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Tag: Coral

Help! We’re Sinking: The Drowning Atoll Island Communities

Posted on by Kayra Salih
Figure 1. A typical atoll island, source: http://www.ventanasvoyage.com/images/coral%20atoll.jpg
Figure 1. A typical atoll island, source: http://www.ventanasvoyage.com/images/coral%20atoll.jpg

What is sea level rise (SLR)?

The term is pretty self-explanatory in the sense that sea level is rising globally; it has risen by ~3.1mm yr-1 since the 1990s (Goelzer et al., 2015). This is due to the complex interactions of many drivers under recent climate change (Figure 2). This SLR is having global consequences including the loss of low-lying land, of which atoll islands are of the most vulnerable and threatened (Nicholls et al., 2007).

Figure 2. Diagram illustrating the causes of SLR, source: https://deq.nc.gov/about/divisions/coastal-management/coastal-management-hot-topics/sea-level-rise
Figure 2. Diagram illustrating the causes of SLR, source: https://deq.nc.gov/about/divisions/coastal-management/coastal-management-hot-topics/sea-level-rise

Atoll Island Communities

Atolls are mid-ocean annular reefs surrounding a central lagoon (Figure 1) (Woodroffe, 2008). Atoll islands are notoriously vulnerable to the effects of SLR for three main reasons (see Figure 3 below) (Woodroffe, 2008):

Figure 3. The three main impacts of SLR on atoll islands.
Figure 3. The three main impacts of SLR on atoll islands.

Impacts on Humans

These environmental changes inevitably have impacts on the surrounding ecosystem; affecting the terrestrial, aquatic and marine communities, including human populations. The world is now experiencing a wave of ‘climate change refugees’ (Farbotko & Lazarus, 2012) who have been forced to seek asylum in other countries, for example the islanders of Tuvalu.

Tuvalu is a country in the South Pacific solely consisting of low-lying coral and atoll islands (Figure 4) (Farbotko & Lazrus, 2012). Residents have already been forced to evacuate their homes due to flooding, in addition to saltwater incursion rendering their groundwater drinking source unsuitable (Connell, 2016). Sea level around Tuvalu is currently rising by ~5.1mm yr-1 (Connell, 2016). This is a common tale throughout Earth’s atoll islands, and one which is likely to become more common in the future.

Figure 4. Map of Tuvalu showing its many atoll islands, source: http://www.nanumea.net/Photos%20page/Tuvalu%20Map%20with%20arrow%20and%20ack%20-%20from%20Smithsonian%20(a).jpg
Figure 4. Map of Tuvalu showing its many atoll islands, source: http://www.nanumea.net/Photos%20page/Tuvalu%20Map%20with%20arrow%20and%20ack%20-%20from %20Smithsonian%20(a).jpg

Effects on Marine Organisms

The marine ecosystem surrounding islands is also experiencing adverse and damaging impacts from sea level rise. For example, the health of coral reefs is already being degraded by warming oceans contributing to coral bleaching (Figure 5).

Figure 5. Infographic explaining coral bleaching and its causes, source: http://oceanservice.noaa.gov/facts/coralbleaching-large.jpg
Figure 5. Infographic explaining coral bleaching and its causes, source: http://oceanservice.noaa.gov/facts/coralbleaching-large.jpg

It can be argued that rising sea levels may in fact protect corals from overexposure to sunlight as they are deeper (Woodroffe & Webster, 2014). However, this will mostly mean that corals are too deep to allow their symbiotic algae to survive, which will ultimately lead to coral death (Woodroffe & Webster, 2014).

These impacts lead to wider community impacts on marine organisms; coral-dependent fish will either migrate or die (Andréfouët et al., 2015). The decline in fish stocks will also affect human populations which depend on this resource. Furthermore, the whole community will be affected by changes in food resources and suitable habitat, possibly leading to the collapse of the ecosystem (Andréfouët at al., 2015).

The future…

More areas are predicted to be underwater in the future according to SLR projections (Goelzer et al., 2015). This will not only have an impact on the animal populations dependent on fragile atoll ecosystems; but also on human populations- with an increasing number of environmental asylum seekers. The future will likely see increasing numbers of atoll island communities drowning!

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References

Andréfouët, S., Dutheil, C., Menkes, C.E., Bador, M. & Lengaigne, M. (2015). Mass mortality events in atoll lagoons: environmental control and increased future vulnerability. Global Change Biology. 21:195-205.

Connell, J. (2016). Last days in the Carteret Islands? Climate change, livelihoods and migration on coral atolls. Asia Pacific Viewpoint. 57:3-15.

Farbotko, C. & Lazrus, H. (2012). The first climate refugees? Contesting global narratives of climate change in Tuvalu. Global Environmental Change. 22:382-390.

Goelzer, H., Huybrechts, P., Loutre, M.F. & Fichefet, T. (2015). Future rates of sea-level rise from long-term coupled climate-ice sheet projections. In: EGU General Assembly Conference Abstracts. 17:15590.

Nicholls, R.J., Wong, P.P., Burkett, V.R., Codignotto, J.O., Hay, J.E., McLean, R.F., Ragoonaden, S. & Woodroffe, C.D. (2007). Coastal systems and low-lying areas. In: Parry, M.L., Canziani, O.F., Palutikof, J.P., van der Linden, P.J. & Hanson, C.E. (Eds.). Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press: UK. pp. 315-356.

Woodroffe, C.D. (2008). Reef-island topography and the vulnerability of atolls to sea-level rise. Global and Planetary Change. 62:77-96.

Woodroffe, C.D. & Webster, J.M. (2014). Coral reefs and sea-level change. Marine Geology. 352:248-267.



Undeniable, unequivocal, underwater.

Posted on by Sarah Mayson

Climate change is undeniable (don’t argue), unequivocal and impacting underwater ecosystems.

Figure 1: A coral reef before and after the occurrence of coral bleaching. Source: climate.gov
Figure 1: Goodness reefuss! The devastation of Coral Bleaching. Source: climate.gov

Expanding from ‘Finding Nemo’, coral reefs are diverse underwater ecosystems playing host to symbiotic algae called Symbiodinium (Baker, Glynn and Riegl, 2008). This symbiotic relationship is mutually beneficial; algae capture sunlight and perform photosynthesis providing oxygen and nutrients to coral, whilst coral provides algae with a protected environment and photosynthetic compounds. However, this relationship is vulnerable to climate change, existing exclusively within narrow temperature limits associated with shallow, sunlit waters (Frieler et al., 2012). When exposed to above-normal temperatures, stressed corals expel dinoflagellates (Symbiodinium) from its tissues exposing its bleach-white skeleton (‘witwoo’) in a process called Coral Bleaching(figure1&2).

Figure 2: The following schematic describes the coral bleaching process. If the stress-caused bleaching is not severe, coral have been known to recover. However, if the algae loss is prolonged and the stress continues, coral eventually dies. Source: Oceanservice.noaa
Figure 2: Back to shoal special! This educational schematic describes the coral bleaching process.  Source: Oceanservice.noaa

The IPCC (2007) reported with HIGH confidence that observed changes in marine systems are associated with rising ocean temperatures. This is obviously not linked to the average 0.8℃ global ‘human-induced‘ temperature rise between 1961-2010 (NOAA, 2016) (figure 3); yes I’m rolling my eyes. Average tropical sea surface temperature (SST) has risen by 0.7℃ since 1970 (NOAA, 2016; figure3), parallel to atmospheric temperatures and with considerable variability, from our friend El Nino (NOAA, 2016). This is ultimately driving Coral Bleaching.

Figure 3ab: It's getting hot in here...and coral are literally taking off their clothes.
Figure 3: It’s getting hot in here…and coral are literally taking off their clothes. Source: left: www.epa.gov/climate-indicators right:www.metoffice.gov.uk

Still not convinced?

Bleaching has been SCIENTIFICALLY-PROVEN to correlate with climate-induced temperature rise, notably after 1970. For example, a 35% increase in Caribbean bleaching incidence between 1980-1990 resulted from a 1℃ regional SST rise (Baker, Glynn & Riegl, 2008). Case-studies are summarised in figure4ab.

Figure 4ab: Documented case studies of worldwide bleaching. Since the early 1980s, episodes of coral reef bleaching and mortality, due to climate-induced ocean warming, have occurred almost annually with increased frequency and intensity. Africa remains to be an outlier and yet to report a coral bleach event. Source: Baker, Glynne and Riegl, 2008.
Figure 4ab: Is anywhere safe? Since the early 1980s, episodes of coral reef bleaching and mortality, due to climate-induced ocean warming, have occurred almost annually with increased frequency and intensity (Baker, Glynn & Riegl, 2008). 
Source: Baker, Glynn & Riegl, 2008.

The third global bleach was designated by the NOAA in 2016; the first (1998) decimated 16-19% of the world’s coral (NOAA, 2017). A strong el-Nino (2016-2017) worsened the bleach and as of February 2017, the on-going global bleach continues to be the longest and most prevalent on record (NOAA, 2017; figure5).

Figure 5: The NOAA coral reefs watch indicates bleaching heat stress continues to build. There is a 60% chance that the displayed heat stress levels will occur. Multiple coral reefs are experiencing Alert Level 1 and Alert Level 2 bleaching stress (associated with widespread coral bleaching and significant mortality). Source: https://coralreefwatch.noaa.gov/satellite/analyses_guidance/global_coral_bleaching_2014-17_status.php
Figure 5:  Uh oh Alert! (1 and 2). The NOAA coral reefs watch indicates bleaching heat stress continues to build with a 60% chance that the displayed heat stress levels will occur. Source: https://coralreefwatch.noaa.gov

The ecological impacts of coral bleaching and related mortality you say? I’ve chosen my favourites.

Figure 6. Clown fish keep their fronds close but their anemones closer. Source: cargocollective.com
Figure 6. Clown fish keep their fronds close but their anemones closer. Source: cargocollective.com

Coral reefs are underwater rainforests. Covering 1% of the ocean floor, they support a 1/4 of all ocean life by providing the foundations for complex food webs and essential nurseries, spawning, breeding and feeding habitats (Jones et al., 2004; Bellard et al., 2012). An 8-year study in Papua New Guinea saw a dramatic decline in coral cover and a parallel decline in fish biodiversity; 75% of reef species declined in abundance (Jones et al., 2004). Yes folks, this includes much loved ‘Nemo’, the Pomacanthidae family(figure 6).

Coral diseases (figure 7) have been observed to correlate with temperature anomalies and bleaching events (Weil, 2004). Bleaching in the US Virgin Islands (a piece of the Caribbean ‘disease-hotspot’), followed by a disease outbreak (2005), resulted in severe reef degradation; the amount of living coral cover decreased by 60% (Jackson et al., 2014). Reported impacts included a reduction in live coral cover and considerable changes in community structure, diversity and abundance of reef-associated organisms (Weil, 2004).

Figure 7. Common coral diseases in the Caribbean. (A) Diploria strigosa with black band disease, (B) Dichocoenia stockesii with white plague, (C) Acropora cervicornis with white band and (D) Montastraea faveolata with yellow blotch syndrome. Source: www.reefresilience.org/coral-reefs/stressors/coral-disease/disease-impacts/
Figure 7: No wonder their as white as a sheet…and yellow…and black!                    (A)  black band disease, (B) white plague, (C) white band and (D) yellow blotch syndrome. Source: www.reefresilience.org

 

 

Bad news, the Worlds Resource Institute reports 10% of coral reefs are permanently damaged; even worse, global warming trends suggest SST will reach that pesky 1℃ resulting in increased bleaching frequency and intensity (Burke et al., 2011). If we continue business-as-usual, 90% of coral reefs will be in danger by 2030 and all by 2050 (Burke et al., 2011).

 

 

 

 

 

 

 

References

Baker, A.C., Glynn,P.W. & Riegl,B., 2008. Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuarine, Coastal and Shelf Science, 80(4), pp. 435-471.

Bellard, C., Bertelmeier, C., Leadley, P., Thuiller, W. & Courchamp, F., 2012. Impacts of climate change on the future of biodiversity. Ecology Letters, 15(4), pp. 365-377.

Burke, L., Reytar, K., Spalding, M. & Perry, A., 2011. Reefs at Risk Revisited , s.l.: Worlds Resource Institute .

Frieler, K., Meinshausen, M., Golly, A., Mengel, M., Lebek, K., Donner, S. & Hoegh-Guldberg, O., 2013. Limiting global warming to 2 ◦C is unlikely to save. Nature Climate Change, Volume 3, pp. 165-170.

IPCC, 2007. Climate Change 2007: Synthesis Report, Valencia: IPCC.

Jackson, J., Donovon, M., Cramer, K. & Lam, V., 2014. Status and Trends of Caribean Coral Reefs: 1970-2012, Washington, D.C. : Global Coral Reef Monitoring Network.

Jones, G. P., McCormick, M. I., Srinivasan, M. & Eagle, J. V., 2004. Coral decline threatens fish biodiversity in marine reserves. PNAS, 101(21), pp. 8251-8253.

National Oceanic and Atmospheric Administration (NOAA), 2016. Global Analysis- Annual 2016. [Online]
Available at: https://www.ncdc.noaa.gov/sotc/global/201613

National Oceanic and Atmospheric Administration (NOAA), 2017. Coral Reef Watch. [Online]
Available at: https://coralreefwatch.noaa.gov/satellite/analyses_guidance/global_coral_bleaching_2014-17_status.php
[Accessed 20 03 2017].

Weil, E., 2004. Coral reef diseases in the wider Caribbean. In Coral health and disease (pp. 35-68). Springer Berlin Heidelberg.

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