Tangaroa — Week 4, 21-27 February 200821-24 February 2008Rocky Bottoms
After losing 24 hours research time to rough weather, the last four days have been spent completing core station transects from the edge of the Ross Ice Shelf, and down the continental slope. These are the stations where all our sampling equipment is deployed.
The DTIS (Deep Towed Imaging System) video and still images have shown us that much of this area of seabed west of Iselin Bank, adjacent to Cape Adare, is very rocky compared to the southern shelf areas sampled earlier in the voyage. The seabed is covered with rocks ranging in size from a couple of centimetres up to a metre or more across. Unlike most of the world's seabed, the rocks we are seeing were not formed in situ but have been ice rafted from the Antarctic mainland.
The numerous massive glaciers on shore pick up rocks on their slow flow to the coast from inland Antarctica. The rocks are carried on the surface or buried deep within the glacier. These rocks (known as glacial erratics) often show evidence of this movement, with smoothed faces and scratches worn deeply in their surfaces. When the glacier fronts reach the coast they break off, forming icebergs that carry their rock load with them until the bergs melt, dropping the rocks to the seafloor. Also contributing to this rock transport is the collapse of the steep cliffs onto the surrounding sea ice. The sea ice breaks up and moves offshore during the summer thaw, melts and the ‘drop stones’ fall to the seabed further offshore. Evidence of this process is seen as far north as the Chatham Rise, east of New Zealand.
The presence of these rocks has made it very hard to successfully collect quality biological samples and the gear regularly comes back on board in need of repair. Science ReportCephalopods
Cephalopods (squid, octopus, and their relatives) are highly specialised molluscs and the most advanced invertebrates (animals without a backbone). The Ross Sea region is famous for the colossal squid which feeds on sperm-whales and toothfish. As a group, however, the cephalopods are of far more importance than just their spectacular diversity. Their role in the dynamic ecosystem is likely to be important and we are collecting samples to address questions about both their diversity and their trophic interactions. During the survey, we have seen a wide range of cephalopods. Some of the most appealing cephalopods are octopus, particularly the Dumbo octopus.
Dumbo octopus are known from all oceans and are generally found in water deeper than 300m, although in cooler waters, such as Antarctica, they can be found at shallower depths.
Dumbo octopus come in a variety of forms but all species have a semi-gelatinous body, a pair of fleshy ‘fins’ on the mantle (head-like body), strong webbing between the arms, and a row of cirri (minute fleshy finger-like projections) along each side of the sucker row on each arm. Most species are an orange/red/purple colour and all species lack chromatophores (pigment filled sacs under individual nervous control), so they are incapable of changing colour, unlike most other cephalopod groups.
The behaviour and ecology of these largely deep-sea species is poorly known. Most species live close to or on the seafloor. Dumbos generally feed on small prey with low swimming speeds, such as small crustaceans (including amphipods - like the sand-hoppers found at the beach, and shrimps), and worms. Unlike inshore and oceanic cephalopods, which often move rapidly using jet propulsion, dumbos generally move at a more sedate, energy-efficient pace; crawling along the bottom, drifting with the current, swimming using their large fins, or by pumping their webbed arms.
Mesopelagic trawl catches The change in catches from the mesopelagic trawl going from the inner Ross Sea shelf to the Ross Sea slope has been quite dramatic. Fish catches on the shelf were almost exclusively Antarctic silverfish with occasional juvenile and adult crocodile icefish. In contrast, fish catches over the slope have been much more diverse and numerically dominated by several species of lanternfish (e.g., Electrona sp. and Gymnoscopelus spp.), deepsea smelt (Bathylagus sp.), and barracudina (Notolepis spp.). The invertebrate catches have also differed markedly with shelf catches dominated by crystal krill, and slope catches dominated in weight by large jellyfish. Individuals have weighed up to 15 kg, with tentacles up to 4 m long.
25-27 February 2008Back through the ice barrierOur survey of the inner Ross Sea shelf and slope has now been successfully completed, with a total of 29 stations and 143 separate gear deployments. At least 400 different invertebrate species have been collected and nearly 75 different fish species identified.
We finished our time on the inside of the ice barrier with a perfect Antarctic day — clear and sunny skies with great views of the distant Admiralty Ranges of Northern Victoria Land, including Mt Herschel (3335 m), Mt Sabine (3714 m) and Mt Minto (4163 m), along with great sunrises and sunsets.
It is now time to leave the inner Ross Sea. The workable area is reducing as the end of the summer season arrives and the freeze starts. Water temperatures are down to -1.85°C and new ice is becoming common. We are now starting our steam northwards through the 120 mile wide ice barrier heading towards open water where we will continue our sampling programme on the Antarctic seamounts and the abyssal plain (3000-3500 m) in the outer reaches of the Ross Sea region.
Science ReportZooplankton, written by Julie HallZooplankton (free-floating animals) are an important component of the marine food web, providing food for many fish species. During our voyage we have been using a Multiple Opening and Closing Net and Environmental Sensing System (MOCNESS) system to sample some of the larger zooplankton at specific depths from the surface to the seafloor. The plankton community changes with depth and this has implications for interpreting energy transfer through the food web. By using a MOCNESS rather than a more traditional simple plankton net that cannot be opened and closed off at a specific depth, the changes in plankton diversity and abundance through the water column can be more accurately estimated.
At the stations above the slope in the Ross Sea, we have found that the zooplankton populations are dominated by salps (planktonic relatives of sea squirts) in the surface waters and at deeper depths by crustaceans. We have collected several interesting types of zooplankton, including pteropod (image below) and ctenophore species many of us have not seen before (image below). The pteropods (planktonic snails) have a shell made of carbonate, which makes them particularly susceptible to the predicted decrease in pH (i.e. increasing acidity) in the ocean due to increasing atmospheric carbon dioxide. We have also caught larval fish and juvenile squid with the MOCNESS.
Marine symbioses in Antarctica, written by Stefano SchiaparelliFeeding interactions between living organisms may be direct, as in the cases of herbivorous (eating plants) and predatory (eating other animals) relationships, or indirect, as in the case of symbiotic relationships. The word ‘symbiosis’ is often used to mean an association between organisms from which both gain an advantage but its proper definition includes parasitism (living in or on another organism and eating its tissues or its food). Direct feeding relationships are easier to account for than symbiotic or parasitic relationships when trying to understand or quantify the dynamics of feeding relationships.
We have just discovered two new parasites of the holothurian (a group of echinoderms with soft, cylindrical bodies, including sea cucumbers) known on the Tangaroa as ‘sea pigs’. The first parasite is a small mollusc and, in Fig. 9, two of these snails can be seen happily embedded in the body wall of a sea pig. They live permanently in this position, feeding on the body fluids of their host using their long proboscis (bottom right). The second is a tiny crustacean which lives completely inside the sea pig and feeds on its internal tissues (Fig. 10).
Hydroids, written by Malcolm Clark & Stefano SchiaparelliHydroids are coral-like animals, and many are soft-bodied forms that are difficult to catch and preserve. Last week in the southern Ross Sea, we obtained photographs and samples of a likely new species of hydroid. It is much larger than others known from the area, and also differs in colour and shape. Our first encounter was during a DTIS camera drop at 650 m. The figure below shows its bright orange colour and amazing flower-like structure where it sat on the seabed. Later, a specimen was caught in the trawl at about 400 m, and confirmed its large size, measuring about 6-7 cm across at the ‘head» and a stalk that was at least a metre long. This makes it 3-4 times larger than other species in this group that we know of in the Ross Sea. It also highlights the value of using different types of equipment during the survey, enabling both in situ observation and specimen collection.
The Liparidae (snailfishes) is a very unusual and taxonomically challenging family of fishes. The different species are difficult to distinguish, and accurate identification generally requires sophisticated techniques such as X-ray counts of numbers of vertebrae and fin rays. However, by careful examination of the specimens, and comparing the high quality colour photographs, it is clear that we have already caught at least five different species from the shelf and slope of the Ross Sea. Most species of snailfishes are relatively small with a length of 15–20 cm, but we have caught several specimens of Paraliparis sp. of almost double the length at 30–35 cm. Two days ago we completed our deepest bottom trawl to date at almost 2000 m depth and caught eleven specimens representing at least three different species — a veritable snailfish heaven!
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