| Send this page to a friend |
Tidal Flat Species
Recently on the mudflats at Wynnum and Empire Point, Ormiston some of us came across Nudibranchs. What are Nudibranchs you say? Nudibranchs are marine snails (gastropod molluscs) that have no shell, they can be found from Antarctica to the tropics generally on the seafloor. However, some are pelagic (living at or near the surface of the sea), floating upside down on the ocean surface feeding on blue bottles or Portuguese man-of-war's (Physalia physalis) and By-the-wind sailors (Velella velella), others feed on goose barnacles attached to flotsam and jetsam. Nudibranch means 'naked gills' because their gills are on the rear of the back (posterior dorsal) of some species or along the side covered by a protective flap as these species tend to bury into sand or mud. They generally range in size under 10cm, however the largest species grows to 40cm. They come in a range of colours, some extremely colourful and spectacular. Nudibranchs appear to live for about one and a half years depending on food and conditions. When food is plentiful the numbers increase, as the food source is consumed or decreases for natural reasons, numbers decline. Water temperature and climatic conditions may also play a part in the Nudibranch chances of survival. It should be noted, some Nudibranchs have toxins in their mantle glands, taken from their food source, which they secrete when disturbed. The life style of a Nudibranch can be categorised as:
Moreton Bay has many species of Nudibranch, it's a lifetime consuming passion to see them all.
The Rose Petal Bubble Snail, Hydatina physis, has a papery thin globular shell of a dirty white colour covered with numerous brown to black spiral lines. The common name refers to an animal, which is rose to mushroom in colour with blue edges. Shell grows to about 40 mm and the animal extends to about 95mm. They are common and are found in sand, sandy-mud, seagrass and rubble, intertidal and sub tidal zones to 15 m. Seen at Wellington Point beyond King Island on the sand banks.
An epiphyte is a plant or animal that attaches itself to another plant, including seagrass. Bacteria and diatoms are usually the first to colonise a seagrass leaf, followed by larger algae and invertebrates. Like the seagrass itself, most epiphytes photosynthesise and so contribute significantly to the overall productivity of seagrass ecosystems and are frequently grazed by fish, gastropods and crustaceans. A thick covering of epiphytes, often caused by high nutrient levels in the water, will however reduce the ability of the seagrass to photosynthesise. The seagrass' only defence against epiphytes is to shed their leaves. Next time you're out seagrass watching check the age of the leaves the epiphytes are on, and which seagrass species seem most susceptible. Moreton Bay's seagrass grows quite rapidly, compared to seagrass in southern Australia, with Halophila ovalis having one of the most rapid leaf turnover rates. That's why their small oblong leaves usually look nice and clean.
|