Navigation Links
Tropical crab invades Georgia oyster reefs -- but the long-term impact can't be predicted
Date:9/4/2007

A dime-sized tropical crab that has invaded coastal waters in the Southeast United States is having both positive and negative effects on oyster reefs, leaving researchers unable to predict what the creatures long-term impact will be.

Unlike native crabs that eat baby oysters, mussels and fish, the green porcelain crab Petrolisthes armatus is a filter feeder, extracting its food from the water much as oysters do.

The fast-reproducing invader therefore isnt directly attacking oyster populations, though it may be competing with them for food and may impact the predators that normally attack the oysters.

Researchers at the Georgia Institute of Technology have spent more than three years studying the effects of the crab, and are reporting their findings in the journal Biological Invasions. The research, believed to be the first to document effects of the crab on oyster and mussel populations off the Southeast coast, was supported by the U.S. Environmental Protection Agency, the National Oceanic and Atmospheric Administration, and the Harry and Linda Teasley Endowment to Georgia Tech.

Were seeing opposing effects from these crabs, said Mark Hay, a professor in Georgia Techs School of Biology. They are probably having more impact on the ecosystem by being prey than by being predators. Other members of the ecosystem are feeding on them, and that is changing the rate at which fish and other crabs are feeding on the native species.

The impact of the crabs is important because oysters are a foundation species essential to the health of coastal ecosystems because their reefs provide homes to dozens of other creatures.

These non-native crabs slow the rate of growth for organisms like oysters that they compete with, but they enhance the ability of those same organisms to survive when young, Hay noted. They are probably competing with the oysters for food, but the native crabs have switched to eating these green porcelain crabs rather than eating the baby oysters. Even though their growth is suppressed, the baby oysters are not being attacked as much now by the native consumers.

Though the crabs arent killing existing populations of oysters, their long-term impact could still be significant. For instance, Hay noted, their availability as food could potentially increase the population of native crabs, disrupting the delicate balance between those predators and the oysters.

But assessing the long-term impact of the crabs has been difficult because the creatures reproduce and grow rapidly, flooding the shallow coastal waters with their young. In research conducted off Skidaway Island and Sapelo Island on the Georgia coast, the researchers found extraordinarily high populations of the crab as many as 11,000 individuals per square meter.

To assess the impacts of the non-native crab population, graduate student Amanda Hollebone placed oysters and mussels into large baskets and located them on mud flats away from existing oyster reefs. Some of the baskets contained only oysters and mussels and were intended to serve as controls, some had a community of oysters, mussels, oyster drills and native mud crabs, while others had the same community spiked with non-native crabs. The distance from the existing oyster reefs was expected to prevent adult green porcelain crabs from reaching the baskets.

However, the researchers found that within a month, the control baskets also had large populations of the green porcelain crabs that had reached the containers as juveniles settling from the water column. Entry of the crabs to the control baskets interfered with the researchers ability to compare the traits of communities with and without the non-native crabs.

You get a true understanding of the sheer densities of these crabs only when you actually pick up or dig through clumps of oysters and oyster shell hash, said Hollebone, who is now a temporary assistant professor at Georgia Southern University in Statesboro. Particularly in the summer months, I was never able to find a patch of oysters in the Savannah area that did not have the green porcelain crab.

Because the green porcelain crabs quickly took over the control baskets, the researchers only had valid comparison data for 4-6 weeks. However, information from their baskets supported the observations made under more controlled but less natural conditions at Georgia Techs laboratory at the Skidaway Institute of Oceanography near Savannah.

As in the lab experiments, the researchers found that the crabs slowed the growth of small oysters, but not small mussels -- another common filter-feeder.

The long-term effects of the massive crab population are difficult to predict. Their large numbers could lead to population growth among the native crabs and fish that now prefer eating them instead of their normal diet. But if the predator population should grow large enough to control the non-native crabs, that could lead to a decline in their numbers and force the predators back to their traditional prey of oysters and mussels.

Were not sure whats going to happen, Hay said. We cant really raise the alarm because we dont have the data to say these crabs are doing something bad. Its possible that they will not have a huge effect at all.

Long-term observation of the oyster reefs may ultimately provide answers. We have observed both positive and negative impacts on oysters and oyster-related biota at small scales, but we cannot definitively answer our concerns about oyster reefs at larger scales, Hollebone added. With continued monitoring of large expanses of reefs, we may begin to understand the long-term, large-scale effects.

The green porcelain crabs were observed in Florida during 1990s, but have since appeared in large numbers in coastal waters of Georgia and South Carolina. Researchers dont know if they hitched a ride northward in the ballast of ships, whether warming water temperatures encouraged a northerly migration or both.

Though not much is known about them in their native habitat, Hay said the crabs appear to be thriving in their new home. Population densities observed in the South Atlantic Bight are as much as 37 times higher than the greatest densities reported in their native habitat.


'/>"/>

Contact: John Toon
jtoon@gatech.edu
404-894-6986
Georgia Institute of Technology Research News
Source:Eurekalert

Related biology news :

1. Finding Cures For Tropical Diseases: Is Open Source An Answer?
2. An (ecological) origin of species for tropical reef fish
3. Tropical Deforestation affects rainfall in the U.S. and around the globe
4. Birds and bats sow tropical seeds
5. Tropical dry forests receive international recognition
6. Scientists must offer solutions for conserving tropical forests in a rapidly changing world
7. Tropical Atlantic cooling and African deforestation correlate to drought, report scientists
8. Diverse tropical forests defy metabolic ecology models
9. Tropical forest CO2 emissions tied to nutrient increases
10. Agriculture and tropical conservation: rethinking old ideas
11. New understanding of parasite cell structures may provide treatments for serious tropical diseases
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:12/15/2016)... ... announced the addition of the "Global Military Biometrics Market 2016-2020" ... military biometrics market to grow at a CAGR of 7.5% during the ... an in-depth market analysis with inputs from industry experts. The report covers ... report also includes a discussion of the key vendors operating in this ...
(Date:12/12/2016)... 12, 2016  Researchers at Trinity College, Dublin, ... by combining the material with Silly Putty. The mixture ... detector able to sense pulse, blood pressure, respiration, ... The research team,s findings were ... here:  http://science.sciencemag.org/content/354/6317/1257 ...
(Date:12/7/2016)... , December 7, 2016 BioCatch , ... expansion of its patent portfolio, which grew to over 40 granted and ... , , ... recently filed patent entitled " System, Device, and Method Estimating ... that enables device makers to forego costly hardware components needed to estimate ...
Breaking Biology News(10 mins):
(Date:1/12/2017)... ... January 12, 2017 , ... ... of performing routine electrochemical biosensing has increased dramatically. Primarily driven by the ... and quantification of various analytes in complex samples. , Screen-printed ...
(Date:1/12/2017)... Oregon and Pune, India , January 12, 2017 /PRNewswire/ ... vitro Toxicity Testing Market by Type and End Users - Global Opportunity Analysis and ... $7,813 million by 2022 from $2,921 million in 2015, growing at a CAGR of ... ... Allied Market Research Logo ...
(Date:1/11/2017)... Mass. (PRWEB) , ... January 11, 2017 , ... ... in rural and urban clinics in Peru studying the pathogens that cause malaria ... her on a career path of discovery. , Now, as an assistant professor ...
(Date:1/11/2017)... ... January 11, 2017 , ... Microbial genomics leader uBiome, is ... most recent microbiome impact grant award has been made to Dr. Eon Rios ... use of oral antibiotics, prescribed for skin conditions, on the gut microbiome. ...
Breaking Biology Technology: