A distinct decline in horseshoe crab numbers has occurred that parallels climate change associated with the end of the last Ice Age, according to a study that used genomics to assess historical trends in population sizes.
The new research also indicates that horseshoe crabs numbers may continue to decline in the future because of predicted climate change, said Tim King, a scientist with the U.S. Geological Survey and a lead author on the new study published in Molecular Ecology.
While the current decline in horseshoe crabs is attributed in great part to overharvest for fishing bait and for the pharmaceutical industry, the new research indicates that climate change also appears to have historically played a role in altering the numbers of successfully reproducing horseshoe crabs. More importantly, said King, predicted future climate change, with its accompanying sea-level rise and water temperature fluctuations, may well limit horseshoe crab distribution and interbreeding, resulting in distributional changes and localized and regional population declines, such as happened after the last Ice Age.
“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.
The research substantiated recent significant declines in all areas where horseshoe crabs occur along the West Atlantic Coast from Maine to Florida and the eastern Gulf of Mexico, with the possible exception of a distinct population along the Yucatan Peninsula of Mexico
These findings, combined with the results of a 2005 study by King and colleagues, have important implications for the welfare of wildlife that rely on nutrient-rich horseshoe crab eggs for food each spring.
For example, Atlantic loggerhead sea turtles, which used to feed mainly on adult horseshoe crabs and blue crabs in Chesapeake Bay, already have been forced to find other less suitable sources of food, perhaps contributing to declines in Virginia’s sea turtle abundance. Additionally, horseshoe crab eggs are an important source of food for millions of migrating shorebirds. This is particularly true for the red knot, an at-risk shorebird that uses horseshoe crab eggs at Delaware Bay to refuel during its marathon migration of some 10,000 miles. Since the late 1990s, both horseshoe crabs and red knot populations in the Delaware Bay area have declined, although census numbers for horseshoe crabs have increased incrementally recently.
“Population size decreases of these ancient mariners have implications beyond the obvious,” King said. “Genetic diversity is the most fundamental level of biodiversity, providing the raw material for evolutionary processes to act upon and affording populations the opportunity to adapt to their surroundings. For this reason, the low effective population sizes indicated in the new study give one pause.”
These studies should help conservation managers make better-informed decisions about protecting horseshoe crabs and other species with a similar evolutionary history. For example, the 2005 study indicated males moved between bays but females did not, suggesting management efforts may best be targeted at local populations instead of regional ones since an absence of enough females may result in local extinctions.
“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.”
Background on Horseshoe Crabs
Horseshoe crabs are not crabs at all – in fact, they are more closely related to spiders, ticks and scorpions. While historically horseshoe crabs have been used in fertilizer, most horseshoe crab harvest today comes from the fishing industry, which uses the crab as bait, and the pharmaceutical industry, which collects their blood for its clotting properties. While the crabs are returned after their blood is taken, the estimated mortality rate for bled horseshoe crabs can be as high as 30 percent.
The research, Population dynamics of American horseshoe crabs—historic climatic events and recent anthropogenic pressures, was published in the June issue of Molecular Ecology and was authored by Søren Faurby (Aarhus University, Denmark), Tim King, Matthias Obst (University of Gothenburg, Sweden) and others.
The 2005 study, Regional differentiation and sex-biased dispersal among populations of the horseshoe crab (Limulus polyphemus), was published in the Transactions of the American Fisheries Society and authored by Tim King, Mike Eackles Adrian Spidle (USGS) and Jane Brockman (University of Florida).
Catherine Puckett | EurekAlert!
How does the loss of species alter ecosystems?
18.05.2017 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig
Excess diesel emissions bring global health & environmental impacts
16.05.2017 | International Institute for Applied Systems Analysis (IIASA)
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
24.05.2017 | Physics and Astronomy
24.05.2017 | Physics and Astronomy
24.05.2017 | Event News