Marine Plants

KRM Branch February Meeting

 The speaker for our first meeting of 2019 was KRMB member Daniel Heald who gave a talk, supported by photographs, on marine plants of the local area. He started with a brief summary of the structure of seaweeds—a general term that covers all forms of marine algae. The structure is much simpler than that of flowering plants, in that they do not have roots (they have a holdfast at the base of the body that anchors them to a firm surface such as a rock), or distinct stems or leaves. Seaweeds are grouped into divisions largely corresponding to their colour.

The first grouping Daniel presented was that of the Green Algae. He showed photographs of species that fall into this grouping include the Acetabularia (Mermaids Cup) and a Bryopsis sp. (found by Daniel on rocks on the sea floor after winter storms had washed away the sand). After this, there followed photos and discussion of several species of Caulerpa including C. cactoides, C. flexilis, C. longifolia, C. racemosa (Grape Weed) and C. sedoides. Other green algae included Codium sp., Derbesia sp. and Halimeda cuneata (Green Shields). The last species in this grouping was the Sea Lettuce (Ulva australis), an edible alga that can often be located one week but gone the next, due to grazing.

The next group of seaweeds were the Brown Algae, which includes the kelps. The first genus shown was a Colpomea sp., a lump of jelly like material. Then he showed us a Cystophora sp. and Dictyota dichotoma (Doubling Weed), one of the fan-shaped algae. The next image was of a true kelp, Ecklonia radiata; the kelps form kelp forests in cool waters. Other brown algae shown were Padina sp. (another fan-shaped alga), Sargassum sp. (a genus with a built in buoyancy system allowing it to float free—it is found at Point Peron at certain times), Scabaria aghardi and Turbinaria gracilis, a bushy species.

The Red Algae was the next grouping discussed. These included Dicranema revolutum (which grows only on the stems of sea grass); Gelidium (Turf Algae), which can be collected and boiled down to produce agar; Gloiosaccion sp.; Hennedya crispa; Osmundaria prolifera; and Sarcothalia radula, which forms large blades with pimply growths on the surface.

The last group of algae Daniel discussed was the Red Coral Algae. These are characterized by the fact that calcium carbonate is incorporated in their structure. This group include Amphiroa sp. which can stay on a beach for weeks due to the strengthening calcium carbonate. This contrasts with other seaweeds that typically break down very quickly once washed ashore. Other genera in this group are Metagon sp. and Neogoniolthon sp..

During his presentation Daniel also discussed Sea Grasses, which are true flowering plants. They can form very productive meadows that stabilise sandy sea floors and provide habitat for marine flora and fauna. The first species of seagrass he presented was Wireweed (Amphibolis antarctica), which has male and female flowers on separate plants. The seeds germinate on the parent plant and after about 7-12 weeks the seedlings break off the parent and become free floating with a comb of bristles that hooks on to the surface of a substrate. From this comb, roots develop that anchor the plant. Another local species is the Fireball Weed (Posidonia australis). The leaf of this species disintegrates into masses of fibres that are rolled into fibre balls by wave action and are often encountered washed up on the shore.

Seaweed Specimens

Following the presentation, members of the audience were invited to study a table full of specimens of local seaweeds collected by Rosalie Barritt at Point Peron that afternoon. This collection contained many of the species shown by Daniel. There was one species in the collection that Daniel was not familiar with. It had a net or lace-like structure. Daniel photographed it and sent it off to the South Australian Herbarium for identification and received a response from Carolyn Ricci.

Hydroclathrus clathratus

It was Hydroclathrus clathratus – a brown alga with a highly unusual net-like morphology that is found in warm and temperate seas worldwide. The SA Herbarium has requested permission to use the photograph submitted by Daniel on its interactive identification website as currently they have only images of pressed specimens to use. It was a really good find.

The audience thanked Daniel for his presentation and Rosalie for collecting the specimens.

Colin Prickett