Zebra mussels were NOT brought in by pleasure boats. They were introduced by cargo ships who blew their ballast tanks. Here's just one example (of many) citing the research http://www.great-lakes.net/envt/flora-fauna/invasive/zebra.html

Same thing with Quagga mussels. http://www.aquaticinvasions.net/2011/Supplement/AI_2011_6_S1_Vaate_Beisel.pdf Quote: "Bij de Vaate(nl)(2010) concluded that the introduction in the Rhine delta was the result of ballast water transport by sea-going freighters. From there,(nl)quagga mussels were transported by inland navigation. On the other hand, the same vector could be used by the species to jump from the(nl)Danube basin into the Rhine basin." So yes ballast water again, but they also cite unspecified "inland navigation". How much was inland navigation specifically by pleasure boats? Probably not a majority, but in any event -- any restriction is just not effective unless the commercial sector is equally treated at minimum.

If pleasure boats are a vector, they are a minor player. I still don't see how the San Diego regulations are (as you wrote) helpful in curbing pleasure boats as a vector for transporting invasive species.

Your argument does not hold water. The regulations don't stipulate that pleasure boats should be cleaned on any schedule nor before or after leaving port, and they don't state anything about collecting growth that is shed from cleaning.