MARIN ACADEMY RESEARCH COLLABORATIVE​
STUDENT BLOGS
THE EFFECTS OF OCEAN ACIDIFICATION ON THE GROWTH AND SHELL DEVELOPMENT OF THE PACIFIC MOLE CRAB EMERITA ANALOGA
Brian Little
ABOUT ME
For my entire life I have had a deep passion for the ocean and marine science. With the rise of global warming and ocean conditions rapidly changing for the worse, I have always wanted to do something to help with these issues. The Marin Academy Research Collaborative has allowed me to create a study that will identify the effects of ocean acidification on the growth and shell development of the Pacific mole crab.
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BACKGROUND
The health and biology of marine organisms is hugely threatened by rising ocean acidity levels. Ocean acidification–a term used to describe changes of the ocean's acidity levels and overall chemistry–is a rapidly growing issue in today's world. pH is expected to drastically drop within coming years, making the ocean more and more acidic (1). The pH scale measures how basic or acidic a substance is on a scale of 14, with 14 being the most basic and 0 being the most acidic. If a substance has a pH of 7 it is neutral, or equally basic as it is acidic. Previous studies have concluded that the pH in the ocean's surface is estimated to drop close to 0.4 units by 2100 and 0.77 units by 2300 (1). Due primarily to human produced pollution (2), ocean acidification is a direct result of increased CO2 emissions in the Earth's atmosphere (3, 4).
Countless studies have concluded that ocean acidification has a generally negative trend on the biology of marine organisms. Bylenga et al. (2017) reported the harmful effects of ocean acidification on the shell development of Laternula elliptica larvae (a species of saltwater clam). Increased ocean acidity results in larval deformities and abnormalities of this species, such as cracking and pitting on shell edges, hinges, and surfaces. Some L. elliptica larvae are even left uncalcified as a result of ocean acidification. These harmful deformities consequently reduce the juvenile recruitment and overall survival of L. elliptica, resulting in an expected decrease of the species' population in coming years (5). Doney et al. (2005) found that rising ocean acidity reduces the concentration of carbonate ions (CO32-), a form of aragonite, in ocean waters. The decrease of aragonite poses a threat to many marine organisms that rely on the substance in order to survive. Undersaturation of CO32-, which is predicted to emerge in coming years, will highly affect the health and survival of aragonite seeking organisms such as cold-water corals. Being a keystone species, cold-water corals have many organisms that depend on their health. Ocean acidification is therefore expected to not only alter the health of the corals, but also the health of coral-dependent organisms (6).
The purpose of this study is to identify the effects of ocean acidification on the growth and shell development of the Pacific mole crab (Emerita analoga). Growing to a maximum of 35mm long and 25mm wide, the mole crab is typically found buried in the swash zone along the Pacific Coast. The swash zone is the area on sandy beaches that ranges from the lowest to highest point that waves can reach at any given time. The mole crab has many predators, including fish, water birds, shore birds, and even some mammals such as sea otters. Because the mole crab is a vital food source for a number of animals, the crab is an integral member of the food chain and its ecosystem (7). This means that any possible impacts ocean acidification may have on the mole crab threatens the greater food web and marine ecosystem as a whole.
Numerous research studies of the mole crab have been published in the past. One study of the mole crab analyzed the relationship between burrowing behavior and body shape, concluding that a narrower body shape allows for a faster burrowing rate in coarser sands and on beaches with harsher intertidal conditions (8). Another study discovered that parasite infection of Profilicollis altmani has a negative impact on mole crab burrowing time (9). Despite these studies, little is still known about the effects of ocean acidification on the species Emerita analoga. Discovering these impacts is imperative in understanding how the health of the mole crab will be affected in coming years. Additionally, with this information scientist can better predict how the species' greater food web will be impacted as well.
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Caldeira, K., Wickett, M.E. (2005). Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean. Journal of Geophysical Research, 110.
Stocker, T.F. et al. (IPCC, 2013). Climate change in 2013: the physical science basis. The Intergovernmental Panel on Climate Change, pp. 1535.
Sabine, C.L. et al. (2004). The oceanic sink for anthropogenic CO2. Science, 305, pp. 367-371.
Millero, F.J. (1995). Thermodynamics of the carbon dioxide system in the oceans. Geochima et Cosmochimeca Acta, 59, pp. 661-677.
Bylenga, C.H., Cummings, V.J., & Ryan, K.G. (2017). High resolution microscopy reveals significant impacts on ocean acidification and warming on larval shell development in Laternula elliptica. Plos One, 12(4), pp. 1-13.
Doney, S.C. et al. (2005). Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature, 437, pp. 681-686.
Farallones Marine Sanctuary Association. 2010. The Pacific Mole Crab: Fact Sheet. http://limpets.org/wp-content/uploads/2015/01/PacificMoleCrabFS_Oct2010.pdf. Date accessed February 8, 2018.
Veas, R., Hernández-Miranda, E., Quiñones, R.A. (2014). Body shape and burial behavior of the sand crab Emerita analoga (Stimpson 1857) in a reflective to intermediate morphodynamic range of sandy beaches. Marine Biology, 161, pp. 2345-2357.
Kolluru, G.R. et al. (2011). Parasite infection and sand coarseness increase sand crab (Emerita analoga) burrowing time. Behavioral Processes, 88(3), pp. 184-191.
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NEWS
December 11, 2018
This semester I finished building the experiment and control tank systems, and began writing the procedure for my experiments. I have been in contact with Dr. Diara Spain at Dominican University and Mr. Benjamin McInroe at UC Berkeley. They have both helped me finalize my procedure, specifically with Mole Crab husbandry. I plan to have my experimental procedure finalized by the start of next semester. My next step is to begin testing carbon dioxide bubbling rates in the experiment tank system and determine how much gas is needed to reach specific pH levels. By February, this will be complete. I will then collect the crabs and begin the six week experiment.
January 15, 2019
After getting back from winter break I have been preparing the final steps of my experiment to begin in February. Next week I am going to make sure the tank systems run properly, and the following week I plan to begin carbon dioxide bubbling tests. I submitted a permit application to collect sand and mole crabs from Upton Beach in February, and I am still waiting to hear back. My teacher and mentor, Stori, has been in touch with the Monterey Bay Aquarium, where I will get seawater to run the experiment. I am also working on finalizing my experimental procedure.
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January 22, 2019
Yesterday I got the experiment tank system running with water, and it was a success for the most part. I have to fix the flow rate of the water coming out of the carbon dioxide mixing tank and into the individual containers that will house crabs, and I will use a flow valve to do this. Other than this minor adjustment, the tank system is runs properly with an aquarium chiller, protein skimmer, and water filter. Next week, Stori is going to the Monterey Bay Aquarium to collect seawater to begin testing pH bubbling rates with. The crab and seawater collection permit for the experiment is currently under review, and I will hear back soon.
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January 29, 2019
There is not much news on the development of the tank system. I am still working on fixing the flow rate of the water coming from the carbon dioxide mixing tank. I originally planned to collect crabs, seawater, and sand this weekend, but because of the minor setback on the tank system I will be collecting on another weekend. Stori is going to MBARI tomorrow to collect seawater to begin pH tests on.
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February 5, 2019
The sea water from MBARI arrived last week, and this week I plan to begin testing pH bubbling rates. I was planning on collecting sand and water from Upton Beach this past weekend, but there was a storm so I could not. I plan to do that this upcoming weekend. I am also setting up excel spreadsheets so I am ready to take growth and weight measurements of the crabs as soon as they are collected.
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February 12, 2019
Over the weekend Stori and I drove to Upton Beach to collect seawater and sand. Yesterday I got the experimental tank system running, and I set the flow rates so the carbon dioxide mixing tak wouldn't overflow. I am spending this week testing carbon dioxide bubbling rates, and I hope to collect crabs this weekend or the next.
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March 5, 2019
The experimental and control tank systems are set up and running properly. There has been a delay collecting the crabs because of poor weather conditions and time off from school, but this weekend I am going to Ocean Beach to collect the mole crabs. I also will collect more sand and water for the control tank system. Once collected, the crabs will be left in the tank system with normal pH conditions so they can acclimate to their new habitat before the testing begins.
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March 13, 2019
Last weekend on Sunday March 9th, Stori and I went to Ocean Beach to collect sand crabs. We collected approximately 86 crabs, as well as additional seawater for the control tank system. The crabs are currently housed in the control tank system, and I am using the experiment tank system this week to determine the carbon dioxide bubbling rates needed to lower the pH. The crabs are being left in the tank for a week while they acclimate to their new living conditions. The water in both tanks is at 54 degrees Fahrenheit.
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March 19, 2019
I have started testing the carbon dioxide bubbling rates needed to lower the pH to around 6.5 units in the experiment tank system, and I have found that the flow valve is extremely sensitive and it is very hard to get the flow rate to reach an exact pH level. I am using this week to continue figuring out the carbon dioxide bubbling so I can determine how to get the pH to 6.5 units and stay constant until the gas is shut off. As soon as this is done, hopefully by the end of the week, I will sort transfer half of the crabs over to the experiment tank system.
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March 26, 2019
This week I am sorting the crabs into their houses and splitting them up half and half into the experiment and control tank systems. A few of the crabs have already died, but most of them seem to be doing well. I have to constantly monitor the water levels of the tank systems to make sure that they aren't overflowing or losing water, but overall the tanks are running properly. I am feeding the crabs plankton weekly.
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April 16, 2019
Over spring break the tanks overflowed, destroying one of the computers monitoring the pH of the water. Fortunately, most of the crabs survived. However, I've decided to alter my project slightly because the tank systems have been too delicate to bubble carbon dioxide into, and I have not been able to maintain a stable pH level when CO2 is bubbled in. I am doing online research and reading articles about altering the water temperature, possibly simulating an El Niño year or gradual ocean warming, and possible effects it has on marine invertebrates. I am continuing to feed the crabs as well, as the majority of them are still alive.