Naturally South Australia

Dear reader

This week has been hot with temperatures hovering around the mid 30s- perfect weather for a dip in the ocean. Although our urban beaches are perfect for swimming it is the more rugged coastline further south that always attracts my attention. As a keen snorkeler and underwater photographer the cliffs, headlands and rocky reefs, interspersed with fine, sandy beaches, create a tempting environment for anyone interested in marine life.

Port Noarlnga jetty showing growth of mussels and beach

Consequently, last Saturday morning found me donning my summer wet suit and sliding into the water under the Port Noarlunga jetty; a favourite dive location only a 45 minute drive south of Adelaide’s CBD. Like many of South Australia’s jetties; this one is the legacy of bygone days when wooden ketches collected grain from coastal farming communities. The old wooden structure juts out from a sheltered beach and is sandwiched between low limestone cliffs and an estuary. Two hundred metres out to sea it intersects a reef that runs parallel to the shore. Although the reef is a marine sanctuary there is limited fishing allowed along the first three quarters of the jetty. Most divers go to the end of the jetty and drop straight onto the reef. However, on this occasion I had decided to swim under the jetty and look at the way the environment and marine life changes with depth and proximity to the reef.

Starfish on jetty pile amongst coraline algae and green algae

 The first few metres were quite a surprise. I had expected bare sand and little life. Instead I found quite a community of organisms in the shallow warm water. Small schools of mullet and yellowfin-whiting and some bream were patrolling the sandy bottom searching for small crustaceans and worms. A few large razorfish, a fan shaped mollusc that buries its pointed end in the sand, protruded amongst the small outcrops of rock and sparse seagrass patches while several sand crabs scuttled for cover in the weed as I swam over them.

Razorfish amongst seagrass

In the shallow zone, the jetty piles are constantly exposed to air and sun as the tides and winds vary. Only a few grey snail shells and worm tubes clung to them finding moisture and protection in the cracks in the wood. As the water became deeper a coating of small black mussels shaded the grey wood of the piles and a mixed growth of algae, sea squirts, sponges and other encrusting organisms started to appear. In the open water schools of baitfish would occasionally appear in tightly choreographed formations; a group strategy evolved for minimising successful attacks by predators. Closer to the surface, I caught sight of the occasional garfish and even a small group of squid chasing after a fisherman’s lure.

Squid in open water near the jetty attracted by angling lures

As I approached the end of the jetty, the character of the environment changed dramatically. The growth of invertebrates covering the wooden supports had thickened and a veritable garden of different organisms of every texture and colour imaginable competed for space and food. Small patterned fish and shrimps darted amongst these marine jungles and an occasional starfish also moved slowly though them in search of prey. The baitfish had been replaced by a mixed school of sea sweep and old wives.

School of sea sweep with a few striped old wives in the background

When I reached the end of the jetty I used the aluminium dive ladder to climb out and sat for a while on the wooden walkway and watched a few divers exploring the reef. A quick glance at my dive watch indicated that I had been in the water for well over an hour. The time had passed quickly and I had been more than pleasantly surprised by the marine life under the jetty….worth another visit.

Cheers

Baz

Baz

Tags: jetty, marine fish, sea sweep, south australian marine life, squid, starfish, underwater photography