rusty nut

My DW and I called our travel agent to change our dining schedule from early seating to MTD. We received the confirmation by email and noticed that the TA added "prepaid gratuities" to our reservation. This is for a 4 night cruise and the prepaid gratuities total $96.00. Is this $96 the prepaid tips for the entire cruise or is it just for the dining staff? It doesn't specify in the confirmation.