Several hundred dead gumboot chitons

At Monterey State Beach near the municipal wharf. Today's tide was very low and there were several hundred dead gumboot chitons washed up on the sand. I also saw close to a hundred dead leather stars and knobby stars, two dead decorator crabs, and what i think was a dead sea hare. There weren't any more dead molas like I saw a month or so ago. Any idea what causes these mass die offs?