The intertidal zone is the area of a beach that is exposed at low tides. To be exact, it is the area between the higher high water mark and the lower low water mark. Also, pollution in the form of heavy metals and chemicals can have toxic effects on marine life. Foot traffic on beaches, crushes plants and animals, has been documented to alter the diversity of organisms.
Breakwaters can alter current patterns and sediment deposition.
Yes, there are many non-native species that have established here. The Pacific Oyster and the Japanese Littleneck Clam both were intentionally introduced earlier in the 20th Century. There are also several unintentionally introduced species. These include the Varnish or Mahogany clam and most recently, the European green crab. Varnish clams have since spread throughout the Strait of Georgia and are also found in adjacent American waters.