Necrolei Creature Guide and Details | Subnautica 2

Seeing these indicate that the ecosystem is in poor health.

Anthobrachia necrolei. A clonal stalk of large jellies, similar to Earth's stauromedusae. Each jelly remains moonred to the stalk, rather than maturing into a free-swimming medusa.

[1] Enormous size and hunger
Rather than feeding on prey, the necrolei gathers dead matter from the seawater. The size and height of the stalk are directly related to the rate of death and decary up-current.

[2] Acid-yielding metabolism
The necrolei has adapted to low-oxygen seawater. It ferments much of the matter it collects in a central 'basket' stomach, a process which requires no oxygen and yields strong acids. The necrolei concentrates these acids around its eggs as a defense.

Assessment: large numbers of necrolei in this region indicate a bloom, a population explosion caused by a flood of nutrients. This is a poor sign for the health of the ecosystem and perhaps for the state of the global climate.

Produces egg clusters that can be processed into strong acid.

While there are still other creatures present, when you see these, there will be little other life in the area.