What are strandlines? They are generated where the sea ends and the land begins – the high water mark on any given tide. They are composed of organic and inorganic flotsam. The position of the strandline changes with each deposition event – so you find strandlines at various points up the shore.
In the picture above, a line of fresh wet seaweed at the edge of the retreating tide marks the formation of a new strandline.
Newly formed strandlines – like this one at Studland Bay in March – have colourful fresh wet weeds; living seashore animals like molluscs; and deeper water creatures like jellyfish; empty shells; dead animals like crabs, fish and birds; driftwood and synthetic objects.
The new strandline provides a wonderful larder for seashore creatures – invertebrate and vertebrate. Smaller animals like sandhoppers demolish the food really quickly, leaving just a hazy trace on the beach of the organism just eaten. Birds and mammals then feed on these tiny crustaceans. On sandy beaches, the remains of the strandlines become integrated with the beach sediments, enriching the ecosystem by recycling nutrients, and preventing erosion by promoting dune formation.
The photograph above shows dried seaweed and empty shells marking the height of the previous high tide at Studland Bay. In older strandlines the weeds dry out, dead animals decompose and get eaten, the sand begins to blow over and cover, the debris is crushed underfoot and buried. It’s not only people but also horses, dogs, and quad bikes that trample the strandlines at Studland.
I never see any rubbish on the beach there. There are lots of bins along the shore and, in the main, they are conscientiously used. The general absence of man-made flotsam may either have something to do with the presence of the Training Bar offshore, or it may be regularly cleared by patrolling National Trust wardens.
The photograph above shows how wind-blown sand and traffic along the beach begins to bury the empty shells and dried weed on one of the strandlines at Studland Bay. The composition of the strandlines varies depending where you are along the shore at Studland. In the photographs below, the strandline looks very different from those pictured previously. It shows that at in one location, on one occasion, flint pebbles dominated with just a few isolated razor shells.
Strandlines can vary in different parts of the same seashore. Flints dominate the strandline in this location on Studland Beach.
The picture below shows broken flints, coarse sand, and empty razor shells in one particular place at Studland Bay.
Revision of a post first published 8 June 2009
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