Dynamics of Supralittoral Freshwater Rock Pools in the Gulf of Maine

Appledore Island, located six miles off the coast of Portsmouth, NH, has over 500 freshwater peripheral pools situated above the intertidal zone and range in size from semi permanent pools measuring 15 centimeters across to larger permanent pools up to about 10m diameter. Seventy eight pools were physically monitored once every four days from June to August 2006 and have provided us with a deeper understanding on dynamics of pond community organization and how organisms cope with rapid and major physical changes. Pools were monitored for temperature, conductivity, pH, dissolved oxygen, water color and clarity, and presence or absence of key macrofauna. The color and clarity of pools, which we used as a proxy for phytoplankton levels, varied throughout the summer and ranged between being always opaque to always clear, or cycling between these two states. Cycling of pools is important for the macrofauna because it indicates varying conditions that organisms must contend with. Clear pools had significantly lower dissolved oxygen levels, pH values and presumably, based on water clarity, lower phytoplankton stocks, while opaque pools had higher levels of both dissolved oxygen and pH and usually very high phytoplankton levels. Diel vertical migration by Daphnia. pulex was observed in these island pools which is interesting because of the lack of vertebrate predators. Significantly higher densities of D. pulex occurred in the top 10cm during the night than day. With the absence of significant predators, physical or genetic factors must explain the observed migration to the surface at night by D. pulex