Crab Feces in Subnautica 2: Location & Bioreactor Use

In Subnautica 2, crab feces is a biofuel item that can be found near crab nests in the Twisted Shallows and used in a bioreactor to generate power, yielding more energy than most raw organic materials. You collect it by hand from the seafloor or from crab burrows, and it is a reliable early-game fuel source once you have built a bioreactor. Below is everything you need to know about finding it, using it, and avoiding common mistakes.

Formula

The energy produced by crab feces in a bioreactor is calculated as:

Total Energy (MJ) = Number of Crab Feces × 210 MJ

Each crab feces item provides 210 MJ of energy when burned in a bioreactor. The burn time is 1.5 minutes per item, so the total burn time is simply the number of items multiplied by 1.5 minutes. In the calculator above, enter how many crab feces you have, and it will show the total energy and total burn time.

Worked Example

Using the default value of 1 crab feces:

• Energy = 1 × 210 MJ = 210 MJ
• Burn time = 1 × 1.5 min = 1.5 minutes

So one crab feces gives you 210 MJ of power, which lasts for 1.5 minutes. If you have 10, you get 2100 MJ for 15 minutes.

What Is Crab Feces in Subnautica 2?

Crab feces is a type of biofuel introduced in Subnautica 2 (currently in early access). It is a brown, lumpy item that drops from the large crab-like creatures that inhabit the Twisted Shallows biome. Unlike some other organic materials, it has no use in crafting or cooking—it exists purely as a fuel source for bioreactors.

In the game’s lore, crab feces is the waste product of the local crab population. It is rich in organic matter, making it an excellent source of energy when processed in a bioreactor. It is one of the few items that can be stacked in your inventory (up to 10 per slot), which makes it convenient to collect in bulk.

Where to Find Crab Feces

Crab feces is found exclusively in the Twisted Shallows biome, which is the starting area of the game. You can locate it in two ways:

• On the seafloor: Look for small brown piles on the sandy bottom, often near crab nests or under overhangs.
• Inside crab burrows: Some crabs dig burrows into the terrain; you can sometimes find feces inside those burrows.

The best method is to follow the crabs themselves. They tend to wander in specific areas, and they drop feces periodically. If you see a crab, wait a moment—it may leave a fresh pile behind. You can also check the areas where crabs are most active, such as near the wreck of the Meridian or around the large coral arches.

There is no need for a tool to collect it; just swim up and press the interact button. It does not require a knife or scanner.

How to Use Crab Feces in a Bioreactor

To use crab feces as fuel, you first need to build a bioreactor. The bioreactor blueprint is unlocked early in the game, and you can construct it with:

• Titanium (x3)
• Quartz (x1)
• Copper Ore (x1)

Once built, place the bioreactor in your base or on a foundation. Open its inventory and drag crab feces from your inventory into the bioreactor’s storage slot. The bioreactor will automatically start burning the fuel and generating power for your base. The power output is 210 MJ per item, which is enough to run most early-game equipment for a short time.

One important detail: the bioreactor burns items one at a time. If you put in 10 crab feces, it will burn them sequentially, providing power for 15 minutes total. You can add more fuel at any time, even while it is running.

Common Problems and Mistakes

Players often confuse crab feces with other organic items like fish or kelp. While those also work in a bioreactor, they yield much less energy (fish give 80 MJ, kelp gives 50 MJ). Always check the item description—crab feces is specifically labeled as “high-energy biofuel.�

Another common mistake is trying to use crab feces in a fabricator or as a food source. It is not edible and cannot be used in any crafting recipe. Do not waste inventory space carrying it if you don’t have a bioreactor yet.

Also, note that crab feces despawns after a while if left on the seafloor. If you see a pile, collect it immediately. If you are farming, it’s better to collect in short trips rather than leaving piles to accumulate.

Comparisons to Other Biofuels

When deciding what to feed your bioreactor, consider the energy per inventory slot:

• Crab feces: 210 MJ per slot (stack of 10)
• Fish (e.g., Peeper): 80 MJ per item, but only 1 per slot
• Kelp: 50 MJ per item, stacks to 10
• Acid mushrooms: 100 MJ per item, stacks to 10

Crab feces is one of the most efficient stackable fuels. A full stack of 10 gives 2100 MJ, which is enough to power a small base with a fabricator and a light for about 15 minutes. In contrast, a stack of kelp gives only 500 MJ. The only downside is that crab feces is location-specific—you must return to the Twisted Shallows to get more.

Frequently Asked Questions

Can crab feces be used for anything other than bioreactor fuel?

No. As of the current early access version, crab feces has no other use. It cannot be eaten, crafted into items, or used in the fabricator. Its sole purpose is as a biofuel.

Does crab feces respawn?

Yes, crab feces respawns over time. The crabs continue to produce waste, so new piles appear in the same general areas. However, the respawn timer is not immediate; you may need to leave the biome and return after a few in-game days.

How much energy does a bioreactor need to run a base?

The energy requirement depends on what you have connected. A basic base with a fabricator and a light consumes about 10 MJ per minute. So one crab feces (210 MJ) would run that for 21 minutes. Larger bases with water filtration or scanners will drain faster.

Can I use crab feces in a nuclear reactor?

No, nuclear reactors require uranium fuel rods. Crab feces is only compatible with bioreactors.

Is crab feces affected by the “organic� upgrade for bioreactors?

Yes, if you install the “Organic Efficiency� upgrade module, the energy yield from all organic materials, including crab feces, increases by 50%. That would make each crab feces produce 315 MJ instead of 210 MJ.

Safety and Storage Tips

While crab feces is not dangerous to handle, it is a biological material, so it is wise to store it in a dedicated locker near your bioreactor. This keeps your inventory free and prevents accidental use. Also, if you are exploring deep areas, remember that crab feces is heavy—each item takes one inventory slot, so don’t over-collect unless you have a plan to use it.

In terms of game safety, the crabs that produce the feces are not hostile unless provoked. They will attack if you get too close, so it’s best to collect feces after the crab has moved away. Keep a safe distance and use a stasis rifle if you need to immobilize them for easier collection.

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in t | Number of crab feces | - | 1 | 0 | 100
out energy | Total energy (MJ) | MJ | t * 210 | 0
out time | Burn time (min) | min | t * 1.5 | 1