Ponds in the Treetops
Tree-dwelling Fish and Other Oddities of the Nanboo Forest
On Earth, bromeliad flowers are well-known for their tendency to accumulate rainwater in their centers, forming small pools in which insects and small animals breed and shelter. A similar phenomon, but on a greater scale, occurs in the nanboo forests of Serina.
The individual pseudostems of the nanboo colony resemble palm trees, and consist of a large clump of strap-like leaves atop a tall, smooth stalk. The leaves are waterproof and originate in a radial pattern from a central crown, and as a result of the nearly daily rainfall which occurs in the tropical regions which support the nanboo forest, this cup-shaped crown of unfurling leaves tends to accumulate rainwater much like the leaves of Earth's bromeliads. Because nanboo grows rapidly however, adding several feet of height per day in good conditions, the water that accumulates in their crowns is regularly lost and replaced. Lower down on the plant, however, water collects in the axles where the leaf stems meet the trunk. These pools are much longer lasting, remaining full until the leaf sheds anywhere from three months to a year after it unfurls, and they can accumulate large quantities of water. A large stalk can hold as much as a gallon of water in some of these leaf puddles - each a veritable pool in the forest canopy which provides habitat to many animals which, without this unusual feature of the local flora, could not survive here.
The most abundant inhabitants of the nanboo ponds are insect larvae that feed on the biofilm of algae and bacteria which grow on the plant tissues inside the pool. Predatory spider-like mites scurry along the edges of the pool, fishing out any stragglers which stray within range, while tiny brightly-colored mudwickets that skip across the wide leaves in pursuit of tiny insect prey retire periodically to the pools to rehydrate. Small changelings not much larger than bumblebees, which feed on the abundant nectar of the nanboo blossoms, drop their eggs in the pools where they initially feed on the algae and insect larvae but within weeks leap from the canopy ponds down to the forest floor, burrow themselves into the leaf litter, pupate in a cocoon of mucous, and emerge soon after in their diminutive adult forms. The nanboo pools also host several endemic species of fully aquatic snails, shrimps, and most bizarrely even several small guppy-like fish species, all of which presumably first reached these pools - and continue to disperse by - attaching sticky eggs to the legs of passing animals. Most of them mature quickly by necessity and reproduce prolifically, because when the leaf supporting their home eventually withers and drops away, taking its water with it, they will have no means of reaching another. One species however, the nanboo puddlesucker, is able to make an escape when the going gets tough by inching itself out of the water with hooked pelvic fins and adhering to the tops of the foliage with a sucker-like mouth. Just two centimeters long, this nearly transparent, algae-eating guppy can travel for quite some distance, even vertically, in humid conditions until it can locate an adjacent pool to colonize. It breathes during this time by gulping air into its gut, where has developed a primitive labyrinth organ to absorb oxygen from the atmosphere. The puddlesucker is also unusual as it is a live-bearing fish, and appears to have colonized this habitat not by eggs but directly from more traditional stream habitats, where its relatives have adapted to climb up waterfalls.
Surely some of the most frequent dispersers of the other tree fishes' eggs are many species of arboreal crabs, all of which have lost their ties to the see and reproduce in fresh water. Some of the crabs lay their eggs in the pool, where the larvae hatch and develop. Others utilize the pools only to facilitate the transfer of sperm to the female's eggs, which are secured beneath her carapace and briefly moistened every so often by a quick dip into the water, and carried with her overland until they hatch into miniature versions of the adults. Many of the crabs feed upon the leaves of the trees themselves, a few on fungi or algae, and still others on animals. Many of them are no larger than fingernail at maturity and rarely leave the shelter of the pools, but others are large and well-adapted for long-distance travel through the canopy. Long-legged predator crabs lie in wait within the dense vegetation to pounce upon passing crickets or mudwickets and dismember them with their large pincers; the largest among them reach legspans of twelve inches and can even consume birds. To secure a purchase on the smooth leaves and stems of the nanboo, they have developed sticky pads of microscopic setae on their legs that give them a gecko-like grip. Other relatives giants include the sloth crabs, slow moving herbivores that can weigh as much as two pounds. They are grazers, feeding on the leaves of the nanboo, and spend most of their lives clinging upside down to the sturdy central ribs of the leaves while they skeletonize the rest of the leaf tissue around it. Due to their lethargic nature, growths of algae and moss often develop on their shells and serves to camouflage them from potential predators.
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There is as well a genus of nanboo which have begun to evolve some benefit to itself from the pools of water that collect in their leaves. Rather than allow their pools to be used as refuges, they have become traps, similar to Earth's pitcher plants and certain wellwood trees. The leaf stems are highly elongated and form a deep, narrow well where they meet the trunk. Glands in the stem extrude beads of sugary nectar, which draws in insects. The inside of the tube is highly slippery and the insects drop into the pool, where they drown and are slowly broken down by a weak digestive acid. Organic matter broken down in the pool is then absorbed into the tissue of the trunk.