Nearly two miles below the ocean’s surface, we are building new worlds. You might be surprised that these ecospheres are wooden—little log cabins hosting a cornucopia of sea life.  By controlling the size of these wooden homes, we can begin to answer fundamental questions about how the oceans will adapt to climate change. In our most recent, paper we are beginning to grasp the extent that food controls biodiversity, biological novelty, and the competition among species.

On the seafloor, chunks of wood—we call them wood falls—play host to a variety of invertebrate species often not found anywhere else in the ocean.  These species live their entire lives on waterlogged timber; settling out of the water column as larvae to consume wood, or to prey upon other species that do.  Once on a wood fall, these organisms can never leave, their dispersal limited to the beginning of their lives as plankton. And for all of these reasons, the island communities created by wood falls serve as the perfect experiment.

Because of humans, the oceans are radically changing.  They’re becoming warmer, more acidic, and less oxygenated.  But an even more disturbing trend has been uncovered; the oceans may be becoming less productive, providing less food and carbon for its denizens.  Scientists do not really have a handle on how life in the oceans will react to this finding. What will happen to individual species and whole communities of species?  This is an intractable question in many ways because it is hard to test. We cannot easily experimentally adjust how much food a swath of ocean gets. Or can we? In a wood-fall experiment we can change the amount of food the community receives by simply adjusting the size of the log. These species cannot leave to look for better meals once they arrive.  They are wholly dependent on the log we’ve provided in an otherwise barren patch of the deep ocean floor.

In 2006, Jim Barry (MBARI) and I placed 16 logs with a remote operated vehicle (ROV) over 2 miles down on the deep-sea floor off the California coast. We left them there for five years and then remotely and robotically harvested them.  After sorting, identifying, and analyzing, these wood falls are revealing yet another fundamental insight.

How does more food, or more specifically more carbon, allow for more species?  To explain the science, let’s visit a donut shop. At this donut shop, there are three types of donuts: chocolate, plain glazed, and raspberry filled. I ask the donut maker to make three new donuts and provide extra ingredients for them to do so.  

In Scenario A, the donut maker produces chocolate, plain glazed, and raspberry filled along with a dark chocolate, a plain glazed with sprinkles, and a blueberry filled.  The donut shop is still just serving three basic types of donuts: chocolate, plain glazed, and fruit filled. These new donuts are just slight deviations. We will call this Scenario A donut packing.  The donut maker is just packing the menu with variants of the original donuts.

Much like donuts in a shop, we can think of species in a community the same way.  As food increases and the number of species increase, are we getting slight deviations (donut packing) or something truly novel (donut expansion)?  In the ecological sense, are niches, i.e. the full set of characteristics that describe a species and their requirements, being packed into the community or are we expanding the overall niche diversity.

And so for our wood-fall species, we put numbers to each of their niches describing their feeding habits, how well and even if they move, as well as their preference for space on the wood fall. We found that as you increase the wood-fall size, and the amount of wood, you do not get truly novel species, rather you pack these species into the community.  They are just slight deviations. This suggest that increased food reduces competition among animals allowing them to coexist peacefully. Species do not have to be completely novel to join the community.

In the end this means that decreases of productivity in the oceans, will limit diversity by not allowing species to coexist.  Species will be vying for the same spots and in the end many may lose.

McClain, C.R., C.L. Nunnally, A. Chapman, and J. Barry. (2018) Energetic Increases Lead to Niche Packing in Deep-Sea Wood Falls. Biology Letters 

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The biodiversity of Lophelia pertusa bioherms in the North Atlantic rivals the diversity of a shallow water tropical reef (Rogers 1999). More than 800 associated species have been documented in association. L. pertusa and Oculina varicosa also provide nursery habitat for redfish Sebastes viviparous (Fossa et al., 2002), gag grouper Mycteroperca microlepsis, and scamp Mycteroperca phenax (Gilmore and Jones, 1992).

Gorgonian colonies are refuge to rockfish (left). Gorgonacea range to 6000m depth, and they are broadly distributed on continental shelves and seamounts wherever suitable substrate exists (Bayer 1956, 1961). So, any human activity that disturbs the seabed can be assumed to destroy anthozoan habitat in one form or another, unless proven otherwise.

This is important, because gorgonians create structural complexity in a relatively featureless environment, deeper than matrix forming scleractinia. They generate habitat for associated species of fish (Heifetz 2002, Etnoyer & Warrenchuk 2007), invertebrates (Krieger & Wing 2002, Buhl-Mortensen and Mortensen 2005), and microbial fauna (Penn et al 2006).

Deep gorgonians generate structure where you might not otherwise expect to find it, and they provide nursery habitat like bioherms do. Large Primnoa reseadeformis colonies have been photographed on the Olympic Coast with gravid dark blotched rockfish hiding in the branches (above). Catsharks in the Pacific Northwest lay their eggs on Plumarella sp., another primnoid type gorgonacean octocoral.

The question remains whether gorgonian habitat is obligate or facultative for the fishes (Auster, 2005). Do the catsharks need gorgonians specifically, or can they lay their eggs anywhere? We’re still not sure. However, there are few choices of substrate in the deep-sea, so coral may provide nursery habitat simply due to a lack of alternatives. Deep corals need protection from non-discriminate fishing gears and wreckless anchoring practices. Too many animals depend on these corals to justify careless destruction.

References:

Auster, P. 2005. Are deep-water corals important habitats for fishes? Pages 747-760 in A. Freiwald and J. M. Roberts, eds. Cold-water corals and ecosystems. Springer-Verlag Berlin Heidelberg.

Bayer, FM (1956) Octocorallia. In: Moore, RC (ed) Treatise on invertebrate paleonotology. Part F, Coelenterata. University of Kansas Press, Lawrence, Kansas, p 166-231

Bayer, FM (1961) The shallow-water Octocorallia of the West Indian region. A manual for marine biologists. Stud Fauna Curacao and other Caribbean Islands 12. Martinus Nijhoff, The Hague

Buhl-Mortensen L, Mortensen, PB (2005) Distribution and diversity of species associated with deep-sea gorgonian corals off Atlantic Canada. In: Freiwald A and Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Heidelberg, p 849-879

Etnoyer P, Warrenchuk J (2007) A catshark nursery in a deep gorgonian field in the Mississippi Canyon, Gulf of Mexico. Bull Mar Sci. 81(3): 553-559.

Fossa, J. H., P. B. Mortensen, and T. M. Furevik. 2002. The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts. Hydrobiologia 471: 1-12.

Gilmore, R. G. and R. S. Jones. 1992. Color variation and associated behavior in the epihepheline groupers, Mycteroperca microlepis (Goode and Bean) and M. phenax Jordan Swain. Bull. Mar. Sci. 51: 83-103.

Heifetz, J (2002) Coral in Alaska: distribution, abundance, and species associations. Hydrobiologia 471:19-28

Krieger KJ, Wing BL (2002) Megafauna associations with deepwater corals (Primnoa spp.) in the Gulf of Alaska. Hydrobiologia 471: 82-90

Penn K, Wu D, Eisen JA, Ward N (2005) Characterization of Bacterial Communities Associated with Deep-Sea Corals on Gulf of Alaska Seamounts. App Env Microbiol 72(2): 1680-1683

Rogers, AD. 1999. The biology of Lophelia pertusa (Linnaeus 1758) and other deep-water reef-forming corals and impacts from human activities. International Review of Hydrobiology 84(4):315-406.

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