Human Impacts on Ecosystem

Catalina Island is the most populated of all the Channel Islands and population has gradually increased over the last hundred years, leading to a number of problems for the island’s fragile ecosystem. Invasive plants and animals have become a significant threat to native population. As humans migrated to the island, they brought many garden and landscaping plants like flax-leaved broom, genista, and fennal, which easily outcompete native plant populations. Non-native species make up 36% of the island’s flora, and currently, 76 invasive plant species are in need of control or eradication (Knapp, Oak Ecosystem Restoration pg. 35). Rare and endemic plants have suffered the consequence of this invasion, and many endemic plants have become rare and endangered including but not limited to Catalina ironwood, Catalina Island mountain mahogany, St. Catherine’s lace, and Catalina Manzanita (Catalina Island Conservancy, Rare and Endangered Plants). There are 6 federally listed threatened or endangered plant and animals species, 4 of which have been identified as being threatened with extinction by invasive plants. The island oak populations have been especially threatened by invasive species which increase fire frequency; affect oak ecosystem food webs; alter vegetation structure and composition; and compete for resources such as water, sunlight, and nutrients (Knapp, Invasive Plant Management Program pg. 36). Humans also brought animals to the island that the ecosystem is not adapted to support. These animals outcompete native animals for resources and also destroy much of the native plant life. One such example is bison, which were brought to the island in 1924 to film a movie and left on the island thereafter. The bison population exploded on an island ill-adapted for large ungulate animals, reaching 600 at its peak. Additionally, bison have exacerbated the invasive plant problem by spreading their seeds through their hair (Bison Study Executive Study). Native animal species have also suffered as a result of human activity. The Catalina Island Fox was declared critically endangered in 2004 after a population crash in 1999 caused by an outbreak of distemper most likely brought to the island by someone’s pet. The population once totaling at 1300 plummeted to the brink of extinction in a matter of years (Shahagun).
Terrestrial life is not all to have paid the price of human activity; water pollution has dramatically increased on the island within the last few decades. Avalon Beach Harbor has consistently ranked as one of the most polluted in the state within the last decade. On a national scale, the harbor has been declared one of the most chronically polluted beaches in the nation for failing state health tests 73% of the time (Barboza). The cause of such severe water pollution has been traced to the island’s outdated sewer system made of clay and metal pipes that are a century old (Barboza). The water leaches from these decrepit pipes into the groundwater and eventually into the bay. Marine habitats around the island have also suffered as a result of such sever water pollution.