Category Archives: Ecology & Evolution

Is the Earth’s sixth mass extinction looming near and large?

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Fossil fish sculpture. Rae Allen. CC BY 2.0.
Ideally, your expenses are offset by your paycheck, so as you spend money for say, rent and food, you have cash coming in.  On the surface at least, this is similar to the dovetailing of extinction and speciation.  The vast majority (~99%) of all the species ever to have existed on Earth are extinct, never to be seen alive again.  However, this process is balanced by new species evolving, a process known as speciation.  So what happens when species extinctions far outpace species creation?  Mass extinctions, timeframes during which 75% of species are lost in a relatively short period (usually less than two million years and sometimes significantly less), have occurred five times (the Big Five) in the past 540 million years.  They are unique, singular events that stand out above the background level of extinction that is constantly ongoing.  However, more and more modern extinctions are being observed, amidst the myriad of human-derived disturbances, such as rapid climate change, invasive species introductions, habitat fragmentation, directly killing species, among others.

It is not a straightforward task to ascertain whether or not we are on track to another mass extinction—data from the fossil record must be comparable to historic and modern species assessments.  In a paper recently published in Nature, Dr Anthony Barnosky and colleagues point out why data comparisons of this type are difficult and proceed to broadly get around them by looking at the global picture.

The fossil record is not evenly distributed across taxa or geographies.  Fossils are particularly meager in some broad swathes of Earth, such as the tropics.  On the other hand, distributions are known for many modern species.  In terms of taxa, or groups of species, usually only animals with hard bits fossilize well.  Studying modern species is easier, because they’re still around, but less than 2.7% of known species have been assessed for risks (e.g. endangered, extinct in the wild, etc.) by the International Union for the Conservation of Nature (IUCN).  There’s also trouble with the species concept.  Fossils are usually identified at the genus, rather than species, level; modern work frequently uses genetic approaches to identify individuals to species.  Fossils are also not distributed evenly through time.  Fossil extinctions are recorded when a certain group of animals vanishes from the fossil record, the extinctions known are likely underestimates since most species have no fossil record.

In spite of these caveats, the researchers evaluated the existing data and show that it is possible to circumvent these various data comparison issues by taking a ‘big-picture’ global approach.  Conservatively, mass extinctions occur when the extinction to speciation ratio becomes so unbalanced that three quarters of species disappear, usually within less than two million years.  If two million years sounds like a leisurely long time, bear in mind that the Earth is ~4.54 billion years old. Most living things forever blinking of out existence in roughly 0.04% of that time is a colossally unique situation indeed.

Using a rate-based method, the researchers compared extinctions per million species-years (E/MSY)1 from throughout the fossil record and modern time.  By using various paleontology databases and accounting for data biases, they were able to establish a background rate of extinction.  Through this approach, it is clear that the maximum extinction rates since about 1,000 years ago are much higher than the average fossil rate and the recent average extinction rates are also significantly higher when compared to pre-anthropogenic (that’s pre-us, mind you) averages.

Another way to consider this is by splitting up the fossil record into 500-year intervals and calculating the likelihood that extinction rates were as high in many of these 500-year intervals as they were in the most recent 500 years. In the case of mammals, which have an average of 1.8 extinctions per million species-years, only 6.3% of these 500-year segments could have extinction rates comparable to the current 500-year interval in order to preserve the background E/MSY.  So no, it is supremely unlikely that many of these past 500-year bins had extinction rates that were as high as they are today.

But would these current rates produce a large magnitude extinction event?  By using modern species assessments of very well-surveyed groups coupled with fossil data, Dr Barnoksy and his team calculate that extinction rates for mammals, birds, amphibians, and reptiles are as quick or quicker than all rates that would have been responsible for the previous five mass extinctions.  If all threatened species (defined by IUCN criteria) are lost within a century, and the current extinction rate continue, land-based amphibians, birds, and mammals would reach mass extinction thresholds in ~240 -540 years.  This slows down a bit if ‘only’ critically endangered species disappear within the next 100 years to ~890 – 2,265 years for those same groups of animals. Current extinction rates are higher or as high as those that preceded and caused the previous mass extinctions.  The researchers point out that while a pressing need for new research exists, the 75% species loss threshold could occur within the next three centuries.

Modern species losses are serious but does not pass the threshold for a mass extinction event yet.  Relatively small numbers of species surveyed historically have been lost, although scores of species have yet to be discovered and/or evaluated.  However, the researchers point out that losing critically endangered species would put us on the fast track to mass extinction, and losing endangered and vulnerable species would achieve the sixth extinction even faster, within a few hundred years. Sobering commonalities between the present-day and the past mass extinctions exist:

It may be of particular concern that this extinction trajectory would play out under conditions that resemble the ‘perfect storm’ that coincided with past mass extinctions: multiple, atypical high-intensity ecological stressors, including rapid, unusual climate change and highly elevated atmospheric CO2. [Barnosky et al.]

The diversity of life should be preserved while it’s still here.

 

1  Think of this as man-hours (or really person-hours).  On a purely mathematical basis, if you had one million species and an extinction rate of 1 per million species-years, one species would go extinct a year.

Barnosky AD, Matzke N, Tomiya S, Wogan GO, Swartz B, Quental TB, Marshall C, McGuire JL, Lindsey EL, Maguire KC, Mersey B, & Ferrer EA (2011). Has the Earth’s sixth mass extinction already arrived? Nature, 471 (7336), 51-7 PMID: 21368823

Image:  Rae Allen on Flickr (cc).

This article is also posted at The Urban Times.

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Crushing predators reinvade the Antarctic benthos

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In Gotham, Batman drives a batmobile that shoots fire out the back and has all sorts of mechanical wizardry so he can catch fiends in style.  Or something close to that, unless my childhood was dreadfully misinformed.  He isn’t supposed to turn up in a St. Patrick’s day parade in New Jersey, pedaling away on a two-wheeled crime-fighting vehicle adorned with no fewer than 13 (count them!) bat symbols.  I feel that witnessing that would be strange–similar to the feeling you get when you discover your keys in the refrigerator next to the milk.  Simply out of place.

Recently, Antarctica has its own version of things showing up in the wrong place.  King crabs, predators that the Antarctic underwater shelf has not seen in over 40 million years, appear to be making a rapid comeback.  The endemic (unique to a specific, defined locale) nature of Antarctic shelf organisms is the result of a massive climatic cooling event in the middle Eocene, approximately 41 million years ago (Ma)1.  From 41 to 33.5 Ma, coastal sea surface temperatures decreased as much as 10°C, even before the onset on glaciation; this led to the eventual extinction of shell-breaking (durophagus) predators, such as modern bony fish, decapod crustaceans, and most sharks and rays. These groups have not returned due to their lack of an ability to physiologically cope with magnesium, one of the major cations present in seawater, at low temperatures.  Under one degree C or so, these magnesium ions are lethal to these organisms1.  Due to the fact that in the Antarctic, shallower seawater is slightly colder than that of the deep, they are effectively shut out of the shallows.

Distribution of epifaunal suspension feeders before and after the Eocene cooling at 41 Ma. The graph on the left shows temperature data derived from oxygen isotope values in bivalve shells. The schematic on the right shows the relative abundance of fossil concentrations of brachiopods, stalked and unstalked crinoids, and ophiuroids. Aronson et al. 2009, PLoS ONE.

Paleontological findings on Seymour Island, near the Antarctic Peninsula, reveal that dense populations of ophiuroids (Ophiura hendleri) and crinoids (Metacrinus fossilis and Notocrinus rasmusseni) were present on the soft substrate after the 41 Ma cooling event, but not prior1.  Both ophiuroids and crinoids are vulnerable to durophagy, and thus reduced predation pressure is implied after the Eocene cooling event.  This is quite straightforward:  if the things that normally eat you are no longer there, the size of your population increases, and you can invite the folks down the way to come over and watch Buffy the Vampire Slayer and enjoy your mean gin and tonics with a decreased sense of doom2.

Even today, these and other suspension feeders are abundant across the Antarctic shelf3.  However, in the past 50 years, sea surface temperatures off the Antarctic Peninsula have risen 1°C4, and as a result, predatory crabs and duropaguous fish may be able to enter this isolated shelf environment.  Anomuran king crab populations have already been found in slightly warmer, deeper waters nearby5 and it was reported on Sunday by the Washington Post that a recent expedition observed hundreds, potentially primed for invasion into the shallows of the continental shelf.  Dr. Sven Thatje and colleagues are currently searching thousands of seafloor images for evidence that predation by these crabs is ongoing.

Current climatic warming is essentially opening a physiological door for these polar predators to reclaim their place in the Antarctic benthic community via range extensions and human-induced introductions5.  This reinvasion has the potential to drastically alter ecological relationships, perhaps even eliminate populations of dominant suspension feeders and homogenize the unique Antarctic nearshore benthos with higher latitude communities.

Images/figure:  1) Michael Bocchieri/Bocchieri Archive, from Flickr user Foto Bocch (cc).  I have been itching to find an excuse to use it since I saw it as NPR’s photo of the day. 2) From Aronson et al. 2009, PLoS ONE (cc).

1. Aronson RB, Moody RM, Ivany LC, Blake DB, Werner JE, & Glass A (2009). Climate change and trophic response of the Antarctic bottom fauna. PloS one, 4 (2) PMID: 19194490
2. I’m actually unaware of any invertebrates that enjoy Joss Whedon shows or G and T’s.  Pity for them.
3. GILI, J., ARNTZ, W., PALANQUES, A., OREJAS, C., CLARKE, A., DAYTON, P., ISLA, E., TEIXIDO, N., ROSSI, S., & LOPEZGONZALEZ, P. (2006). A unique assemblage of epibenthic sessile suspension feeders with archaic features in the high-Antarctic Deep Sea Research Part II: Topical Studies in Oceanography, 53 (8-10), 1029-1052 DOI: 10.1016/j.dsr2.2005.10.021
4. Clarke, A., Murphy, E., Meredith, M., King, J., Peck, L., Barnes, D., & Smith, R. (2007). Climate change and the marine ecosystem of the western Antarctic Peninsula Philosophical Transactions of the Royal Society B: Biological Sciences, 362 (1477), 149-166 DOI: 10.1098/rstb.2006.1958
5. Thatje, S., Anger, K., Calcagno, J., Lovrich, G., Pörtner, H., & Arntz, W. (2005). CHALLENGING THE COLD: CRABS RECONQUER THE ANTARCTIC Ecology, 86 (3), 619-625 DOI: 10.1890/04-0620

Frontiers: The deep sea and climate

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When we think about climate change and the ocean, many minds turn immediately to images of shallow-water corals, bleached white from the lack of zooxanthellae (internal, photosynthetic symbionts), driven away by heat and other types of stress.  However, the consequences of an increased atmospheric CO2 reach much deeper into the ocean.  The global ocean has an average depth of 3800 meters and comprises 71% of the total area of Earth, making the deep-sea far and away the largest biome on this planet.  In terms of volume, the deep-sea pelagic—the water-column itself—contains over a billion cubic kilometers of seawater.  Less than 5% of the deep benthos (the seafloor) has been remotely sensed, and less than a hundredth of one percent has been observed directly, sampled, and studied.  Even so, species diversity in the deep-sea is among the highest known1.

As a society, we still collectively get excited about the discovery of new species. And we should—such discoveries are essential to science.  The public being interested in new species is also quite importance for the continued funding of exploratory research.  Since 1840, 28 new habitat or entire ecosystems have been discovered in the deep ocean.  Not simply new species, but entirely new environments. Cold seeps, hydrothermal vents, brine pools, xenophyophore fields, just to name a few—these are all habitats that have only been known since the 1970s1.

Year of discovery of new habitat/ecosystem in the deep sea since 1840 (Ramirez-Llodra at al. 2010)

However, the lack of taxonomists to classify and describe the new species in these novel habitats dampens the spirit of discovery somewhat—specimens languishing in collections, as of yet unidentified due to the lack of support for specialists, harkening back to the last, frustrating scene in Raiders of the Lost Ark.

Atmospheric carbon dioxide concentrations are predicted to exceed 500 ppmv before 21002,a value not seen in the past few million years3.  This is contributing towards both warming and ocean acidification4,5.  It is uncertain how benthic organisms and their associated ecosystems as a whole will react; particularly little is known regarding the effects of climate change in the deep-sea. Continue reading →

Deepwater Horizon Revisited

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A recent study found oil and soot blanketing multiple areas of the seafloor in the Gulf of Mexico,  seemingly inundating the microbes that usually consume oil and leaving behind dead benthic animals.

Above is an absorbing and important lecture by Dr. Peter Roopnarine from last year on the ecosystem impact of the Deepwater Horizon disaster.  Dr. Roopnarine does really interesting work on mollusks, extinction, and food webs.

[Video source:  California Academy of Sciences, cc]

Distinct communities on a Tyrrhenian seamount

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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

Lunar cycles and reproduction in the deep sea

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Some biological patterns in marine species, particularly concerning reproduction, are related to the moon.  Shallow-ocean corals, for example, undergo mass spawning events (the synchronous release of eggs and sperm into the water column to combine), the timing of which, are set to the lunar clock.  Reef fishes, shallow-ocean echinoderms, mollusks and more, also time spawning events in respect to the phase of the moon.

The deep-sea, the largest biome on Earth, covering more than 326 million km2, has not been explored in terms of this lunar-synchronicity.  The dearth of photosynthetically-useful sunlight below 200 meters* would appear to make such moonlight-related cycles unlikely at best.

However, in a recent paper, Annie Mercier and her colleagues have shown that this may not be the case.  They demonstrate in both lab and field settings evidence of lunar periodicity in the reproduction of 6 deep-sea species, containing members from two different phyla:  Cnidaria and Echinodermata.

The researchers examined preserved samples of Phormosoma placenta (a deep-sea echinoderm) collected at various stages of the moon.  They found that despite being collected from between 700 – 1400 meters beneath the waves, physiological signs of recent spawning in both sexes coincided with the new moon.

Back in the lab, gamete and larval releases (reproduction events) were observed in captive specimens from 5 different species according to lunar patterns.  These specimens were collected between 100-1000 meters, with most species collected below 400 meters.  A minimum of 3 lunar months’ worth of data was compiled; some species actually repeated breeding periods in this timeframe.

The question remains if these animals are displaying internal rhythms that are kept in time by some sort of lunar cue, or if they are responding to something externally that follows the lunar period.  But what cues, or drivers, of a lunar period could be detectable at such great depths, where even sunlight wanes or is essentially eliminated?

Organic matter from surface waters falls into the deep sea; there is the possibility that these fluxes of sustenance may show lunar patterns.  Previous work has shown growth bands in some species of deep-sea corals that may correspond to monthly or lunar periods.  Other hypotheses include the idea that these animals can somehow directly perceive moonlight at great depths, or that deep tidal (related to lunar phase) currents exist.

In this study, internally brooding corals released larvae during the full or during the waning phase.  The 4 free-spawning species released gametes with the new moon.  The authors note that while this is opposite to the mass spawning events in shallow-ocean corals, which release during the full-moon, this may be due to the very different environmental and biotic factors in shallow areas versus the deep sea.

 

* This is the reason that little to no primary production occurs (that is, organisms producing chemical energy) in most, but not all, ecosystems known in the deep-sea.  Some deep-sea organisms are capable of undergoing chemosynthesis and can use inorganic chemicals, rather than sunlight as in photosynthesis, as an energy source.  However, even with a widespread lack of primary productivity and severe food limitation in most areas, diversity in the deep sea is among the highest on the planet.

Image:  Flicker user ZedZap (cc 2.0)

Sources:
ResearchBlogging.orgMercier A, Sun Z, Baillon S, & Hamel JF (2011). Lunar rhythms in the deep sea: evidence from the reproductive periodicity of several marine invertebrates. Journal of biological rhythms, 26 (1), 82-6 PMID: 21252369
Ramirez-Llodra E, et al. (2010). Deep, diverse and definitely different: unique attributes of the world’s largest ecosystem Biogeosciences, 7 (9), 2851-2899 : 10.5194/bgd-7-2361-2010

Smaller corals potentially more resilient

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“Professor Peter Mumby and Dr Laith Yakob from the University of Queensland report on their findings this week in the Proceedings of the National Academy of Sciences that small short lived corals which are taking over from large corals in some parts of the world are more resistant to disease.”

The authors warn that this finding, while seeming like a positive thing, actually has negative implications for the life coral reefs support.  Smaller corals mean less complexity, meaning less fish and associated invertebrates.

via Smaller corals take the heat › News in Science (ABC Science).

Boom: the destruction and rebirth of a marine ecosystem.

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In 1883, the world shuddered as the loudest known sound in human history echoed from its epicenter in Indonesia.  The noise generated by Krakatoa, a volcanic island in the Sunda Strait, was heard over 3,000 kilometers aways both to the east and west; the resulting tsuanamis produced waves over 30 meters in height and killed 36 thousand people.  The eruption altered weather globally. The volcanic dust suspended in the atmosphere halted a proportion of the solar radiation able to reach the Earth–in the year that followed global temperatures were reduced by as much as 1.2 degrees Celsius, not reverting back to normal until 1888.

From this volcanic destruction (two thirds of Krakatoa sank into the sea due to the blast), the island of Anak Krakatau-‘child of Krakatau’-was born, rising from Krakatoa’s crater less then 80 years ago.  This newly emerged island presents a unique opportunity to witness to the early stages of ecosystem development.

Eruptions on Anak Krakatau have been active recently, leading some to speculate whether or not another epic volcanic event is on the horizon.  Interestingly, fringing coral reefs have since formed on Anak Krakatau and nearby areas.  The recovery of the island’s terrestrial ecosystems has been subject to much attention and research.  However, the marine communities have largely been unstudied until the last decade.  In a work published this year in Coral Reefs, Dr. Starger and colleagues examined the genetic diversity in two reef-building corals, organisms within a marine ecosystem that was totally obliterated by the eruption in 1883.  Using microsatellites–short, repeating sequences of DNA–the researchers found that the genetic diversity in Pocillopora damicornis and Seriatopora hystrix, has largely recovered due to initial larval migration from other upstream sources.  Further analyses indicate that the coral populations within the Krakatau region may be self-recruiting at this point, and may even be providing larvae to other regions.

So these species of corals have recovered after an sudden, violent eruption.  What can we glean from this?  Coral reefs worldwide are in trouble, experiencing rapid decline, with mass mortality events projected.  In the face of such degradation, more data are needed for conservation, particularly in order to design effective marine protected areas (MPAs).  Connectivity is paramount in placing reserves.  Coral reefs can serve as larval sources, able to provide offspring to other areas, or sinks, which cannot.   The researchers show the repopulation of a destroyed marine ecosystem in the Java Sea from other sources, eventually becoming self-seeding.  This larval transport, especially in corals, may not permanently sustain reef populations over time, but can help to initally repopulate areas, for example, after a giant volcano pops its top.  Understanding the source-sink dynamics of these hugely-diverse ecosystems will likely be imperative in conservation planning.  Recovery of reef environments after disasters is dependent on healthy, nearby larval sources, giving importance to identifying and protecting these areas in networks of MPAs.

C. J. Starger, P. H. Barber, Ambariyanto, & A. C. Baker (2010). The recovery of coral genetic diversity in the Sunda Strait following the 1883 eruption of Krakatau Coral Reefs, 29, 547-565 : 10.1007/s00338-010-0609-2

Image 1:  Anak Krakatau. NASA EO-1 Team; Image 2:  Krakatoa, 1888 lithograph. Wikimedia Commons.

A Planetary Experiment: Ocean Acidification and Biology

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Ocean acidification is a relatively newly recognized threat to marine ecosystems. Even coral reef scientists, many of whom are now feverishly investigating the effects of changing seawater chemistry, ranked ocean acidification as 36th out of 40th potential threats to coral reef ecosystems in 2004 [1]. Recently, the magnitude of the shifting chemical balance in the ocean has become strikingly apparent [2].

Atmospheric carbon dioxide concentrations  are predicted to exceed 500 ppmv by 2100 [3]. Today, atmospheric carbon dioxide concentration is above 380 parts per million, a value not seen in the past 740,000 years, conservatively [4]. The ocean functions as a massive carbon sink and absorbs up to a third of atmospheric carbon. As carbon dioxide dissolves into seawater, it reacts to form carbonic acid, which dissociates to form bicarbonate ions and protons.

Read the entire article at The Urban Times , a recently launched online magazine that I contribute to, and will be acting as editor of Seas and Ocean content.  Check out the Sea and Ocean archive here, and you can follow updates via Twitter here.