Living Life as a Sea Urchin Momma

Hailey Conrad, Rutgers University

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Me working hard to make my sea urchin babies

For my project I am using the same technique that the father of genetics, Gregor Mendel, used to establish his Laws of Heredity: cross breeding. So, I have to breed and raise a whole lot of sea urchins. For a refresher, I’m trying to determine if there is heritable genetic variation in how sea urchin (specifically an Arbacia punctulata population from Woods Hole, Massachusetts) larvae respond to ocean acidification. To do this, I’m rearing sea urchin larvae in low and high carbon dioxide conditions and measuring their skeletal growth. I’m breeding 3 sea urchin males with 3 sea urchin females at a time, for a total of 9 crosses. To tease apart the impact of genetic variation on just the larvae themselves, I will be fertilizing the sea urchin eggs in water aerated with either current atmospheric levels of carbon dioxide, about 410 parts per million, or 2.5 times current atmospheric carbon dioxide levels, about 1,023 parts per million. Then, I will be rearing the larvae in water aerated with either 409 ppm CO2 or 1,023 ppm CO2. This will give me four different treatments for each cross, giving me 36 samples in total. By fertilizing and rearing them in the same and different levels of carbon dioxide I will be able to see how much of an impact being fertilized in water with a higher carbon dioxide concentration has on larval growth versus just the larval growth itself. It’s important for me to make that distinction because I just want to identify genetic variation in larval skeletal growth, and separate out any extraneous “noise” clouding out the data. I’m rearing the larvae in a larval rearing apparatus. Each of the 36 samples will be placed in jar with water aerated with the correct CO2 treatment. Each jar will constantly have atmosphere with the correct CO2 concentration bubbled in. Each has a paddle in it that is hooked to a suspended frame that is swayed by a motor. This keeps the larvae suspended in the water column. The jars are chilled to 14 C by a water bath.

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My larval rearing apparatus

After a 6-day period the larvae are removed from the jars and their skeletal growth is measured. They are preserved with 23% methanol and seawater and frozen.

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An Arbacia punctulata pluteus

You’re probably curious how the heck I am able to measure the larva’s skeletons. They’re microscopic! Well, I use a microscope coupled to a rotary encoder with a digitizing pad and a camera lucida. Which, looks like this:

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A microscope coupled to a rotary encoder with a digitizing pad and a camera lucid hooked up to a computer

This complicated-sounding hodge-podge of different devices enables me to do something incredible. I can look through the microscope at the larva, and also see the digitizing pad next to the microscope, where I hold a stylus in my hand. When I tap the pad with the stylus and the coordinates of various points on the anatomy of the plutei that I am tapping at get instantly recorded on my computer! The rotary encoder is the piece attached to the left side of the microscope and it enables me to record coordinates in three dimensions. Then, I can use those coordinates to calculate the overall size of the skeleton. My favorite part of doing science is learning how scientists are able to do the seemingly impossible- like measuring something microscopic.

After I gather all of my data, I will do some statistical analysis to see the affect that the male parents have on the skeletal growth of their offspring. I will not be focusing on the impact that females have on the skeletal growth of their offspring. The quality of the egg itself could be an influencing factor on the size of the offspring, whereas sperm is purely genetic material. Like how I’m trying to isolate the influence of ocean acidification during larval rearing from during the act of fertilization, I am trying to isolate just genetic influences on larval skeletal growth from egg quality. Check back to see how it goes!

Special thanks to the National Science Foundation for funding this REU program, the College of Charleston and Grice Marine Laboratory for hosting me, and Dr. Bob Podolsky for mentoring me!

 

 

 

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Playing with Plutei

Hailey Conrad, Rutgers University

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Me! Photo Credit: Kady Palmer

Ocean acidification is known as climate change’s evil twin. When the pH of ocean water drops, carbonate ions in the water form carbonic acid instead of calcium carbonate. Calcium carbonate is the form of calcium that marine animals that have calcium-based skeletons (like us!) and shells use to build their bones and shells. Having smaller and weaker skeletons or shells impacts their ability to survive. However, some individuals within certain species or populations of species have genes that make them more resistant to ocean acidification. If these individuals are able to pass on these genes to their offspring, then the species has the ability to evolve in response to ocean acidification instead of going extinct. This summer I’m working with Dr. Bob Podolsky in College of Charleston’s Grice Marine Field Station to study the extent to which ocean acidification affects Atlantic purple sea urchins, Arbacia punctulata. We are specifically trying to see if any individuals within a population from Woods Hole, Massachusetts, have any heritable genetic resistance to the negative impacts of ocean acidification. We hypothesize that there will be genetic resistance given that the northern Atlantic coast naturally has lower levels of saturated calcium carbonate, so a population that has evolved to live in that type of environment should have some resistance to lower calcium carbonate levels already (Wang et al 2013). We’re using a basic cross breeding technique to rear Arbacia punctulata larvae to their plutei stage, when they have four main body rods. At this stage they look less like sea urchins than they do like Sputnik!

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A sea urchin pluteus larvae with four body rods

Then, we will look to see if any of the male parents consistently produce male offspring that are more resistant to ocean acidification.  If males like these exist within this population, then the species has the capacity to evolve in response to ocean acidification, instead of going extinct! This is a very big deal, and could potentially be very hopeful. Even if we don’t get the results that we are hoping for, the results of this research could inform policy and management decisions.

Literature Cited:

Wang, Z. A., Wanninkhof, R., Cai, W., Byrne, R. H., Hu, X., Peng, T., & Huang, W. (2013). The marine inorganic carbon system along the Gulf of Mexico and Atlantic coasts of the United States: Insights from a transregional coastal carbon study. Limnology and Oceanography, 58(1), 325-342. doi:10.4319/lo.2013.58.1.0325

Thank you to the National Science Foundation and College of Charleston’s Grice Marine Laboratory for funding my project. And, special thanks to Dr. Bob Podolsky for being a wonderful and supportive mentor!

 

Are New Englanders more tolerant than Southerners? A test of latitudinal variation in Atlantic sea urchins

Kaelyn* Lemon, Macalester College/ Dr. Bob Podolsky and Grice Marine Lab

If you’re not a climate change denier, you know that global climate change, mainly driven by the increasing amounts of carbon dioxide that humans release into the atmosphere, has been raising the Earth’s average temperature and will continue to do so for the near future. If you are particularly well-versed in your environmental science, you know that these increasing amounts of carbon dioxide are also causing the oceans of the world to become more acidic (see: coral bleaching) (1). Unless you are a marine or climate scientist, though, you probably don’t know why climate change is causing ocean acidification or how this will affect ocean animals besides probably not being the best thing ever for them.

Our oceans actually absorb around 30% of the carbon dioxide we release into the air (2). This CO2 hangs around as a gas mixed into the water and goes through a series of chemical reactions that both release hydrogen ions (the H in pH), therefore lowering the pH of the water and making it more acidic, and reducing the amount of carbonate available in the water for ocean animals and other organisms to use (2). Animals like sea urchins that build shells or skeletons out of calcium carbonate (the main ingredient in limestone) find this task more difficult when there is less carbonate around.

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Ocean acidification due to greater amounts of carbon dioxide in the atmosphere leads to less carbonate in the water (from http://www.i-fink.com/ocean-acidification/)

While the thought of sea urchins will bring to mind their hard, spiny exterior, these animals (yes, there are body tissues inside those aquatic pincushions) are actually most affected by ocean acidification during their larval stage of life, when they build a skeleton that allows them to swim around and eat (3) (urchin larvae are like insect larvae in that they behave and look very different from the full-grown animals they will eventually become). When oceans become more acidic and less carbonate is available, urchin larvae are smaller, which makes it harder for them to eat at the same time as they are more at risk of being eaten themselves (3). Unfortunately, a world with a lot fewer urchins would be a world where seaweed would easily overgrow ocean habitats and predators of urchins (like the adorable fuzzy otters that lay on their backs in the ocean and hold hands- google it) might have more difficulty finding food.

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One of the sea urchins from South Carolina with some of the seaweed they like to eat (photo credit: Kaelyn  Lemon)

I’m looking into whether sea urchins (specifically the species Arbacia puntulata, which is found in the Atlantic ocean) from Massachusetts and South Carolina will react differently in higher acidity. If one group of urchins can produce larvae that maintain a larger body size under more acidic conditions than the other group, then we will know that there is some degree of variability within the species. This would be a positive result for the sea urchins (and therefore for oceans in general) because it would mean that these urchins may be able to adapt to acidified waters more easily than we can currently expect.

Sources:

1. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

2. Clark D, Lamare M, Barker M. 2009. Response of sea urchin pluteus larvae (Echinodermata: Echinoidea) to reduced seawater pH: a comparison among a tropical, temperate, and a polar species. Marine Biology. 156: 1125-1137.

3. Sheppard Brennand H, Soars N, Dworjanyn SA, Davis AR, Byrne M. 2010. Impact of ocean warming and ocean acidification on larval development and calcification in the sea urchin Tripneustes gratilla. PloS One. 5:1-7.

Funding from the NSF and support from the College of Charleston

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