Wood-eating squat lobsters of the deep

Deep-sea ecosystems do not receive enough light from the sun to fuel photosynthesis and inject energy into the food chain. Therefore, the myriad creatures inhabiting the deep subsist on either geo-chemical phenomena, such as hydrothermal vents and cold seeps, or food-fall from the surface. The epic TV documentaries “Blue Planet” and “Planet Earth” have displayed classic examples of this by sinking whales and fish and recording the subsequent feeding frenzies.

Recently, researchers have begun to describe deep-sea ecosystems based on trees that fall into the ocean and eventually sink. Mollusks are the most common organisms associated with these wood falls, followed by arthropods. The crustaceans found on these wood falls include isopods, amphipods, and decapods. The decapod order consists of crabs, lobsters, and some shrimp. One prominent decapod found in the wood-falls is the squat lobster, Munidopsis andamanica.

Munidopsis andamanica

Squat lobsters are actually more closely related to hermit crabs than the large, delicious, true lobsters that most people are familiar with. They lead diverse lifestyles in a wide variety of marine habitats. Typically, squat lobsters are generalist scavengers. However, M. andamanica has apparently evolved specializations for feeding on wood. These adaptations include claws and mouthparts ideal for tearing off and processing strips of wood tissue. In addition, the guts of these animals contain bacterial colonies that may assist in digesting plant tissue.

Partially digested plant xylem and symbiotic bacteria from the gut of M. andamanica.

These squat lobsters play an important role in wood fall ecosystems. Their ability to digest plant xylem tissue, producing nutrient-rich waste, injects useful energy into the environment. Furthermore, the discovery of wood fall ecological communities supports the stepping stone hypothesis of deep-sea colonization. It is thought that animals found in all habitats of the deep sea evolved in shallower waters and invaded the deep gradually by hopping from one sunken nutrient mass to another: Eventually reaching the deepest extremes of the oceans.

References:
Hoyoux, C. et al., 2009. Wood-based diet and gut microflora of a galatheid crab associated with Pacific deep-sea wood falls. Marine Biology, 156(12), 2421-2439.