Week 4: Benthos – life on the seabed

During the voyage to the Ross Sea, we sampled benthos. So what is benthos, and why do we want to know more about it?

Benthos is everything that lives on the seafloor: sea stars, sea squirts, sea slugs, corals, crabs, clams, whelks (sea snails), worms, sponges, urchins, anemones and a great many more things. Benthos begins at the edge of the ocean, and many of the organisms we find in the Antarctic will be very similar to those you will know from rock pools and beaches at home.

Studying benthos (or benthic organisms) is important to understanding how ocean ecosystems work. Often, these animals occur in very high numbers and with high biological diversity, which leads us to think they play an important role in the way that energy (food) flows through the ocean ecosystem.

Antarctic benthic organisms live in extremely cold water and have been isolated through continental drift from the rest of the world’s oceans for many millions of years. This combination of cold and isolation has resulted in the evolution of very special animals.

During this voyage, we asked questions such as ‘Why are these animals where they are?’, ‘How do they come to be there?’ and ‘Why are they different from similar animals elsewhere?’

IPY blogs week 4

Sampling the benthos

The benthic animals we study range from bacteria to massive sponges and can live both above and within the seabed. In order to sample all of them, we tow cameras close to the seabed, allowing us to observe the distribution and abundance of the species and how they interact with each other and their environment. We use sleds and trawls to catch organisms that live on the seabed and a multicorer that takes samples of the seabed mud and any animals living in it. This will allow us to assess biodiversity, learn more about food chains and understand the evolutionary history (how the organisms came to be there) of the Ross Sea ecosystem.

Written by David Bowden

The spineless catch of the day

As the catch from sleds and trawls arrives on deck, the benthic team springs into action. Three weeks into this voyage, they have already processed more than 2 tonnes of mud, sand and rocks from the Antarctic Ocean. The catch appears like a chaotic jumble of fish and invertebrates like sea stars, sponges and worms, smothered in copious amounts of mud. The fish are picked out by the fish team, while the benthic team bins, weighs, sorts, records and properly preserves everything else on deck in our small enclosed hut. Back in Wellington, these samples will be analysed to learn about species diversity, distribution, food webs and the evolution of the Antarctic benthos.

Written by Kareen Schnabel

Multicoring

One of my roles on board is to conduct experiments on the rate that organisms in the sediment use oxygen in the areas that we are sampling. We use the multicorer to get sediment cores and bottom water from the seabed. Both the core and the overlying water are then incubated in a waterbath at the same temperature as the sediment at the bottom of the ocean. Throughout incubation, the dissolved oxygen level of the water inside each tube is measured at roughly 4-hourly intervals. When animals breathe, they consume oxygen – faster oxygen consumption indicates more life in the mud!

Written by Matt Knox

Sea cucumbers

Sea cucumbers (holothurians), which are particularly common, result in hours of sorting for the benthic team. Perfect for a sea cucumber biologist! One sea cucumber (Scotoplanes globosa), known on the Tangaroa as the ‘sea pig’ for its pig-like peg legs and snout-like tentacle oral crown, lives abundantly in the deep sea of Antarctica. It was initially seen in our DTIS (Deep Towed Image System) crawling along mud substrate balancing on 5–7 pairs of sturdy feet. Following this, we caught numerous sea pigs in a 30-minute trawl. Generally, sea cucumbers in the deep sea are deposit eaters, crawling on the bottom unselectively engulfing mud and extracting nutritious food. Hence, sea cucumbers have been known as ‘hoovers’ of the sea.

Written by Niki Davey

Marine symbioses in Antarctica

Interactions between living organisms can be direct and simple (predator eats plant eater) or more complex 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). We found two new parasites of sea cucumbers (holothurian). The first parasite is a small mollusc that lives permanently embedded in their host’s skin, feeding on the body fluids. The second is a tiny crustacean that lives completely inside the sea pig and feeds on its internal tissues.

Written by Stefano Schiaparelli (Italian National Antarctic Museum, Section of Genoa)