Background

The East Australian Current (EAC) is increasing in current strength and has warmed the Tasman Sea by over 2 degrees in the past century. The strength of the EAC can generate eddies between 30-100 km diameter, in the region of the Stockton Bight off the city of Newcastle, central New South Wales. Stockton Bight is anecdotally recognised as an unusual nursery area for NSW fisheries.

Eddies are large, gently rotating bodies of water caused by the strength of the EAC. Coastal eddies have a clockwise rotation on eastern Australia, while the offshore ones are typically anti-clockwise. In a previous voyage in October 2006 the team from the University of New South Wales sampled such an eddy revealing dramatic concentrations of late stage larvae of commercial fishes (pilchards, blue mackerel, trevally).

The fisheries and ecological significance of EAC eddies are unknown, despite the importance of eddies in the Gulf Stream, the Kuroshio and the Agulhas Current. These eddies are probably crucial for our fisheries and they can also affect marine parks.

The spring is also a time of salp swarms. Salps are large, fast-growing gelatinous zooplankton that grazes on unlimited
picoplankton and bacteria. They occur in dense blooms that can alter the food chain by significantly removing phytoplankton from the water and remains have also been recorded in the guts of many fish.

Salps are the fastest growing animals on the planet and may increase in 10% of their length per hour. Salps clearly have a major role in global carbon flux, but are essentially unstudied in the EAC since the work of Dr Andy Heron and others 20 years ago. By feeding on particles 1000 fold smaller than themselves, salps confound typical food web theory.

In 1938-1941, the CSIRO’s research vessel M.V. Warreen exhaustively sampled the waters of eastern Australia for salps and other plankton - the first and only dedicated survey of Australian zooplankton. The lead scientist Dr Harold Thompson used a particular kind of plankton net that was use throughout the North Atlantic. On this voyage we
have re-built Dr Thompson’s unusual plankton net to determine if salps have indeed increased since his comprehensive study.

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Glossary – in context of this research

Eddy or eddies (plural)
An eddy is moving, swirling water that creates a reverse current as it flows past an obstacle or strong current moving in the opposite direction. The eddy can often draw in, and isolate, water that is different from the adjacent current. In addition, plants and animals can be trapped and concentrated in the swirling water.

An Australian Salp. Image credit – Anita Slotwinski, Tasmanian Aquaculture and Fisheries Institute

Salps
A salp is a barrel-shaped, free-swimming, gelatinous animal. They are more closely related to humans than jellyfish, even though they look very similar to jellyfish. As larvae, salps resemble small tadpoles and have a notochord (a primitive spinal cord). It is this feature which links them to humans, yet is lost when the animal transforms into an adult.

Salps move by pumping water through their body, by a series of contractions. This water is strained by internal filters that serve to feed the salp by sieving bacteria and picoplankton (incredibly tiny plankton between 0.2 and 2 microns in size) from the water as it moves along.

Sampling sites

In preparation for the voyage during September and early October scientists at the University of New South Wales have examined MODIS images (Moderate Resolution Imaging Spectroradiometer) and BlueLink forecasts to search for the development of small, 50 km diameter, coastal eddies. With the aid of this information before departure the scientists will have a clearly defined sampling region.

Objectives of the project

• to sample the plants and animals located within small (<50 km diameter, and possibly larger) eddies off the Stockton Bight in comparison to coastal waters
• to document the ecology and vertical distribution of salps in shelf waters

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Methods used for gathering information

• SeaSoar - a towed vehicle used to deploy a wide range of oceanographic monitoring equipment and will create a profile of the ocean recording nutrients such as nitrate, nitrite and ammonia
• ADCP - Acoustic Doppler Current Profiler - a type of sonar that attempts to produce a record of water current velocities over a range of depths
• CTD - measuring conductivity (or salinity), temperature and depth of water samples
• Towed nets - EZ net trawl will be used to examine vertical distribution of salps.
  

Itinerary

Depart Sydney 1500hrs, Friday 10 October,
Arrive Newcastle 0800hrs, Monday 20 October

Voyage track

Map showing location, intending sampling route and ports of embarkation and completion.

Modified: 10/11/08

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