We made a smooth transition from geological perspectives on coastlines to an ecological perspective by studying how the dynamic sedimentary environment of a beach controls and affects the organisms trying to make a living there. Most visitors to a beach are there to relax, enjoy the lovely scenery, perhaps take a swim, and their thoughts of what might be living there (not just visiting) are dominated by the obvious, such as seagulls looking to steal a cookie, or perhaps wariness of what large toothed fish might be lurking in the waves. A look at the sands below our feet might not stimulate thoughts of life, yet that is where we are looking in this block of Marine Ecology.
The intrepid students had completed a beach profile, documenting the slope of the beach face, and we carefully observed and recorded features of the wave environment, such as breaker height, wave period, and distance of breakers from shore. All of these affect how much the sands are moved by wave action, which can make it easier or more difficult for organisms living there. We learned what allochtonous matter is, an obvious example being the seaweeds ripped up during a recent storm and washed up on the beach, and how that provides a food source for various consumers. With our observer senses on high alert, we started rooting around for organisms, to see the life that might escape the casual observer’s notice.
On the east side of Popham Beach, with its steeper slope and more dynamic wave swash zone, we found fewer forms of life, dominated by small crustaceans called amphipods, sometimes called “beach fleas”, though they do not look like fleas, and do not bite! Larger ones were found in the wrack stranded in the high intertidal. Vigorous digging along a line towards the water revealed no other visible forms of life, but once we reached the swash zone, where water rushes back and forth from the breaking waves, we found abundant smaller amphipods, happily tumbling in the sands, accessing the organic matter stirred up by wave actions. A fine mesh sieve was needed to sample these critters; without it, they would have escaped our notice. The shorebirds, little sandpipers, were certainly well aware of the amphipods and feasted while we sampled.
The west side of the beach, with a much shallower slope, sand bars, and much calmer swash zone, harbored a greater diversity of life forms, particularly various worm forms down in the sediments. We even found fish, sand lance, hiding in the sands awaiting the tides’ return. The amphipods of the east beach were much less abundant here, showing us how different energy regimes support very different life forms.
All in all, the students enjoyed some lovely days at the beach, learned a great deal about life they hadn’t noticed before, and forged the connection between the physical/geological environment and how that constrains and shapes the community of organisms there. There were a few sighs of melancholy bidding farewell to the beach, but many interesting ecosystems await our attentions!