Crab Watch!

Crab Watch is a citizen science initiative developed as part of the Sea Change Project. The initiative will explore how citizen science can be used as a tool for increasing Ocean Literacy, as well as collecting valuable scientific data. Crab Watch will generate data to enhance our knowledge of the changing distribution of native and non-native crabs, as well as information to support environmental management.

Anyone finding a crab on the shore for the first time will experience a sense of excitement and wonder (and maybe a bit of trepidation if it is a particularly large one!). The goal of Crab watch is to harness this enthusiasm to encourage participation in this citizen science scheme. Crabs are charismatic, and with a little guidance can be found around Europe in all marine and some freshwater habitats. They have great commercial and cultural significance in many countries, making them a popular subject for art and folklore. They are also impacted by the activities of humans, including warming seas, invasive species and overexploitation, making them an ideal subject to help demonstrate how humans and the Ocean are inextricably linked.

Hemigrapsus sanguineus FrontView
The Asian shore crab (Hemigrapsus sanguineus) is spreading rapidly around Europe and may impact native crab populations

Several species of non-native crab, in particular the Asian shore crab (Hemigrapsus sanguineus), brush-clawed crab (Hemigrapsus takanoi), sally light-foot crab (Percnon gibbesi) and Chinese mitten crab (Eriochier sinensis) are present in multiple European countries. There is evidence to suggest that the Asian shore crab (H. sanguineus) in particular is likely to negatively impact populations of the native European shore crab (Carcinus maenas). Participation in the project aims to raise awareness of the impact of non-native species and encourage people to think more about marine biosecurity.

‘Crabbing’ is a popular past-time in the UK and it is hoped that Crab Watch will encourage other European residents to take up this hobby with the added incentive of contributing to science. Free resources will promote crab welfare and environmental good practice among ‘crabbers’ old and new. By providing encouragement to visit the sea and interact with marine creatures in a meaningful way, the scheme will encourage people to think positively about the marine environment and participants will be encouraged to explore and learn about the great diversity of life found in the Ocean.

paper plate crab
‘Crabby’ crafts at a Crab Watch event

The coastlines of Europe range from the negligible tides and sandy shores of the Mediterranean to some of the highest tidal ranges in the world on the rocky Atlantic coasts. To account for this variation, the scheme includes 3 key elements, each designed to maximise engagement and cater for people with different levels of interest and in different geographical areas. Ad-hoc recording of crabs using a specially developed App will form the core of the initiative. More in-depth and structured survey protocols have been developed for use in the intertidal zone and from the shore in areas where intertidal surveys are not possible. These methods include the crab-friendly mark and recapture method using lipstick tagging to avoid unnecessary retention of live animals. These activities will form the basis for Crab Watch events and provide a ‘next step’ for anyone engaging with the App and wanting to get more involved. By establishing a scheme to record and report crab distribution and an associated team of Crab Watchers around Europe, it is hoped that new arrivals will be quickly detected, allowing for appropriate management action.

Data collected through the app will be georeferenced and participants will be able to use their records alongside those of others to create their own maps. It will also incorporate a key, which is being developed in collaboration with a group of interested teenagers in the UK. Data collected will be checked and validated before being passed to relevant marine and wildlife data hubs (e.g. EUROBIS) where they will be freely accessible to all.

Crab Watch surveys have been taking place around Europe to test protocols and draft resources as well as to collect feedback from different audiences. The scheme will be more widely launched for resource and system testing in March 2017 with a full launch in June. The team is even exploring the idea of establishing International Crab Day to promote this wonderful group of animals!

If you are interested in getting involved with Crab Watch, in particular promoting the project or running your own Crab Watch survey events, contact Jack Sewell (

A Crab Watch survey underway on an Estuary in the south west of England in 2016