A team led by Bangor University alumni and Te Herenga Waka–Victoria University of Wellington Professor of Marine Biology, James Bell including Professor Rob McAllen from University College Cork and Professor John Turner from the School of Ocean Sciences, Bangor has been studying the loss of possibly thousands of sponges from the underwater cliffs inside Lough Hyne (Loch Oighinn). The team secured funding from the National Parks and Wildlife Service of the Irish Government's Department of Housing, Local Government and Heritage, to study this unusual event.
While it remains unclear why so many of these sponges experienced such a strong decline in numbers between about 2010 and 2015, in the past couple of years, there have been signs of a potential natural recovery of the affected species.
In a recent paper published in Science of the Total Environment, the authors discuss the possible reasons for the drop in numbers and the implications for life in other temperate mesophotic ecosystems (TMEs), a layer of the sea floor typically extending from about 20 metres to 30m below the surface to 150m, and home for numerous invertebrates like sponges, sea fans and sea anemones.
The researchers used 30 years of scientific surveys (1990-2019) and opportunistic observations on the subtidal communities of Lough Hyne to gain insights on the long-term stability and vulnerability of those ecosystems. They then considered the possible causes of observed changes and discussed the importance of regular monitoring for TME conservation around the world.
John Turner of Bangor University's School of Ocean Sciences first dived lough Hyne in 1981 while leading a student expedition from the University of Bristol, and returned to use video to record changes to subtidal communities throughout the 1990s during Bangor diving field courses to Lough Hyne.
This data has been combined with other long term data collected by a team from the National Museums of Ireland, from James Bell’s PhD work at University College Cork from the late 1990s (which stemmed from his undergraduate research during a Bangor field course) and recent surveys by a Wellington-Cork-Bangor co-supervised PhD student, Valerio Micaroni.
The Lough Hyne Marine Nature Reserve is the only one of its kind in Ireland and the first statutory Marine Reserve in Europe, designated 40 years ago.
Minister: "I’m delighted to support this important work in Lough Hyne"
It is also a scientific curiosity and haven for scuba-divers, because its rich mesophotic cliff communities occur in far shallower conditions than elsewhere in the Atlantic Ocean, a consequence of its relatively murky waters and sheltered location.
Professor Turner highlights the importance of long term studies in detecting changes to generally unseen deep water communities.
‘’Our study was unfortunately not continuous, but consisted of several sequences of opportunistic detailed observations by different scientists which have been combined to give a long term view of community changes on the submarine cliff faces of this unique sea lough’’
Professor Bell says long-term sponge abundance reconstruction showed the number of sponges on the cliffs had been relatively stable for at least 20 years until 2010.
“We don’t know for sure, but a range of opportunistic observations indicated that the decline in numbers occurred between 2010 and about 2015. The innermost sites were affected the most, suggesting the change originated inside the lough or that its sheltered conditions exaggerated an effect starting from the surrounding coast.”
There were several possible causes, including outbreaks of disease, increases in nutrients or heatwaves. Research is still ongoing into the cause, although changes in water chemistry remain one highly likely causes.
However, the team have also witnessed a recovery with young sponges now beginning to re colonise the underwater cliffs.
For PhD student Valerio Micaroni, the research was a chance to apply his interest in marine biodiversity conservation and in “animal forests”, those habitats formed by animals permanently attached to a substrate, like sponges, corals and anemones.
“I liked the project because it allowed me to apply my knowledge to a real problem and to contribute to the conservation of an important ecosystem.”
The Minister of State for Heritage and Electoral Reform, Malcolm Noonan, says the Irish Government is happy to support more work at the lough.
“I’m delighted to support this important work in Lough Hyne—a site that has been globally recognised for its richness in biodiversity—and to hear of the early signs of potential recovery from its recent declines.
“I am also committed to providing ongoing support to these scientific investigations so that we may better understand the causes of the decline, and what is influencing its potential recovery, so that we can apply those lessons to our wider marine environment, and to help secure a biodiverse, resilient marine environment.”
The paper’s authors are James Bell and PhD students Valerio Micaroni and Francesca Strano at Te Herenga Waka -Victoria University of Wellington, Rob McAllen and Luke Harman of University College Cork, John Turner of Bangor University, and Christine Morrow and Bernard Picton of Queen’s University Marine Laboratory and National Museums Northern Ireland.