Hasn’t the weather been extraordinary? Spring came late. Insects we normally see in early September didn’t emerge until November. Then when it finally broke, it was almost continuous rain and wind for a month (the kind of weather we would have had in September in years past). An ongoing Sudden Stratospheric Warming has brought unseasonally strong northerly and westerly winds and rain. Which meant visibility for snorkelling has been pretty poor and may remain that way periodically through much of summer. Yesterday was the first time for a while that conditions have been reasonable enough to snorkel in Beaumaris Bay. Temperature in the water was about 21 degrees.
Beaumaris Bay and Green Coral
The ecosystem here has changed since last year. The seagrass, which is washing up in vast quantities on our beaches, is starting to thin. There were a few Widebody Pipefish in the remaining patches. Winter’s sargassum and caulerpa are dying off leaving a more barren substrate covered in mussel shells – are we seeing the resumption of shellfish reefs? Barrens are normal. The bay’s ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More cycle through in waves every few years. It’s essential for the green coral.
In great news, that green coral is coloured again. Last year it bleached. Now there are exquisite patches of intense green, as well as browns and blues. The coral bommies in this area appear to be among some of the oldest in the bay. This area, as I’ve surmised before, may be just as important as Rickett’s Point but it’s not as well recognised.
All in all a nice swim. Nothing particularly remarkable but it was nice to see the usual characters around. Tasmanian Blennies are common, along with abundant hermit crabs, the Black-margined Sea Slugs and shovelnose stingarees buried beneath the sand.
Assessing underwater visibility
There has been a lot of talk about visibility on the chat groups of late. In truth, it’s a very difficult (maybe impossible) thing to predict. I never bother. If you use the risk of poor visibility as yet another excuse not to swim, chances are, you’ll miss out on more good swims, than you will risk bad ones.
Unless there has been a prolonged period of strong onshore winds (which bring heavy waves), visibility tends to settle down. But there are two different systems that prevail.
In the short-term, sediment can be lifted from the seafloor. These tend to be heavier particles. This usually results in one or two days of poor visibility before it settles and clears again. The other is sediment introduced from the Yarra River. The latter is a critical part of the bay’s ecology. If we don’t have strong spring plumes from the river, the penguins at St Kilda can’t find food! But for us snorkelers, it’s a bit of a pain.
But the river sediment is finer and lighter than the beach sand. It gets carried in the freshwater. This floats over the clearer, heavier and saltier bay water, to form lenses that morph around depending on winds and currents. Offshore winds, for instance, will tend to push these lenses in closer to the coast. Southerly winds will push them north. Over time, winds will dilute this sediment into the water column but it takes over 234 days for this to flush out of Port Phillip Heads.
It’s a complicated situation and can change hourly. Even the most complex hydrodynamic models can barely predict the consequence on the scale at which we are swimming.
Which means there really is no way to predict it. Last year we had a dry spring and vis was good most of the year. The year before we had huge spring rains and a sewage spill and conditions were pretty awful most of the year.
My best advice is this. If the weather has been offshore (e.g. blowing out from the coast to the sea) for a day or so, the chances are conditions will be calm. This means local sedimentation is likely to have subsided. If you arrive and find the water is a bit milky, alter your concentration and look for the small stuff in the shallows.
There’s always plenty to see ; )
