Featured Research

from universities, journals, and other organizations

Denser seagrass beds hold more baby blue crabs

Date:
September 12, 2013
Source:
Virginia Institute of Marine Science
Summary:
A new study in Chesapeake Bay shows that it's not just the presence of a seagrass bed that matters to young crabs, but also its quality -- with denser beds holding exponentially more crabs per square meter than more open beds where plants are separated by small patches of mud or sand.

The researchers used a powerful vacuum called a suction sampler to collect blue crabs from seagrass beds during their study. Plover is the name of a VIMS vessel.
Credit: Virginia Institute of Marine Science

When it comes to nursery habitat, scientists have long known that blue crabs prefer seagrass beds compared to open areas in the same neighborhood.

A new study by researchers at the Virginia Institute of Marine Science refines that knowledge, showing that it's not just the presence of a seagrass bed that matters to young crabs, but also its quality -- with denser beds holding exponentially more crabs per square meter than more open beds where plants are separated by small patches of mud or sand (compare images).

The study, led by VIMS graduate student Gina Ralph, appeared in the August issue of Marine Ecology Progress Series. It is co-authored by VIMS Marine Scientist Kathleen Knick along with faculty members Rochelle Seitz, Robert "JJ" Orth, and Rom Lipcius.

"Vegetated habitats, particularly marsh and seagrass, have long been known as nurseries for blue crabs," says Ralph, "with many previous field and lab studies showing higher density, survival, or growth of juveniles in seagrass habitats compared to un-vegetated areas nearby."

"Our study," she adds, "is one of the few to address the role of habitat complexity within seagrass beds, and the first to show on a broad scale that -- all else held equal -- denser, higher-quality grass beds hold more juvenile crabs."

Ralph says that on average, "there were 30% more crabs for every 10% increase in the percentage of seagrass cover within a bed during 2007, and 14% more crabs for each 10% increase in seagrass coverage in 2008."

Ralph says the team's findings are important because they "suggest that the quality of seagrass habitat can influence the population dynamics of blue crabs on a baywide basis." That raises concern given the historical decline in eelgrass -- the Bay's main seagrass species -- and projections of the continued decline of this cool-water species as water temperatures rise during the coming decades due to climate change.

"The potential for a future disappearance of eelgrass from the Bay is quite disconcerting given that the blue crab fishery was declared a federal disaster in 2008 and only recently recovered due to management actions by the Virginia Marine Resources Commission and other agencies in the Bay," says Lipcius. Tempering the team's concern are studies suggesting that blue crabs may also be able to use other, more heat-tolerant species like widgeon grassfor nursery habitat as the Bay warms.

The team conducted the fieldwork for their study between 2007 and 2008, recording blue crab numbers and the percentage of seagrass coverage at 104 randomly selected sites along the eastern and western shores of the lower Bay.

Team members caution that their study was conducted at a time when historically low numbers of juvenile blue crabs were entering the population each year, likely due to overfishing and environmental factors. That might help explain one of the study's more unexpected results: contrary to basic ecological theory, the observed increase in the number of crabs did not level off as seagrass coverage approached the highest levels.

"The crab's lack of a threshold response to vegetation cover could have been caused by low densities of juveniles overall," says co-author Lipcius. "We'd like to repeat our study during a period of high recruitment to test the generality of the findings."

The good news is that they may be able to do that fairly soon, given the growing number of adult females in the Bay since 2008 in response to the fisheries management framework established that year. Each adult female spawns an average of three million new crabs each brood, and releases about three broods per year.


Story Source:

The above story is based on materials provided by Virginia Institute of Marine Science. The original article was written by David Malmquist. Note: Materials may be edited for content and length.


Journal Reference:

  1. GM Ralph, RD Seitz, RJ Orth, KE Knick, RN Lipcius. Broad-scale association between seagrass cover and juvenile blue crab density in Chesapeake Bay. Marine Ecology Progress Series, 2013; 488: 51 DOI: 10.3354/meps10417

Cite This Page:

Virginia Institute of Marine Science. "Denser seagrass beds hold more baby blue crabs." ScienceDaily. ScienceDaily, 12 September 2013. <www.sciencedaily.com/releases/2013/09/130912155800.htm>.
Virginia Institute of Marine Science. (2013, September 12). Denser seagrass beds hold more baby blue crabs. ScienceDaily. Retrieved September 21, 2014 from www.sciencedaily.com/releases/2013/09/130912155800.htm
Virginia Institute of Marine Science. "Denser seagrass beds hold more baby blue crabs." ScienceDaily. www.sciencedaily.com/releases/2013/09/130912155800.htm (accessed September 21, 2014).

Share This



More Plants & Animals News

Sunday, September 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: San Diego Zoo Welcomes Cheetah Cubs

Raw: San Diego Zoo Welcomes Cheetah Cubs

AP (Sep. 20, 2014) The San Diego Zoo has welcomed two Cheetah cubs to its Safari Park. The nearly three-week-old female cubs are being hand fed and are receiving around the clock care. (Sept. 20) Video provided by AP
Powered by NewsLook.com
Chocolate Museum Opens in Brussels

Chocolate Museum Opens in Brussels

AFP (Sep. 19, 2014) Considered a "national heritage" in Belgium, chocolate now has a new museum in Brussels. In a former chocolate factory, visitors to the permanent exhibition spaces, workshops and tastings can discover derivatives of the cocoa bean. Duration: 01:00 Video provided by AFP
Powered by NewsLook.com
Could Grief Affect The Immune Systems Of Senior Citizens?

Could Grief Affect The Immune Systems Of Senior Citizens?

Newsy (Sep. 19, 2014) The study found elderly people are much more likely to become susceptible to infection than younger adults going though a similar situation. Video provided by Newsy
Powered by NewsLook.com
Jury Delivers Verdict in Salmonella Trial

Jury Delivers Verdict in Salmonella Trial

AP (Sep. 19, 2014) A federal jury has convicted three people in connection with an outbreak of salmonella poisoning five years ago that sickened hundreds of people and was linked to a number of deaths. (Sept. 19) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins