For some reason, my mermaids have gone vegetarian - ethics, the decline in fish species, or they’re just no longer in the mood for meat. The main issue: will they survive?

They live in coastal saltwater areas, rather than being deep-sea creatures, and can only be in air for the same length of time as a human can be underwater (probably 1-2 minutes; you’ll get the odd ‘freediving’ mermaid who can go for much longer, but that’s an anomaly), and they really struggle to move around when not in water, so gathering anything from the land is probably going to be limited. There’s also no trade between merfolk and humans, so they can only rely on what they find, forage, or grow themselves.

What could they eat that will give them enough calorific intake to survive? (Assuming the same 2,000-2,500 kcal intake advised for normal humans). I’m not fussed about geographic location, so if there’s a region of (present-day) Earth better suited to support their existence, that’s fine.

I’ve pictured them as wanderers rather than settled, so a hunter-gatherer approach is more what I had in mind. However, I’m happy to be persuaded if an agricultural society would be more conducive to their new way of living.

Ideally, I’d like my merfolk not to need to spend 14 hours of every day eating (like pandas) just to get what they need, while also having a nutritionally complete diet. If there’s something that’s calorie dense but isn’t necessarily balanced, then I’ll take that. And if this vegetarian lifestyle isn’t going to work, I’ll just have to convince them to go back to omnivorousness.


Sorry, forgot to include this: I’ve had a look at this question, but while it mentions herbivorous merfolk, it seems to be less interested in the constitution of their diet.

  • $\begingroup$ "a hunter-gatherer approach is more what I had in mind." That's a bit contradictory, no? $\endgroup$
    – RonJohn
    Dec 7, 2018 at 17:20
  • $\begingroup$ @RonJohn - fair point. I could pretend that I’d meant that to refer to their previous existence (therefore the lifestyle that they’re used to), but I honestly didn’t spot it. Thanks for noticing! $\endgroup$ Dec 7, 2018 at 17:33
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    $\begingroup$ The problem with a vegatarian diet particularly a restricted one is making sure you consume all the vitamins that you need. Some are quite ease to replace but others such as B12 more difficult. Of course your merfolk arn't human they will need a different set of vitamins to us. $\endgroup$
    – Sarriesfan
    Dec 7, 2018 at 19:27
  • $\begingroup$ Vegimite maybe? $\endgroup$
    – dot_Sp0T
    Dec 9, 2018 at 7:21
  • $\begingroup$ @Sarriesfan B12 is produced by fecal bacteria, sea water and any stream wild water has B12, in incredibly high quantities actually because it contains bird's and fish feces. No animal contains naturally B12 in their flesh, in the modern world people get their B12 because it is injected in animals but before the modern era we used to get it by eating veggies and drinking wild water. reddit.com/r/vegan/comments/7ujsaf/… . $\endgroup$
    – user58325
    Dec 14, 2018 at 13:51

4 Answers 4


Seaweed is definitely the way to go

There are many types of seaweed and they vary in protein and calories, among other things. They will have less bulk if dried, which is very easy to do. If the mermaids can build things, they can create floating drying racks that are tethered. The lower tech method would be to find some flat rocks that are never underwater, then farm or harvest during high tide for better access.

Dried seaweed will not reconstitute immediately so it will still be concentrated, even if the mermaids have to eat it underwater.

The protein content of our sea vegetables ranges from to 16% to 28%. The red sea vegetables, Dulse and Laver, are higher than the browns, Kelp and Alaria. The amino acid composition of these sea veggie proteins is generally well balanced and contains all or most of the essential amino acids (the ones your body can't produce by itself). Thus the sea veggies provide higher quality protein than certain grains and beans that are lacking one or two essential amino acids, although the sea vegetables provide less quantity per serving. (from Maine Coast Sea Vegetables, one of my favorite suppliers.)

Laver appears to be highest in calories of the seaweeds commonly eaten by humans. It's used to produce nori.

100 grams (about 3.5 oz) of raw laver contains:
35 calories
5.81 grams protein

100 grams (about 3.5 oz) of dried laver/nori contains:
400 calories
40 grams protein

To get 2500 calories, they'd need to eat 625 grams (22 oz) of dried nori seaweed. That's really not hard. They'd end up with too much protein this way too, 250 grams. (It's not a dangerous too much, but it's more than they need.)

But wait, there's more!

Seagull eggs might be something they could harvest, though most gulls would build their nests too far away to reach. They actually contain a lot of Vitamin D (while the mermaids get a fair bit of sun, they might have higher Vit D requirements because they're usually underwater and their evolutionary diet would include a lot of Vit D rich seafoods).

Seagull eggs are high in calories and protein too. One seagull egg is the equivalent of 3 medium chicken eggs.

1 seagull egg (3 medium chicken eggs) contain:
189 calories
16.58 grams protein

Add to this caches of fish eggs on the beach or elsewhere (already laid eggs that do not require killing a fish) and a few herbs, leaves, roots, fruits, etc that they can harvest from the shore.

With time, they can also start some gardens of plants that can live right next to the water but aren't there in large quantities. This means that their diet after 2-5 years will be more varied than their diet in the beginning, allowing for a transition if they prefer.

So, yes, this is quite doable.

  • $\begingroup$ "They will have less bulk if dried, which is very easy to do." How easy is it when you can only come out of the water for a minute or two at a time? $\endgroup$ Dec 10, 2018 at 16:44
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    $\begingroup$ Very easy. Collecting the seaweed is all done in the water. Hauling the seaweed to the drying location is also easy (especially if they've repurposed a human's lost fishing net). The drying location is a warm sunny area. At high tide they can bring the seaweed to the beach just above the hide tide line or on flat(ish) rocks that never go completely under water. Or they can repurpose or even build (if possible) floating drying racks that are tethered to buoys or other locations. These are all ways humans have dried seaweed for much of history. $\endgroup$
    – Cyn
    Dec 10, 2018 at 16:52
  • $\begingroup$ @Cyn Drying food makes no sense because even tough it weights less, inside the stomach it will occupy the same space by absorbing the liquids, it's like eating dried sponges. $\endgroup$
    – user58325
    Dec 14, 2018 at 13:47
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    $\begingroup$ @Hollow, Dried seaweed takes a lot less time to eat than raw seaweed (they're both "raw" but you know what I mean). It satisfies the requirement that the mermaids not spend all day eating. One's stomach doesn't reconstitute dried food to the same water proportions as before. I am not bloated after eating sushi rolls, or dried fruit. Eating crackers and beef jerky doesn't fill the stomach like eating several roast beef sandwiches. $\endgroup$
    – Cyn
    Dec 14, 2018 at 15:13

While there are a variety of possible foods for a vegetarian mermaid, the bulk of their diet is probably going to be seaweed of different varieties as that is going to be the easiest and quickest to harvest in bulk (as opposed to something like algae).

To pick one example, kelp gives about 43 calories per a 100g serving (raw). So that would be approx. 5.8 kg of seaweed a day to get 2,500 calories.

The average human consumes about 2.5 kg of cooked food a day, but we also consume about 4kg of water.

  • $\begingroup$ Gorillas spend a lot of time chewing roughage with their big molars, large jaw muscles and small craniums. These mermaids won't have time to do much else, either... $\endgroup$
    – RonJohn
    Dec 7, 2018 at 17:19
  • $\begingroup$ @RonJohn I've been to japanese restaurants many times, particularly all you can eat ones, I can eat 1kg of seaweed salads (raw seaweed) in less than 20 minutes... you don't actually have to chew it, I've even ate bamboo there, it's quite tender and easy to eat. Gorillas are just lazy. $\endgroup$
    – user58325
    Dec 14, 2018 at 13:59

Since they are coastal mermaids there are many more options. One of the best would be mangrove tree fruits. These are easily reachable from the water and can also often be found floating in the water. Sea grape trees are coastal and could possibly be reachable within a a few minutes. Any plant that grows near the water has a chance of falling or blowing into the water and thus being collected, so things like coconuts would be accessible. Seaweed type plants of various species, and various algae. A google search of "fruit that grows at the beach" brings up some interesting possibilities as well.

Possibly these mermaids have learned how to cultivate the land plant closer to the water. Those who were able to train their selves to be on land for the maximum amount of time have brought the plant closer to the waters edge. Also, they have developed tools using things like sticks and rope which can pull the edible parts of the plants in without going on land.


The original mermaids were actually manatees, and they feed on kelp.

So, TL;DR of the other answers: they may live on kelp.

If you want a more varied diet, I suggedt playing a videogame called Acquaria. You control a marine humanoid - kinda like a mermaid with legs - and cooking is part of the game. Some dishes are vegetarian. Here is the list of recipes from a wikia site, just ignore recipes with meat in them.

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    $\begingroup$ Kelp, not kelpie. A kelpie is NOT a kind of seaweed, it's a creature like the nixie or selkie. (Or an Australian dog breed...) $\endgroup$
    – jamesqf
    Dec 8, 2018 at 5:52

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