Jessica Vevers
MSc graduate, Swansea University
Cymraeg
Cymraeg
English
Croeso
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A long-term photo-quadrat survey reveals a persistent shift in an epibenthic vertical wall community at Skomer Island
A long-term photo-quadrat survey reveals a persistent shift in an epibenthic vertical wall community at Skomer Island
11 comments
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QUESTION FROM LIVE PRESENTATION -
Clare Trotman: @Jessica - great presentation, thank you. I was a bit unclear about the link between the decline in A.digitatum and the increase in potting? Is it causing a change in assemblage of species overall? You mentioned an increase in bryzoans, eg
Hi Clare, thank you for the question. I did respond to your question on the live Q&A panel but I will put my answer here as well in case you'd like to refer back to it.
As A.digitatum was a dominant member of the community before, the decline (and absence) of A.digitatum in the last decade at the site means there has been a change in the assemblage of species on the wall. Short bryozoans and tall hydroids increased in recent years. This was likely due to the increase in substrate available for bryozoans and hydroids to colonise (provided by the decline of A.digitatum). In terms of specific species of bryozoans and hydroids, species level was not determined as image quality was not good enough for species level identification of these groups (although bryozoans were mainly Bugula spp).
I hope this answers your question.
QUESTION FROM LIVE PRESENTATION -
Ffion Mitchell:
Not really a question, but a big well done to Jessica. It's great to see a fellow recent graduate presenting at this event. At times it can be daunting - you did an excellent job.
Thank you very much
Well done on your presentation - very clear and concise! You mention that you looked at temperature and turbidity I believe - were there any possible associations here?
Thank you. for your question. An increase in commercial potting was the main potential link to the changes in community composition seen.
Temperature was not associated with the change in composition over time (and was not individually associated with the decline in Alcyonium digitatum and increases in short bryozoans and tall hydroids). However, only winter seabed temperature was looked at as summer seabed and mean seabed temperature data was not complete. Winter seabed temperature was still not available for the whole 34 years so earlier years may have been overlooked and access to this data may change the results regarding temperature. I plan to further investigate the effect of temperature by collating records of sea surface temperature. However, in my opinion, I don't think the small changes seen in the area would have had an effect on the decline of A.digitatum as A.digitatum is present in regions that have varying temperatures. However, this is not to say that future warming won't affect the wall community!
In regards to turbidity, A.digitatum did also decrease with an increase in turbidity. Turbidity was measured using Secchi depth readings and so this could imply increases in sediment OR phytoplankton. However, the decline is more likely to be related to an increase in sediment. The increase in sediment may have potentially affected the settlement of larvae and/or affected the efficiency of their feeding (this is just a thought and needs further investigation).
I hope this answers your question.
@jessicavevers2 Great - thank you.
QUESTION SUBMITTED LIVE:
Emyr Martyn Roberts:
@Jessica Vevers Do you have any thoughts on the mechanism by which increased potting might lead to a decline in A. digitatum? Sorry if I missed this-fantastic talk and a lovely timeseries dataset (please think about publishing this work!).
Hi Emyr, thank you for your question. I did respond to your question on the live Q&A session but will put my answer here as well in case you would like to refer back to it.
The potting could be causing removal of the A.digitatum colonies as they are vulnerable to this due to their upright structure. The pots and sink line could be causing abrasion to the surface of the A.digitatum and this damage could potentially affect their survival on retrieval and deployment of the pots (although this is just a thought and needs to be investigated!).
Thank you so much
Excellent work and so good to raise awareness and importance of long term data sets. Skomer MCZ sets the bar there. I'd be less inclined personally to see commercial fishing as the main contender for the decline in A.dig in this instance (but who knows?). I think there is a lot going on that we don't yet fully understand. What I do think your work (and that of others) highlights is that unless we have areas of the seabed that we can properly study away from the disturbance of human activity (as much as possible - at least an area with no extraction) then how on earth are we going to understand basic natural marine ecological functioning? Only when we get that as a 'control' can we then start to begin to understand human impacts properly. This has been something that has been proposed as an idea for Skomer for many many years and it is frustrating that we still have not got this badly needed scientific resource that could help us with so much else. It is not just an academic exercise; it could really help fisheries impact assessments generally - for the benefit of the industry as well as that of conservation.
Hi Sue,
Yes, the long-term dataset from Skomer is certainly impressive- it was very interesting to analyse. I completely agree that an area with no extraction (e.g. no potting) within the MCZ is very important and would be beneficial (please see the regional discussion forum where I have submitted this as a suggestion). A control area is so important to decouple changes related to human impacts and those occurring due to natural fluctuations in marine communities. Hopefully, this can be an addition to the MCZ in the future.