CATALINA ISLAND NATURAL HISTORY
During my time on Catalina, I researched the natural history of the island. Prior to the collection of the following material, numerous sources existed with misleading data sets leading to erroneous conclusions concerning the formation of Catalina Island. The United States Department of Agriculture Soil Survey of 2008 on Santa Catalina Island (Catalina Island) available at (http://soils.usda.gov/survey/online_surveys/california/catalina/Catalina_CA.pdf) was the consolidating source of the following excerpt from the Naturalist Training which Frank Hein and I developed and implemented for tourists and business of Catalina Island.
Catalina Island is about 22 miles off of Southern California and has never been attached to the mainland. This means that all organisms colonizing the island had to cross the water. The close proximity increases the likelihood for terrestrial vertebrates and invertebrates to make the voyage on vegetation mats or swimming, but this likelihood is still minuscule preventing a large influx of new organisms and permitting endemism to occur.
Island endemism is initiated by the founder populations and any subsequent arrivals of the same species because these are the genetic founders. Any genes they do not have can not become fixed in the population, limiting genetic variation, and a genetic bottleneck occurs (Frankham 1998). In addition to the bottlenecking, low rates of gene flow from mainland populations aid in the insular isolation affecting the genetic structure of the island population (Franks 2010).
As each new generation grows and reproduces on the island, the more the selective pressures of the island take effect, and eventually a new species forms that is unique to that island. Ironically, the same bottlenecking that starts off the endemic species formation also prevents the population from being resilient to disturbance and invasive species competition (Frankham 1998).
Catalina Island has a major basement layer of metamorphic rock which formed 200 MYA during the Jurassic period (Box 1.2). Millions of years ago the area where Catalina Island is today was very active geologically with subduction events which created molten rock under the sea floor. This molten rock formed when the Faralon Plate collided with the North American plate, moving east more than 200 million years ago.
As the Faralon Plate subducted and moved under the North American Plate it became the Juan De Fuca Plate which is still in existence off shore of Northern California. The eastern edge of the Faralon Plate is now under the Eastern part of the United States. Currently, the Pacific plate borders the North American plate where Catalina sits today.
Prior to the subduction events, ocean activity allowed ocean deposits and sedimentary rocks to form on the North American Plate and Faralon Plate border. The intense heat from the subduction changed these sediments into the metamorphic rock complex containing blueschist, greenschist, amphibolite, serpentinite, Garnet-schist and other rocks that makes up most of the basement material of Catalina Island (United States Department of Ag…2008).
As the Cretaceous period ended (65MYA), the rate of subduction and uplift slowed allowing for erosion to outpace the uplift occurring in the surrounding areas. The same metamorphic rock that Catalina Island is made from was a highland at this time, evident from the sediments found across the other Channel Islands and the California Coast. Catalina Island however was still under water and would not emerge from the ocean until 5 million years ago.
Erosion outpaced uplift for 40 million years. This started to change 30MYA when the converging tectonic plates (Pacific Plate and North American Plate) stopped converging head-on and began moving laterally. This change of direction caused the sea floor to start spreading, inducing a period of volcanic activity, breaking apart faults and repositioning of land (United States Department of Ag…2008).
Seventeen million years ago these processes started the ascension of Catalina (Draut 2008). Subaqueous extrusions of andesite, adjacent to the quartz diorite on the East End, suggest Catalina Island was underwater during most of the Miocene Epoch (23.8-5.3 MYA) when high volcanic events were occurring (United States Department of Ag…2008). These andesite deposits on the East End suggest Catalina emerged from the ocean around 5 MYA.
Most likely the first organisms to colonize the island would be sea birds and marine life, including crabs, sea otters, seals and sea lions and other creatures that existed 5 million years ago. As time progressed, Catalina became more and more exposed, soils continued developing and changing, with major soil formation occurring in the Late Pleistocene (Box 1.2).
Once enough soil had developed plants were able to germinate on island and start colonization. Since the time when Catalina Island emerged from the Pacific Ocean, the island has been subject to alternating sea levels, erosion, and colonization by organisms which make Catalina Island the gem it is today.
Soils on Catalina Island are still changing. In the last 5,000 years dust from the Mojave has been accumulating on the island (United States Department of Ag…2008). Just as the soils are still changing, Catalina Island is still subject to tectonic action. In 1993, Larson and colleagues extrapolated data suggesting that Catalina Island is currently moving at a rate of 6.7mm +/- 0.9mm/year.
As each new species arrived and colonized, island ecology changed. Some species became new species through these interactions leading to 40+ endemic invertebrates, 7 endemic plants (1 extinct and 6 extanct), 5 endemic mammals, and 3 endemic birds.
This rate of change however has been slow with few species in the world going extinct each millennium. Approximately 400 years ago is when the rate of change was accelerated due to European movement around the world donning the “Age of Exploration” and an era of invasive species.
The arrival of Europeans to an area is how native vs. non-native is defined for two reasons (1) Europeans were one of the first people to move species around the world at high rates and (2) because Europeans were great collectors, allowing us to know what species were found somewhere prior to their arrival.
On Catalina Island, the arrival of Russian Otter Hunters in the 1800’s is the marker of invasive introductions. This is due to the fact that few records exist before then and at this time is when western culture really took interest in Catalina Island. Even though Cabrillo and Vasquez, two Spanish explorers, reached the island in the 1500’s, the island was rarely visited by westerners until the otter hunts.