Tiles take damage despite being surrounded by liquid.

Tiles are damaged under high pressure environments:
https://oxygennotincluded.wiki.gg/wiki/Liquid#Pressure_Damage
This behavior is consistent with the game to date, your salt water at 1334.1kg (the cell you've highlighted) is 234.1kg above it's pressure threshold of 1100.

There are a few things you can do to avoid this. But this problem does invite the opportunity to consider a new  "aquatic farm" tile that is Mesh and (potentially) allows the plant to get liquid fertilizer from the environment.

Changed Status to Fixed

• Liquid pressure damage now takes into consideration liquid pressure from the opposite side of a wall, so tiles surrounded by liquid will not be damaged as easily.