If you have been to Quintana Beach lately you may have noticed weird spiky shells spread along the shore. While surveying for non-breeding shorebirds along Quintana Beach, I came across these shells and figured out that they belong to Longnose Spider Crabs. These crabs are actually part of the decorator crab group. They are often yellow or brown with long spider-like legs, which is where the “spider” in the name comes from. This crab has 6 curved spines along its sides and back, and one long, forked rostrum, or nose, between its two eyestalks.
The Longnose Spider Crab can be found in coastal and estuarine habitats. They are very tolerant to salinity and temperature. They are a benthic species, meaning they live along the bottom of water bodies. Juveniles prefer seagrass beds where they can hide easily from predators, and adults typically live in open, sandy areas. The native range of this particular crab is Cape Cod, Southeastern Texas, Bahamas, and Cuba. Longnose Spider Crabs are a type of scavenger, so they feed on plants, animal tissue, and detritus, or dead stuff. They can also feed on the transparent part of jellyfish.
Longnose Spider Crabs are actually a type of decorator crab, meaning that they decorate their shells with outside material. Only the juveniles cover their shells, while the adults keep their shells clean. As juveniles, they are most at risk of getting predated by larger fish and birds, due to their small size.
Velcro-like hairs called setae carpet the back of their carapace. With these hairs, the crabs can easily attach plants, algae, and small invertebrates to help them blend or camouflage themselves within their environment. The plants and algae are often unpleasant to eat, so predators are more likely to spit the crab out. Unlike other crabs, their pincers are incredibly small and weak, so they rely on camouflage to protect them.
During their larval stages, Longnose Spider Crabs can actually be seen clinging onto the inside of cannonball jellyfish. This symbiotic relationship with the jellyfish is commensal. Commensal is defined as one species benefiting from the other species while the other species is neither benefitted nor harmed. The larvae uses the jellyfish for food, protection, and transportation, while the jellyfish doesn’t benefit from the crab larvae. This type of relationship is, unfortunately, short-lived because when the larvae molts into a large juvenile, the jellyfish then becomes food for the crab.
Similar to other crabs, Longnose Spider Crabs need to molt in order to grow. In the fall, they often molt in very large groups called pods. In the winter, they are known to hibernate in dense patches. They typically mate in the spring. Females tend to be smaller than males. Like other crabs, you can easily tell them apart from each other by looking at the abdomen.
The females are broader and flexed to brood eggs. Once the male fertilizes the eggs, they develop into larvae. The larvae go through three planktonic stages before they molt into juveniles within nine days.
Photo captions:
Longnose spider crab carapace: Pictured is a Longnose Spider Crab carapace found while surveying for non-breeding shorebirds along Quintana Beach, Texas. Photo taken by Taylor Bennett.
Spider crab setae: Zoomed in photo of the Velcro-like hairs located on the carapace of the Longnose Spider Crab. Photo taken by Taylor Bennett
