CCAMLR

This paper is presented for the Commission’s consideration and sets out the projected outcome of the budget for 2006, a draft of the 2007 budget and an indicative forecast for the 2008 budget. The presentation is in the format determined by the Commission at its 2002 Meeting.

The Southern Ocean south of Australia is oceanographically complex, being characterized by double branches of the Sub-Antarctic Front (SAF), Polar Front (PF) and Southern Antarctic Circumpolar Current (SACCF), in addition to the Southern Boundary (SB) of the ACC. From 25 February to 3 March 2002 a 2150-km Continuous Plankton Recorder (CPR) transect was conducted along 140°E, between 47.02°S and 66.36°S, crossing each of these frontal zones. Surface temperature, salinity, and fluorescence were measured at 1-min intervals in conjunction with CPR samples. Additional physical data for the region south of 61°S was provided by nine CTD stations. Multivariate and Indicator Species analysis of the high resolution (~9.2 km) zooplankton samples identified six distinct assemblages which were strongly correlated with frontal/oceanographic zones. These assemblages appeared to be structured by a combination of zonal differences in water mass structure, phytoplankton regimes, and small scale intra-zonal features (e.g. eddies). The northern branch of the SAF was the strongest biogeographic boundary, separating a high proportion of sub-tropical and temperate species from the waters to its south. The study area differed from other sectors of the Southern Ocean in that the northern PF, equivalent to the PF in other sectors, was not a zone of distinct ecological transition. Two of the identified assemblages were located with the seasonal ice zone, south of the northern SACCF. Although Euphausia superba larvae were a component of both of these assemblages, this species, together with appendicularia, was most abundant south of the SB. The seasonal ice zone north of the SB was dominated by small copepods (Oithona similis and Ctenocalanus citer), appendicularia and foraminifera. Although the physical characteristics of the frontal zones can be subtle, the demarcation between zooplankton assemblages was clear. Cross-frontal changes in zooplankton assemblages highlight their role in long-term monitoring programs as indicators of environmental change.

A repeat transect was run south of Tasmania, along ~140°E, during November and December 2001. NORPAC nets were deployed during a CTD transect on the southern leg, sampling four depth zones at each of 19 stations: 0–20, 20–50, 50–100 and 100–150 m. A Continuous Plankton Recorder (CPR) was deployed on the northern leg (average sampling depth = 10.5 m). Both net systems were harnessed with 270 ?m mesh and all sampling was conducted between 47°S and the Southern Polar Front (S-PF) at ~61°S. Zooplankton in the top 150 m of the water column demonstrated strong, small-scale, vertical distribution patterns. Species richness and diversity increased with depth, and were lowest for CPR samples. Conversely, dominance decreased with depth and was highest for CPR samples. Evenness was similar for all sample groups, indicating that all communities had a similar distribution of abundance amongst species. There was little variation in abundance between NORPAC depth zones (average = 82 ± 47 individuals m–3), while abundance was substantially higher in the CPR samples (average = 144 ± 103 individuals m–3), despite it under-sampling fast-moving and delicate components of the plankton community. The higher CPR abundance was due to significantly higher abundance levels of Appendicularia, Oithona similis and Rhincalanus gigas nauplii. The NORPAC samples showed that these three taxa were most abundant in the surface waters. The significant increase in abundance in the CPR samples was attributed to the growth in size during the period between the NORPAC and CPR surveys (minimum 15 days) increasing their catchability. Both the NORPAC nets and CPR surveys identified distinct communities to the north and south of the Southern Sub-Antarctic Front. Owing to its shallow towing depth, the CPR focuses on species with surface distributions. Despite under-sampling some components of the zooplankton, the CPR provided sufficient taxonomic resolution to identify biogeographic zones in the Southern Ocean. The utility of the CPR as a long-term monitoring tool in the Southern Ocean is discussed.