Anyone know what this could be attributed to? The cracking inside the front compartment under the bed. Its only cracked on the port side internally and the gel coat is spider cracking around the external area as well. How serious is it and how should I fix it?

Drill a 1/8" hole into the stringer at the point of attachment close to both ends. Inspect the wood.....deteriorated....black.....like dust.....wet?
Any of those means rot from fresh ( not salt) water. If no, then grind it out and replace with another piece of the same dimension and bond it to the hull. It is (slightly) possible they originally put in in dry or with a mix at the top end of kicking.

Small job.

If wet...black....powder...big job. Cut until you find good wood...could go on and on....