Students Examine the Factors Affecting Marine Biodiversity

Located on the elbow of Cape Cod, the town of Chatham, Massachusetts is a unique natural laboratory for studying marine biology. Estuaries, which are extensions of the sea where fresh water meet salt water, are a common feature of this area, and provide interesting sites for studying the marine flora. Muddy Creek empties its waters into Pleasant Bay just inside a barrier beach that separates Chatham from the Atlantic Ocean. The estuary is home to thousands of species of plants and animals throughout the year. Students in Chatham High School's Marine Science class have been studying the Muddy Creek estuary to determine what factors affect biodiversity, or the number of species living in a certain area.

Marine Science is a hands-on, field-based course. There is little bookwork. Students study physical, chemical, and biological oceanography by utilizing Chatham's abundant natural resources. As a class, we regularly take collecting trips to various marina docks, marshes, beaches, and estuaries throughout the town. The students enjoy catching animals and bringing them back to our aquaria for observation, for drawing, or for use in laboratory investigations. To enhance the student's educational experience, I also wanted them to participate in a quantitative investigation that could be conducted in the field, and then report their results to the community.

During our collecting trips over the past three years, I had noticed that the number and types of animals caught at the Muddy Creek estuary seemed to vary throughout the year. There are a number of factors that influence the Creek's biodiversity, including the nearby road, the golf course on the hill above it, the stone revetment, and the ebb and flow of the tide. Theoretically, however, the temperature of the water and the amount of sunlight it receives should have the biggest effects on biodiversity due to their influences on the phytoplankton at the base of the food chain. So, here was an idea for a quantitative study right in front of me, just waiting to be investigated: What are the effects of temperature and light intensity on the marine biodiversity of the Muddy Creek estuary?

Coincidentally, I had just learned about a data logger from Onset Computer Corporation (in Bourne, MA) that could measure temperature and light, and store the information even if disconnected from a computer. The company provides free loans of its data loggers to K-12 teachers and students through its iScienceProject program.

Last year, with support from two local organizations, the Friends of Pleasant Bay and the Friends of Chatham Waterways, I purchased a class set of waders, seine and zooplankton nets, and several HOBO® data loggers with temperature and light sensors.

The data loggers were the key to quantifying the relationship between temperature, light, and biodiversity. In the past, students had measured temperature with thermometers, but this only provided data for the few minutes we were at the site on any particular day. Light intensity could be measured with hand-held light meters, but this can also only be done while at the site. The other limitation of hand-held light meters is that the actual light intensity under the water could not be measured. The data loggers, in contrast, proved able to perform continuous monitoring of both temperature and light, and could even be submerged in water.

As a class, we decided on procedures to standardize our collection methods. Students then "launched" a number of HOBO loggers by connecting them to our classroom computer and programming them to record temperature and light data once every 30 minutes. The loggers were then disconnected from the computer and sealed in clear plastic waterproof cases.

On our next collecting trip, the students submerged and anchored the data loggers in the estuary below the low tide level throughout our study area. The loggers remained on the ocean floor until our last collection date, when we cut them loose from their anchors and returned them to the classroom. The loggers were then reconnected to the computer and, with the click of a button, two months worth of continuous data appeared as graphs on our computers.

In the graphical representation of the temperature and light data, students could instantly see the daily rise and fall in water temperature and sunlight. Long-term trends also became clear. By exporting the data into Microsoft Excel students could produce charts of moving averages (to smooth out the daily fluctuations in temperature) and post the results to a class website created to communicate the results with the community.

Analysis of the quantitative data provided by the data loggers and the animal collections reveals a direct relationship between the biodiversity and the ocean temperature. This relationship is easy for students to see when represented graphically. It also eliminates the need to assume that ocean temperatures rise and fall continuously over the seasons, an assumption that was made in earlier studies that could not quantify temperature or light data. The Muddy Creek estuary biodiversity study is now in it's second year and student interest remains high. In the future we plan to augment the temperature and light data with information about water chemistry to create a complete picture of what is affecting biodiversity in the estuary.

HOBO is a registered trademark of Onset Computer Corporation. For more information about data loggers, please visit the company's Website or call 1-800-LOGGERS.