Benthic Ecology

Dr. Craig Smith leads the benthic ecology team from the University of Hawai’i at Manoa. This group is investigating the community and food web structure of animals in Andvord Bay, as well as determining the environmental drivers that influence these animals so we may understand how this ecosystem might be altered by climate change.

Fjords along the West Antarctic Peninsula are regions of enhanced productivity which provides ample food to the animals living on the seafloor below. In addition, animals living in the fjords are exposed to a wider range of food sources which are not available or as common in regions on the outer Antarctic shelf. Because of this, organisms in the fjords appear to be larger and very abundant as well as quite diverse making these fjords ‘hotspots’ of biodiversity.

Andvord Bay (and many others along the West Antarctic Peninsula) is a deep, glacio-marine fjord; the glacier at the head of the fjord is in direct contact with the ocean. The glacier is, therefore, very sensitive to ocean conditions and will likely respond to significant ocean warming (see more details regarding glaciers in ‘Glacial Dynamics’ section). The glaciers produce icebergs, meltwater and sediment plumes which all influence the organisms living in the fjord. For example, near the glacial front meltwater introduces freshwater and sediments into the water column. The sediments are often very fine particles which can travel down-fjord and settle onto the seafloor as well as on animals. Those organisms which rely on filtering food particles from the water column may become clogged with sediment. Therefore, these organisms are less common in areas of the fjord with high sedimentation.

A schematic illustrating the progression of Arctic fjords (Syvistki et al. 1989)

A schematic illustrating the progression of Arctic fjords (Syvistki et al. 1989)

As the water in these fjords warms over time, a consequence of climate change, glaciers are hypothesized to increase melting which could also enhance the delivery of sediments to the fjord and reduce the ability of filter-feeding organisms to inhabit the fjord. This hypothesis is well-supported by comparison to other high-latitude fjords of the Arctic which experience much greater influxes of freshwater and sediment. The benthic ecology team looks to these Arctic fjords as a predictor of future changes in Antarctic fjords and will compare dynamics between systems.

In order to study the organisms that live on the seafloor in the deep fjords, the researchers will use many different instruments and approaches. First, it is important to determine how much food (plants grown in the surface ocean) rains down to the organisms on the seafloor below. A sediment trap (pictured below) deployed on a long-term mooring will be used to capture the slow-sinking material for more than 1 year. sed trap2Researchers in the team will examine the material and will determine the flux of food to the benthos over time. Next, we need to know what organisms are living on the seafloor and how many. Because the fjord is too deep for humans to dive, the researchers will use a camera to take images of the seafloor communities. The camera, called a yo-yo camera (pictured below), is deployed from the ship and towed slowly, taking images at set intervals. The team will also be using a stationary time-lapse camera to watch the response of organisms to larger pulses of food and to measure rates of their activity.yoyo

The images (example below) can later be analyzed and animals identified. It is difficult to deseafloorfinitively identify animals from simply images so animals will also be collected using a Blake trawl. This very large net is deployed from the ship and dragged along the seafloor scooping up animals from the surface of the  sediment. These animals can then be identified, dissected and sub-sampled for other tests including DNA-fingerprinting and stable-isotope analysis. The diets and positons of animals in the benthic food blake1web can be determined with stable isotopes. When an animal consumes food, the “isotopic signature” of that food is reflected in its tissue. By comparing the signatures of possible food sources and several animals, it is possible to determine who is eating what. Because animals living on the seafloor rely on food from the surface ocean, a MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) will be used to collect pelagic animals like krill as well.

Finally, many small organisms (macrofauna) live in the sediments which cannot be captured in imagery nor by trawls. Boxcore and megacore samples will be collected in order to identify small animals as well as look at the sediment surface. Thebox corese pieces of equipment (shown below) are deployed from the ship and collect undisturbed, intact pieces of seafloor up to 40cm deep. The sediments and animals can then be separated from the sediment by hand or utilized for incubation experiments.

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