Bottom trawl treasures from the Chukchi Sea shelf near the Canada Basin.

Bottom trawl treasures from the Chukchi Sea shelf near the Canada Basin: Sea stars, brittle stars, clams, some snails and crabs. Click image for larger view.

Bristle worm collected with a box core during the 2002 Arctic Ocean Exploration cruise.

Bristle worm collected with a box core during the 2002 Arctic Ocean Exploration cruise. Click image for larger view.

Deep Sea Fauna

Bodil Bluhm
Research Assistant Professor
School of Fisheries and Ocean Sciences
University of Alaska

Katrin Iken
Assistant Professor Marine Biology
School of Fisheries and Ocean Sciences
University of Alaska Fairbanks

Life at the Arctic Deep Sea Floor

Early marine researchers assumed the deep-sea floor to be devoid of any life. We now know that this is not true and that the diversity of species living in the deep-sea may rival that in tropical coral reefs. At first, scientists found the co-existence of manifold species puzzling because they believed that the deep sea was rather homogeneous and harsh; it therefore seemed logical that little variety of creatures would settle and survive there. Today, we think that the small-scale heterogeneity caused by sand ripples, animal tracks and worm burrows may partly explain the high richness of species that more and more researchers are finding at 5,000 feet and beyond. The arctic deep-sea, however, has received much less attention than other deep areas of the ocean world.

Arctic and deep-sea animals have adapted to permanently low temperatures in various ways. One adaptation is that their body processes, such as respiration and reproduction, work at a slower rate than those of organisms in warmer waters. This does not mean that deep-sea organisms do not do as well as organisms from warmer waters. Rather, these animals' body chemicals and life-maintaining processes work best at ambient low temperatures and at high pressure. Most deep-sea organisms would die in tropical temperatures or if they were kept in an aquarium. A consequence of the slow 'rate of living', deep-sea and Arctic animals tend to grow very slowly. In fact, some arctic deep-sea organisms grow as much in 10 years as some tropical organisms grow in one year! Slow growth usually also means high longevity. A polar sea urchin can get as old as your grandparents, but a tropical one would likely die before its 10th birthday.

High longevity, slow growth and late reproduction are partly consequences of low temperatures, but food also plays a very important role. Sea floor animals depend primarily on food particles that rain down from the top of the water column where microscopic algae, the bottom of the so-called food web, grow and provide a rich food source. A good portion of these algae are eaten by animals in the upper water column, leaving the deep-sea creatures with what little is left over or with fecal pellets and molts of those animals at the ocean surface. The food that does reach the seafloor often is no longer fresh and has lost much of its nutritional value. Moreover, ice-covered areas get less algal production than non-ice-covered areas, resulting in even less “food rain” for the Arctic deep-sea benthos. As a result, many deep-sea animals, especially bristle worms, ingest sediment and extract whatever organic matter is left within it.

What we learned during the 2002 Arctic Ocean Exploration cruise

During the 2002 cruise, we mainly explored the infaunal community at the Arctic deep-sea floor, or those animals living within the sediment. This community was dominated by polychaetes (bristle worms) as is typical for most soft bottom regions of the world oceans. Other groups found were bivalves and crustaceans of various sorts. Among the crustaceans, we discovered at least three new species of isopods (crustaceans related to pill bugs). Overall, the density and biomass of the infaunal animals was low which again is typical of deep-sea areas elsewhere. The species richness (number of species), however, was rather high and was dominated by species of Atlantic origin even at sites geographically closer to the Pacific. This phenomenon is caused by the bathymetry (depth of the ocean floor) and history of the Arctic. Today's connection of the Arctic to the Pacific, the Bering Strait, is shallow (only 50m or 150 feet), so that deep-water species cannot pass it. In contrast, there has been a deep-water connection to the Atlantic throughout the history of the Arctic, so that species from the deep Atlantic could migrate into the Arctic when conditions were right.

On a few occasions during the 2002 cruise, we were able to put an 'eye in the sea' to look at the large benthic (sea floor) fauna living on top of the sediment. The footage recorded by the remotely operated vehicle showed that filter-feeding groups such as ascidians, feather stars and cnidarians seemed to prefer the particle- and current-rich areas while few large-bodied species occurred in the motionless, muddy central basin. Since none of these specimens could be collected and few observations could be made, we will focus the effort of the 2005 cruise on the large megafauna species.

Our Goals for This Cruise

Our first expedition to the Canada Basin in 2002 allowed a glimpse into what lives at the Arctic deep-sea floor and what the fauna survives on in terms of food. As so often in science, every expedition inspires more questions than it produces answers. We are excited to have another opportunity this year to visit one of the most unexplored sea areas and try to find answers to our questions.

A snail fish in the Canada Basin at roughly 6000 feet water depth.

A snail fish in the Canada Basin at roughly 6000 feet water depth, photographed by the Global Explorer ROV camera. Click image for larger view.

Valuable deep-sea mud from the Canada Basin.

Valuable deep-sea mud from the Canada Basin. Most animals here are live inside the sediment and can, therefore, not be seen on this picture. Click image for larger view.

During our second Arctic Ocean Exploration expedition, the benthos group aims to identify how habitat features affect species distribution and richness at the Arctic deep-sea floor, and whether habitat heterogeneity may be a driver of biodiversity. What are the discriminating species at the abyssal plain versus the steep continental slopes? Why could that be? To look at these questions, we hope to observe, collect, quantify and identify the Arctic deep-sea megafauna, which are comprised of the animals large enough to be seen on photographs of the seafloor. We will use two photographic tools: a newly-designed photo platform that can reach even the deepest parts of the Canada Basin at over 10,000 feet as well as a remotely operated vehicle with a collection arm for shallower and intermediate stations. Although highly challenging in the deep-sea and in ice, we will try to deploy a trawl net to actually - for the first time - collect the larger benthic fauna including the fishes from this area. Why is deployment challenging? At 10,000 feet water depth, about 30,000 feet of cable are needed to run a trawl - an operation that can require 10 hours, enough ice-free area to operate in and a highly skilled crew. Let's see if we get lucky. If trawling will not work, we will deploy a box core to collect more infaunal organisms.

Our second goal is to improve our understanding of the food web of the high Arctic. As described above, food can be scarce in the high Arctic, and we are therefore curious what food resources different species exploit. A collection of video observations, stomach content analysis and naturally occurring isotopes will serve as our tools. We hope to trace food sources and follow organic matter flowing through the realms of the water column, the sea ice and benthos. The results will tell us which species feed on relatively fresh material (good quality food), which feed on other animals, and which survive on old, reworked detritus (bad quality food). The food web analysis of a whole ecosystem will help us identify key players as well as environmental key factors in the largely unexplored Arctic deep-sea ecosystem.

This expedition contributes to the Arctic Ocean Diversity project (ArcOD) of the International Census of Marine Life.