I braved the cold today and managed an hour and a half swim. There aren’t a lot of fish about right now. If you look offshore towards Portarlington you’ll see a lot of birds. Most of the fish life moves out into the middle of the bay in winter, which is a topic I covered in a recent blog. Today was the chance to take a look at the habitat at Ricketts Point as it grows in the winter. A lof of the time the ‘barrens’ you see in summer are the senescent period for the Caulerpa and Sargassum. The majority of the sanctuary comprises a complex mosaic of these species.
A huge diversity of life
In between these extensive fields of green are occasional bare patches where the urchins are to be seen. Incidentally, Caulerpa is poisonous to sea urchins, so I suspect they go into a kind of torpor in the winter. They’d re-emerge in summer to graze on algae, which is really important, considering our sanctuary is quite overwhelmed with nutrientsEnergy 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 from the Yarra.
I took one photo and identified as much as I could (below). I’ve probably missed 5-10 smaller species. Plus, there would be other sponges and bryozoans under the overhangs. It’s enough to see the diversity though. The dynamic is really interesting to watch unfold over the year. Not many people look in winter but it’s a really important time for the system to bounce back from the stresses of summer (warm water, nutrients etc). Interestingly, while there is a focus on culling sea urchins, the far more abundant sap sucking slugs (there were emergences of billions this year) wipe out hundreds of hectares of Caulerpa every year leaving only bare ground.
In 90-minutes I didn’t see any barren areas today and I covered the majority of the middle of the sanctuary. There are some great spots where Golden Kelp is self-seeding. These are in the usual places … but again, the growth is among Caulerpa. The same goes for the green coral you can see in the image above. I can see at least 13 colonies in the image.
Japanese Kelp
What is slightly concerning is the rampant growth of Japanese Kelp on teahouse reef. This had a lot more golden kelp two years ago. I worry that the culling of sea urchins here may have created conditions suitable for this invasive species to establish.
