“The deep sea is the Earth’s largest continuous ecosystem and largest habitat for life. It is also the least studied,” says Dr. Chris German, who along with hundreds of other Marine Life scientists from around the globe is shedding light on these mysterious depths through an unprecedented census of deep-sea marine inhabitants. Their recordings have yielded astonishing findings of more than 17,500 species of often bizarre marine creatures – from oil-eating tubeworms to elephant-eared octopods – inhabiting the blackest depths between 200 meters and up to 5, 000 meters (~3 miles) below ocean surface. Even more remarkable is the ability of these deep-sea creatures to live and thrive in topographically challenging environments where food availability is marginal, at best.
Until now, one could be forgiven for believing that without the life-sustaining food process of photosynthesis, marine life would become scarce or nonexistent the further one probes into the murky recesses. But according to Edward Vanden Berghe, who manages the census inventory of marine life observations, OBIS (Ocean Biogeographic Information System), the reason that the number of records falls off dramatically at deeper depths is simply because of a lack of sampling conducted in the deep sea.
Data collection for a census of this magnitude has required the efforts of 344 scientists throughout 34 countries and across 14 field projects. Five of these projects devote their study of marine life to progressively deeper and darker waters where investigations are marked by the topography they cover: COMARGE (Continental Margins Ecosystems); MAR-ECO (Mid-Atlantic Ridge Ecosystem Project); CenSeam (Global Census of Marine Life on Seamounts), which explores the mountainous terrains jutting from the seafloor; CeDAMar (Census of Diversity of Abyssal Marine Life); and the project marking the vents, seeps and chemically-driven ecosystems in the deepest ocean trenches known as ChEss (Biogeography of Deep-Water Chemosynthetic Systems).
Survival in the deep
The success of each project is measured by the abundance, diversity and distribution of observable marine life in the furthermost reaches of our oceans. When species are observed at deeper than 200 meters, the depth where darkness prevents the life-sustaining process of photosynthesis from taking place, it begs the question: how can any marine organism survive in the absence of food?
According to Robert S. Carney of Louisiana State University and co-leader of the Census project COMARGE, “Abundance [of deep sea marine life] is mostly a function of available food and decreases rapidly with depth. The transition[s] from abundant food made by photosynthesis to darkened poverty display the intriguing adaptations and survival strategies of amazing species.”
He explains that abundance of marine life in the deep sea is dependent on one or more factors such as swift current, increasing an animal’s chance of encountering food; populations of long-living animals whose growth rates are numerous in spite of meager diets; the presence of food in higher layers that settle to the depths or to which animals can migrate; and an alternative to photosynthesis as a food source, such as chemosynthetic production.
While distribution of marine populations changes according to depth, the diverse range of species in existence is more difficult to comprehend, especially when the mud on the deep sea floor seems an unlikely food resource. Says Dr. Carney, “to survive in the deep, animals must find and exploit meager or novel resources, and their great diversity in the deep reflects how many ways there are to adapt.”
It pays not to be fussy
An example of just how resourceful these creatures can be comes from a discovery of a tubeworm (formally known as Lamellibrachia) by COMARGE explorers in the Gulf of Mexico in 2007. When a robotic arm lifted the worm from a hole in the Gulf floor at 990meters (~ .6 miles) the flow of crude oil from both the animal and the open hole left observers surprised to find the creature dining on chemicals from decomposing oil. And at 2, 750 meters (~1.7 miles), an odd, transparent sea cucumber (Enypniastes) was discovered creeping along on its many tentacles while sweeping detritus-rich sediment into its mouth before blooming into a curved shape and swimming away to find its next meal.
A CeDAMar team of scientists, who investigate the muddy floor of ocean plains, also discovered what is perhaps the most ingenuous food source in their recording of a whalebone-eating worm at about 500 meters (0.3miles) into the Antarctic ocean.
Further below, from 1, 700 to 4, 300 meters (~1.25-1.5 miles), MAR-ECO explorers report a collection of creatures of unusual shapes and varying sizes. Coryphaenoides brevibarbis, nicknamed the rat-tail, is a creature with bones in its ear known as otoliths which have growth bands similar to tree rings to reveal the fish’s age. It lives on crustaceans it catches just above the seafloor and its growth rate is indicative of the amount of food present at this depth.
In similar depths, researchers have collected a large specimen of a rare, primitive animal known as cirrate or finned octopod, commonly called “Dumbos” because they flap a large pair of ear-like fins to swim. Measuring nearly two meters (~6 feet) long and six kilograms (~13 pounds), this particular gelatinous “Dumbo” is the largest of only a few specimens of the species ever obtained.
On a 2009 voyage to a range of New Zealand seamounts, a CenSeam team discovered abundant vibrant coral gardens at 1, 000 meters (~.6 miles) and below in an area of seamounts nicknamed “the graveyard” where the speed of currents provides an ideal habitat for these animals that feed on suspended food.
Never before seen findings is the norm
For the CeDAMar project team, investigations on the abyssal floor reveal that deep mud contains biodiversity that escapes detection by video and photography since most of the animals are only a few millimeters in size and hide amongst the sediment. In this highly inaccessible realm, the vast majority of creatures collected from the abyssal plains are new to science. Of 680 specimens of copepods collected on a recent CeDAMar voyage to the southeastern Atlantic, only seven could be identified; 99 percent were new to science.
Says CeDAMar expert David Billet of UK’s National Oceanography centre, “the abyssal fauna is rich in species diversity and so poorly described that collecting a known species is an anomaly.”
Far more rare than new species in the mud is the capture of a new species of sea cucumber and rarer still, a new genus. What researchers found most startling was that the most abundant sea cucumber around the Crozet Islands—thousands of speciments at abyssal depths—was a species never seen anywhere else before, now dubbed Peniagone crozeti.
At depths of 4, 000 meters or greater, the work of ChEss researchers found evidence for chemically enriched plumes in the water column, signaling the presence of seafloor hot vents hundreds of meters deeper still. Funded by NASA’s Astrobiology program, the team used a hybrid robotic vehicle as a free-swimming autonomous underwater vehicle (AUV) and then as a tethered, battery powered remotely operated vehicle (ROV) to track the plume to its source. Poor weather thwarted the investigation and will be resumed by ChEss in 2010.
The magnitude of these discoveries alone invites further speculation about the mysteries of the deep sea. According to Dr. Billett, “In addition to the boundaries caused by underwater topography…there are unseen, and as yet unexplained, walls and barriers that determine supplies of food and define the provinces of species in the deep sea.”
A treasure to be respected and protected
One can no longer be forgiven for viewing the deep sea as, in Dr. Carney’s words, “ a wasteland where few to no environmental impacts could be of any concern.” The careless attitude to “mine it, drill it, dispose into it, or fish it—what could possibly be impacted?” is one that Marine Life scientists fear. According to Dr. Carney, “Census of Marine Life deep realm scientists see and are concerned.”