Biomedical bleeding may affect spawning behavior and movement of horseshoe crabs – ScienceDaily



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Horseshoe crabs that have undergone biomedical bleeding tend to reside in deeper water and approach mating beaches less frequently, according to a new study published in The Biological Bulletin. In "Effects of the biomedical bleeding process on the behavior of the American crab-horseshoe, Limulus polyphemus in their natural habitat", Meghan Owings and his colleagues report the results of an investigation of the behavioral and physiological effects that the bleeding process has on horseshoe crabs which are released back into their natural environment. The results suggest that biomedical bleeding can affect the reproductive yield of females of horseshoe crabs during the season in which they were bled.

Horseshoe crabs are harvested by the biomedical industry in order to create the Limulus amoebocyte lysate (LAL), which is used to test medical devices and endotoxin drugs. During the process, about 30% of the blood of a crab is extracted before being returned to its natural environment.

Owings & # 39; s study is one of the first to examine the behavioral impacts that the bleeding process has on horseshoe crabs, since they are returned to nature. "With the increasing demand for LAL as the world's population expands, medical advances improve and medical needs increase, understanding the consequences of the biomedical bleeding industry on the fitness and population dynamics of horseshoe crabs is critical," Owings wrote .

Owings and his co-authors recovered 28 horseshoe crabs from a spawning site on the Great Bay estuary in New Hampshire. Half of the crabs were randomly chosen to undergo the bleeding process and then all of them, both bled and controls, were fitted with acoustic transmitters and released where they were captured. The transmitters were used to monitor the movements, depth and timings of the horseshoe crabs when they were active. The transmitter data were recorded by a set of acoustic receivers that were installed throughout the estuary.

All 28 horseshoe crabs were successfully screened in the Great Bay Estuary from May 15 to December 6, 2016. Data were also obtained from 23 of the horseshoe crabs the following year, from April 14 to October 4 2017.

The impact of biomedical bleeding on horseshoe crabs was analyzed in terms of spawning activity, biological rhythms, total range of motion, depth and activity levels, taking into account also the natural changes in their behavior that accompany the seasons change. on the Great Bay estuary.

The authors found that in the first week that the animals were released back to the Bay of Bighorn, the bled animals seemed to spawn less than the control animals. The difference was especially pronounced in females, with control females appearing to spawn on average 4.8 times, while females bled seemed to spawn on average 2 times.

Another notable trend was that in May and June 2017, bled animals did not approach shallow areas in Great Bay but remained in the deepest channels. This poses a problem as May and June are the months when horseshoe crabs typically move to shallow water to spawn in the estuary.

For one possible explanation, Owings and his colleagues mention two previous studies, one that took place in a laboratory and one in the field on Cape Cod, which found that biomedical horseshoe crabs had interrupted orientation and movements that were more randomized than crabs- control. This disorientation may prevent horseshoe crabs from finding spawning beaches, they write.

They also suggest that recovery from the bleeding process – crabs take from three to seven days to regain blood volume, and up to four months for amoebocytes to return to baseline – could make the crabs simply not have as much energy to put in to spawn as they normally would.

These results are especially worrisome, since females are already favored in the bleeding process because of their larger size. "If bleeding animals, especially females, have changes in their biological rhythms and mating behaviors, it is likely to further alter the sexual proportion on spawning beaches, reduce reproductive output, decrease population levels, and decrease fitness and survival of these key species, "they write.

The authors recommend that more research be needed to better understand the impact of biomedical bleeding, both in terms of spawning behavior and seasonal movements, so that improvements can be made to reduce the lethal and sublethal impacts of the process.

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