Summer of the giant jellyfish
The recent finding of a giant jellyfish on a beach south of Hobart (Howden, February 2014) highlights the exciting fact that there are still things in nature, and the ocean in particular, that we know little about.
The jellyfish was measured 1.5m in diameter and it has been confirmed as the most rarely seen of the three species of lion’s mane jellyfish found in Tasmania. The lion's mane can grow to be one of the largest of all jellyfish. Although not deadly, the species will deliver a nasty sting and a cold pack should be used to reduce the pain.
The summer of 2014 has seen many jellyfish species occurring in massive numbers (jellyfish blooms) in southern Tasmanian waters but it is not known why.
Dr Lisa-Ann Gershwin from the CSIRO said it was not clear if the large numbers were an anomaly or a sustained invasion but it would appear to indicate that something was wrong.
The impact of such large numbers of jellyfish on the ecosystem is unknown. In a well-functioning ecosystem, jellyfish play an important role as a food source for other marine species, including turtles, and providing a hiding place for some small fish. When jellyfish blooms occur, the jellyfish consume a huge amount of plankton, competing with fish that other marine species and humans rely upon for food.
Blooms occur when jellyfish reproduce in mass numbers in a small area. Environmental cues, like changes in water temperature or salinity, tell the polyps (the part of a life cycle of the jelly in which it will asexually reproduce and make copies of itself) to turn on. Large-scale blooms can smother an area, demolish all fish eggs, clog the water intake of boats and ships and contaminate ballast water.
There is anecdotal evidence that jellyfish blooms may be associated with overfishing (http://www.npr.org/). In recent years, Namibia and Japan have experienced serious jellyfish blooms.
Marine life feeling the heat
Tasmania’s marine waters are warming much faster than the global average rate. As the east Australian current pushes the warmer water further south, species such as kelp are moving south towards cooler waters. The warmer Tasmanian waters are also encouraging some fish species usually seen in subtropical and tropical waters to head further south. (http://www.redmap.org.au/article/changes-in-tasmanias-marine-ecosystems/)
One way of monitoring the response of different marine species to changes in the marine environment, such as ocean warming, is to map sightings of marine species that are ‘uncommon’ in local seas.
Redmap is a ‘citizen science’ project that will use the local knowledge and sightings from some of the 3 million everyday Australians who go fishing, diving or boating each year to map which Australian marine species may be extending their distribution range. Any uncommon marine species not usually sighted in a particular area are being reported, logged, photographed if possible and entered into a database via the Redmap website http://www.redmap.org.au/.
Species of particular interest, namely those indicated by scientific or anecdotal information to be extending or shifting their range, are listed on the Redmap website. Each species is listed with some key identification information. The list also contains a few invasive species but so little is known about many marine invasive species or their current ranges that they are not the main focus of the project.
The Redmap project began in Tasmania in 2009 and was launched Australia-wide in December 2012. The Institute for Marine and Antarctic Studies (IMAS) at the University of Tasmania is the national host and data custodian of Redmap Australia.
Recent verified sightings in Tasmania waters include a manta ray on the east coast and a leatherback turtle north of King Island as well as a Port Jackson shark on the east coast and an endangered loggerhead turtle at Howrah Beach.
Tassie’s unwanted guests: marine pests
Australia has over 250 introduced marine species (not all of which are pests) which have established since European settlement. The exact number of marine invaders in Tasmania is not known, but over 70 introduced marine species have been identified in the Derwent Estuary alone. Most pests have arrived as a result of shipping traffic through ports, with the two most common methods of transport/arrival being through discharged ballast water and hull bio fouling (where organisms attach to the hull of a ship that has not been kept clean)
Other ways in which marine pest species are introduced include:
• travelling inside internal seawater pipes of commercial and recreational vessels
• through aquaculture operations (accidentally and intentionally)
• through aquarium imports
• on marine debris and on natural ocean currents.
While most introduced marine species appear to have little impact, some are highly invasive and aggressive, threatening our native species and marine ecosystems.
Tasmania’s worst marine pests are described below.
(source: taken directly from DPIPWE website)
Northern Pacific sea star (Asterias ammurensis)
This highly invasive species is a voracious eater of shellfish and other marine animals, with few predators. It is responsible for hastening the decline of the endangered spotted handfish in Tasmania.
New Zealand screwshell (Maoricolpus roseus)
This invader rapidly spreads and competes for food and space with native screwshells and scallops on sandy sea floors. It has few predators.
European green crab (Carcinus maenas)
A small but voracious predator, this menace preys on scallops, mussels and oysters. It invades the habitat of native crabs and causes havoc in aquaculture farms.
Japanese kelp (Undaria pinnatifida)
A highly invasive species, Japanese kelp grows rapidly and excludes native seaweeds. Spores are transported aboard boats, on fishing and dive gear, and in natural currents.
Long-spined sea urchin (Centrostephanus rodgersii)
This species is native to the coast of the east Australian mainland but as the ocean’s temperature increases, its range has extended further south and now reaches down the entire eastern coast of Tasmania. In large numbers, without predators, the urchins completely transform lush, productive kelp beds into lifeless bare rock. One of the few predators able to break into their spiny shells are very large rock lobsters, which are found in marine protected areas.
Control
Marine pests are almost impossible to control. The Department of Primary Industries, Parks Water and the Environment (DPIPWE) is the lead agent for the management of marine pests in Tasmania and has useful information on identifying marine pest species on its website. Physical, chemical and biological control of a number of species have been attempted with only limited success. Some pest species, including the Pacific oyster and European green crab are edible. A few marine pests are being harvested on a small scale for commercial gain (including the long-spined sea urchin and Japanese kelp). Early detection and rapid emergency response are the preferred alternatives, to prevent marine pests from becoming established in Tasmania.
Report sightings
If you see anything you think might be a marine pest or disease, please call the 24-hour Disease Watch hotline 1800 675 888 (Australian Government Department of Agriculture) or your nearest DPIPWE office.
Meg Lorang