I think it is some kind of wrack
No interactions present.
Perhaps you can move this observation (along with your other seaweed observations) to the plants group by selecting the 'edit' tab above the observation title and selecting the 'plants' category from the correct drop-down. Then your observation can be more easily compared to other ones :)
Lat/Lng: 51.5368, -4.2097
OS grid ref: SS468843