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.
Everybody loves going to a nice sandy beach. We set out to learn more about the health of beaches by analyzing the abundance of mole crabs at beaches near cities and beaches in more remote areas.
Although they are no bigger than the size of your thumb and seemingly unimportant creatures, mole crabs are very significant animals on sandy beaches. Their numbers are also indicative of the general health of the entire beach because they are in the middle of the food chain. This means that they are affected by both a scarcity in their prey or predators.
So, how do mole crab populations vary from urban beaches to remote beaches?
We collected data about sand crabs from Ocean Beach. From the data, we came up with a question about the sand crabs, and supported it with the data we collected. We compared our findings to that of other scientific resources, like the “Pacific Mole Crab” article. We were able to see if sand crabs changed from the time the articles were made to now. When we looked at the findings, we could come up with possible causes. We gathered the information and began to put it into a blog. This process helped us become more confident in science and in writing. It’s amazing that our research is contributing to the scientific world.
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.
There are many reasons why it is important for beaches to be clean. Beaches that are covered in litter are not ideal places for life to thrive. Our group found this from the two sites that we visited. The first was the San Leandro Marina. This beach was covered in litter, and clearly was not well-maintained. There was not even a beach, only broken concrete filling the 10-foot gap from the walking path to the water. The only life we found here were seagulls and algae. Seagulls don’t even live on the beach, so they aren’t really affected by this, and algae will grow regardless of the lack of effort in supporting the site. However, compare this to Ocean Beach. This site is well taken care of, and the multitudes of species that live there illustrate this fact. These include the Western Snowy Plover, and the topic of this blog, the Sand Crab.
When our group went out and had an awesome time researching the sand crabs at Ocean Beach, we started to wonder if there were more females in the population of more male. Our question is concerning the sex ratio between males and females. Sex ratio is defined as “The proportion of males to females in a given population, usually expressed as the number of males per 100 females.” Are females dominating males in the sand crab population?
On September 14, 2013, students scavenged a 50 meter portion of Ocean Beach for sand crabs. The wind was strong and water was cold but we were persistent to dig deep into the sand under the heavy rain to find sand crabs. We walked along the beach experiencing the habitat that most organisms can not live in but the habitat sand crabs call “home sweet home”. From the bigger pregnant females, to the smaller males, we realized the importance of sand crabs.
We learned that sand crab monitoring is important because the data collected contributes to a better understanding of the health of the beach. Variation in sand crab abundance can also help indicate this. [ We believe that coastal squeeze is going to be a bigger issue in the future and affect the health of the beaches. ] Sand crabs are a common food source for many animals on the beaches in California. Surfperch, surf scoters, and shore birds along with many other organisms depend on sand crabs to stay alive. Sand crabs are crucial to the ecosystem if not the most important and abundant species on the beaches in California. Continue reading →