Beach Sweep—July Young Naturalists Excursion

July 23 was a pretty wet and miserable day, but several young families and adults appeared regardless of the weather. We had just decided to go for a short walk collecting any plants, animals and plastic, when down came the rain. This happened 2-3 times so each time we scuttled back to our cars. The weather was perfect for collecting fresh specimens as the sea weed and sea-grasses were still coming in.

When we returned Mike Gregson went through the main groups. He described the green, brown and red algae due to different colour pigments. Quite a few seemed to contain agar which can be extracted on a mass scale for icecream, tomato sauce and laboratory agar.

Two genera of algae, Caulerpa and Codium, have the distinguishing feature of having just one big cell with nuclei dispersed throughout the structure.

Mike talked about the sea grasses that are descended from land plants, which then re-invaded the sea and have flowers that are pollinated underwater. He showed us Posidonia coriacea or ribbon weed and the thicker version P. australis which is responsible for the fibre balls that can often be seen on the beaches. There were two species of wire weeds, Amphibolus antarctica and A. griffithii, where many small organisms settle on it. The juveniles had the little grappling hooks, to enable them to catch onto anything and settle down. Most of the sea grasses are poisonous, but Paddle Weed, Halophilia ovalis, is often grazed by little fish and Dugongs up north.

sea grass seedling

One of the sea-grasses was a seedling. On the Monday following, I sent the photo to Marion Cambridge from the Oceans Institute at UWA who said it was a tropical seagrass seedling of Syringodium isoetifolium.

She thought it had a red seed too.  The next day she went down to the beach and after checking her seagrass books, it turns out that the seagrass we collected (S. isoetifolium) has hard, dark coloured seeds a few (4-5) mm long (see sketch). Marion thinks our specimen probably had some sort of orange/red ascidian attached to it. She also sent a male flower with anthers attached.

As usual we had many sponges-Porifera, some of which were brightly coloured, which ranged from soft sponges used in the bath, to coarse ones. All contain spicules and the really coarse ones are made of spongin. The sponges when alive can have many colours.

From Cnidaria (which can include corals) we saw a large number of the floating colonial blue bottles (below), which consist of a large gas filled float and several tentacles including a large fishing tentacle, feeding tentacles and reproductive tentacles. It is the long fishing tentacles that have stinging cells which can be so dangerous in the tropics.

A small colony of Physalia utriculus showing the horizontal float with the polyps beneath. Note the main tentacle is long, frilled and beaded in appearance. 

Photo by Clay Bryce,
copyright WA Museum

We also found Velella—a hydrozoan with polyps with a sail filled with gas which floats around the ocean.

By Velela – Transferred from [1]: 2005-01-31 15:27 . . Velela . . 1808×1108 (688230 bytes), Public Domain, Link


From Mollusca we saw Violet Shells which also have bubbles so can float around on the surface.

The only other molluscs we saw were the inevitable Spirula shells which are the shell of an octopus like animal that lives out in the open ocean and uses air chambers to move up and down in the water column.

The only Echinoderms were sea urchins; mainly the large red sea urchin Heliocidaris which has a sharp set of five teeth. Using a hand lens, you could see where the tube feet emerged.

There were many sea squirts which are Ascidians with simple sac like bodies, and an inhalant and exhalant siphon. Their tadpole like larvae has a notochord and it’s here that there is a link to vertebrates. The notochord is a precursor to the vertebrate backbone, and this makes the Ascidians (Tunicates) part of the Phylum Chordata.

There were many colonial ascidians as well. The photo is the calcareous tube of a Spirorbid worm according to Claudia). These are miniature fan worms that are epiphytic (grow on plants and many other surfaces). These are miniature fan worms that are epiphytic (grow on plants and many other surfaces).

The only other vertebrates we saw were a Skate egg case and Globe Fish plus a large fish skull which Claudia Mueller took back to her Department of Animal Biology at Murdoch University. The skull was examined to try to locate the otoliths from the inner ear, to determine the species. Unfortunately they were missing.

We were so lucky to have Mike Gregson who shared his wealth of knowledge with us and also Claudia Mueller who was extremely helpful both on the beach and taking some samples back to Murdoch University as well, for feedback.  Unfortunately Lisa Kirkendale and Megan Cundy were unable to attend. Needless to say, given the weather conditions we all managed to have a great time and got the job done!

Just spotted Tom Hallam’s post in WA Naturalists’ Club facebook  group

Maureen Gardner