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177

Blue Hole In the waters near your island, there is a place where no merfolk dares swim. It is an underwater sinkhole. Legend says that at the bottom dwells the god of death. Any merfolk who attempts to swim down to the bottom finds that, less than halfway down, their gills can no longer bring them enough air to breathe: they either drown, or frantically ...


78

A mermaid that "realistically" evolved would look very different from the traditional mermaid in many ways. But let's assume that your mermaids do look like the classic type. Why do they have hair? Option one: Sexual selection Your mermaids evolved from a human-like species. The hair was so important to their mating process that it remained even as other ...


77

I'm sorry to disappoint you but they wouldn't look like anything special. Unlike crafts designed to operate underwater, these supermarines (yes, that is indeed what they are called, I will have my +1, thank you) would not need to contend with enormous pressures. Further more these supermarines would not need any fancy mechanisms to keep the water sealed. ...


67

Sky Burial (or rather the undersea equivalent) Certain cultures in south Asia have a practice which is termed sky burial. Basically, the dead bodies are taken to a remote location (normally high on mountains) and left for scavengers. In contrast to Western culture where scavengers are viewed as evil and unclean, in cultures with sky burial the particular ...


49

From the point of view of propulsion there is no real advantage either way. The orientation of fish as opposed to marine mammals is almost certainly an accident of evolution rather than a positive adaptation. There are a few cases (stingrays, flatfish, etc) where orientation matters and in those cases it's evolved to the behavior that is useful for that ...


43

When I think of real people with long hair under water, I think of a large cloud of hair. That kind of obfuscation could be quite an advantage against any predator that likes to strike quickly and forcefully. For bonus points, the more mermaids there are, the bigger the cloud of hair. At this point, I'm thinking of zebras and the striped blur the herd ...


43

A mercenary war. You are not going to win this fight human to merfolk. But as you mentioned the merfolk are not a unified people. There are warring tribes. You also have technology that they don't have. You can make leather armor and metal weapons. Send your diplomats. Find the most hated, misplaced tribe. Maybe there is an uncle that believes he deserves ...


42

Why would a mermaid have a blowhole? A blowhole is a cetacean's nose, where as mermaids are generally depicted as having human-like facial features including a nose. Remember that you don't need to tread water in an upright position to breathe, you could also breathe on your back. If mermaids have any different sort of respiratory apparatus to humans, then ...


40

Mermaids perform surgery like this: The patient is laid out on a table with the body part to be operated on at the highest point. A transparent sea shell is then lowered over the target area. Clean air, brought from the surface in shells, is released under the shell until the entire area is "dry". This prevents the blood from clouding the water above the ...


38

It makes more sense if we consider mermaids to be the origin for the siren legend. In this legend sirens/mermaids called to sailors and fooled them into wrecking their boats on reefs or cliffs. Presumably, the sailors then become food for the mermaids. In order for this deception to work, they have to look like beautiful women, and beautiful women have ...


36

Quipu is an option. This was the Andean "writing" system, which consisted of colored string with coded knot patterns. Supposedly Hawaiians and Chinese also experimented with similar schemes. That ought to work just fine underwater. It was pointed out in the comments that this would require access to some kind of fiber with which to make string that would ...


35

Wouldn't sinking the bodies in waters around the island have negative effects on local marine life? Quite the contrary. While dead organisms release potentially toxic amounts of nitrites and phosphates in a closed ecosystem such as an aquarium, larger marine ecosystems actually depend on this circle of life-- like trees do for our air, algae feeds off of ...


34

Gills and lungs are a lot like each other, from a physiological point of view. They are highly vascularized, and have a large surface-to-volume ratio, so as to have as much gas exchange efficiency as possible. Lungs work well for air because they allow ventilation through air pumping. Expand to pull oxygen-rich air in, contract to push oxygen-poor air out. ...


32

Make open water access difficult. If the merpeople need to breath air, then what they need is a very defensible surface entrance to their city. A deep cave with a single entrance near the surface allows for simple surface defences while maintaining underwater access. With the entrance being surrounded by a reef or an atoll, any invaders must wade through ...


31

When I was a kid I remember there were two types of amateur apnea fishermen: those who knew how to catch an octopus out of his lair using an harpoon those who had no clue how to use an harpoon, and relied on copper(II) sulfate. Spreading it in front of the octopus lair forced the animal to escape it and become an easy prey. Your middle ages men are in the ...


31

If you can live with the drag, hang long lines from the bow of the ship having sharp barbs. The merfolk would need to deal with them before cutting through the hull or be cut up. Mount short blades (10" - 20") along the hull. Of course, this would lacerate anything else that comes near the ship, too. Double-hull the ship and fill the space between with ...


30

A walrus A hippo Both of them can swim much faster than a human being, despite the clumsy looking proportions and giant weights. Next are the winners of different length swimming contests in Dubai 2010 (FINA) as stated on the wikipedia page. I am only posting their names and not their swimsuit images to evade creating controversy here. Ranomi ...


30

Basically everything that you thrust. The issue with underwater combat is, as you mention yourself, the drag. Thus every weapon that relies on swinging or other movement in order to abuse its weight to make it hit harder will be at a disadvantage due to it being harder to move it against the water. Everything you thrust straight forward though will be very ...


29

Very interesting. Cooking was an important thing in our evolution. By essentially moving part of our digestive system outside our bodies, we lost chewing muscles and got more nourishment extraction with a smaller digestive system. Experiments show that people trying to live on raw food like chimps will give up, not finish their day's ration and get sore, ...


28

I'd favor the horizontal case, largely because it cooperates properly with the rest of a humanoid body, regardless of whether it's a fishtail or not. For proper swimming motion, they'd have to have the plane of their tail fin aligned with the plane of their body, like this: Fish in general might also have a fusiform body, like this: which doesn't strictly ...


26

So, it's really hard to breathe water. The biggest problem is not where the gills are on your body but instead how gills might exist at all. The fundamental limit you'll run into when designing something like this, whether it's through biological engineering or something like artificial gills is that water only has so much oxygen in it- around 10 mg/L. ...


25

There are a bunch of options, each with benefits and drawbacks. And don't forget that the merfolk are smart too. So here's a few things to chew on: 1: Just plate the hulls with metal. It doesn't need to be thick, just hardened. Coral and stone tools have a difficult time cutting wood. A thin plating of metal would prevent them from finding purchase at ...


25

Why dispose of them? Life under the sea is difficult. Acquiring enough nutrients to survive is always done at great difficulty. It's not like they can plant their food like humans do. They must constantly hunt fish, scavenge or gather whatever they can, and, occasionally, trade with the humans nearby. Therefore, when one of them tragically dies, they don't ...


23

Crypt. source On the island is an ancient building which the merfolk now use as a crypt. It was not built by the humans who live there now, nor was it built by the merfolk; its builders are long gone and it is not known what manner of beings they were, why they built or what it was originally for. It may have originally been completely underwater, and ...


22

Think Venice (but with the water kept clean and non-polluted). The city could actually be built out over the sea so regular currents go through the canals to keep them clean. Alternatively if the merfolk can breath and survive in fresh water then rivers could be channeled through the city to help keep it clean. The lower parts of the buildings would ...


22

When we were first getting into space, we started with very fast, high-flying aircraft. Look at the X series of rocket-powered aircraft used by NASA to test all sorts of things related to space travel. For us, it was a logical step to first be able to get into the air, and then get into space from there. For an underwater species, there would be a third ...


22

Let me list a few ideas: Metal products. It is very unlikely that there would be many merfolk willing to spend prolonged periods of time outside of water just to craft metal objects. Metal products can be many, from weapons(most likely harpoons, or other weapons that are meant to stab) to tools, jewelry and ornaments. While rare, you don't need to use much ...


21

A clean room makes just as much sense underwater as on dry land. Just fill a room with purified and oxygenated saline/water. Mount some pumps outside with a reserve of additional purified and oxygenated saline/water and pump it in as needed to wash away the stale and blood contaminated water. As for maintaining vascular blood pressure,... clamps and ...


21

Long hair is inherited from the common ancestors of humans and merpeople. In-hair-itance As whales evolved from an ancestor of the hippopotamus and manatees from an ancestor of the elephant, merpeople evolved from an ancestor of humans. Thus merpeople are a hominin species with aquatic adapted physiology and joined legs. DJMethaneMan's answer to "Why ...


21

1. Science/because we can The main reason we haven't already tried that in real life is moral. It is considered wrong to alter the human DNA. Remove that moral bias and there is no reason why scientists would not try to create humans that can live under water or fly or have scales and are super strong... And that is the problem with that reason. You ether ...


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