Sandy Beach at Eagle Cove

While looking at the smooth sandy beach at Eagle Cove, it is hard to believe that many microscopic animals spend a portion of their lives, or their entire life cycle, in the interstices between the sand grains.  In small samples of sand from the beach we found diverse invertebrates from several phyla, including polychaete annelids, gastrotrichs, nematodes, copepod crustaceans, and various larval forms. Click here to learn more about these fascinating nimals that are  interstitial animals, which are collectively referred to as "meiofauna."

sand core
Katie taking a sand core sample at low tide

In addition to using special techniques to separate the meiofauna from the sand, we also used small nets to seine the edge of the water.  There we found a number of small arthropods including mysid shrimp, cumaceans, isopods, and cladocerans ("water fleas"). These invertebrates live either on the surface or just under the surface of the sand.

A mysid shrimp seined from the top of the sand

Microscopic polychaete found in sand

Because low tide exposes the beach to direct sunlight, extreme temperature fluctuation is a potential source of stress for small meiofauna in the sand.  We used small data loggers (iButtons ® ) to record temperatures at different depths in the sand during an extreme low tide series.  A temperature record was taken every 12 min for three days at the surface, 2 cm down, 4 cm down, and 8 cm down into the sediment.  The degree of temperature fluctuation was dramatically different on the two low tides when we had complete records (see figure, below).  On July 3rd, which was overcast and cool, temperatures increased less than 5°C to a maximum of 15°C at the surface, and maximum temperatures differed by no more than 2°C among depths.  On July 4th, which was cloudless and hot, the surface temperature rose to 32.5° C and the maximum temperature reached differed by 12°C from the surface to 8 cm below the surface.  As a result, temperature fluctuation within days and between days is less extreme at greater depths.  Because oxygen availability may also vary as a function of depth, we predict that meiofaunal animals will not be distributed randomly in the sand, and might even vertically migrate within the sand as conditions changed.  Sampling the meiofauna from different depths under different temperature conditions would be a useful way to test this prediction.

Visit these additional links to learn more about locomotion , feeding , reproduction & protection strategies of invertebrates living in the sand beach at Eagle Cove.

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