Invasive species aren’t your typical type of alien. They don’t come from outer space or fly in ships. Invasive species are both plants and animals that are not native to an area, causing harm to the native species of said area. In California, some examples of invasive species include Ice Plants, which arrived in California in the early 1900’s as a form of erosion control along railroad tracks. Also, the European Green Crabs which were discovered in the Bay Area in 1989, and most likely were brought here accidentally with commercial fishing boats. These species, if not controlled, can be detrimental to the California coastline. Luckily, there are efforts in California to remove or minimize these invasive species.
Red-vented Bulbul Bird Perching on a Branch, Courtesy of Viswaprem CA
The first thing to understand about invasive species is what they are and how they spread, because they rarely become invasive without spreading outside their native habitat. According to Executive Order 13112, which is a signed, written, and published directive from the President of the United States that manages operations of the federal government, an invasive species is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” These species can be anything from plants, insects, and other animals. Invasive species are usually spread unintentionally, such as when a species of mussels attaches to a ship that sails to different parts of the world, taking and spreading the mussels with it. However, non native species are sometimes purposely taken to different habitats for varied purposes, like when people buy plants for their yard that aren’t natural to the area, resulting in the spread of that invasive plant.
Of course, climate change also affects the spread of invasive species. For example, if an area that normally would be too cold to suit a certain species has now gotten warmer, an invasive species can invade and take over an area it couldn’t have invaded before. Additionally, a species’ natural habitat can become inhabitable due to climate change, causing it to move somewhere else and infest that new area. However, with ice plants, climate change may pose a threat to their adaptation. Ice plants have a tolerance for the cold, and as temperatures continue to rise, they may struggle to outcompete more drought resistant plants. In the end, there are many types of invasive species and many ways for them to move across the world to different habitats.
As mentioned previously, the Ice plant is an invasive species in California. If you live anywhere near the California coast, you’ve probably seen it. These plants are succulent like shrubs, often green and red in color. They originate from South Africa according to the California Department of Fish and Wildlife, and they were introduced to California in the early 1900’s. In this case, the plants were purposefully taken to this new ecosystem to prevent erosion along railroad tracks, but since California’s coastal climate is similar to that of South Africa, they thrived and spread quickly. According to the South Bay Park Land Conservancy, Ice Plants can grow up to three feet per year and spread fast because their seeds are moved so easily. These plants are deadly to their ecosystems as well. They grow very thick, creating these mat-like structures that completely block the sun from the native species, preventing them from photosynthesizing. Essentially, they choke out their competition. They also change the composition of the soil as the soil found in California’s coastal ecosystem contains a lot of salt and the ice plant “thrives on [the salt] and concentrates that salt. As older leaves on lower layers of ice plant mats die off and fall to the soil, the concentrated salt is passed to the soil” according to the South Bay Park Land Conservancy. This high concentration of salt in the soil then makes it much harder for other plants to grow in this soil, as if the Ice Plant is poisoning all the others. To make matters worse, the Ice plant has shallow roots and grows very heavy, which means that it causes landslides because the sand, soil and roots can’t hold its weight. This means that not only does the ice plant harm native wildlife, it doesn’t prevent erosion like it was intended to..
Another invasive species that is quite common is the European Green Crab, which is a small crab that inhabits the shore of the Atlantic Ocean along the coast of north Africa up to Iceland. Here, in their natural habitat, they have predators that keep them in control, but when they spread to other areas where there are no natural predators, they grow exponentially. They were first noticed in the Bay Area in 1989. It is theorized that they were brought here by commercial fishing boats transporting bait, unaware of the crabs on board. Once they are brought to a new coast, they are moved further by currents, having invaded the West Coast from Monterey to British Columbia in Canada. These crabs are "considered one of the most invasive species in the marine environment" according to the National Oceanic and Atmospheric Administration. These crabs are highly skilled predators, because they are effective when it comes to opening the shells of organisms like bivalve mollusks, soft shell clams, and mussels. They can also kill other species of crab. Since these crabs are so good at hunting and their populations are growing at an alarming rate, they have severely decreased biodiversity along the coast. This is a bad thing because when the biodiversity of an ecosystem is low, it is harder for that ecosystem to withstand and recover from challenges. For example, if there were two droughts, one in a low biodiversity area and one in a high biodiversity area, the one with the high biodiversity would bounce back quicker. This is because it is more rich in species variation and therefore has a higher likelihood of some species having the traits to survive and repopulate the area. California ecologists have been monitoring an inlet in the San Francisco Bay called Seadrift lagoon that has experienced a boom in the green crab population, and one of these ecologists named Kate Brimrose spoke on the crabs effect on other species populations. “When we first started this project, there weren’t much in the way of other species. Pretty much everything you got was all green crabs," said Brimrose. Another concern that has risen is that the commercial fishing market is taking a blow because of these crabs. For example, the soft shell clam industry is struggling because of the crabs ability to prey on them. According to the University of Maine, predation has gotten so severe that less than .01 percent of clams survive more than a year.
Despite all the negativity surrounding the invasive species problem, there is hope. There are plenty of policies and initiatives that are important to learn about, so that further strides can be made. One of these is the Executive Order 13112, which is a directive signed by the President of the United States (President Clinton in this case) that aims “to prevent the introduction of invasive species and provide for their control and to minimize the economic, ecological, and human health impacts that invasive species cause.” This order outlines the establishment of the National Invasive Species Council, whose job it is to monitor government agencies to make sure they aren’t doing things that could cause the spread of invasive species among other things. They have supported technological advancement in the fight against invasive species, and funds to detect invasive species early on. Another way people are mitigating the effects of invasive species that should be recognized is through volunteer work. For example, students at Gault Elementary School in Santa Cruz have taken it upon themselves to help tackle the Ice Plant problem at the Monterey Bay National Marine Sanctuary. The Ocean Guard School restoration project is funded by the National Oceanic and Atmospheric Administration and is an amazing opportunity where students, teachers, and volunteers get to learn from scientists about monitoring invasive species and the effects of coastal erosion. They remove Ice Plants from the beach and also plant native species in its place. The beaches are already starting to see improvements in the numbers of native species. Scientists are also getting involved in the battle, like the ecologists from the Green Crab Project that monitor the Seadrift lagoon, an inlet in the San Francisco Bay. They were constantly going and setting traps to remove the invasive crabs from the lagoon in hundreds, and after some experimentation, they found a method where they left some of the adult crabs in the lagoon because they had cannibalistic tendencies to prey on the younger crabs, and this seemed to keep the population mostly in check. This appeared to work and eventually the ecologists noticed that other species of crab and some shrimp were starting to pop up, where before the lagoon was almost entirely green crab. As an added benefit, they used the removed crab as fertilizer for nearby farms. The Smithsonian Environmental Research Center in Marin, in partnership with the Green Crab project, stated that they “have been told by the farm owners that the green crabs make for great crop fertilizer due to the large amounts of calcium in their exoskeleton combined with nitrogen in the tissue.” The volunteers and partners (such as The Smithsonian Environmental Research Center in Marin and UC Davis) with the Green Crab Project have been donating these crabs to local farms, where they crush the crabs after they die to turn them into fertilizer, which is rich in calcium and nitrogen and has been a big help in growing crops.
In the end, the removal or prevention of invasive species is extremely important to the promotion of biodiversity, which is why it is important to be educated and understand how you can help. There are so many volunteer opportunities like the Ocean Guard project, so go find one in your area and see how much you can improve the world around you. Alternatively, do research on what species are native to where you live and be sure to plant them in your yard as a substitute to a non-native plant species. These are great ways to create change and to keep our planet healthy.
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