Day 10 The foundation of an ecosystem: Chantelle Cook

How does an ecosystem start? Where does it begin? How does it flourish? Phytoplankton! Plankton have been described as the ‘biological heartbeat of our oceans’ by the IMOS Australian Plankton Survey—a joint project of CSIRO Marine and Atmospheric Research and the Australian Antarctic Division. The phytoplankton absorb sunlight and build nutrients to fertilise the ocean. In turn, this attracts zooplankton, little fish that feed off the plankton, and other predators to eat the zooplankton. Voilà, a food chain has begun and an ecosystem is underway!

Most phytoplankton are unable to be seen by the naked eye. However, large amounts can sometimes be seen as coloured patches in the water, if they are present in high enough numbers.

Two nights ago, we deployed a Continuous Plankton Recorder (CPR) off the back of the ship. CPR surveys are one of the oldest running biological marine tracking programs in the world. They have their roots in Plymouth, UK, having been invented by Sir Alistair Hardy in the early 1930’s. The CPR has provided marine scientists with a standard measure of plankton recording that has remained unchanged since 1948.

The CPR is designed to be towed from the back of a ship at a depth of about 10 metres. Water passes into the instrument and the plankton are filtered onto a spool of silk, which is then covered by a second layer of silk. The silk and plankton are then rolled into a holding tank that contains the preserving agent, formaldehyde.

Today, we assisted (watched and took photos really) as the crew, Ben and Linda, brought the CPR back on deck. Once on deck, Ben removed the holding tank. We then took it to the sea water lab, where more formaldehyde was added. The sample will be safely stored until we reach our port where it will be sent on for analysis.

The samples are analysed in two ways. Firstly, by the colour of the silk—it is measured and given a value based on its ‘greenness’ against a colour chart.  The green colour comes from the amount of chlorophyll in the plankton. This measured value is called a Phytoplankton Colour Index and gives an estimation of the phytoplankton biomass. Secondly, the sample is placed under microscopic analysis and individual phytoplankton and zooplankton are identified and counted.

This data will be used by marine scientists for a range of things such as:

• mapping plankton biodiversity and distribution
• developing the first long-term plankton baseline for Australian waters
• documenting plankton changes in response to climate change
• providing indices for fisheries management
• detecting harmful algal blooms
• validating satellite remote sensing
• initialising and testing ecosystem models.

Essentially, all of this information will help us to ensure the health and vitality of our oceans.