A hadron is made up of valance quarks ($qqq$ in the case of baryons and $q\bar q$ in the case of mesons) and sea quarks ($q\bar q$ pairs). Since all internal quantum numbers of quarks and anti-quarks are opposite, sea quarks cannot contribute to e.g. the overall strangeness or baryon number. That been said, the spin of a quark is equal to that of it's anti-quark. Thus if the $q\bar q$ pair are in a triplet state one would expect the possibility of sea quarks contributing to the overall spin of the particle - but since (as far as I know) we get only $J=0$ and $J=1$ mesons this does not appear to happen. Thus my question is:
Can sea quarks contribute to the overall spin (or even isospin) of the hadron? if so why and if not why?