Complex sentence: Recent studies have shown that "Postelsia" grows in greater numbers when such competition exists-a control group with no competition produced fewer offspring than an experimental group with mussels; from this it is thought that the mussels provide protection for the developing gametophytes.
Split into simpler sentences: Recent studies have shown that "Postelsia" grows in greater numbers when such competition exists. A control group with no competition produced fewer offspring than an experimental group with mussels; from this it is thought that the mussels provide protection for the developing gametophytes.