The Atlantic Horseshoe Crab
Horseshoe crabs date back millions of years ago (Smith, Brockmann, Beekey, King, Millard, & Zaldívar-Rae, 2017). However, the number of horseshoe crabs has been decreasing steadily as time goes by. To make the matter worse, the decrease in the number of horseshoe crabs pose a significant danger to the survival of many shorebird species. This paper explores the independence between shorebirds and horseshoe crabs and why the protection of these species is needed.
What Is about this Interrelationship between the Horseshoe Crab and the Red Knot (And Other Shorebirds) that Has Put these Species in Jeopardy?
Shorebirds species, such as sanderling, ruddy turnstone, and red knot rely highly on the eggs belonging to horseshoe crabs deposited on the banks of the Delaware Bay for their nutritional welfare (Wetlands Institute, n. d.). However, the red knot relies the most on horseshoe crabs for its survival. One female horseshow crab lays approximately 100,000 eggs per season (Bittel, 2017). Most of these eggs are tucked beneath the sand. However, waves usually dislodge the eggs exposing them to the surface, and this makes them available to a wide array of hungry mouths. One of the animal species that depend highly on the dislodged eggs belonging to horseshoe crabs is the red knots (Bittel, 2017). The horseshoe crabs eggs are very nutritious for the shorebirds. For example, Krisfalusi-Gannon et al. (2018) argue that these eggs have a high content of fatty acid, which is crucial for the migrating shorebirds. These birds need a massive amount of energy to sustain them in their enormous migration paths.
According to Burger, Tsipoura, and Gochfeld (2017), studies have revealed that the quantities of heavy metals in the blood of red knots are correlated with the amount of chromium, arsenic, mercury, lead and cadmium in the eggs of horseshoe crabs. These studies confirm that horseshoe crabs are the main source of food for red knots. Wendy Walsh is a lead biologist in the U.S Fish and Wildlife Services specializing in red knots. Walsh argues that approximately 90% of all total rufa red knots across the world inhabit the Delaware Bay area when the horseshoe crabs spawning season comes (Bittel, 2017). This statistic underscores the extent to which shorebirds and horseshoe crabs are interdependent. When the number of horseshoe crabs reduces, egg availability plummets, resulting in a decrease in the proportion of the shorebirds on Delaware Bay (Burger et al., 2017). As such, the population of red knots is likely to decrease significantly if the population of horseshoe crabs in the bay does not produce an adequate number of eggs.
Why Is their Preservation Important?
Already, the population of the red knots and the Atlantic horseshoe crabs has been on a decreasing trend over the years. For example, the number of horseshoe crabs inhabiting the Delaware Bay has reduced by approximately 90% within the last 15 years (Wetlands Institute, n. d.). Besides, fewer red knots are reaching their target weight. On this note, the proportion of red knots reaching their suitable weight reduced by 70% between 1997 and 2002 (Krisfalusi-Gannon et al., 2018). This phenomenon may be attributed to these birds arriving late in the Delaware Bay. Also, horseshoe crabs are facing habitat degradation and overharvesting. Smith et al. (2017) argue that coastal changes as a result of hardened shorelines as well as erosion accounts for the decrease in the proportion of suitable habitat for horseshoe crabs. Besides, many of the harvested horseshoe crabs die upon their release back to their habitats. The mortality rate of the harvested horseshoe crabs is around 10-30% (Krisfalusi-Gannon et al., 2018). The harvesting and collection procedures used for breeding horseshoe crabs account for the mortality of this species. For example, some of the harvested horseshoe crabs die from blood loss (Krisfalusi-Gannon et al., 2018). Besides, horseshoe crabs have significant biomedical applications. For example, the blood of horseshoe crabs coagulates when it comes into contact with a bacteria or fungi (Bittel, 2017). For this reason, it is being used to screen vaccines, flu shots, artificial hips and pacemakers for nasty infectious agents before they can be used in patients. Besides, horseshoe crabs act as bioturbators and controllers of various benthic invertebrates (Krisfalusi-Gannon et al. 2018). This makes the conservation of the two species is ecologically essential.
What Actions Are Being Taken to Preserve Them and Why?
To begin with, there is a regulation of the number of horseshoe crabs that are taken away of their habitat to provide blood used in biomedical applications. For example, horseshoe crabs Fishery Management Plan (FMP) was approved in 1998 by The Horseshoe Crab Management Board (Krisfalusi-Gannon et al., 2018). The plan provided guidelines for the initial conservation of the Delaware Bay. Besides, the Adaptive Resource Management (ARM) framework was developed by Addendum VII in 2012 (Krisfalusi-Gannon et al., 2018). The framework serves to ensure that the implementation of regulations for the shorebirds and horseshoe crabs protection is done with the population of these species in mind.
At the same time, there is a campaign aimed to recruit beachgoers or volunteers to participate in preserving the horseshoe crabs. The campaign dubbed Return the Favor calls upon beachgoers and volunteers to flip the horseshoe crabs they find lying on their backs (Bittel, 2017). The initiative is aimed at ensuring that horseshoe crabs do not succumb to harsh weather conditions or get stumbled upon by beachgoers.
At the same time, there are organizations involved in the collection of eggs belonging to horseshoe crabs. For instance, the Wetlands Institute is involved in the collection of fertilized horseshoe crab eggs (Wetlands Institute, n. d.). The harvested eggs are reared in controlled conditions. The resulting horseshoe crabs are then reintroduced into the original habitats. The initiative is aimed at ensuring that as many horseshoe eggs not only hatch but the resulting offspring reaches adulthood. Besides, the red knot bird is now part of New Jersey’s endangered species list (Wetlands Institute, n. d.). This initiative is aimed at ensuring that more resources are provided in the measures aimed at preventing further extinction of this species of bird.
In conclusion, this paper has demonstrated that the existence of red knots and the horseshoe crabs is so interrelated. Many shorebirds rely on the eggs belonging to horseshoe crabs for their survival. Fortunately, there are many measures that have been put in place with the goal of ensuring the continued survival and thriving of horseshoe crabs.
References
Bittel, J. (2017). This tiny seabird’s colossal migration is in danger from all sides. Retrieved from https://www.nrdc.org/onearth/tiny-seabirds-colossal-migration-danger-all-sides
Burger, J., Tsipoura, N., & Gochfeld, M. (2017). Metal levels in blood of three species of shorebirds during stopover on Delaware Bay reflect levels in their food, Horseshoe Crab eggs. Toxics, 5(3), 20.
Krisfalusi-Gannon, J., Ali, W., Dellinger, K., Robertson, L., Brady, T. E., Goddard, M. K., … & Dellinger, A. L. (2018). The role of horseshoe crabs in the biomedical industry and recent trends impacting species sustainability. Frontiers in Marine Science, 5, 185.
Smith, D. R., Brockmann, H. J., Beekey, M. A., King, T. L., Millard, M. J., & Zaldívar-Rae, J. (2017). Conservation status of the American horseshoe crab (Limulus polyphemus): A regional assessment. Reviews in Fish Biology and Fisheries, 27(1), 135-175.
Wetlands Institute. (n. d.). Horse crab conservation. Retrieved from https://wetlandsinstitute.org/conservation/horseshoe-crab-conservation/