In 2008 we began to look at finer-scale characteristics of eelgrass beds. SCUBA divers placed underwater sensors on moored buoys in select eelgrass beds in Provincetown, Jeremy Point, the Eastham Flats, and Plymouth.
These sensors continuously record light and temperature data, both of which are instrumental in determining the distribution, productivity, and survival of eelgrass. The collection and analyses of these data from multiple sites over time, will give insight into the variation in eelgrass habitat health we observe at these sites.
Data from these sensor show clear cycles in both diel and seasonal variation.
Diel Variation: Over the course of a 24-hour period there is variation in both light and temperature. At the surface, light and temperture are primarily affected by time of day and weather. At the bottom these parameters do not vary as much as surface conditions. In addition to time of day and weather, the light and temperature conditions at the bottom are also strongly influenced by the tidal cycle. The weather and tidal conditions of Oct 2 and 3 demonstrate the affects of these variables on both light and temperature. For example, the peak in light at the bottom coincides better with low tide (late afternoon), whereas, the peak in light at the surface coincides better with time of day, i.e. when the sun is directly overhead (early afternoon). The change in weather from sunny to cloudy has more dramatic affects on the surface conditions.
Seasonal Variation (bottom sensors only): Over the course of the field season there is variation in both temperature and light. Bottom temperatures slowly increase to a peak in August before declining during the fall. Light is affected both by seasonal changes in available sunlight and by water clarity.