Bladderwrack seaweed

A recent study undertaken by Professor Juliet Brodie and the Big Seaweed Search team has been published.

The Big Seaweed Search: Evaluating a citizen science project for a difficult to identify group of organisms

Using four years of publicly collected Big Seaweed Search data, this study analysed and mapped the distribution of 14 different seaweeds. Collecting and studying this data over time allows us to spot trends in how our coastlines may be changing in response to environmental factors like sea temperature rise.

The study also showcased the amazing efforts of Big Seaweed Searchers and allowed us to review progress and make decisions on future project developments.

Student engaging in the Big Seaweed Search on Rottingdean Beach Kate Whitton

Credit: Kate Whitton

Seaweeds in the UK

The UK coast is rich in seaweed species. Seaweeds capture carbon, act as nurseries for fish, and support a diverse array of organisms. However, seaweed species are declining or disappearing altogether because of environmental change. Rising CO2 emissions, coastal pressures caused by human population growth, and consumption of finite resources, such as fossil fuels, are increasingly putting seaweeds at risk.

Monitoring of seaweed distribution and abundance has been inconsistent over time and there is limited data available to track changes. Challenges in accessing remote locations and a lack of professional seaweed scientists makes it difficult to carry out this work nationwide.

The Big Seaweed Search

To gather this data on seaweed species around the UK, the Big Seaweed Search citizen science project asks members of the public to record their observations of the state and abundance of various species. The 14 species monitored by the project are either non-native in the UK or can indicate sea temperature rise or ocean acidification.

people seaweed searching

Credit: Kate Whitton

How was the study carried out?

Data collection

Starting an hour before low tide, participants surveyed a five-metre-wide plot on a UK beach for around one hour and recorded how many of the 14 target seaweed species they spotted there. They then uploaded their findings to a website, along with photographs of the survey location and each species they spotted.


Each record was validated using the photographs provided as part of the project. Validation included confirmation that the seaweed was attached and alive and that the species had been identified correctly by the search participant.

Big seaweed search paper map

Map 1: Survey locations for accepted records

What did the research find?

  • Data from June 2016 to May 2020 were analysed (378 surveys, 1414 people, 1531 hours)
  • The highest number of surveys were carried out in the Southwest and Celtic Seas regions (43.7%) [Map 1]
  • The seaweed that was most often correctly identified was the common low shore species, Serrated wrack (Fucus serratus, 66%)
  • The least correctly identified species was the invasive species, Wakame (Undaria pinnatifida, 5%) [Graph 1]
  • Calcified crusts and coral weeds were most often recorded as patchy across survey plots
Big Seaweed Search paper

Graph 1: Correct identifications for each species (%)

What did we discover?

After verification, 1,007 data records were accepted and have been used in a Red List assessment of British seaweeds. A Red List categorises species according to how endangered or at risk from extinction they are, proving how important this data is.

Whilst some of the data could not be verified, this still provides the research team with insight into the challenges associated with the methodology design or species identification. This information can allow future work to focus on developing areas of the project to improve data quality and make the project more accessible for participants.