by Agatha Bedi
Conspicuous strange piles of mud piled up on the forest floor. For a moment, my imagination took over as I stared deep into the eerie figures before me that were surprisingly blended into the mysterious mangrove swamp. I pictured the earth suddenly rumbling. Triggered by an extra terrestrial phenomenon, numerous volcano shaped like piles of mud simultaneously erupted onto the surface and thus completely deforming the landscape.
I snapped back to reality. Reality still seemed to be fictitious. Dried brown piles of mud or mounds capped with moist jet black mud were omnipresent. The black mud had a whiff of sulfur. Some mounds were separate from the others, while other mounds toppled over each other forming little ‘islands’ ranging from 6 to 24 meters in diameter.
In hopes of unraveling the mystery of the mounds, I hastily started excavating the pile of encrusted mud which revealed clean and firm looking tunnels converging into one tunnel. All sorts of little creatures were crawling out of the mound, but there was no doubt that the engineer of the mound still lay there…patiently hiding underground.
After digging for several meters now, the tunnel didn’t seem to end. Was the endless tunnel going to swallow me and lead me to another dimension?
My arms started to ache, and the presence of mangrove roots supporting the mound was making the task more tedious for my arms. I lost patience and stuck my arm deep into the narrow tunnel – hoping, in desperation, to touch something that would pacify my curiosity. Murky sea water slowly started filling the tunnel. I finally surrendered for the day and later found out that the same damaged mound had been deliberately clogged with jet black mud.
WHAT WAS HAPPENING?
My internship centered on the very mysterious and understudied alien-like creatures, engineers of the 2-3 meter high volcanic-like mounds, found in the mangrove eco-park of Ibajay which is located in the province of Aklan, Philippines. With the guidance of Dr. Primavera and the Zoological Society of London, I was given the task of poking around the scorpion mud lobster’s mounds and learning more about these amazing creatures. They are crustaceans of the genus Thalassina that look like lobsters with their elongated abdomen, but they are closely related to the family of the ghost shrimp (Callianasa).
The scorpion mud lobsters are found in mangrove swamps throughout Southeast Asia. Two kinds of mud lobster species, Thalassina anomala and Thalassina squamifera, are present in the Philippines. They are known as ‘uson’in Aklano , ‘mangla’ in Cebuano, ‘kolokoy’ in Tagalog. ‘Uson’ means backward because the animal crawls backward when threatened (see link: https://www.youtube.com/watch?v=k_L7H0HPPM4)
No scientific publication was ever made in the Philippines about these species. These nocturnal mud feeders are rarely eaten, but they are considered as a delicacy in some places such as Quezon. It is not a common dish due to its bland taste and lack of meat. Unfortunately, the burrowing activity of the mud lobster damages the bunds of commercial prawn and fish ponds, making them leak water and collapse. The soil excavated acidifies when exposed to oxygen and can pose a threat to agricultural development.
They can be seen as a menace or an eyesore by the farmers, but they are considered ‘engineers of the mangrove ecosystem’ by the scientists.
Deep in the Mound
Due to the lack of scientific information and information dissemination, their role seems to be unknown to the general public. Their mounds are commonly seen, but the engineers are rarely spotted outside of the mound.
I’d find myself wandering around the forests, poking on things and destroying (for research purposes) the mound. These creatures are so resilient; they continuously repair the mounds that were partially broken with fresh black mud, hours to days after being destroyed. The timid but cunning mud lobsters would outsmart the bamboo snare trap left at night. They would fill the trap with black mud and create another exit hole. (Grrr!)
Sometimes, as I’d step into the forest, I’d feel my hair stand on end. My imagination would take over again. I’d imagine faintly hearing their ‘crustaceanic’ laugh echoing in the mound as I catch a glimpse of their antenna slowly retracting deep in the burrow, and their unequal sized claws waving in the air. Clever and conniving creatures. They were probably monitoring my every move from the comfort of their sturdy bunkers or celebrating my failed attempts to capture one of their comrades via my bamboo snare trap.
Their victory was short lived. Several attempts to capture mud lobsters turned to be fruitful. Several individuals of Thalassina anomala, the common mud lobster, were finally captured. Thalassina squamifera, a bit smaller than the latter and known to be found in the country, wasn’t found.
However, another species that hasn’t been recorded in the Philippines, called Thalassina spinosa, was found.
( It was a delight to study mud lobsters and easily discover an unrecorded species in the Philippines in a span of weeks. It makes me wonder how many species scientists can discover in our country and how much of valuable knowledge would be unearthed if provided the ample amount of time and funds for research. To go further, how would the coastal communities be able to sustainably benefit from the harnessed natural wealth and scientific findings in the process? )
Unlike T. anomala, T.spinosa is covered with more spines. Spines are present in the cervical groove, characteristic of its species. No surprise there. There are many species found in the Philippines waiting to be discovered!
The bright red color of mud lobsters makes them vulnerable to predators such as birds, otters, snakes, monitor lizards and crabs. Their powerful digging claws and armed body shield are possibly some of numerous defense mechanisms of the underground creatures to ward off predators. Fortunately, their bright red color is usually covered with mud due to their burrowing activities providing them camouflage against the mangrove soil. When threatened, they retreat to their mounds or they curl their abdomens and crawl backwards as they wave their claws menacingly in the air.
Niche in the Mangrove Ecosystem
Mud lobsters are considered a keystone species, meaning that a certain kind of biodiversity solely depends on their presence. Mud lobster mounds provide refuge from predators and high tide to at least 13 different species(snakes, snails, crabs, ants, hermit crabs, worms, fish, spiders, etc.).Once the mound is inundated by sea water, other sea creatures enter the mounds to forage or seek shelter. A trapped juvenile goby fish was once spotted buried in the mound, surviving in its own shrinking puddle of water hours after the tide had ebbed.
Certain plants that love acidic soil such as sea hollies and mangrove ferns are found flourishing on the mounds. The mound is filled with other small tunnels and holes created by the other residents. As a result, the presence of mud lobsters upgrades the dynamics and diversity of the area- increasing the biomass of numerous species subject to human consumption.
Just like mixing with a spoon instant powder that has settled on the bottom of a glass of water, the mud lobsters serve as instruments that efficiently mix the sediments in the mangrove soil. Their burrowing activity brings the nutrients, stuck in the bottom of the compact mangrove soil, to the surface as they continuously filter mud for food. In addition, the activity renders the nutrients accessible to different fauna and flora and allows oxygen to penetrate deep into the anaerobic and acidic mangrove soil— stimulating the growth of nearby mangrove trees.
Mud Lobster Mound
The pungent smell of the black mud is not mud lobster poop. The fresh mud deposited outside the hole was excavated from inside the mound where sea water originating from the swamp is found. It smells because it was excavated deep in the anaerobic mangrove soil where organic matter decomposes very slowly.
Mounds are created as mud lobsters excavate deep into the mangrove soil. It is said that burrowing activity takes place at night, but recent activity was spotted during the day. They are often mistaken as crab mounds as crabs can be seen burrowing in the the mud lobster’s home.
The burrowing activity allows the ‘turnover’ of sediments and the oxygen to penetrate into the mangrove soil. Large mounds and to century old mangrove trees found in the heart of the eco-park seem to have a positive correlation. Despite the presence of mature and acidic soil that can harm Avicennia species as opposed to Rhizophora (bakhaw), the presence of Avicennia is proof of good drainage and aeration made possible by the excavated tunnels of near by large mud lobster mounds.
Gems of the Swamp
The engineers are unknown but slowly reveal themselves to be a very important component in the mangrove ecosystem. Their mounds prevent erosion, redirect water flow, stimulate mangrove growth and serve as a condominium for countless species. They enhance the mangrove ecosystem’s capacity to provide regulating (carbon storage, erosion control), provisional (consumable resources) and cultural (recreation, educational values) services to the local community.
The symbiotic relationship of mangroves and mud lobsters raises the possibility of perhaps equally promoting and protecting the species in pursuit of facilitating mangrove reforestation programs to reduce the impact of climate change.
The presence of mud lobsters in the mangrove ecosystem reinforces unquantifiable services that nature provides to man.The conspicuous strange looking mounds, perhaps useless to the untrained eye, serve as a visual proof of interconnection that links terrestrial life to the marine, the underground ecosystem to the surface, and man’s basic needs to Nature’s bank of overflowing wealth.
Towards the end of my internship, the mounds seemed to slowly lose their eerie and alien-like character. Gazing into the mounds for the last time, my imagination took hold once again and a spectrum of vivid colors now seemed to overflow from each pile of mud. The colors were casting light into the dense mangrove forest with its radiant hue. Still possessing an air of mystique and potentially a moundful of unearthed data still unknown to man, the existence of mud lobsters and all its wonders, is a beauty to behold.
Aga finished Management and Conservation of Nature and recently graduated from a course called Analysis and Inventory Techniques of the Biodiversity in France. She plans to go back to the Philippines and work for the environment. She is currently still struggling with her French and working with Ecotone Resilience (www.ecotoneresilience.org).