Divers and snorkellers across the globe are being enlisted to help save the seas and oceans.
The cuttlefish is just one of many species a diver might encounter
They are being asked to record the health of the marine environment, including coral reefs, mangrove swamps and coastal waters, for a new project.
Divers log observations on a website for Earthdive, backed by the United Nations Environment Programme (Unep).
Founder Chris Long warned of "dire consequences for the global population" if threats such as pollution continue.
Mr Long, himself a keen diver, said: "Earthdive wants people with an interest in diving to understand that what they see in the oceans is not just beautiful, it also sustains human life, and they can help to preserve it by simply recording what they see."
Membership of Earthdive, which is supported by Unep through its World Conservation Monitoring Centre (WCMC) in Cambridge, UK, is extended to divers and snorkellers of all abilities.
The logs will record the key species and the anthropogenic - or human - impact on them, for example through tourism, litter or over-fishing.
There are 30 ecological regions across the globe and each region has its own set of five indicator species.
Anyone taking part in the project will receive briefing packs on how to do it. They will also be given information on the regions.
Earthdive director, Angela Bawtree, explained: "The divers or snorkellers will note down numbers on an underwater slate.
Divers can built a global snapshot by estimating species numbers
"There is an abundance scale that allows divers to estimate rather than provide an exact number for each species.
"For the UK, which is in the European region, for example, divers will look for all types of lobsters, John Dory, marine mussels and plaice.
"It will build a global snapshot of where species are abundant and where they are not, where they are increasing in number or decreasing over time.
"The website will also provide a good resource for divers and snorkellers, where they can look up dive sites and access other divers' logs."
In order to fully access the website, people will be asked to pay £10, £5 of which will go to selected marine conservation organisations.
Peter Raines MBE, founder of Coral Cay Conservation, another of Earthdive's partners, said: "Recreational diving is a fast-growing sport, with more than 1.5 million new divers being certified each year.
"Earthdive has a unique opportunity to unite this rapidly-growing community in vital conservation activities, which are ultimately of enormous benefit to us all."
The Earthdive website is at www.earthdive.com