From: David A Gabel, ENN
Published August 31, 2010 10:56 AM

Study: Horseshoe Crab Decline Connected to Climate Change

The horseshoe crab is one of the most ancient animals on the planet today. They have survived massive upheavals throughout the Earth's history and have remained intact and unchanged. Recently their numbers have been in decline, and this is thought to be due to coastal habitat destruction and overharvesting (they are often used as bait or in fertilizer). However, new research from the US Geological Survey (USGS) indicates that their population size also parallels changes in the climate. With predicted climate change in the future, their numbers may continue to decline.

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The largest source of horseshoe crab decline remains overharvesting and habitat destruction. The new research suggests that climate change can play a role in altering the amount of successfully reproducing horseshoe crabs. According to Tim King, scientist with the USGS and lead author of the study, the accompanying sea-level rise and water temperature fluctuations may limit horseshoe crab distribution and interbreeding. This can lead to localized and regional population declines. This would mirror what occurred after the last ice age as temperatures rose.

"Using genetic variation, we determined the trends between past and present population sizes of horseshoe crabs and found that a clear decline in the number of horseshoe crabs has occurred that parallels climate change associated with the end of the last Ice Age," said King.

Significant declines have already been occurring along the entire eastern seaboard of the United States and eastern Gulf of Mexico. Further declines may have a devastating impact on the ecosystems which rely on nutrient-rich horseshoe crab eggs for food each spring. Species that have been affected include migrating seabirds such as the Red Knot, which feeds on the eggs at Delaware Bay during its 10,000 mile annual migration. Also, the Atlantic loggerhead turtle, which feed on the adult horseshoe crabs of Chesapeake Bay, have been forced to look for less desirable sources of food, affecting their population size.

Conservation managers can use the findings from this study to make more well-informed decisions on how to protect horseshoe crabs and other related species. For example, one finding indicated that males moved from one bay to the other, but females remained in one spot. Since females are more important in order to reproduce, devising local strategies may be more important than regional strategies.

"Consequently, harvest limitations on females in populations with low numbers may be a useful management strategy, as well as relocating females from adjacent bays to help restore certain populations," King said. "Both studies highlight the importance of considering both climatic change and other human-caused factors such as overharvest in understanding the population dynamics of this and other species."

The study was published in the journal, Molecular Ecology. It was authored by Tim King, Soren Faurby of Denmark, Matthias Obst of Sweden, and others. A previous study on this subject was also authored by Tim King and others in the journal, Transactions of the American Fisheries Society.

Link to published article in Molecular Ecology: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2010.04732.x/abstract

Link to published article in Transactions of the American Fisheries Society: http://afsjournals.org/doi/abs/10.1577/T04-023.1

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