Ove Hoegh-Guldberg speaks on climate change in the ocean

From the 2011 National Council for Science and the Environment conference in Washington, D.C.  You can find out more about Dr Hoegh-Guldberg at his laboratory site.

Video:  John Bruno on Vimeo (cc).  Via SeaMonster.

Crushing predators reinvade the Antarctic benthos

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

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

The future of shallow-sea coral reefs

Coral reefs, in case you haven’t been keeping up, are increasingly threatened by overfishing, ocean acidification, and warming, among other human-derived factors.  Recently, much buzz has been created on the web (e.g., here, here, and here) in the wake of an updated assessment from the World Resource Institute and its partners concerning the global status of shallow-sea coral reefs.

I confess I have not had the chance to dive into the full report, but here are some key snippets from the  executive summary:

  • 60+ % of the world’s coral reefs are threatened by local sources, such as overfishing, destructive fishing methods and pollution
  • Overfishing is the “worst immediate threat,” affecting 55% of reefs.  Coastal development and land-based pollution, and maritime pollution and damage from vessels come in second and third, affecting 25% and 10% of reefs, respectively.
  • 75% of shallow-sea coral reefs are threatened by the aggregation of local and thermal stresses.
  • Despite that 25% of reefs are within protected areas, many of these are inadequate or only partial protected.

The report also offers map-based information for the current status of these ecosystems and predictions for 2030 and 2050, integrating both local and global threats.  WRI offers KLM files of these assessments/probable future scenarios here, which I quickly threw into Google Earth and centered the maps over southeast Asia, generally acknowledged to the ‘epicenter of marine diversity’.  Click on the images to embiggen; the cool-colored dots represent sites with low risk and the red – maroon dots represent sites that are increasingly threated1.

Today

 

2030


2050


Visit the World Resources Institute to check out the report, the summary, map files, and lots more (cc 3.0).  The executive summary also has a nice list of ways you can help.

 

 

1 If anyone knows how to import .kmz files into the far more figure-friendly Google Maps without wading into the land of ESRI and QGIS, and is willing to share, that would be excellent.

 

 


Smaller corals potentially more resilient

“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).

This is not helpful.

From the Pew Research Center:

A 53%-majority of Republicans say there is no solid evidence the earth is warming. Among Tea Party Republicans, fully 70% say there is no evidence. Disbelief in global warming in the GOP is a recent occurrence. Just a few years ago, in 2007, a 62%-majority of Republicans said there is solid evidence of global warming, while less than a third (31%) said there is no solid evidence. Currently, just 38% of Republicans say there is solid evidence the earth is warming, and only 16% say that warming is caused by human activity.

Read more here.

A cautiously-optimistic call to arms in coral reef science

Coral reef ecosystems are under assault from multiple stressors.  These range from local to global disturbances, some falling into the realm of naturally-induced. Some of these disturbances can be exacerbated through anthropogenic means.  Some of the most insidious threats to these ecosystems are completely human-induced, such as the current inextricable acidification of the global ocean.

There have been mechanisms proposed that corals could theoretically use to deal with a rapidly changing global environment, particularly a warming surface ocean.  Existing coral reef ecosystems are built around a symbiosis between the corals themselves and an intracellular photosynthetic dinoflagellate symbiont, within the genus Symbiodinium.  Shallow-sea corals are capable of capturing bits of organic matter and small plankton in the water column for subsidence, but these organisms garner most of their energy from their photosynthetic tenants.  Bleaching occurs when this symbiosis is compromised–one common mechanism is heat stress.  Other causes exist, but bleaching via heat stress is an increasing dominant phenomenon; stark bleaching predictions related to oceanic temperature anomalies were recently announced for most of the Caribbean.  Scleractinian corals (stony, hypercalcifying, reef-building corals) show variability in terms of which species bleach at certain thermal thresholds, as well as their geographic locations around the world.  This variability may be at least partially explained by the different symbiont types within the corals.  All types of coral symbionts are apparently not equal in how they can deal with warmer temperatures.  For example, evidence exists that type D symbionts are more abundant after severe bleaching episodes and the ensuing mortality1.  One proposed hypothesis states that  reef-building corals can switch out their existing internal symbionts in exchange for more heat-tolerant symbiont types.  A study in the Public Library of Science2 warns that this mechanism may not the panacea hoped for.  Colonies of a scleractinian coral, Porites divaricata, were bleached and then exposed to symbiont types not usually found associated with this species.  Some colonies were actually able to uptake these new symbionts–the first time that this environmental acquisition has been shown experimentally for scleractinian corals–however, this was an evanescent acquisition.  Only the original symbiont types proved to be stable during the bleaching recovery, implying that not all corals have the capacity to acclimate to a warming ocean by uptaking more heat-resistant symbionts.

However, a recent review of coral reef resilience3 by Dr Terry Hughes and collagues reveals guarded optimism for these heavily-impacted ecosystems, provided that action is taken.  In this context, resilience is the ability of an ecosystem to absorb and adapt to disturbances, without  ecosystem functions being profoundly altered.  These disturbances can vary in their rates of change; for instance, when long-term stressors are at a low level, reefs can be acted upon point (acute) disturbances of greater magnitude and speed and still recover.  The authors point out that natural dynamics are inherent in complex biological systems–Heron Island on the Great Barrier Reef loses almost all coral cover on a decadal basis due to cyclones, yet can recover due to their locally high resilience.  However, this is proving to be the exception, rather then the rule:  many reef systems have been pushed near the proverbial tipping-point, rending them ecologically unable to recover from acute, high-magnitude disturbances.  Hurricanes are enormously powerful disturbances, yet resilient reefs will recover relatively quickly.  However, even a gradual shift away from a coral-dominated ecosystem from long-term chronic impacts, say increased levels of pollution or sedimentation, can reduce resilience over time.  These types of local stressors can accumulate and produce community changes without acute, large disturbances.  Even some deep reef sites, below wave action and thus unaffected from hurricanes, have been gradually moved away from normally coral-dominated ecosystems, undergoing phase-shifts.  Unfortunately, these local impacts can be compounded by global impacts such as invasive species, warming, and ocean acidification. Phase-shifts refer to a change in the species assemblage to one that is not normally dominant.  Consider the Caribbean.  Coral cover has declined by ~80-90% since the late 1970s at sites throughout the region, while macroalgae cover has increased markedly.  In a nutshell, many grazing fishes were once present, keeping the macroalgae at bay and allowing for both the persistence of coral-dominated reefs and the settlement of coral larvae.  Once these grazer populations were exploited by overfishing, a sea urchin became the dominant grazer until it was decimated from a disease epidemic in the early 1980s.  This die-off was a pivotal event, and phase-shifts to algal systems become to become more common and many reefs are still operating under this alternative stable state today.  Atolls in the Pacific are thought to be much more resilient to these types of ecological changes, due to lower fishing pressure and less directly-induced human impacts overall.  On the other hand, the isolation of these oceanic oases means that these sites are much more self-dependent than other sites, due to reduced larval connectivity (e.g. coral reef organisms’ larvae have less success getting to isolated sites, simply due to distance and ocean currents).

So is there good news to be had?  These phase-shifts have been shown to be reversible in some cases.  Diadema antillarum populations in the Caribbean is recovering, albeit slowly and in spatially discrete locations, providing increased herbivory on some reefs–at these locations, the macroalae is being grazed back and coral-dominated systems are possible again.  This is not widespread currently, as most Caribbean reefs continue to be algal-dominated.  Another example of the reversibility of these trends involve No-Take-Zones (NTAs), a type of Marine Protected Area (MPA).  In the Bahamas, NTAs have resulted in higher densities of herbivorous fishes, contributing to declining macroalgal cover and more young corals settling on the reef.  MPAs have also been shown to increase coral cover on a global basis.

Rather than dealing with each threat to coral reefs individually, a common approach, they must be dealt with in an integrated, proactive fashion, rather than reactively after the damage is likely already done.  Hughes et al. stress the need for:   the enforcement of harvesting regulations, local education, integrative decision-making via better access to “international networks of expertise”,  and the confrontation of climate change by rapidly reducing greenhouse gas emissions.  Rapid climate change and ocean acidification will ultimately undo any management policies for coral reef ecosystems.  It is imperative for the state of coral reefs worldwide to be recognized for what it is: “a crisis of governance.”  Though the situation may be daunting, these systems can be saved.

[This article has been cross-posted, albeit with a different image 1, at The Urban Times, an online magazine.]

Images  1:  Close-up of a scleractinian brain coral. From Flickr user Laszlo Ilyes (cc) 2: Scleractinian coral colonies shown before (A) and after (B) one month of increased temperatures (Coffroth et al 2010).

References:

1. Baker AC, Starger CJ, McClanahan TR, & Glynn PW (2004). Coral reefs: corals’ adaptive response to climate change. Nature, 430 (7001) PMID: 15306799

2. Coffroth MA, Poland DM, Petrou EL, Brazeau DA, & Holmberg JC (2010). Environmental symbiont acquisition may not be the solution to warming seas for reef-building corals. PloS one, 5 (10) PMID: 20949064

3. Hughes TP, Graham NA, Jackson JB, Mumby PJ, & Steneck RS (2010). Rising to the challenge of sustaining coral reef resilience. Trends in ecology & evolution (Personal edition) PMID: 20800316

Arctic Sea Ice, Shipping, and Dispersal

 

The National Snow and Ice Data Center reports that the Arctic sea ice extent recently reached its third lowest for the month of September since we’ve had satellite data.  The minimum extent occurred on September 19th, with 4.6 million square kilometers of ice.  This melt season has since ended; the 5-day average ice extent was recorded at 5.44 million square kilometers on October 1st.

On September 20th, the U.S National Ice Center identified the opening of the Northwest Passage as  satellite images indicated minute levels of multi-year ice present there.  The first commercial ship, the MV Camilla Desgagnés, successfully navigated through the Passage in 2008, potentially leading the way in utilizing this new route for trans-ocean shipping.  However, the opening of Arctic sea ice could bring more than just cargo.  The Arctic has served as a major biogeogaphic barrier since the mid-Pliocene (~3 million years ago).  It has recently been pointed out that with temperature shifts and decreased ice, marine organisms are likely to use the Arctic as a throughway between the Pacific and Atlantic oceans, with unknown ecological effects1.  This may be already occurring to some extent:  a Pacific diatom was observed in 1999 in the Labrador/Irminger seas, betwixt Canada and Greenland.  This particular species was known to have last lived in the north Atlantic more than 800,000 years ago, according to sediment records2.  Shipping is expected to assist this trans-Arctic dispersal of species.  This opening of the Arctic has also spurred claims to the seafloor among Russia, Denmark, Norway, Canada, and the US in order to be able to capitalize on oil and gas reserves likely present there.

Images:  1) National Snow and Ice Data Center, 2) Bill Rankin, Radical Cartography (cc)

1. Sutherland, W., Clout, M., Côté, I., Daszak, P., Depledge, M., Fellman, L., Fleishman, E., Garthwaite, R., Gibbons, D., & De Lurio, J. (2010). A horizon scan of global conservation issues for 2010. Trends in Ecology & Evolution 25 2. Reid PC (2008) Trans-Arctic invasion in modern times. Science 322

Common Climate Change Arguments

From David McCandless’ Information is Beautiful (CC licensed).  The interesting thing about this infographic is that its creator deliberately choose not to speak with any climate experts, as to see what it was like for people to learn about climate change online using only publicly available data (click to embiggen and go to source).

If you’d really like to fling yourself into this field, the IPCC’s AR 4 is a great place to start–don’t worry, this (freely accessible!) tome has a technical summary.