Serina: Weedy Calacarna & Sea Pony (Patreon)

The vast oceanic habitat of the floating forest is a veritable undersea jungle, harbouring hundreds of unique endemic species living in close proximity. Many relationships between different animals have developed over millions of years as the environment grew and evolved. Those of predator and prey, parasite and host, niche partitioning of competitors, and the symbiotic relationships which benefit both parties. 

The sea pony is a relatively small species of sea horse, growing between four and five feet in length, and lives in great herds in the floating forest, sometimes hundreds strong. Their rotund bodies are rather buoyant, and they rarely stray deeper than a hundred feet underwater, for they thrive on the countless hundreds of miles of macroalgae that drifts near the surface and grows with such speed and quantity to the sea ponies it is functionally infinite. Indeed, they defecate almost as quickly as they feed, fertilizing the seaweed and accelerating its growth. Their striated hides acts as perfect camouflage as they slowly cruise through the sunlit understories of the vast seaweed forest. Sea ponies are born with a much brighter yellow colouration, which helps the adults easily keep track of them in the green-blue waters. As there are few predators in this habitat capable of hunting an adult sea pony, breeding is slow, with one large calf generally born every two or three years, and mortality rates are generally low. Care is communal, with all adults in the group tolerating juveniles, although close family members tend to be more actively protective and willing to respond to play initiation. 

Large calacarnas and sea serpents are the primary hunters of sea ponies, but these are generally vagrants to the floating forest, as this is an oasis which does not support life at such a scale. The nimble sea pony can easily nestle itself deep into the masses of floating algae and become impossible to reach for larger predators. Their smooth shape allows them to root deep into the colonies of seaweed to graze on the newest and softest growth, as well as find the fruit-like sporangia when the algae flowers, and they even sleep by resting on top of denser clumps of the kelp-like vegetation near the surface. Although they are in fact small enough to actually haul themselves onto the surface of the floating forest like a seal, as they are still recently enough descended from a land animal that they still retain some adaptations for supporting their body weight out of the water, although their mobility is obviously very poor.

As the aquatic tribbetheres push their way through the tangled root-like growths, they disturb and flush out many smaller organisms which dwell within the seaweed fronds, and this has not gone unnoticed by the weedy calacarna, a small species reaching about a metre in length (including mandibles). The weedy calacarna is too small to be a threat to a sea pony, even a calf, and often follows their herds, snatching up any small fish, snarks, annelids, and other small aquatic creatures accidentally unearthed from their foraging. Its thin jaws, lined with numerous fine serrations, are well-adapted tools for grasping small, slippery prey, but basically useless restraining animals close to their own size. The calacarnas swim very close to the sea ponies, shadowing their movements, changing the patterns and colours of their own skin to closely match theirs, making their presence and approach unnoticeable as they close in on their prey, which are not automatically alerted to danger by the passive movements of the harmless herbivores as they would be to the predator alone. Sea ponies are a preferred host due to their peacefulness, large size, and numbers, allowing the calacarnas to quickly move between individual sea ponies as they close in on prey, which usually ignore them. However, weedy calacarnas are not obligate symbionts of sea ponies and just as often found by themselves, so the prey does not grow to associate the presence of sea ponies with the calacarnas.

The calacarnas have short, rounded fins and an elongated body; this makes them slow-moving while swimming in open water, but it is able to lithely crawl its way through the floating forest vegetation with easy, using its fins like arms and legs to push its way through. Indeed, its slow swimming speed makes it seem like less of a threat to its prey, which sometimes do not even register it until it surges forward with a short and sudden burst of speed. Away from the herds of sea ponies, it can hunt by hooking its tail fins into the seaweed and hiding with only its mandibles exposed to the open water, and lunging forward to snap any small swimmer that gets close enough. The snarks form pairs or small family groups and defend this communal hunting ground. When in the presence of sea ponies, they make themselves useful by scrapping away dead skin from the hides of the tribbetheres and removing dermal parasites, which helps to clean the sea horses, although the calacarnas are more interested in an easy food source to supplement their normal diet. Sea ponies have also learned to recognize some of the visual signals the calacarnas, such as the rapid flashing indicative of approaching danger. The weedy calacarnas will also actively make themselves useful to the sea ponies by helping herd their offspring and steer them towards the herd if they stray too far, which helps the ponies tolerate their presence. In these ways, the sea ponies are benefited by the snarks' presence.

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(This is a sponsored commission for a floating forest symbiosis between a species of sea horse and a species of calacarna)