EUREKA – WE CAUGHT A SALP!

The Southern Ocean pelagic ecosystem is known to be highly variable among different Antarctic regions and to show dramatic variation among both seasons and years. This year, many people have commented on the unusual amounts of remaining ice. Perhaps Austral Spring is late this year. Our studies will help analyze this variation in species composition and abundance over time and space. Prof. Joe Warren (Stony Brook University) and his students – carrying out another salp project on our cruise – are measuring “biovolume” of our plankton catches. At SBU, other students will determine the abundance of different zooplankton species in the preserved samples. These data will be compared with results from other Southern Ocean regions and years.

Figure 1. Living Southern Ocean krill soon after capture.

Our zooplankton catches have been rather smaller than we expected. – but with many different species. Important for our study, we have sampled dense patches of juvenile and adult Southern Ocean krill (Euphausia superba; Fig. 1). Krill are a keystone species for the pelagic ecosystem here and dominate the zooplankton assemblage in biomass and abundance. They are an important species for us too, since they are important player in the dynamic balance between salps and krill in the Southern Ocean food web. Our goal is to understand the population dynamics of both species in relation to the zooplankton community and environmental conditions in the Southern Ocean.

Figure 2. Station locations for the Salp Survey cruise, including sites in the Drake Passage (Stns 4-11) and Bransfield Strait (Stns 14-21). We have completed work at stations with red numbers.

Back to our unfolding oceanographic adventure! Yesterday the winds blew at 30 – 40 kts as we steamed SE in the Drake Passage from our Stn 11 (Fig. 2), where we had completed work in a patch of good weather amidst days of howling winds and high seas. We arrived at Stn 12 during the morning, but the seas were still up and swells were coming from two directions. We waited until conditions calmed down and went to work in the early evening.

Figure 3. Fifteen seconds of fame for the first salp caught on our cruise! With the star is its biggest fan, UConn PhD student Paola Batta-Lona. Photo Ann Bucklin

Eureka! We caught our first salp in Net 4 (which sampled from 200 – 100 m) in our fifth MOCNESS tow of the cruise. We preserved the salp separately to give it some special attention (Fig 3). We hope to find many many many more salps! And we may catch a bit of luck with weather, with forecasts for winds between 15 and 20 kts for the next 24 - 48 hrs in our area. That should give us time to sample our northern-most stations and head back south through Bransfield Strait, where we should find some protection from the westerly winds. Salps, Ho!

-- Ann Bucklin (University of Connecticut)