iNaturalist Southwest Coastal records in 2025

Summary

This report synthesises iNaturalist observations from the South West coast of England, with particular focus on records submitted during 2025. Contributions from structured citizen-science initiatives, particularly the Big Rock Pool Challenge, account for a substantial proportion of this increase. While observation counts do not represent population size, the data can reveal clear patterns in recording intensity, species detection, and emerging biodiversity signals.

Data Source and Scope

All data analysed in this report were obtained from iNaturalist, an open, global biodiversity data platform that enables users to record, photograph, and identify species observations. Records are supported by photographic evidence and undergo community review, providing a transparent and verifiable data source.

iNaturalist data do not derive from systematic survey designs and therefore reflect patterns of observer effort as well as species occurrence. However, the scale, accessibility, and temporal resolution of the platform make it a powerful repository for examining changes in biodiversity recording, detecting novel or rare occurrences, and supporting regional ecological assessments.

South west coastal records in 2025

This section quantifies the total number of iNaturalist observations recorded from the South West coast during 2025 and compares them with records accumulated prior to 2025.

There were 51,778 iNaturalist records from the South West coast in 2025, compared with 107,412 records accumulated prior to 2025.
The number of records added in 2025 corresponds to 48.2% of the total number of records accumulated before 2025.

Top 10 species recorded on the Southwest Coast in 2025

The Top 10 species with the highest number of records on the SW coast in 2025 are shown in the table below.

Photo	Common Name	Latin Name	Count
	European Green Crab	Carcinus maenas	814
	Atlantic Beadlet Anemone	Actinia equina	800
	snakelocks anemone	Anemonia viridis	669
	Montagu’s Crab	Xantho hydrophilus	568
	Cushion Star	Asterina gibbosa	439
	Purple Topshell	Steromphala umbilicalis	438
	Strawberry Anemone	Actinia fragacea	432
	Atlantic Dogwhelk	Nucella lapillus	404
	Edible Crab	Cancer pagurus	402
	Lined Top Shell	Phorcus lineatus	348

The Big Rock Pool Challenge

Run by The Rock Pool Project, the Big Rock Pool Challenge returns to the same site once every month, and records are collected using iNaturalist in free public competitive BioBlitz Battle games.

Here, the number of observations added in 2025 are summarised, and compared with earlier project records, and species recorded by the project for the first time in 2025 are identified.

These results demonstrate how structured, repeat-visit citizen-science initiatives can substantially enhance the value of open biodiversity platforms such as iNaturalist, both by increasing record volume and by expanding documented species richness.

Full Big Rock Pool Challenge records for 2025 can be explored on iNaturalist.

The Big Rock Pool Challenge recorded 9,200 iNaturalist records from surveys at hubs on the South West coast in 2025, compared with 1,865 records accumulated prior to 2025.
The number of records added in 2025 corresponds to 493.3% of the total number of records accumulated by the project before 2025.

There were 417 species recorded for the project for the first time in 2025.

Top 10 species recorded in Big Rock Pool Challenge surveys on the Southwest coast in 2025

The 10 species with the highest number of records from the Big Rock Pool Challenge in 2025 are listed below.

Photo	Common Name	Latin Name	Count
	European Green Crab	Carcinus maenas	388
	Atlantic Beadlet Anemone	Actinia equina	383
	Montagu’s Crab	Xantho hydrophilus	329
	snakelocks anemone	Anemonia viridis	327
	Strawberry Anemone	Actinia fragacea	237
	Cushion Star	Asterina gibbosa	227
	Atlantic Dogwhelk	Nucella lapillus	226
	Purple Topshell	Steromphala umbilicalis	196
	Common Coralline	Corallina officinalis	194
	Edible Crab	Cancer pagurus	185

New South West coast species for 2025

178 species were recorded on iNaturalist on the South West coast for the first time in 2025. Notable examples include Spurilla neapolitana (16 records), Fucellia (8 records), Maeridae (7 records), Tubularia (6 records), Sertularella (4 records).

The appearance of these species in 2025 highlights the value of iNaturalist as a dynamic biodiversity data repository, capable of capturing emerging records of both conspicuous and previously under-recorded marine taxa through sustained public participation.

As with all opportunistic citizen-science data, first records on iNaturalist may not necessarily indicate recent arrival, but do provide an important timestamp for when species become observable, identifiable, and verifiable at regional scale.

Species with highest standardised change

Here, standardised change for pre-2025 and 2025 record counts is presented to allow comparison of relative change among marine species with different baseline frequencies (ie. relatively more rare or more common).

Standardised change values allow comparison among species with very different baseline frequencies by scaling change relative to previous recording levels.

Species increases

Below are presented the 10 species with the highest standardised increase in records in 2025 compared with records in previous years.

Figure 1: Species with highest increases in iNaturalist records in 2025 compared with pre-2025 records, according to standardised change

Species decreases

In 2025, several coastal species showed relative declines in records on the Southwest coast, Those with the highest decreases in records are presented below.

Figure 2: Species with highest decreases in iNaturalist records in 2025 compared with pre-2025 records, according to standardised change.

Several rocky shore species show declines relative to expected records in 2025, including common spider crab Maja brachydactyla, common starfish Asterias rubens, bladder wrack Fucus vesiculosus and blue-rayed limpet Patella pellucida.

Full records of standardised change values for Southwest coastal species may be found here.

Notable species changes in 2025

There were several coastal species which have been highlighted in media and by anecdotal reports as having particular notable changes in abundance in 2025 compared with previous years. Here, we investigate these reports in the context of iNaturalist records in 2025 compared with previous years, and present standardised change values for each species. These values can be used to provide context to reported apparent dramatic increases or decreases in records of these species.

Common Octopus Octopus vulgaris

In 2025, 25 records of Octopus vulgaris were submitted on iNaturalist, compared with 7 records prior to 2025, representing a standardised increase of 4.2 (SES = 4.2).

European lobster Homarus gammarus

In 2025, 34 records of Homarus gammarus were submitted on iNaturalist, compared with 79 records prior to 2025, representing a standardised decrease of 2.27 (SES = -2.27).

Furrowed crab Xantho hydrophilus

In 2025, 568 records of Xantho hydrophilus were submitted on iNaturalist, compared with 623 records prior to 2025, representing a standardised increase of 5.18 (SES = 5.18).

Sea slugs

Hair curler sea slug Spurilla neapolitana

In 2025, 16 records of Spurilla neapolitana were submitted on iNaturalist, compared with none prior to 2025, representing a standardised increase (SES = 5.15).

Depilatory seahare Aplysia depilans

In 2025, 2 records of Aplysia depilans were submitted on iNaturalist, compared with none prior to 2025, representing a standardised increase (SES = 1.7).

Rainbow seaslug Babakina anadoni

In 2025, 25 records of Babakina anadoni were submitted on iNaturalist, compared with 3 records prior to 2025, representing a standardised increase of 5.08 (SES = 5.08).

Sea hare: Aplysia punctata

In 2025, 217 records of Aplysia punctata were submitted on iNaturalist, compared with 139 records prior to 2025, representing a standardised increase of 7.97 (SES = 7.97).

Non-native species

iNaturalist can be a powerful tool for early indication and monitoring of established and emerging introductions of non-native species. Records collected in 2025 by iNaturalist users provide useful information about the presence of non-native species on the Southwest coast. Several key species are highlighted below.

Pacific oyster Magallana gigas

In 2025, 144 records of Magallana gigas were submitted on iNaturalist, compared with 192 records prior to 2025, representing a standardised increase of 0.93 (SES = 0.93).

Wireweed Sargassum muticum

In 2025, 234 records of Sargassum muticum were submitted on iNaturalist, compared with 246 records prior to 2025, representing a standardised increase of 3.8 (SES = 3.8).

Red ripple bryozoan Watersipora subatra

In 2025, 113 records of Watersipora subatra were submitted on iNaturalist, compared with 78 records prior to 2025, representing a standardised increase of 5.51 (SES = 5.51).

Figure 3: Geographic spread of species records for notable species on the Southwest coast in 2025 (toggle specific species on and off using check boxes)

A note on iNaturalist

Although iNaturalist data are influenced by observer behaviour and do not replace systematic ecological surveys, the platform represents a uniquely powerful and transparent repository for regional biodiversity information. When analysed carefully, these data provide valuable insights into recording effort, species detectability, and emerging patterns that can inform conservation awareness, guide future monitoring, and support community engagement with coastal biodiversity.