A glimpse at Davidson Seamount

Seamounts (underwater mountains) make up a a huge cumulative habitat type in the ocean, and distinct biological communities can exist on the same underwater feature.  As a part of an investigation by MBARI, Davidson Seamount and others offshore of California were surveyed with an ROV, and yielded some pretty spectacular underwater footage.

You can read more about this work at Davidson in this PLoS ONE article, authored by Dr. Craig McClain (of DSN notoriety) and colleagues.  If you listen closely to the narration in the video, you’ll hear Lonny Lundsten, a coauthor on the study, mention the idea that seamounts, while providing unique habitat in the open ocean, are not necessary the hosts of endemic species (species that are restricted to a single geographic locale).  More about that here.

[video:  MBARI on YouTube]
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Live deep-sea footage

The Visions ’11 cruise is streaming live deep-sea video footage via an ROV puttering around in the depths.  Read more about the cruise here and check out the live video feed here.  (If you’re having trouble with the feed, right click/command click on the video, hit ‘settings’ and uncheck the ‘enable hardware acceleration’ box.)  This leg of the cruise is over Axial Seamount in the Pacific.

Via Alden Denny, geology and GIS extraordinaire.  You can follow expedition updates on the twitter machine @VISIONS11ops.

Distinct communities on a Tyrrhenian seamount

Using a Remotely Operated Vehicle, researchers surveyed a large seamount in the Tyrrhenian Sea off the coast of Italy, finding three distinct biological communities.  Seamounts, undersea mountains, can hugely affect the way water flows in an area and can provide hard substrate for benthic animals.  These features are generally acknowledged to be potential hotspots in terms of how many species are in a given area (known as species richness).

Marzia Bo and colleagues1 detail the the species composition of the Vercelli Seamount in a paper appearing in PLoS ONE.  Similar to other Mediterranean seamounts, the  relatively shallow summit of Vercelli hosts kelp  and algal-dominated communities at the very top (60-70 meters depth).  A bit further down, from 70-80 meters, the southern flank of the seamount hosts mostly organisms that are well-suited for a high-flow environment, such as octocorals. Species found on the northern flank are adopted for lower-flow regimes and feed by active filter-feeding, for example, sponges and ascidians.

The study of seamounts, these seemingly esoteric oceanic peaks, is still very exploratory due to the difficulty in sampling in the open and deep ocean.  Only a few hundred seamounts have been sampled biologically out of the estimated hundreds of thousands or millions thought to be present in the global ocean2. This work illustrates that seamounts can consist of multiple habitats over relatively little area. This is likely due to the different environmental conditions that are created by the feature itself, such as varying hydrodynamics (especially relevant here, with active and passive filter-feeders grouped), as well as slope and depth gradients.   Bo et al. note that the conservation value of Vercelli should be focused on the variety  of different communities the seamount supports and the diversity of life contained therein.

Though a seamount may have the impression of being remote and singular, the total global area represented by large seamounts is roughly equal to the size of Europe and Russia combined.  This estimate is actually quite conservative and only takes into account seamounts with greater than 1500 meters in relief3.

This is an open-access paper; read the original work here.

The figures shown above are from Bo et. al. 2011 (cc).


Sources:

1. Bo M, Bertolino M, Borghini M, Castellano M, Covazzi Harriague A, Di Camillo CG, Gasparini G, Misic C, Povero P, Pusceddu A, Schroeder K, & Bavestrello G (2011). Characteristics of the mesophotic megabenthic assemblages of the vercelli seamount (north tyrrhenian sea). PloS one, 6 (2) PMID: 21304906
2. Wessel, P, Sandwell, DT, & Kim, SS (2010). The global seamount census Oceanography, 23 (1), 24-33
3. Etnoyer, PJ, Wood, J, & Shirley, TC (2010). How Large Is the Seamount Biome?Oceanography, 23 (1), 206-209

Seamount mythbusting

Seamounts—mountains beneath the waves—may not be conventionally thought of as large habitats on the global ecological stage, compared to say, forests or estuaries.  But there’s quite a bit of them to say the least, perhaps in the hundreds of thousands. The global seamount biome, or the total area represented by seamounts within the global ocean, has been shown to be larger than the whole of Australia.  Large seamounts have a global area of nearly 10 million square kilometers, more than wetlands, seagrass, or temperate grassland biomes. This is actually a conservative number:  if smaller seamounts (rising between 1000-1500 meters from the seafloor) are included, the global seamount area rises to 28.8 million square kilometers (Etnoyer et al.2010).

Unidentified cnidarian from Davidson Seamount. MBARI, NOAA-OER.

Fewer than 200 seamounts have been intensively sampled.  Even so, the ecological structure and evolution of seamount biological communities has been expounded upon and debated for more than a few years now.  For example, it is a possibility that seamounts, as submarine islands, are ecologically isolated to a degree and function within the island biogeography paradigm, having high levels of endemic species (species that are found no where else).  A new study in Marine Ecology (Rowden et al. 2010) has   compiled the evidence for and against the existing concepts in seamount ecology and serves as a healthy breath of context.

Unsupported:

Seamounts function as islands and have hydrological mechanisms, e.g. Taylor columns, that limit dispersal of larvae, and have high numbers of endemic species.  Although, it should be noted that cryptic speciation (micro-endemism) has been recently indicated on seamounts.

Plausible:

Seamounts as stepping-stones for the dispersal of species (seamounts provide relatively shallow substrate in the open ocean), host increased numbers of species and biomass, and are highly productive.

Seamounts are distinct from other deep-sea habitat at the same depth, have high species richness, are population sources for continental slope sinks, and can act as refugia from dire oceanic-basin scale events.

Supported:

Seamounts are vulnerable to fishing (remember the precipitous collapse of the orange roughy fishery?) and to bottom trawling.

With the scarcity of seamounts actually visited and sampled, keep in mind that Unsupported and Plausible concepts could very well be supported (or not) in future studies.  For one, seamount endemism is a hotly debated topic, and more research is surely ongoing.  This work is interesting not only for providing a review of the evidence, but by doing so, it highlights the need for additional research in the deep ocean and gently suggests that some operating ideas for seamount ecosystems may not be as cut in stone as previously thought, or at least have more variability from seamount to seamount.  This is a great example of science being an evolving body of work and methodology, not only a compilation of knowledge.  As a former professor of mine once told me, “what we know is not as important as know we know it.”

One idea that Rowden et al. 2010 list as Plausible is that seamounts could shelter biota from environmental changes.  The threat of ocean acidification—the alteration of seawater carbonate chemistry—not only impacts shallow corals, but is thought to put deep-sea corals at risk.  By using predicted values for environmental parameters, for example, aspects of seawater chemistry, and global habitat suitability models, Tittensor et al. (2010) show that seamount summits are consistently less impacted by ocean acidification than the surrounding benthos under various IPCC scenarios.  The researchers also point out that the largest areas of suitable habitat for deep-sea corals are around New Zealand and in the North Atlantic.  These areas are largely within various countries’ Exclusive Economic Zones, rather than the high seas, suggesting that habitat conservation measures taken by individual nations could have large effects for these potential oceanic refuges.

References:
Etnoyer PJ, Wood J, Shirley TC (2010). How large is the seamount biome? Oceanography, 23 (1), 206-209
Rowden, A., Dower, J., Schlacher, T., Consalvey, M., & Clark, M. (2010). Paradigms in seamount ecology: fact, fiction and future Marine Ecology, 31, 226-241 DOI: 10.1111/j.1439-0485.2010.00400.x
Tittensor, D., Baco, A., Hall-Spencer, J., Orr, J., & Rogers, A. (2010). Seamounts as refugia from ocean acidification for cold-water stony corals Marine Ecology, 31, 212-225 DOI: 10.1111/j.1439-0485.2010.00393.x