Seagrass contributes to the formation of the peat when it dies and decomposes.
although it takes a long long time.
putting it in potholes just holds the water and when it decays it forms more of an unstable mush (We all know what it smells like after its been sitting wet for a few days)

So it is a short term solution but in the long run it creates more problems than it solves. Makes good compost though!!!