A new report from NatureScot and SAMS sheds light on the significant changes occurring in Scotland’s rocky intertidal zones.

The study, which surveyed 167 sites around Scotland’s coast, reveals how seaweed populations are being affected by climate change.

Here are some key findings:

1. Overall Shift Towards Warmer Water Species: The study observed a small but significant shift in community composition towards warm-water species, indicated by an increase in the Community Temperature Index (CTI) of 0.14°C. This change is in line with a slight increase in average sea surface temperatures between the 2014-2015 and 2020-2022 survey periods.

2. Changes in Specific Seaweed Species:

– The bladderless variant of bladder wrack, Fucus vesiculosus var linearis, increased at locations all around Scotland, while the normal growth form of the species decreased.

– Chondrus crispus (carrageenan or Irish moss) increased in most locations, while Mastocarpus stellatus (false Irish moss) declined in the south and west.

– Palmaria palmata (dulse) showed variable patterns, with large increases at some sites and declines elsewhere.

– Scytosiphon lomentaria (a cylindrical and hollow brown seaweed) declined everywhere except the far northwest.

3. Regional Variations: Changes were not uniform across Scotland, with the shift towards warmer water species more evident on the outer west coast.

Continuing decline of blue mussels

Another major finding of the study is the continued ongoing decline of intertidal blue mussels on rocky shores, SAMS reported. Blue mussels are a characteristic species of Scotland’s rocky shores and are an essential source of food for species such as otters, oystercatchers and starfish. The mollusc decreased in number across Scotland’s rocky shores, particularly along the southwestern and southeastern coasts. Healthy populations were only found on exposed outer coasts, such as those on Orkney and Shetland.

The study highlights the effectiveness of repeated surveys in detecting biodiversity changes and provides a crucial baseline for future monitoring.

The NatureScot Research Report – Marine Biodiversity and Climate Change (MarClim): Scotland 2020-2022 – can be found online.