Pinus nigra is the European, sometimes called Austrian black pine, it is a single flush of growth pine, techniques used for it are more or less the same as techniques for Scotts or Scotch pine, Pinus sylvestris. Do not decandle like you would a Japanese black pine.
Some needles falling in autumn is normal, especially 3 year old and older needles. Your tree does not look healthy, you have a problem. I suspect the previous posters are right, soil is too wet, or alternated between too wet and too dry.
Since your winters are mild, if you can keep the tree from frost, you might be able to get away with repotting now, if you have a good media on hand, like pumice and akadama. But if your new media is not much better than what the tree is already potted in, wait until spring, be careful with watering, don't just automatically water the tree every day. Don't let it get too dry, and don't let it stay wet and saturated.
If you do repot, it is important to keep it above freezing. Ideally between 0 C and 4 C (or 32 F and 40 F ) for the winter. If the tree will be exposed to freezing temperatures, then do not repot until spring.