Seagrass on the seabed at Holy Loch is defying the odds by making a spectacular comeback according to a recently published report in the Glasgow Naturalist.
Holy Loch, which feeds into the Firth of Clyde, was once a biodiverse marine habitat but was severely affected during the mid-to-late 20th century with the presence of a U.S. Navy submarine base.
Dredging and chemical contamination, particularly with copper and zinc as well as agricultural and forestry run-off, are thought to have led to the local disappearance of seagrass beds around the shores of the loch.
Native seagrass species have declined sharply in the UK over the past century due to coastal development, pollution, physical disturbances due to anchoring and dredging, and disease outbreaks. Indeed, recent estimates suggest that over 90% of seagrass cover has been lost in the last one hundred years.
The comprehensive report, entitled ‘Natural regeneration of the seagrass Zostera noltii in the Holy Loch, Argyll, Scotland’ has been compiled by Dr Neil Hammatt and Phil Rawlins.
Dr Neil Hammatt, Holy Loch Nature Reserve warden and the report’s co-author, explained: “Seagrasses have a vital role to play in marine ecosystems. They stabilise sediments, cycle nutrients and provide a nursery habitat that encourages the repopulation of fish and invertebrates.
“Crucially, they also capture carbon which plays a major role in mitigating climate change.
“Since the base closed in 1992, the loch has experienced gradual ecological improvement, though no active restoration of seagrass has been undertaken.
“This report details the findings of a survey in mid-2025 that identified natural regeneration of Z. noltii within the Holy Loch. The first few stems were noticed in 2022.
“Since then, area expansion has occurred and beds have become denser. Most recent UK examples of seagrass growth have relied on planting efforts but this regeneration appears to be spontaneous and the discovery provides valuable information as to the conditions under which passive recovery may occur as well as underscoring the importance of protecting such areas.
“Approximately 20 hectares of loch bed were surveyed at low tide with types of sediment, vegetation cover and visible signs of seagrass presence recorded.
“Given the history of industrial contamination on Holy Loch, these findings are ecologically significant, and we suggest that dispersal from nearby lochs, such as Loch Long or Gare Loch via tidal currents may have contributed to the propagation.
“Ultimately, this is evidence of nature’s ability, when left to its own devices, to bounce back from environmental degradation and is good news when it comes to tackling climate change,” added Dr Hammatt.
