oh no!!! hermits facing death!

gerald's hermit crab passed away last night! can you believe? now i really wonder if i have the skill or the required basic cabitat for my 3 little buddies to stay alive and wander around. indeed, marine animals are hard to please. but one thing remains a mystery, why did gerald's hermit crab died given the cabitat? is it the lack of sun since the shore is always facing the sun's glare? or food? or temperature?