PRAWN DIE OFF: The mass die off of what have been identified as glass shrimp took place last week at Forsters Bay.
PRAWN DIE OFF: The mass die off of what have been identified as glass shrimp took place last week at Forsters Bay.
The giant star fish
SHED owners on Forsters Bay, Narooma early last week saw and then smelled a mass die-off of what appeared to be tiny prawns.
The thousands and thousands of crustaceans washed up under the sheds just around from the Narooma marina.
Based on photographs sent by the Narooma News, the Department of Primary Industries identified them as glass shrimp.
“It is always difficult to identify marine invertebrates based on a photograph, however, we believe that this is a species of shrimp, sometimes known as glass shrimp,” a DPI spokesperson said.
“Such species are common and they often occur in large swarms.
“It is not uncommon for swarms, or parts of them, to become stranded on intertidal flats.
“This appears to be a normal occurrence, and may happen without external influences.”
A local oyster grower and boatman contacted by the news had however not seen such a phenomenon before.
Spectacular sea stars
Meanwhile locals have been impressed by huge eleven-armed sea stars in Wagonga Inlet, which have now been positively identified as (Coscinasterias muricata), the largest species of sea star found in Australia.
Jenny Edwards from the Nature Coast Marine Group tells us apparently they have been in the inlet for some time although they have grown much bigger over the years. Obviously their food supply is plentiful.
The Eleven-armed Seastar (Coscinasterias muricata) is the largest species of seastar found in Australia. It has a mottled appearance and the colours can be be quite variable. The ones in Wagonga Inlet are relatively bright orange with cream patches.
It has rows or short spines along its arms. However, despite its common name, the species can have between seven and fourteen arms.
Since the individuals can regrow from just one or more arms as long as they are attached to a piece of the central disc, it is not surprising that the arms vary in number and size. You can see this in the photo even though the water covering the animal does tend to distort the image.
These seastars prefer sheltered waters where they can scavenge and prey on attached invertebrates. They can evert their stomachs and digest anything organic that is below them. Lately they have been seen along the southern shore of Wagonga Inlet where the ocean-going launches tie up east of the camp area between the wooden wharf and the concrete cycle path.
It would be interesting if someone could accurately measure one from arm tip to arm tip. According to some reference books they are supposed to reach a maximum size of 25cm, but those who have seen they say the local individuals look much bigger.
This species of sea has been called a keystone species because it has such a large effect on its environment in proportion to its numbers. Scientific studies by Robert Paine in 1966 of another large seastar on the coast of NW America found that if they were removed the diversity of other invertebrates suffered and the rocks were smothered by just one species of shellfish. It is probable that the Eleven-armed seastars in Wagonga are helping maintain the biodiversity of the Inlet.
