Prior to 1967, the environmental extremes of the deep were thought to limit life. The deep sea is dark (can’t-see-your-hand-in-front-of-your-face dark), cold (only-four-degrees-above-freezing cold), and under an extreme amount of pressure (one-elephant-on-each-square-inch-of-your-body pressure).  This suite of factors should make survival challenging, and thus for a century, scientists assumed the deep sea was biologically a desolate wasteland.  Even after the discoveries of animals living at extreme depths in the late 1800s, Victorian scientists expected that there could not be a diverse array of animals surviving in the deep sea.  Enter Robert Hessler and Howard Sanders who in 1967 used newly developed sampling devices to discover that the deep sea is shockingly diverse, and perhaps just as diverse as tropical shallow-water habitats. 

Scientists were completely baffled as to how high diversity could occur in such a bleak place.  They began to throw out theories, but they were limited by the little data that had been gathered from a poorly explored deep ocean.  The scientific publications of this time on deep-sea diversity read like there were a few people in a room with a whiteboard, writing everything they remember from their ecological textbooks, talking through each theory, slowly crossing off possibilities, and working their way down the list.  

Howard Sanders began by writing “Specialization” on the whiteboard with his paper introducing the Stability-Time Hypothesis in 1968.  He suggested that because the deep sea is monotonous and predictable (i.e., it is stable), populations have the evolutionary time to become newly specialized in how they feed. Over time, these populations become so specialized they evolve into totally new species, eventually driving diversity up.  Further research and explorations indicated that the premise of this argument was wrong- the deep sea is actually not that stable.

Then, Paul Dayton and Robert Hessler walked up to the board and scratched off the “Specialization” idea with their paper in 1972 entitled “The role of biological disturbance in maintaining diversity in the deep sea.”  The pair do not argue against the idea that the deep sea is predictable and stable.  In fact, they favor the idea… except for the part where they proved that deep-sea species are actually not more specialized than shallow water species.

“Specialization” got a strikethrough on the whiteboard, and Dayton and Hessler wrote “Predation” below it.   The duo introduced a specific type of predation pressure they labelled “biological cropping.”  No, biological cropping is not deep-sea animals learning agricultural techniques… but a combination of predation and deposit feeding.  Animals can eat other animals either intentionally (e.g. hunting down prey) or unintentionally (e.g. stuffing everything you come across into your mouth and it just so happens that you get a live one).  This “cropping,” whether accidental or not, reduces competition by preventing one or a few abundant species from monopolizing the resource.  These species get knocked out, allowing far more species to get a piece of the proverbial pie. Nobody gets sent into extinction by competition.  Dayton and Hessler’s idea is not necessarily that diversity is driven to be high in the deep sea, just that it is not limited.

Dayton and Hessler’s “Predation” idea never got fully scratched off the list, but the difficulty of testing the idea and conflicting results have led many to write large question marks next to it.   Many other ideas now are situated below “Predation,” including: “Disturbance,” “Patchiness,” and “Successional Dynamics.”

Ultimately, those of us in the deep-sea scientific community are still today standing around the dry erase board bouncing many of these same ideas off each other.  Sometimes we manage to cross one off the list, or add one, or at least add to our understanding of the ideas.  One thing is clear though, we still haven’t gotten it all figured out.  So… anyone have a dry erase marker?

The post How is the deep sea so diverse? The struggle is real for late 1900s ecologists first appeared on Deep Sea News.

The authors used chemical analysis to look for signatures of DWH oil, while simultaneously counting and identifying species of meiofauna (microscopic animals such as nematode worms, copepod crustaceans, etc.) and macrofauna (slightly larger, but still small animals such as polychaete worms). In this way, the presence of oil compounds could be compared with the number of deep-sea species present and the abundance of different organisms.

Aaaand, there’s no questioning these results. Here’s a map of sample sites, where color indicates impact (red = highest impact, with a high chemical signature of oil, low species diversity, and high nematode:copepod ratios, which is a biological indicator of oil pollution):

Now we zoom in and focus on the area surrounding the wellhead:

Since you can’t sample everywhere in the deep-sea, the authors also used their dataset to model the predicted benthic footprint over a wider area. Remember, red is bad:

And again, zooming into the area directly around the wellhead. Shazaam:

In addition to confirming the impact around the wellhead, this modeling approach picks up on shallow water impacts (orange patches off Louisiana, likely driven by surface transport of oil slicks), as well as a predicted area of moderate impact extending 17km to the southwest of the wellhead (remember that deepwater oil plume? Yeah, it seems to have affected animals living in the mud below it).

Note that the red “severely impacted” deep-sea area is 24.4 square kilometers, and the moderately impacted yellow area is 148 sq km (in total, that’s more than TWO Manhattans impacted by oil. Imagine New York City covered in sticky crude twice over…).

When you think about the size of the deep-sea impact, the road to recovery also seems quite grim. We’re talking possibly decades to return to business as normal:

Full recovery at impacted stations will require degradation or burial of DWH-derived contaminants in combination with naturally slow successional processes….Recovery of soft-bottom benthos after previous shallow-water oil spills has been documented to take years to decades [39,40]. In the deep-sea, temperature is uniformly around 4°C, and TOC [total organic carbon] and nutrient concentrations are low, so it is likely that [oil] hydrocarbons in sediments will degrade more slowly than in the water column or at the surface. Also, metabolic rates of benthos in the deep-sea are very slow and turnover times are very long [41,42]. Given deep- sea conditions, it is possible that recovery of deep-sea soft-bottom habitat and the associated communities in the vicinity of the DWH blowout will take decades or longer.

Reference:

Montagna PA, Baguley JG, Cooksey C, Hartwell I, Hyde LJ, Hyland JL, et al. (2013) Deep-Sea Benthic Footprint of the Deepwater Horizon Blowout. PLoS ONE, 8(8):e70540.

The post The Deep-sea footprint of Deepwater Horizon first appeared on Deep Sea News.

I am very excited today!  My new paper in the journal Ecology will be coming out in April on the regulation of biodiversity in the deep sea.  NESCent is issuing a press release (below) written by our very talented, Communications Director Robin Smith.  Above is a high-definition Youtube video we put together for the occasion.

Durham, NC – Surplus food can be a double-edged sword for bottom-feeders in the ocean deep, according to a new study in the April issue of Ecology. While extra nutrients give a boost to large animals on the deep sea floor, the feeding frenzy that results wreaks havoc on smaller animals in the seafloor sediment, researchers say.

Descend thousands of feet under the ocean to the deep sea floor, and you’ll find a blue-black world of cold and darkness, blanketed in muddy ooze. In this world without sunlight, food is often in short supply.

Animals in the deep sea survive on dead and decaying matter drifting down from above, said marine biologist Craig McClain of the National Evolutionary Synthesis Center. Only about 3-5% of the remains of microscopic plants and animals that feed life at shallower depths actually makes it to the deep sea floor, he explained. “If the ocean’s primary production were a 5-pound bag of sugar, that would be the equivalent of a sugar packet.”

Collaborating with James Barry of the Monterey Bay Aquarium Research Institute (MBARI), McClain traveled to the deep waters off the coast of California to an area of the ocean floor that receives an additional source of food. In a steep, winding, underwater gorge known as Monterey Canyon —similar in size to the Grand Canyon —bottom-feeders get a boost from nutrient-rich sediments that slough off the canyon walls and collect on the canyon floor.

“There’s typically more food available in the canyon than you would see outside the canyon,” Barry explained. “The stuff that rains down from above and accumulates at the base of the cliffs isn’t just mud – it’s food,” McClain added. “There are tiny food particles and bacteria in the sediment.”

The researchers wanted to understand how the surplus food affected deep sea life on the canyon floor. Buried in the sediment and hidden from view, a diverse world of tiny marine animals – snails, worms, crustaceans, clams, and other creatures no bigger than a pencil eraser – live and feed in the canyon mud.

To find out how these animals are affected by the boost of food, the researchers sent a Remotely Operated Vehicle (ROV) equipped with video and sampling equipment to the base of the canyon. Piloted from a control room onboard a ship at the ocean surface, the ROV dove more than a mile to the canyon floor. As the ROV crept across the seafloor sediment, it video recorded everything in its path and pushed plastic tubes into the mud, pulling up cores of and animals and silt.

When they brought the samples back to the surface, they found nearly 200 species in the sediment. But as they sampled closer to the canyon walls, they were surprised to find that despite the extra food and nutrients, the small sediment-dwellers (0.25 to 25 mm in size) became even smaller and less diverse. Why might this be?

A closer look at the video footage suggests the answer lies not in the sediment, but just above. As the ROV approached the canyon walls, the researchers noticed swarms of bigger, mobile animals – crabs, starfish, urchins, sea cucumbers and other seafloor scavengers – crawling on the sediment surface. Normally few and far between, these animals sense that food has arrived and converge at the base of the cliffs, the researchers explained. “The cliff face becomes a smorgasbord for larger animals,” said McClain.

Ironically, more food for big, mobile animals on the sediment surface is bad news for smaller sediment-dwellers buried below. The larger animals devour all the food in their path as they plow across the canyon floor, wrecking habitat and leaving little for other animals to feed on. “Larger organisms come in and they churn up the sediment and eat all the food. That has big consequences for smaller animals that live there,” McClain explained.

“The number of species near the cliff face was reduced by half compared to the middle of the canyon,” said McClain. “More food isn’t always better,” he added.

The team’s findings will be published online in the April 2010 issue of Ecology.

The post When the dinner bell rings for seafloor scavengers, larger animals get first dibs first appeared on Deep Sea News.

• Megafauna–These are the big guys, the ones you would see if you could survive a walk across the deep-sea floor. More precisely, individuals are large enough to be seen in bottom photographs, video, or out a submersible window. A further division is used here between active (errant) and attached (sessile) organisms. The errant megafauna is dominated by echinoderms (brittle and basket stars, sea stars, urchins, and sea cucumbers). To lesser extent you also see decapod crustaceans (crabs, giant amphipods, and the such), fish, pycnogonid spiders, and cephalopods. For the sessile megafauna includes: sponges, including the spectaclular glass sponges; cnidarians including bottom dwelling jellyfish, corals, sea fans, sea pens, and anemones; and crinoids or sea lillies related to the seastars. These organisms range from active predators to scavengers to filter feeders (filtering particles out of the water) to deposit feeders (taking in sediment and stripping the bacteria and organic material out it).

• Macrofauna–These are small guys you wouldn’t see without a dissecting scope. The cutoff for macrofauna is anything retained on a 0.3 mm mesh sieve. These organisms can be either epifaunal or infaunal (on or in the sediment). Although there are representaives of most phyla here, three groups dominate. Polychaetes, the marine worms, make up typically 75% of any given sample. The crustaceans (various cumaceans, tanaids, amphipods, and isopods) with much less of the molluscs (bivalves, gastropods, and scaphopods or clams, snails, and tusk shells scaphopods) make up the remaining 25%. Like the megafauna the group is predators, scavengers, and deposit feeders. A few representatives are also filter feeders and parasites.

• Meiofauna–Really small animals. Individuals are retained on a sieve with a mesh size ≤ 62 μm. The ‘big’ players in this group are the nematodes, ostracods (the seed shrimp), harpacticoid copepods, and foraminifera (1, 2, & 3).

• Bacteria–the most important and most overlooked group. The basis of the food chain starts here.

Next 25 Things You Should Know will cover the ‘stability’ of deep-sea environments followed by notes on how temperatures slow processes in the deep sea.

The post ARCHIVE: 25 Things You Should Know About the Deep Sea: #11 A Variety of Organisms Inhabit the Deep first appeared on Deep Sea News.