The problem confronting terrestrial snakes is best illustrated by what happens to sea snakes when removed from their supportive medium.
1. 纠正网友的说法,这里没有疑问句。what 引导的名词性关系分句。what 等于 the thing that。
2. when removed...的逻辑主语是前文的 sea snakes 一致,符合状语从句省略成分的原则。即省去了 they are。