Gianna, Jack, Peter, and Nathan
Bishop O’Dowd High School
After going on a trip to Ocean Beach in San Francisco and gathering data about the local sand crabs, we wondered how many of them were “recruits,” little crabs which are new to life on the beach. How does this number change over time? Once a recruit settles on a beach, it will spend the rest of its life there. So, a healthy recruit population means that there will be a healthy adult population in the future (unless there is an environmental hazard). As long as there are no environmental hazards or strange weather conditions, the portion of recruits can be used to predict future sand crab growth and decline. Continue reading →
According to Beyonce, girls run the world, but from Bishop O’Dowd’s sandy beach monitoring data, it’s female sand crabs with eggs the run Ocean Beach. Sand crabs are important animals on California beaches because they can indicate the health of the area of the beach in which they live. Also, they are an important species in the food chain. They are the primary consumers on the beach and many other species rely on their existence.
Over the past ten years, the amount of female crabs with eggs has fluctuated greatly. The crabs had fruitful mating seasons in 2009 and 2011, as shown by the graph below. Following the pinnacle of pregnant crab abundance in 2009, Ocean Beach’s sand crab population boomed (see year 2010 in the graph). Most of these crabs were juveniles and possibly offspring of the pregnant females from the year before. This population boom may be due to climate change; recent studies have shown our planet faces challenges that may be devastating for the species that make their home, reproduce, and live in sandy beaches.
Our group research question was, “What is the abundance of Recruits, compared to adult Males and Females, over Time (from 2003-2013) at Ocean Beach from the data collected by a specific school?” Basically, we asked if the number of juvenile sand crabs (aka recruits) has had any significant changes compared to the number of mature adults that are on the beach.
Your initial reaction to this question might be to ask, “Why should we care?”, because until now there’s a large chance you didn’t even know sand crabs existed. To answer that question our group had to take a step back, and understand the crabs role in the marine community. We have since learned that they are important food sources for the shore birds, and local fish so their populations reflect how those predators and even the crabs’ prey are doing. So, by tracking sand crab population,s scientists are able to keep tabs on how healthy places like Ocean Beach are, and to see if that marine community needs more attention.