died off and collapsed.

The marshes in the areas with prevalent recreational fishing were always the ones that were dying off.

The dying marshes had significantly fewer Sesarma-eating predators, many more Sesarma, and the intensity with which Sesarma were eating the marshes was much higher.

The team even did experiments where they tied up Sesarma crabs and left them as sitting ducks for predators to eat. In the waters of dying marshes, the crabs were three times less likely to be eaten than in marshes that were healthy.

Ruling out alternative explanations

The team found that the only difference in fish populations were those of the recreationally fished for crab-eaters. Water and habitat quality among the 14 marshes was equal. Water flow was the same.

Grass-supporting habitats were also equivalent. The team tested for this by caging grass plots. Caged grass grew just as well in the dying marshes as in the healthy controls. The only difference was the higher Sesarma populations at the declining sites.

Even soil-burrowing hardness (for crab burrows) among the marshes was the same.

What to do now?

The most obvious marsh-preserving initial step would be to institute the catch-and-release regulations that are commonly used for inland fisheries.

Anticipated backlash — denial and magical thinking

The lead author revealed that:

“We had to be so careful about dotting all the ‘i’s and crossing all the ‘t’s and making sure that we had ruled out all alternative hypotheses, because even within the scientific community, there are plenty of fishermen who don’t want this to be true,” Bertness said.

“Certainly out in the general public there are plenty of people who are into recreational fishing who don’t want it to be the problem.”

He’s probably right

Rational self-responsibility is not a preeminent human characteristic. Witness the irrationally trumped-up debate about global warming and the frankly idiotic dispute regarding teaching evolution in schools.

The moral? — An apparently thoroughly done study, in the near-equivalent of an environmental microcosm, should make the irrational quality of (anticipated) denial and magical thinking obvious

Sometimes, the only satisfaction Sanity gets is in proving that some people really are fools or self-interested liars.

Not that such proof helps get wise policies adopted.

Think of us as the entire Biosphere’s equivalent of Sesarma crabs. As voracious and about as foresight-filled.

PeteFree.com

High Human Population Numbers Guarantee Problems with the Biosphere — Obvious Concept, yet the Overwhelming Majority of People and Policy-Makers Ignore It — an Illustrative Example Provided by Dying Cape Cod Salt Marshes