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Introduction

Siren is a planet with an Earth-like atmosphere in the far edge of the galaxy. This is our home. It was settled by Precursors from Planet Earth several millennia ago as of our current time, which I have dubbed the Era of Enlightenment _{(it'll catch on eventually)}

Observing from afar, Siren's most notable features are the 30+ moons in variously shaped orbits. The moons make the sky rather crowded, but their number and offset orbits serve to eliminate tidal forces on Siren due to lunar gravitational pull - the pull is smaller and evenly spread out across the planet, instead of being concentrated in any one area (…usually). This is one of two factors which led to the birth of Siren’s extraordinary freshwater sea.

Over 95% of the planet’s surface is covered by this sea but it is not continuous. Billions of years of glaciation in combination with the Coriolis effect have formed the land into a dense network of parallel longitudinal valleys, with narrow ridges of land high above the sea surface making up the majority of dry land. The valleys and ridges have sheltered the sea from substantial mixing by wind, leaving a waterbody that is strongly stratified and has the qualities of a swampy lake in summer, with an anoxic lower layer, submerged brine pools, and unpredictable flows of deadly super-aerated water not dense enough to swim in.

There are photosynthetic plants and native animals (all various kinds of arthropod, to use Earth terminology), gravity marginally lower than Earth’s, high atmospheric oxygen, and a significantly higher incidence of silica and titanium in all organic matter. The most common habitat is a type of reed marsh that covers pretty much all of the hatched areas on the map, but in the continuous land portion of the Eastern continent, there are deserts, arid grasslands, and complex rock formations.

Siren was used as a test-bed by genetic engineers working for an influential corporation, Atom, and specifically its Geneweave department, who wanted somewhere nice and remote to experiment. Somewhere the authorities couldn’t come knocking. Siren was an ideal location to pioneer the creation of genetically engineered recombinant Homo sapiens with adaptations for aquatic life and flight. Their ultimate goal was to produce a variety of less-than-sapient human worker class that could be purchased by their clients in a range of morphologies suited to various tasks.

Thankfully, this monstrous plan never came to fruition, and following a short revolutionary war, Atom corporation deemed Siren uninhabitable, and abandoned it to its own devices.

The genetically engineered aquatic and aerial humans of Siren survived and persisted. Over another few millennia we adapted to fit our new environment even more, and forgot our origins as old technology fell into disrepair or became redundant. We forgot that we were ever aliens on this world, until I, a scholar from Spire university, led a controversial yet brilliant research mission back to the first settlement, where I uncovered the journals of the first-born modified human telling the full story of the Settling of Siren. 

 

1. Planet Siren

 1.1 Moons

There are many many moons of different colours, sizes, and composition the most prominent of which are 

• Davide, the brightest yellow moon. Named for an infamous Atom defector.
• Ishmael, the brightest white moon, often most visible during spring tide events. Named after the first-born Sirenian.
• Cherta, a small and irreguarly-shaped red moon, usually most visible during neap tide events. Named after one of the beta phocids. 
• Siren's Eye, a small white moon which is visible nearly constantly, day and night, over the East continent
• Cold Flame, dim orange moon which seems not to move much from the sky over the South Pole

Moons exert a mostly homogenous pull on the sea of Siren, except when their orbits contrive to have them all pull in the same direction at once, causing a spring or neap tide.

1.2 Atmosphere

The composition of the gases in the atmosphere are still somewhat unknown to us, though our atmosphere is breathable to unaltered Human Precursors for limited periods of time, indicating that it did contain the gas known as 'oxygen' in sufficient quantities. The component of the gases which the Precursors found disagreeable appeared to have had a cumulative effect following repeated exposures. This effect resulted in symptoms of poisoning which were slow to fade, and after enough exposures the effects were permanent (and often fatal). The symptoms included disorientation, bruise-like staining around the eyes and fingernails, discoloured teeth, respiratory upset, and fatal dementia.

1.3 Oceanography

Siren is an Earth-like planet which is 99% shallow freshwater ocean which is aerated by photosynthetic plant-like organisms. The ocean is liquid water (ice at the poles). 

In its previous ice age, glacial action dug all land into a vast stretch of interconnecting glacial valleys. When the ice melted and the ocean filled the valleys, what remained was... mostly unbroken ocean, but also an above-water landmass comprising entirely of the flat-topped mesas in between the valleys. There exists only one area of flat continuous land, which is in the Eastern continent (yellow). All other land, and all of the Western continent, is broken up into these ridges. Imagine a giant Turing pattern of mesas and water. 

 

1.3.1 Tel!am's blood, aka Aerated Water

Water which is not mixed by either a current, wind, or a tide, or some other mixing factor, will stratify. It separates into layers. There’ll usually be an oxygenated layer on top and an anoxic layer underneath, which can only be inhabited by certain extremophiles adapted to low or no oxygen conditions.

This is the normal way of things on Siren when the tides aren’t moving; the ridges of land formed by glaciation that break up the sea are effective wind barriers and mixing is minimal. It doesn’t make a difference to phocids and selkies because these people are air-breathing; in fact this stratification is why all attempts at a human with gills never really made it off the drawing board, they would be less suited to live in this water than an air breathing human. The sea never gets that deep on most of the planet’s surface.

Vents in the sea floor are usually inactive or minimally active, letting out thin streams of gas (same as what makes up the atmosphere; oxygen, nitrogen, etc). However occasionally, an earthquake or other geological event will cause a vent to force out what lies beneath the crust; aerated water. Aerated water is low-density water. It’s used in wastewater treatment plants on Earth right now. And if you fall in, you can’t swim. You go straight through it. (These treatment plants have mechanisms to detect anything entering the water, and a mobile floor will rise up to lift you out of the water)

Aerated water on Siren is known by a variety of ominous regional names as it’s pretty universally feared by sea people. In the stratified water, the aerated layer sits on top of the normal oxygenated later, creating an interface where the less dense water sits on top of the denser water. In particularly rapid flows of aerated water, it can form thick currents on the surface which do not disperse for days or even weeks at a time, and they can be so large and so sudden that entire villages could be wiped out instantly. You can’t swim through aerated water, so you become trapped underneath it. You can’t see the interface easily from below, so it’s hard to judge its edges, it’s hard to see how far it stretches. At best, you might have just taken a breath and you’ll have 30 minutes to find the edge of the flow, but what if you swim in the wrong direction? What results, if people are particularly unlucky, is a mass drowning event of all air-breathing creatures in the area.

The flow usually starts in a linear shape and if it encounters open water with no land ridges, it will slowly begin to spread into a roughly round shape, getting thinner and thinner as it widens out until the layer is too thin to pose any risk. The gas discharge into the normal water can be significant and provides a nice boost for the oxygenated layer. Pelagic people have to be alert for this danger and have drilled responses and emergency flotation devices at their villages, just in case (in fact they make their own underwater hot air balloons to quickly rise to the surface using lighter than air flight)

It’s not just aquatic people who are at risk. Flying people who might think to land on the sea to rest in the middle of a long journey risk landing on an aerated flow that won’t support them, causing them to sink immediately. Ships with the correct displacing hulls and hydrofoil arms that penetrate to the layer of normal water can traverse aerated flows, but rafts and canoes, used by most of the population, are in danger of vanishing below the surface due to the unpredictable handling characteristics. Most modern whaling vessels are hydrofoils.

The final effect of the flow is incredibly rare but it has happened enough to provide fuel for superstitious rumours about flying phocids and selkies; if you’re directly above the vent when the aerated water explodes out, you will be airborne very quickly and also concussed and/or dead from bludgeoning damage.

The first recorded death of a genetically modified human ( Ambla, year 10) was initially blamed on malfunctioning pressure generators in the first settlement and intentional carelessness, though it is highly likely that aerated water being pumped into a test pool was the true culprit. In retribution, Ambla's friends sabotaged climate control systems in the settlement. This was their first act of rebellion.

1.4 Aquatic Wildlife

 

Ultimately there are no plants on Siren as settlers from Earth might know them. Instead, filling this ecological niche we have the sessile generation of the creatures which, in a different active generation, are among the fastest and most active apex predators in the vast freshwater seas of Siren. It took the first human settlers on Siren years to understand that what they were assuming were completely different animals were in fact all the same animal - and, ultimately, it brings into question the definition of 'species’ as it stands.

Tides are regular but slow; a yearly occurrence (when not a neap or spring supertide). When there is no or very little water movement (during a low tide phase), the fresh water forms strongly stratified layers, including an anoxic dead zone near the bottom. the increased water flow of a rising or falling tide increases mixing in the water, and provides enough nutrient flow for the sessile adult phase of the siphos to happily live their lives anchored to the substrate, feeding by suspension. each 'leaf’ has a feeding structure which i have not designed yet, but also uses gas exchange to create air bladders in a process not unlike photosynthesis. the bladders raise and lower the leaves in the water column to take advantage of zooplankton density (diel vertical migration).

Each leaf produces two motile clone larva which break out and swim away. It’s not uncommon for these larva to be released in a swarm when the adult sessile sipho is under attack or being eaten. The two holes in the leaves will slowly refill with the next clones. The larvae swim until they meet larvae of another sessile adult, whereupon they spawn, releasing planktonic gonads for sexual reproduction. the eggs form thick mats on the sea floor (some with an additional 'worm’ stage of joined together eggs which trundles along until it finds suitable substrate) and eventually sprout into more sessile adults.

Whether or not the larva undergo sexual or asexual reproduction depends on oxygen saturation in the water. If the water has a low saturation, it is likely due to a period of stratification in the water column (still water at high or low tide). Because there may not be enough prey for a sessile adult to get by on, it triggers the beginning of the active generation. the larva instead divides asexually and enters a kind of locust phase of rapid development into swarms of nymphs which form most of the “fish” in Siren’s seas.

The nymphs progress through several stages of development, as the water continues to settle and stratify, until ultimately they are able to leave the water. similar to dragonflies, the nymph 2 stage are the largest flying predators native to the planet, and feed mostly on smaller siphos of other species and the insect-like creatures that swarm around the coastlines. the nymphs are sexually active and can lay fast-developing eggs which will hatch into more nymphs. nymph swarms number in the trillions and are very short-lived, taking advantage of only a few weeks of ideal conditions.

during a neap or spring tide year, when the water is liable to undergo extreme, catastrophic changes, the nymph 2 stage will then become fully active adults; too heavy to fly, the adults of the active generation propel themselves via specialised hydrofoil arms. they prey mainly on nymphs of other species (though cannibalism is common) and, since the settlement of Siren, sea-dwelling or even flighted humans. with the ability to travel very far and very fast, these adults are the means by which entire species can uproot and fuck off to a more livable area if the neap tide decides to turn their aquatic home into a new continent.

They do eventually spawn and, depending on oxygen saturation, release eggs that will become nymphs or sessile adults.