By: Melissa Dellatorre

Seemingly simple organisms such as the sea urchin, like many other marine animals, actually have an incredibly complex early life stage as a larva. This summer on Catalina as a Wrigley Summer Fellow, I am looking at how larval physiology changes under environmental stress. A main focus of mine is to determine the effects of acute (short term) and chronic (long term) thermal stress on physiological processes including respiration, protein synthesis, feeding, and excretion. These measurements help us to understand how the organism functions under different conditions, and ultimately allows us to establish mechanisms for handling stress. This can be used to predict the ability for adaptation as the environment changes.

So far, my experiments this summer on Catalina have been with larvae from purple sea urchins, which have reached the very end of their spawning season, and white sea urchins, which are just beginning their spawning season. A female purple urchin, pictured, releases millions of eggs in a matter of minutes! Since urchins are very vulnerable in their early life stages, they have a Type III Survivorship curve, meaning only a small fraction of them will make it through metamorphosis and into adulthood.

In looking at the effect of temperature on organisms, it is well known that higher temperatures increase metabolic rates, which speeds up development. In the images below, you can see two-day old white sea urchins spawned from the same parents at the same time. The difference is that the organisms on the left were placed into 15C seawater, while those on the right were placed in 20C. It’s amazing to see such a difference in growth in two days!

Although there are clear differences in morphology at these two temperatures, the research of the Manahan Lab at USC is interested in how the organisms are changing internally, in addition to externally. Taking respiration rates of the larvae allow us to determine how much total energy (ATP) is available to expend. From there we incorporate the rate which larvae are synthesizing proteins. Protein synthesis is a major component of energy allocation, and very sensitive to temperature change. This synthesis rate can then be used to calculate efficiency, based on how much of the protein synthesized gets deposited in their bodies versus how much of it gets degraded or recycled. Combining this with larval feeding rates and excretion gives a very integrative picture of how physiological rates control an organism’s ability to develop and survive in the ocean.

Our lab group also has some exciting plans for this summer involving first generation lines of Pacific oysters. These are oysters that were spawned here at Wrigley Marine Science Center two years ago and are now mature enough to produce offspring. Since some ‘families’ can handle stress better than others, these oysters will allow us to add another component, genetics, to better understand the potential of resilience of marine organisms in a changing ocean.