It’s starting to get cold! For many of us, Port Phillip Bay snorkelling and water temperature go hand-in-hand. I went for a swim last week (a proper one) without a wetsuit. It was 13.6 degrees. It’s dropped further this week and to be honest, it was slightly uncomfortable on the face yesterday morning, even though I was rugged up in a 5.5m sem-dry and hood. Nevertheless, I managed to find lots of sapsucking sea slugs, including a few of the cryptic ones I reported on just recently.
A change in the season underwater
We did, however, snorkel for about 90 minutes and couldn’t really feel fingers and toes when we got out. On the plus side, the water is nice and clear. The wind has been a light northerly for days which are the predominant conditions in winter. This means the bay’s circulation pattern changes abruptly, creating a huge shift in the distribution and abundance of fish life. This is the time of year when the large schools of fish begin to leave the coastal shores and head into the centre of the bay.
Note how the left hand image (below) shows a change in nutrientEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More front (purple line) reaching from the Bellarine Peninsula to Black Rock. This is where all our snapper go for the winter. It’s also why Ricketts Point Marine Park is important as a lot of the nutrientA substance that contains the raw materials for life. At a chemical level, these are contained inside compounds that are absorbed into the body and essential energy-containing molecules are extracted, so that energy can be transformed into other chemical processes that use the energy for living. More and activity centred on here, which includes about 38,000 penguins from Phillip Island, gets transmitted to our coastline and builds up before spring.
Figure 1: OceanographyThe study of the physical, chemical and biological properties of the ocean. More of Port Phillip Bay. Winter (left / top) with predominant northerly winds; and summer (right / bottom) with predominant southwesterly winds and sea breezes.
A week of warmer air temperatures
This week the sun will warm the sea slightly, as we’ll enjoy 19 degrees above water though any benefit beneath will be lost as the very cold clear nights will sap remaining heat from the surface. Expect to feel the water drop by another degree or so. Time to pop on some gloves and boots, if you don’t already, and perhaps some thermal underlayers for the wetsuit. We also pour some warm water into our suits before entering, to get the layers heating up, which buys us a few more minutes of comfort.
Sap suckers and nudibranchs
Despite all of this, it is one of my favourite times of year. Right now, the sapsucking sea slugs are super-abundant so I returned to fossil beach where I saw them the other day. The clarity of the water can be seen in the landscape featuring two large bommies of green coral, with requisite purple urchin in attendance. Sap suckers like the Winged Slug Elysia below, are vegetarian. They feed on Caulerpa. By contrast, the nudibranchs are carnivorous. Although the bright orange Doriopsilla pictured below, didn’t seem to get the memo! A big and quite brightly coloured Phyllodesmium was a nice find too. Very pretty.
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