Natural bay events - Office of the Environmental Monitor

Natural Port Phillip Bay events



Photo: Basket star on soft coral

Port Phillip Bay is a dynamic marine environment that supports approximately 300 species of fish and several hundred species of crustaceans, jellyfish, corals and sea sponges. Each year a number of natural phenomena occur in its waters and on its beaches.

The Channel Deepening Project has heightened the Victorian community’s interest in the Bay. Events that would otherwise go unnoticed or be of limited public interest are being reported because of their conceivable link to dredging operations.

In some instances the events could be immediately considered natural and dredging as a cause was ruled out.

On other occasions, a field investigation was required before a conclusion could be drawn. For all reports, the Office of the Environmental Monitor sought advice from relevant agencies on these events, and based on that advice was satisfied that the events were a result of natural biological or Bay processes.

To assist the community, the Office has published a history of seasonal biological events in the Bay. Table 1 includes details on the events that have already occurred, their cause as well as photos, if available. Table 2 includes some seasonal events that have not yet occurred during the Project, but that may be anticipated in the coming months or years.

Table 1: Past Bay events

Event
Date of report
Agency that investigated the event
Cause
Photo
Apparent mortality of scallops
16/03/2008
PoMC
No evidence of scallop mortality beyond normal conditions
Empty mud-filled dead scallop shell on sea bed
Photo courtesy of PoMC
Kelp washed up on foreshore at Pt Lonsdale
07/05/2008
PoMC
Result of recent storm activity
Kelp washed up on rocks near Pt Lonsdale with the Queen of the Netherlands in the distance
Seastars washed up on a beach at Seaford
09/05/2008
DSE and EPA Victoria
This introduced marine pest is regularly found on beaches, particularly during the colder months when they move into the shallower waters and are washed ashore during storms
Seastar
Spider crabs washed up on a beach at St Leonards
24/05/2008
DPI - Fisheries Division
The crabs reported to have washed ashore were primarily the shells of Spider Crabs.

Spider Crabs are native to the seawaters of southern Australia and Port Phillip Bay and are known to mate and moult (shed their shells) during the autumn/winter months, particularly during a full/new moon (a full moon had just occurred).

The occurrence of dead Spider Crabs or their shells washing ashore in Port Phillip Bay area is not new or out of the ordinary. The phenomenon is part of the normal life history of these crabs.
Spider Crab shells after moulting
Diver collecting samples of Spider Crab shells
Reported spider crab mortality beneath Rye jetty
30/05/2008
DPI - Fisheries Division
Same as above
Spider Crabs shells after moulting
Storm surge affects on the north of Port Phillip Bay
01/072008
PoMC
Storm surges are a natural phenomenon. A storm surge is a rise above the normal water level along a shore that is the result of strong winds pushing on the water's surface and/or reduced atmospheric pressure and that causes the water to pile up higher that what would normally occur.
Not available
Paper nautilus found washed up on Chelsea beach
30/07/2008
PoMC
Commonly called the paper nautilus, the Argonauta nodosa has a slender body with arms of unequal length. The egg case is white with nodular radial ridges on the sides and a wide grooved keel around the edge. The species generally inhabits oceanic waters but occasionally move into coastal shallows, such as Port Phillip Bay, in large numbers to release their eggs and die.
Paper nautilus
Jelly or Blue Blubbers found washed up on Altona Beach
14/08/2008
Melbourne Aquarium
Commonly called the blue or jelly blubber, the Catostylus mosaicus is a native species that is often found in large numbers in Victoria's bays and inlets. It is the most common jelly fish along the eastern Australian coast.

The species is not poisonous, but if handled can leave an irritating itch on the skin.

The jelly blubber moves with the tide and strong onshore winds can wash the species onto Port Phillip Bay's beaches.
Jelly blubbers on Altona Beach.
Photo courtesy of Hobsons Bay Leader Newspaper


Table 2: Anticipated Bay events

Event
Time of year
Cause
Photo
Noctiluca blooms or "red tides"
Summer
Noctiluca is a microscopic, floating species of algae that occurs from tropical to temperate regions worldwide. While it is present in Port Phillip Bay year-round, it can occasionally form dense aggregations known as blooms or red tides. This typically occurs during the warmer months.
Noctiluca bloom at Brighton Beach
Photo courtesy of EPA Victoria
Krill washing up on beaches
Spring and Summer
Krill are small shrimp-like crustaceans that occur in swarms and are an important food source for fish and some marine mammals and birds. The coastal krill species found in the waters off southeastern Australia (Nyctiphanes australis) swarms during spring and summer. Large swarms are occasionally washed ashore in sheltered coastal bays.
Not available


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