Invasive crabs help Cape Cod marshes

[OKIsItJustMe]

http://news.brown.edu/pressreleases/2013/04/crabs

[font face=Serif][font size=5]Invasive crabs help Cape Cod marshes[/font]

April 3, 2013 | Contact: David Orenstein | 401-863-1862

[font size=4]Ecologists are wary of non-native species, but along the shores of Cape Cod where grass-eating crabs have been running amok and destroying the marsh, an invasion of a predatory green crabs has helped turn back the tide in favor of the grass. The counter-intuitive conclusions appear in a new paper in the journal Ecology.[/font]

[font size=3]PROVIDENCE, R.I. [Brown University] — Long vilified, invasive species can sometimes become an ecosystem asset. New Brown University research published online in the journal Ecology reports exactly such a situation in the distressed salt marshes of Cape Cod. There, the invasive green crab Carcinus maenas is helping to restore the marsh by driving away the Sesarma reticulatum crabs that have been depleting the marsh grasses.

The observations and experiments of the research show that the green crab has filled the void left by the decline of native predators of sesarma crabs, the authors said. In previous research they showed that predator decline has come about because of recreational fishing.

…

“When we started seeing the marshes recover, we were baffled,” Bertness said. “To see very quickly the marshes start to come back, at least this veneer of cordgrass, it seemed pretty impressive. When we started seeing this recovery we started seeing loads of green crabs at the marshes that were recovering. We went out and quantified that.”

…[/font][/font]

http://dx.doi.org/10.1890/12-2150.1

[yellowcanine]

1. And what will we bring in to control the predatory green crabs when they run out of bad guys to

eat and start eating good guys? I can't imagine that the green crabs give a hoot as to what they eat - they probably eat whatever is easy to catch.

[happyslug]

3. Chesapeake blue crab can take care of these Green Crabs

More on European Green Crabs

http://en.wikipedia.org/wiki/Carcinus_maenas

On the Chesapeake blue crab:
http://en.wikipedia.org/wiki/Callinectes_sapidus

http://serc.si.edu/labs/marine_invasions/publications/PDF/DeRivera_et_al_%202005%20_Biotic_%20resistance_to_Green_Crab.pdf

Rocky substrate is common along the New England coast but is rare south of Long Island. Structure provided by rocks is used by Carcinus maenas (European Green Crabs), especially new recruits, to escape predation. Therefore, the geographic shift in rock availability and hence the decreased availability of suitable recruitment grounds south of New York could be responsible for the southern range limit of Carcinus maenas (European Green Crabs). However, we found a large population of Carcinus maenas (European Green Crabs) in southern New Jersey marshes that did not have natural Rocky substrate nearby (none within 28 latitude). Similarly, the strong reciprocal relationship between Carcinus maenas (European Green Crabs) and Callinectes sapidus (Chesapeake blue crab) in Waquoit Bay cannot be attributed to this latitudinal change in rocky substrate.

Temperature may play an important role in the distribution and abundance of Carcinus maenas (European Green Crabs) with latitude. We did not test this hypothesis directly, but four lines of evidence suggest that the direct effects of temperature (thermal stress) on Carcinus maenas (European Green Crabs) are not sufficient to explain the observed patterns. First, temperatures beyond the range boundary fall within the reported temperature distribution observed elsewhere in the world (Carlton and Cohen 2003). Second, the dramatic drop-off (step function) in abundance seen between Cape May, New Jersey, and Chincoteague Bay, Maryland, only Zero Degrees, 88 Minutes south of New Jersey, suggests that climate, which should cause a more gradual change in density, is not the only contributing factor (Caughley et al. 1988). Moreover, the southern boundary, which has been stable for a century, stands in sharp contrast to the fluctuating northern range limits observed on both sides of the North Atlantic (Glude 1955, Welch 1968, Beukema 1991). Third, the variation in abundance of Carcinus maenas (European Green Crabs) within the overlapping ranges of these two species was explained by Callinectes sapidus (Chesapeake blue crab) abundance, not temperature (Appendix A, Table A1). Fourth, a similar result was observed in Waquoit Bay, Massachusetts, which controlled for broader-scale differences across bays.

We hypothesize that temperature operates synergistically with predation to establish a southern limit to Carcinus maenas (European Green Crabs)distribution. Predation pressure on Carcinus maenas (European Green Crabs) may vary across latitudes due to temperature-dependent changes in Callinectes sapidus (Chesapeake blue crab) abundance and activity levels, such as feeding behavior and rate (Williams 1984, Bergman 1987, Hines et al. 1990, Rome et al. 2005). Thus, per capita feeding rate of Callinectes sapidus (Chesapeake blue crab) and the portion of a year with relatively high feeding rates should increase from north to south. The combination of high temperature and predation may affect Carcinus maenas (European Green Crabs) distribution due to prey behavior as well. Escaping Callinectes sapidus (Chesapeake blue crab)or foraging in less productive patches to avoid this crab could decrease the energy budget available to Carcinus maenas (European Green Crabs) for tolerating suboptimal conditions such as warm water

Given that temperature seems to be the biggest factor in how far the Green Crabs can spread, Global Warming may also come into play.

[pscot]

2. On the downside

they eat a lot of oysters and clams.