From the above-mentioned site:

"8. The Price. All prices cover passage and accommodation on board the cruise ship and any port taxes. It does not include on-board catering or any other on-board service or excursions, all of which are available for separate purchase entirely at your option. Optional housekeeping is available for €15 per visit (approximately £10). All on-board services and excursions are priced in both €euros and £ sterling, and payment may be made either by credit or debit card at the time of purchase or by on-board credit account operated by the particular concessionaire. All such credit accounts must be settled in full before you leave the ship at the end of your cruise."

(emphasis added)