Underwater world gives up its secrets
This cranchid squid larva is only 10 mm long but adults can grow up to 2 m. Their bodies remain translucent.
Photo: Russ Hopcroft
|
While the Umitaka Maru and L'Astrolabe focussed on the pelagic (open ocean) realm, the Aurora Australis focussed on the sea-bed communities of the survey region. Common sites were sampled by all three vessels on the continental shelf. Umitaka Maru also surveyed sites north of the continental shelf to look at north-south distribution patterns, and the deep pelagic zone – a poorly sampled habitat known to have a high biodiversity of zooplankton and jellyfish.
Scientists aboard the L'Astrolabe sampled the inshore plankton of the area using a standard 'WP2' plankton net. This is a small net (0.25 m2 mouth area) with 200 micron (0.2 mm) mesh that is ideal for collecting small zooplankton and very young fish larvae. The team also conducted CTD (conductivity-temperature-depth) casts which measured the profiles of temperature, salinity and other physical properties in the water column. Bottles attached to the CTD frame collected water for studying phytoplankton and other micro-organisms that provide food for the zooplankton. While the L'Astrolabe survey was perhaps more routine, it provided continuity with past French surveys in the area.
The Norpac net, consisting of 330 micron and 110 micron nets side by side, was used to study all sizes of plankton.
Photo: Graham Hosie
|
In addition, CTD and bottle casts provided data on the physical and chemical properties of the water. Phytoplankton collected from the bottles were placed in incubation chambers to determine how quickly they grew and therefore how much food they would provide for zooplankton, which in turn support higher trophic groups such as fish, birds and mammals. A WP2 net and a 'Norpac' net, which consists of 330 micron and 110 micron nets side by side, were used to study all sizes of plankton.
Japanese scientists measure the pelagic fish Pleuragramma antarcticum.
Photo: Graham Hosie
|
Both large survey nets produced many good quality specimens that were used by Canadian zooplankton biologist, Russ Hopcroft (Australian Antarctic Magazine 12: 28), to take high quality photos. The photos were taken with a high definition camera/microscope system and image capturing software. The whole system was mounted in such a way as to eliminate the vibration from the ship.
A marine worm (Vanadis antarctica) from the macro-zooplankton.
Photo: Russ Hopcroft
|
Many of the jellyfish captured were new to the researchers and may be new records for the region. Tissue was taken for genetic analysis, to help determine if we have any previously undescribed species. A notable result of the voyage was the high abundance and diversity of jellyfish in the deeper waters down to 2000 m. Large specimens of Stygiomedusa were collected in near-perfect condition. These jellyfish have large bells and tentacles that extend 6-8 m in length. While we need to compare the results with past data, the collective memory of experienced Antarctic biologists on board suggests that the jellyfish are more abundant than before.
We've planned the survey and collected the samples and associated environmental data. The next task is to pull all the information together and address a range of questions such as: have the deep water zone communities changed and will this have an effect on the rest of the ecosystem? Meetings of key CEAMARC personnel are now in train, to begin collating results and building a picture of the biodiversity and ecosystem processes in the survey area.
GRAHAM HOSIE
CEAMARC leader, AAD
Back to Antarctic Magazine 14: 2008 index
Next article Ship's Log: Collaborative East Antarctic Marine Census
