On the Edge of the Blue Line

On the Edge of the Blue Line

The sand is golden with a uniform, rippled pattern to it; like the sole of an old fashioned sneaker. Every few metres small clumps of grassy weed appear until finally the sand merges into an endless green meadow of seagrass. Seagrasses are not algae but true plants with leaves, roots and in most species, flowers. They form a crucial ecosystem in the shallow waters of Gulf St Vincent. As I hover above the dense mass of leaves, a school of tiny silver fish lifts out of their embrace, swims a few metres then blends back into the shelter of the meadow.

Blue line as seen from the sand hills near Henley Beach

I am snorkelling off Henley which is better known as a fashionable beachside cafe strip rather than a dive destination. I decided to arrive a little early and enjoy a cup of coffee while I waited for the sun to get high enough for underwater photography. The water is clear and the ocean warm and inviting at this time of year and it is just a short swim from the local jetty to the blue line where the sand and seagrasses merge. The lush tangle of gently waving blades that surround me are home to one of the planet’s richest marine environments. It is a place where whiting, mullet, blue crabs, giant rays and squid (to mention just a few inhabitants) find food and shelter for themselves and their young.

Seagrass meadow

I swim a little further into the seagrass until I locate a patch of sand with some darker detritus around its edge, indicating that something might have dug into the substrate. I stir the sand with the tip of my dive knife…nothing…I swim a few metres further and repeat the process. On the third attempt I get a result. A dinner plate sized blue swimmer crab bursts out of the sand with pincers extended and full of aggression. These crabs are prolific along the upper gulf in the summer months providing a valuable commercial fishery and great sport for recreational fishers and divers.

Blue swimmer crab

Experience has taught me that the boundary between seagrass and sand is an ideal place to observe different animals. Because I am wearing extra weights I am able to rest effortlessly on the bottom in this zone and wait for something to happen. Over the next few dives my strategy pays off as a small group of juvenile King George whiting settle close to me as they search for worms and molluscs between weed and sand.

Juvenile King George whiting

A little further offshore small sand patches occur regularly in the seagrass meadow. Often there are a few rocks colonised by brown or green algae and even variations in seagrass species in these areas and these slight variations in terrain frequently produce the greatest diversity of marine life. My first sand patch does just that. Lying close to the bottom, I let my eyes adjust to the light and moving shadows produced by the tidal flow and rippling surface. Just a few centimetres from my lens a seahorse clings to a blade of eelgrass using its tail and tiny fins to move in time with the swaying miniature forest of the underwater meadow.

Big bellied seahorse

I have been in the water for over an hour and I am getting a little chilly and besides a cappuccino and breakfast roll beckon back at the Henley Square where many a tourist sips coffee unaware of the glorious marine world just a short swim away.

Cheers

Baz

Tags: Australian wildlife, Beaches, blue simmer crab, King George Whiting, marine fish, seahorse, south australian marine life, South Australian wildlife, underwater photography