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 

The post Wooden Homes on the Seafloor Yield Insights Into the Impacts of Climate Change first appeared on Deep Sea News.

Unfortunately  what we know of deep-sea diversity is based on bigger life like worms like snails, crustaceans, and echinoderms. Little is known about microbial diversity of the muddy ooze that characterize the immense deep-sea floor.  That is until now.  Microbial diversity on the abyssal plains is higher than we thought and dominated by the rare biosphere.

A new study in PNAS by Scheckenbach et al. documents the biodiversity of microbes across the South Atlantic.  Nearly 400 “operational taxonomic units,” shorthand for genetically distinctive organisms, were discovered.  For 73% of these organisms, no closely genetically related organisms are currently known.  Like many other deep-sea organisms, microbial communities are dominated by rare species represented by single to few individuals. And like other deep-sea species found over large areas of the seafloor, in this case over 1000’s of kilometers.

We gauge how well we have sampled an area by viewing a sampling curve, a plot of sampling effort versus the number of new species.  This allows us to determine whether we are likely to find more new species with increased sampling effort.  We hope these curves are “saturated” and that the answer to the previous question is no.  However, this is rarely the case with deep-sea studies and sampling curves rarely reach saturation.  The Scheckenbach et al. microbial study is no different and future sampling is likely to uncover hundreds of new species.

Overall this study challenges the idea of depauperate deep sea.  It will also shape how we strive to understand biodiversity of the deep sea, as hypotheses explaining these biodiversity patterns will have to account for both metazoans and microbes.
Scheckenbach, F., Hausmann, K., Wylezich, C., Weitere, M., & Arndt, H. (2009). Large-scale patterns in biodiversity of microbial eukaryotes from the abyssal sea floor Proceedings of the National Academy of Sciences, 107 (1), 115-120 DOI: 10.1073/pnas.0908816106

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Diversity is a matter of area.  This is because there is a well-known relationship between species and area, called rather cleverly the species-area curve.  You increase the size of the area sampled; you increase the number of species. However, this relationship is not linear as the term “curve” would suggest, i.e. species increase consistently with increasing area.  Rather as area increases, the rate at which new species are encountered decreases, a power law function. Think of it this way…you go to the beach and you begin counting species in a tide pool.  Everything is new to you so your tally quickly increases.  At tide pool 2 you find a few new species but some you have already seen.  10 tide pools in and you pretty much seen everything except an occasional rare species. You can see it might be useful to have set of descriptors that describe diversity over spatial scales.

Whittaker (1972) suggested that diversity had alpha, beta, and gamma components.
•    Alpha diversity-the diversity in a local area with uniform habitat type.
•    Gamma diversity-the diversity of a region, with region defined as a large area without major barriers to dispersal.
•    Beta diversity-is the change in species as you move from one habitat to another. If habitats contain generalists, species well equipped to survive anywhere, then beta diversity will low.  If habitats possess specialists, species geared for a particular set of environmental parameters, then beta diversity is high. This is also referred to as species turnover.

Thus regional, or gamma, diversity is both the number of species in a habitat and how many species the habitats share in common, i.e. Gamma=alpha diversity*beta diversity

Today’s example includes donuts.  I am writing this on Sunday morning before breakfast so you will have to bear with me.  My local donut shop, let’s call them Jimmy’s Donuts Extravaganza, serves 12 kinds of donuts…mmmm donuts.  So the alpha diversity at Jimmy’s is 12.

Now just last week, a new earth friendly, all organic vegan, donut shop opened nearby, Earthchild’s Goodearth Donuts.  They have 6 donut types.  Now there is no way that either of these places have the same types of donuts.  For starters, Jimmy doesn’t even no what vegan means or that alfalfa sprouts are cattle feed.  So there is no overlap in donuts.  If we define beta diversity on scale of 0-1, where 1 is complete overlap in donut types, then beta diversity between Jimmy’s and Earthchild’s is 0. So gamma diversity is 18.

Now a local convenient store, Kwik-E-Mart also carries donuts.  God help anybody who eats them.  Of the 12 they carry, 6 overlap with Jimmy’s.  Beta diversity between Kwik-E-Mart and Jimmy’s is 0.5 and as expected 0 with Earthchild’s. So now gamma diversity is 24 because all 12 of Kwik-E-Mart’s donuts are not new to my area.

Another new store, Big Ol’ Donuts, opens and it really just more of the same except for one new tasty donut that contains coconut sprinkles.  Although alpha-diversity of Big Ol’ Donut is high 19, only one donut is different, and thus donut gamma diversity of my area only increases to 25.

The post Biodiversity Pt. 2: Mmmmm…donuts first appeared on Deep Sea News.