After Pliny’s monstrosity, many centuries went by before this question was really tackled again.  In 1815, Edward Forbes took a ride aboard the HMS Beacon, where he dredged the bottom at depths from 1-1,380 feet (0 – 420 m).  Just so you know, the average depth of the ocean is about 12,000 feet (4,000 m).  So, when I say he was barely scratching the surface, I’m not really exaggerating.  But nevertheless, he dredged the depths that he did and found that the deeper he dredged at, the less things he found.  So naturally, he thought, there must be a “zero point” at which no animals live.  He wildly extrapolated his data and determined that below 1,800 feet (600 m) there exist no animals, and he called this the “azoic zone.” So, Forbes’ answer to how many species in the deep sea was a big fat “not many.”

Luckily this “azoic zone” nonsense only lasted about 50 years.  In 1869, Charles Wyville Thomson and the rest of the crew onboard the HMS Porcupine pulled up animals from 14,610 feet (4,450 m) deep in the waters south of Ireland.  These results were later confirmed by the Challenger expedition which found animals at all depths, all over the globe.  This undeniably proved there was life at all depth of the oceans- but the question still remained.  How many species in the deep sea?

Fast forward to 1992.  Frederick Grassle and Nancy Maciolek conduct a massive (for the time) survey of the tiny animals that live in the sediments in the deep sea.  These are not the cute crawlies that live on top of the mud that had been previously sampled with dredges.  These are the small animals that live their lives between the grains of dirt at the bottom of the ocean.  Of the 798 species that they found, over half were new to science!  Pliny’s head would explode if he heard that more than double the total animals he thought existed in the whole ocean were found just in the mud.

Grassle and Maciolek did some impressive math and ended up calculating that they were finding one new species per square kilometer they sampled.  Let’s break that down.  One square kilometer is equal to a little more than one-third of a square mile.  So, they are basically finding three new species in each one-mile-square block of mud they are sampling.  This means if they were to sample an area the size of New York City, they would find around 782 new species, and if they were to sample an area the size of London, they would find about 1,572 new species.  These new species add up fast – you see, there are 300,000,000 square kilometers (115,830,647 square miles – almost 30 Europes or 431 Texases) of mud deeper than 1000 m in the ocean. The end result of all this is a conclusion of 300,000,000 species living in the mud at the bottom of the deep ocean.  This is not counting swimming things!  That’s a heck of a larger estimate than the 176 species estimate of centuries ago.

.It turns out that this calculation of Grassle and Maciolek was probably a bit of an overestimation.  They realized that much of the ocean is oligotrophic, or not very nutrient-rich and therefore not very productive.  This would mean that in many areas of the ocean, the rate of new species added per square kilometer is probably much less than what they found in their sampling area.   So, they ended up conservatively estimating the true number at more like 10,000,000 species in the mud. This is still a huge amount of diversity in the deep sea.

Grassle and Maciolek’s 10 million species hypothesis sparked quite the controversy, with biologists from many sub-disciplines quickly arguing for or against the high number.  Isopod biologists Poore and Wilson said they had seen even more diversity just among isopods in their samples than the average number of species per 100 samples that Grassle and Maciolek had used in their calculations.  This, they argued, must mean there are even more than 10 million species!  In 1971, though, Thorson argued that there were only 160,000 species in the oceans across all depths- so far less than 10 million could be in the deep sea.  In 1992, May argued that only 500,000 species would be possible in the deep sea.  Lambshead in 1993 reminded everyone that there are a boatload of nematode worms and other animals (collectively called meiofauna) that live in the mud that were too small to be sampled by the gear Grassle and Maciolek used.  This, Lambshead argued, could mean a total of 100,000,000 marine species.  Consensus just could not be reached.

Here’s the problem, though.  It is a hard question to answer.  Each person who has attempted to answer this question was doing the best with the data that they had at the time (except Pliny- that guy was just an idiot okay). However, species diversity and especially how many species you discover in each new deep-sea “block” can vary considerably at different depths, regions, and oceans. Grassle and Maciolek’s encoutering 3 new species per block was based on data from the North Atlantic. Does 3 new species “rule” also apply to other parts of the Atlantic or to the Pacific? So without massive amounts of data, it is likely we will be kept guessing for a few more years to come. So, I can’t tell you exactly how many species are in the deep sea, but I can tell you that we currently have 409,543 named species in the ocean (World Register of Marine Species, accessed 03/18/2019).  The best part is that we are getting better and better at discovering new species, and hopefully in years to come we will be much better equipped to answer this question realistically.

Cover photo credit to Monterey Bay Aquarium Research Institute (MBARI).

The post How many species are in the deep sea? first appeared on Deep Sea News.

But the food not so delightful,


But since we’ve got no place to go,


Let It Marine Snow! Let It Marine Snow! Let It Marine Snow!

In the late 1960’s, two marine biologists, Howard Sanders and Robert Hessler, made a shocking find–the biodiversity of the deep-sea floor is astoundingly high. In an area the size of a coffee table over 300 species can coexist, a number that rivals tropical rainforests and coral reefs. Yet these findings also raised a paradox. High diversity is typically associated with physically complex habitats, like forests and reefs, plentiful with food that allow for a variety of niches. In the food poor, homogenous mud flats of the deep sea, how can so many species coexist? The answer is snow.

The lack of light in the deep oceans precludes photosynthesis. Thus, primary production of carbon, the base of a food web, is virtually absent. Deep-sea organisms are reliant upon a trickle of falling material from the productive shallow oceans overhead. This material is largely a low quality and low quantity mixture of decaying bodies and feces degraded further by bacteria on its decent into the deep. Roughly 2-5% of the total carbon on the ocean’s surface falls to the deep seafloor, the equivalent of roughly 2-3 tablespoons from a 5-pound bag of sugar. This sinking material, marine snow, falls as a dusting on the ocean bottom. But like a light snow in your yard does not form an even layer and Buffalo receives more snow than Miami, marine snow too is denser in some spots whether an area the size of coffee table or an entire ocean.

In this marine snow medley lays the answer for our deep-sea paradox.

In the 1970’s, Howard Sanders, Fred Grassle, and Paul Snelgrove proposed instead of the deep-sea floor being a homogenous wasteland, it was comprised of a variety of patches each with a unique set of organisms, i.e. the patch-mosaic hypothesis. The deep-sea floor is essentially a patchwork quilt of different small habitats. I began this year by publishing a study addressing how heterogeneity in marine snow of distances of just a few yards can lead to completely different communities of organisms. At the end of this year, just today in fact, I with coauthors show this same pattern over several thousands of kilometers.

In 2006, Jim Barry and I during my tenure at the Monterey Bay Aquarium Research Institute sampled a 3203-meter deep site off the Monterey Bay. We collected with the robotic arm of a remotely operated vehicle 44 sediment cores over approximately 400 yards. Each core we sieved and removed the small invertebrates living in the sediment, from worms to crustaceans to molluscs plus much more. Equally important, we measured the carbon content, of the sediment as an indicator of marine snowfall. Largely, we found that invertebrate communities in cores taken adjacent to each other were just as likely to be similar as dissimilar to one another. Indeed, cores adjacent to one another were just 3% more likely to share common species than cores taken 350 meters apart! Why would communities right next to one another be so different? Differences in marine snow accumulation. Invertebrate communities receiving comparable marine snowfall were more similar.

Today in the Proceedings of the Royal Society with collaborators Allen Hurlbert and James Stegen from the University of North Carolina, I unravel the paradox of the deep a little further. Given the difficulty of conducting deep-sea work, patterns of diversity of entire oceans are rare. In 2008, John Allen, working previously with Howard Sanders, published an amazing dataset of deep-sea bivalves taken form 270 sites across the Atlantic Ocean. We combined this dataset with data on bivalve sizes and genetic relatedness with multiple datasets on the environment, including annual marine snow accumulation. We found that the availability of both chemical, i.e. marine snow, and thermal, i.e. temperature, energy explained differences in compositions of bivalves communities across the Atlantic Ocean. Interestingly, and in contrast to current thinking (including my own!) that invertebrates with planktotrophic larvae should be able to disperse everywhere, we also detected the importance of dispersal ability in explaining community differences. In other words, some of what determines where a bivalve is located in the Atlantic is determined by its dispersal ability and the amount of energy it requires.

But we went one step further and developed a simulation. We constructed virtual bivalves allowing them to evolve traits, fill environmental niches, and disperse across a virtual Atlantic Ocean. This is a computationally complex and demanding operation and required a cluster of computers at UNC to run. In each simulation, we could control the dispersal ability and food requirements for the bivalves. For each simulation, we would then compare the patterns that emerged with those in our real Atlantic bivalves communities. This would allow us to determine the exact level of dispersal ability and food requirements of bivalves to produce changes in community compositions across the Atlantic. From our simulations, we found that 95% of bivalves could disperse 749 km from their natal site. We also found that 5% of bivalve juveniles would not be able to persist in habitats that deviated from their optimum habitat more than 2.1 grams of carbon per meter squared per year. That translates to about 1 teaspoon over a dining room table over the course of an entire year! Bivalves are extremely sensitive to the amount food available.

Overall, these studies illustrate that the deep-sea floor is like your Grandma’s quilt presenting a variety of patches of material. These patches, driven by differences in marine snow, whether occurring over inches or miles, provide unique habitats that allow a variety of different animals to coexist. And much like humans prefer different amounts of snow (give me warm weather or give me death!), deep-sea species are uniquely adapted to differences in marine snow.

Craig R. McClain, James C. Stegen, and Allen H. Hurlbert Dispersal, environmental niches and oceanic-scale turnover in deep-sea bivalves Proceedings of the Royal Society B: Biological Sciences published online before print December 21, 2011, doi:10.1098/rspb.2011.2166

UPDATE 1:
Also take a look at the great write ups by Wired and IO9. Love the titles! The Bounty of Species in a Single Scoop of Seafloor Mud and The Ocean Floor is Like a Rainforest Where Feces and Dead Animals Rain From the Sky

UPDATE 2: I was asked for a legend to the animals above.  Hopefully this helps. As for the species, I could give you the actual species names but perhaps that would not be helpful to readers.  Instead I will give you the general groupings that may be more informative.

So in this orientation above from left to right

Row 1 bivalve, polychaete, ophiuroid, polychaete, bivalve, cumacean, amphipod

Row 2 cumacean, anemone, aplacophoran, bivalve, cumacean, bivalve, aplacophoran

Row 3 polychaete, bivalve, cumacean, bivalve, big polychaete, amphipod, 2 oligochaetes

Row 4 scaphopod, bivalve, aplacophoran, long polychaete, cumacean, amphipod, bivalve

Row 5 bivalve, polychaete, aplacophoran, amphipod, bivalve, amphipod, polychaete

Row 6 ostracod, polychaete with tube, bivalve, anemone, polychaete, amphipod, polychaete, bivalve

Row 7 polychaete, gastropod, amphipod, caprellid shrimp, scaphopod, bivalve, polychaete, cumacean

Echinoderms

ophiuroid http://en.wikipedia.org/wiki/Brittle_star

 Molluscs

bivalve http://en.wikipedia.org/wiki/Bivalve

aplacophora http://en.wikipedia.org/wiki/Aplacophora

scaphopod http://en.wikipedia.org/wiki/Scaphopod

gastropod http://en.wikipedia.org/wiki/Gastropod

 Annelids

polychaete http://en.wikipedia.org/wiki/Polychaete

oligochaete http://en.wikipedia.org/wiki/Oligochaete

Crustaceans

cumacean http://en.wikipedia.org/wiki/Cumacean

amphipod http://en.wikipedia.org/wiki/Amphipod

ostracod http://en.wikipedia.org/wiki/Ostracod

caprellid http://en.wikipedia.org/wiki/Skeleton_shrimp

Cnidarian

anemone http://en.wikipedia.org/wiki/Sea_anemone

The post Let It Snow, Let It Snow, Let It Snow first appeared on Deep Sea News.

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.