The internet meme that comes to mind when I start thinking of sections of the ocean is this: A mama whale and baby whale are talking.
Baby Whale: Mama, how do we know when we cross from one ocean to another.
Mama whale: We don’t, borders are social constructs and we should be wary of anyone who takes them
seriously.
And with that I’ll end the essay...well, no, not really.
Let me restart this thing:
To sail the seven seas: The original list of the seven seas, probably from the Greeks, were the Aegean, Adriatic, Black Sea, Caspian Sea, Mediterranean, the Persian Gulf, and Red Sea. Turns out, believe it of not, there is a lot more ocean out there.
But, given all the watery salt waters that infect this planet, how do we go about dividing them up? Is it reasonable to spend some time to quantify and clarify similarities and/or differences in oceanic regions?
A group of authors lead by Mark J. Costello have made an attempt to do just this, that is divide up the areas of the ocean. In the terrestrial world this has been studied, and continues to be, with more frequency. In the terrestrial world there are several versions of ecoregion that divide up all of the land area into hierarchical systems: An ecoregion level III has multiple ecoregion IVs within it. The Environmental Protection Agency (EPA) has a set of ecoregions as does the World Wildlife Fund (WWF). The EPA has brilliant maps of the regions:
Alfred Russell Wallace is famous for coming up with the idea of natural selection independently of Charles Darwin. In his time, Wallace was a more famous naturalist than Darwin, and well-read by the masses. His book about exploring the Malaya Archipelago that is still a good read today (though a bit long winded).
The question becomes, how do we separate areas? What criteria are used. Without going into details of how its thought of from a terrestrial perspective, part of every biology 101 textbook these days, I want to focus on what Costello and his group did, attempt separate the oceans. This, like the terrestrial regions, has been worked on, most notably by Sven Ekman in his book in 1953. (For those in the know this is the same Ekman for which the physical phenomena that occurs with waves, Ekman spirals, is named).
As mentioned already, the region hierarchy on land are ecoregion levels I, II, III, IV : EPA level III Ecoregions, each contain multiple EPA level IV ecoregion (for example). In the oceans the levels are Realms (largest), Provinces, and then ecoregions.
Costello and his group have a number of reasons for their project, one is simply that our thinking is skewed by terrestrial thinking. Water is an alien environment for us, we can visit but cannot stay for long. So what determines the boundaries? Latitude, depth and the physical characteristics that come with them? Certainly the Caribbean is different from the arctic but where is the dividing line?
Here is what the Costello group did:
Briefly, merged or separated areas of the oceans by uniqueness of species. But, how many region do you start with? And at what point are region considered different enough to not be grouped together? Lastly, where do you get all this data about species distribution?
I’ll answer in reverse order:
- The data came from the ocean biological Information system (OBIS) and were matched to the world registry of marine species (WoRMS) database. As mentioned above, Ekman did an analysis in similar fashion but the species known at the point were fewer than 1/2 of those now known so this analysis should be better. The group began by looking at 160,000 species listed in WoRMS. After inspecting the species names for errors; misspelling and previously not recognized synonyms for example, the ended up using 65,000 species.
- To separate out the regions they used a statistical method called cluster analysis. Cluster analysis is exactly what it sounds like. It clusters things, in this case regions, by similarities. A suggestion by other authors is that 10% unique species, or endemicity, was a cut off to separate regions. As we’ll see all the clusters of regions that resulted were above this level of endemicity
- They began by dividing the ocean into 5 degrees by 5 degrees (this is 550 km x 550 km at the equator but gets larger as one moves away). 2056 regions (In looking at their dataset I got 2089, they may have just rounded in their paper)
Some species are widespread throughout the oceans: The top eight species are plankton. Also near the top of widespread species are copepods, tiny arthropods that graze on the phytoplanton. Copepods are referred to as the ‘cows of the sea’ as they are major grazers.
Out of the 2089 (or 2056 this is what the paper reported but my review of the data shows 2089 starting zones) regions the winner (the species with the highest incidence) is the foraminiferan Globigerinita glutinata, observed in 589 of the regions. I don’t know a common name for this species but the group are called Forams. Forams, are tiny species found within the water column or sometimes on the sediment. Globigerinita glutinata is planktonic. It has a calcium carbonate covering, called shell or often a test. Forams often have algae growing with them, a symbiotic relationships, and are considered phytoplankton.
Biogeography aside for a minute:
I wanted to graph all of these species and their incidence among the 2000+ regions but all my graphing programs freaked out at trying to create an X-axis scale with over 65,000 species. Plus, how would I represent them on paper—It would have to be a scroll that you continually rolled out to make longer. Instead of trying to represent all 65,000+ species I took every 100th species (from most abundant to least) and graphed those.
My graph is below: It shows a similar pattern of incidence to other species, for example all the species inhabiting an island, to all the species inhabiting a region of wetlands. This is a widespread pattern of species all around the planet, namely, rarity is common.
I mentioned Ekman earlier. His work in 1953 was one of the first to even look at dividing regions; his work was primarily for coastal regions, and he didn’t have data for the entire planet. Costello and his group of authors consider their proposed realms extension to Ekman’s. The regions do closely match. Other workers also did similar analyses, Spalding and colleagues categorized coastal regions first, then did pelagic regions later (two papers listed below one in 2007 and one in 2012). Their analysis matched for some levels of their hierarchy, those rated realms matched pretty well but lower, more specific levels, like ecoregion, outlined by Spalding’s group did not match as well. The ecoregion designations relied heavily on geographic separations. Another group (Kulbicki and 11 co-authors) analyzed reef fishes to categorize the region of tropical seas. Mostly these were consistent with the work of Costello.
So what is the official designation of ocean realms (and maybe more specific zones like ecoregions)? Well, I have no idea;
I love this analysis by Costello and his group, but. One of the major failings of this analysis is the dataset. What we know of marine species distributions is…nearly nothing. WoRMS, as amazing a resource as it it, has poor information for many species, and no information for most species. So let me rephrase, I love that this analysis was done as it leads to the many gaps in our knowledge and provides a baseline for how to think about ocean realms.
We need more deep sea data:
Deep sea species, this area is still hardly explored and so the contribution by these species is tiny. BUT, there is an analysis of mesopelagic regions (those areas from 200 to 1000 meters deep), by Sutton and a huge group (22 other authors) in 2017. Because of the lack of data (the heading of this paragraph) they relied on multiple methods, including the dreaded expert opinion, to come up with 33 mesopelagic ecoregions from around the globe. Still an large effort that is vitally needed, and as they put it in their paper:
“That the deep pelagial represents a critical gap in our knowledge of global ocean biodiversity has become abundantly clear as various international initiatives attempt to identify important or sensitive areas in the open oceans and deep seas…”
FYI: freshwater systems have not been left behind, Abell and 27 other authors (2008) have done a similar framework for freshwater systems of the world.
Back to Costello:
Even for waters on this planet that are much better known than the deep sea we need better overall distribution data and more realistic species numbers: Costello and that group started with 243,000 possible species pulled from the database, but ended up eliminating most of these due to errors, or poor data (thus their final species numbers used were about 65,000. That is a lot of missing data. But it gets worse, the ocean holds more than 243,000 species surely. Don’t they? How many species are in the oceans? I’ll throw a number out; more than 10 million species inhabit the oceans. If we rerun Costello’s analysis with 10 million species what will it look like?
So much more to explore, and its being extinctified faster than we can study it. (Yes, I’m making up words again).*
Quick end note:
*After writing that I found a discussion of it on the Helmitheros blog:
HELMITHEROS. The blog of Dan Albrecht-Mallinger.
https://helmitheros.wordpress.com/2015/02/10/extinctify-should-be-a-thing/
Sources and Further readings:
Abell R, Thieme M, Revenga C, Bryer M, Kottelat M, Bogutskaya N. et al. 2008. Freshwater Ecoregions of the World: A New Map of Biogeographic Units for Freshwater Biodiversity Conservation. BioScience 58: 403-414.
Allard K, Carricart-Ganivet JP, Moore M, Barr B, Lawson J, Deyoung B, Rothfels M, Kenchington E, Mageau C, Hart D, Loder J, Alvarez TP, Scanlon K, Fogarty M, Zavala-Hidalgo J, Joyce T, Vanderlaan A, Kulka D, Deegan L,Hernandez, A. 2010. Report of the Study Group on Designing Marine Protected Area Networks in a Changing Climate (SGMPAN). Technical Report. International Council for the Exploration of the Sea.
Briggs JC, and Bowen BW. 2012. A realignment of marine biogeographic provinces with particular reference to fish distributions. Journal of Biogeography 39: 12–30.
Costello MJ, Tsai P, Wong PS, Cheung AKL, Basher Z, Chauhdary C. 2017. Marine biogeographic realms and species endemicity. Nature Communications.
Ekman S. Zoogeography of the Sea 417. 1953. Sidgewick and Jackson, London. 417 pp.
Griffith GE, Omernik JM, Bryce SA, Royte J, Hoar WD, Homer JW, Keirstead D, Metzler KJ, and Hellyer G. 2009. Ecoregions of New England (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,325,000).
Kulbicki M, Parravicini V, Bellwood DR, Arias-Gonza`lez E, Chabanet P, et al. (2013) Global Biogeography of Reef Fishes: A Hierarchical Quantitative Delineation of Regions. PLoS ONE 8(12): e81847.
Postuma JA. 1962. Manual of planktonic foraminifera. Bataafse Internationale Petroleum Maatschappij N.V The Hague.
Rueda M, Rodriguez MA, and Hawkins BA. 2013. Identifying global
zoogeographical regions: lessons from Wallace. Journal of Biogeography 40: 2215–2225.
Spalding, M. D., Fox, H. E., Allen, G. R. D., N, Ferdana, Z. A., Finlayson, M., Halpern, B. S. et al. 2007. Marine ecoregions of the world: A bioregionalization of coastal and shelf areas. Bioscience 57: 573-583.
Spalding MD, Agostini VN, Rice J, Grant SM (2012). Pelagic provinces of the world): a biogeographic classification of the world’s surface pelagic waters. Ocean and Coastal Management 60: 19-30.
Sutton TT, Clark MR, Dunn DC, Halpin PN, Rogers AD, Guinotte J, Bograd SJ, Angel MV, Perez JAA, Wishner K, Haedrich RL, Lindsay DJ, Drazen JC, A. Vereshchaka A, U. Piatkowski U, T. Morato T, K. Błachowiak-Samołyk K, Robison BH, Gjerde KM, Pierrot-Bults A, Bernal P, Reygondeau G, and Heino M. 2017. A global biogeographic classification of the mesopelagic zone. Deep Sea Research I 126: 95-102.
Wallace, AR. 1869. The Malay Archipelago: The land of the orangutan, and the bird of paradise. A narrative of travel, with studies of man and nature. Macmillan and Co.
Wallace AR. 1876. The geographical distribution of animals, Vols 1 & 2. Harper & Brothers, New York.
Wallace AR. 1894. What are zoological regions? Nature, 49, 610–613.