Activity 2

The Great Oyster Mystery (click to access the lesson) - National Estuarine Research Reserve System

Researcher sampling oysters in the Mission-Aransas Estuary, TX.

Student Objectives:

Students will:

• analyze oyster abundance graphs and describe how oyster abundance changed over a two-year period in the Mission-Aransas Estuary in Texas

• examine precipitation, stream flow, and salinity data and interpret the effect of changing freshwater inflow levels on estuary organisms

• describe the relationship between oyster abundance and biotic factors, including the presence of oyster parasites and predators

Time: 3 hours (may be broken into three or four lessons)

Grade Level(s): 6th - 9th

Vocabulary:

• Abiotic - non-living characteristics of a habitat or ecosystem that affect organisms' life processes (examples include salinity, temperature, and dissolved oxygen level)

• Biotic - a component of the environment that is or was once alive (examples include predators, such as the oyster drill and stone crab)

• Dermo - a parasite that infects and kills oysters

• Hypothesis - a scientific idea about how something works, before the idea has been tested. Scientists do experiments to test a hypothesis and see if the hypothesis is correct.

• Predator - an organism that preys on (hunts, kills, and eats) other organisms. Oyster drills and stone crabs are predators that eat oysters.

• Range - the area of variation between upper and lower limits on a particular scale. All living things have a range of conditions in which they thrive. Oysters, for instance, thrive best within a salinity range of 14 ppt to 28 ppt. 

• Salinity - the concentration of salts dissolved in salt water usually measured in parts per thousand (ppt)

Description: Oysters are a valuable part of estuary ecosystems. They help purify the water and control erosion. Oyster reefs provide habitat for numerous other species. However, oysters can also be an "indicator species." Like a canary in a coal mine, oyster health and oyster abundance can tell us about changing conditions in an estuary. Studying the response of oysters to short term variations in freshwater inflow into estuaries can help scientists predict how long-term changes, including climate change, may impact oysters and other estuary organisms in the future. 

Over a two-year period, researchers examined the effects of flood disturbance on oysters in the Mission-Aransas Estuary in Texas. Researchers collected oyster samples each month over a period of two years. During one summer, large storms sent increased amounts of fresh water into the estuary. Researchers found that these fresh water surges caused short-term reductions of salinity in the estuary, which in turn resulted in lower oyster abundance. However, in just one year, the oyster population recovered beyond the pre-flood level. The researchers concluded that although oyster abundance decreased dramatically after the floods, the retention of freshwater in the estuary resulted in salinity levels that were too low to support large populations of oyster predators and disease causing parasites. The reduction in parasites and diseases allowed the oyster population to rebound beyond pre-flood levels. In this activity, students will analyze real oyster abundance, precipitation, stream flow, and salinity data to better understand the effects of variable freshwater inflows on estuary organisms.