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Tag: coral reefs

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.

[Word Count excluding title, captions and references: 500]



RIP Great Barrier Reef: a Reef In Peril?

Posted on by Claire Murray

The threat of climate change for coral reef ecosystems across the world

By Claire Murray, University of Southampton student

 

the_sun
Losing Nemo? Are we seeing the demise of the Great Barrier Reef? Source: The Sun, 2016

Coral reefs are unique, awe-inspiring ecosystems; distinctively bright, bursting with biodiversity. However, they are already facing impacts of climate change. Headlines last year claimed the death of the most famous coral reef system on earth – the Great Barrier Reef. Whilst the story was greatly exaggerated, the possibility of the threat is all too real.

 

 

 

 

whitecoral
Good greef! Bleached coral, a contrast with the vibrant reef. Source: The Guardian, 2017

The importance of coral

Coral is a living organism, with algae it’s partnering, symbiotic component. Algae and coral are mutually dependent on each other for survival; providing food and a habitat respectively. However, coral bleaching is the loss of the symbiotic algae, occurring due to intolerance to changing environmental conditions such as increased sea temperatures. This is visually evident as a loss of pigmentation; replacing vibrant colours with the white colour of the coral’s calcium structure (Antonelli, et al., 2013). Increasing sea temperatures are a certain consequence of climate change, meaning that more coral bleaching could occur as temperatures increase in the near future (Antonelli, et al., 2013).

 

vibrantcoral
A vibrant coral reef ecosystem, without bleaching. Source: The Sun, 2016

What’s the catch?

Coral reefs provide important local ecosystem services, including coastal protection and fishery support (Hicks & Cinner, 2014). Corals are the main habitat-forming organism in the reef ecosystem – centrally important for biological and physical structure (Coker, et al., 2014). Various species are supported within the ecosystem, making reefs biodiversity hotspots (Hicks & Cinner, 2014). However, rising global sea temperatures are an environmental driver of the change being seen in ecosystems; threatening the benefits the ecosystem brings.

Threats to coral reefs are two-fold: global climate change pressures, and local anthropogenic pressures (Mongin, et al., 2016). Local stressors include pollution, sedimentation and overfishing (Ateweberhan, et al., 2013). Coral reefs are highly sensitive to the global risks of ocean acidification and warming (Ateweberhan, et al., 2013; Wolff, et al., 2015; Van Hooidonk, et al., 2014). The loss of the physical habitat ultimately threatens the abundance of marine life that depends on coral for its survival, reducing the resilience of the ecosystem as a whole.

 

acropora
Acropora coral, found in the Caribbean. Source: Pinterest, 2017

All bad news?

There is inequity of climate change impacts across coral reefs – for example, the Caribbean is likely to experience only relatively low levels of stress (Wolff, et al., 2015). The rates of environmental change also varies at different latitudes, meaning impacts will be staggered throughout the ecosystems on a global scale (Van Hooidonk, et al., 2014).

Despite the obvious negatives experience by the majority of coral reefs, it’s not bad news everywhere. Acropora corals seen on the northern Gulf of Mexico and on the Florida peninsula are extending their range – resulting in new, ‘novel’ ecosystems (Graham, et al., 2014). The emergence of new communities demonstrates the changing dynamics of the ecosystem.

The diverse environmental changes being seen globally are certainly going to impact coral reef ecosystems, and predominantly in a negative way. However some positives are likely; so not all hope is lost. But in the meantime, it might be worth visiting the Great Barrier Reef before it’s too late…

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References

Antonelli, P. L., Rutz, S. F., Sammarco, P. W. & Strychar, K. B., 2013. A coral bleaching model. Nonlinear Analysis: Real World Applications, Volume 16, pp. 65-73.

Ateweberhan, M. et al., 2013. Climate change impacts on coral reefs: Synergies with local effects,. Marine Pollution Bulletin, 74(2), pp. 526-539.

Coker, D. J., Wilson, S. K. & Pratchett, M. S., 2014. Importance of live coral habitat for reef fishes. Reviews in Fish Biology and Fisheries, 24(1), pp. 89-126.

Graham, N. A. J., Cinner, J. E., Norstrom, A. V. & Nystrom, M., 2014. Coral reefs as novel ecosystems: embracing new futures. Current Opinion in Environmental Sustainability, Volume 7, pp. 9-14.

Mongin, M. et al., 2016. The exposure of the Great Barrier Reef to ocean acidification. Nature communications, 7(10732), pp. 1-8.

Van Hooidonk, R., Maynard, J. A., Mazello, D. & Planes, S., 2014. Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs. Global Change Biology, 20(1), pp. 103-112.

Wolff, N. H. et al., 2015. Global inequities between polluters and the polluted: climate change impacts on coral reefs. Global Change Biology, 21(11), pp. 3982-3994.