Wild Estuaries: Mangrove Tree Crab

For the next couple of posts, I will be introducing you to some extraordinary creatures that thrive above and below in Estuarine habitats.

A crab that climbs trees? I would need to see it to believe it, and I saw it. Let me introduce to the Mangrove Tree Crab. 

When I first saw this, I was dumbfounded, what the heck. I thought all crabs were land dwellers, but I shouldn’t be surprised at all when it comes to nature. Learning that a crab evolved to have the capability to climb mangrove trees is, again, nature’s way of teaching us how diverse and adaptive wildlife is. 

The Mangrove Tree Crab (Aratus pisonii) is a key organism within the mangrove environment. They are omnivores, meaning they consume both animal and plant matter. Their herbivore diet mainly consists of the epidermis layer of red mangroves leaves. If you look closely, you will be able to see the scrapping marks on the leaves. 

Mangrove tree crabs have sharp hook-like points at the end of their legs that enables them to climb trees. – Photo by Alice Mary Herden

As research suggests, mangrove tree crabs spend most of their time hidden within the mangrove trees to avoid predation. They will climb down, if you will, to the roots during low tide to wet its gills, lay eggs, or feed on algae or other organisms.

Mangrove tree crabs are not air-breathing crabs like the Atlantic blue crab. They breathe in oxygen from a thin film of water over the gills. When that film of water begins to dry up, the crab will climb down to re-absorb water into its gills. 

How do they climb trees? They have sharp-pointed tips at the tip of their legs and a distinctly triangular carapace (shell) that enables them to climb. 

They are very cool to observe at first, and if you first experience them -especially if they jump- it kind of freaks you out. I know it did for my husband and me. However strange looking they are, they are an essential part of the estuarine ecosystem.

Photography tip:

Mangrove tree crabs will climb up red mangroves during high tides. – Photo by Alice Mary Herden

If you visit Wall Springs Park in Palm Harbor, the best chance to view the mangrove crabs is on the observation tower’s boardwalk. It’s also has a small selection of red, black mangroves and sea oats that you can observe on the boardwalk’ path overlooking a scenic estuarine habitat. You can find the mangrove crabs scurrying about within red mangrove trees.

Check the tides; mangroves crabs will seek refuge above the water during high tide. Look for them on the tree trunks and branches because, from a distance, they look like blackish or dark brown knobs. They are fast and easily startled, so stroll quietly. If you can see them close up on branches near the railing, they will happily challenge you in a game of hide and seek. 


Links of Interest:

https://ocean.si.edu/ocean-life/invertebrates/mangrove-tree-crab

Publication

Herbivory_and_predation_by_the_mangrove_tree_crab_Aratus_pisonii

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