2015 Coral Reef Bleaching Update

So whilst having a little google to check up on the current El Niño event and its impacts on coral reef bleaching I stumbled across this brilliant website which has introduced me to the XL Catlin Seaview Survey project. This project runs off predictions issued by NOAA Coral Reef Watch programme, responding quickly to take pictures and videos of the areas affected. The result is a website with a rich array of wonderful images and videos that bring to life the true extent of this years bleaching event. Figure 1 shows an example, I recommend readers of this post check it out.

Figure 1. Bleaching in American Samoa (left image: December 2014, right: February 2015) source: globalcoralbleaching.org

Recent publications - a mini review

In the past year there has been a notable amount of publications on climate driven impacts on coral reef fishes. This post will attempt to review a portion of this literature, taking a look at three specific articles which were of interest and relevance to this blog.

The first paper of choice looks at reef fish responses to coral recovery following El Niño disturbances. I chose this paper because it looks at long term coral and fish responses from the 1982-1983 as opposed to the 1997-1998 bleaching event where long term analysis isn't possible just yet. After being reduced to 0% coral cover in Uva Island Reef, Panama, coral response was minimal in the following 10 years, with notable response (35%) occurring by 2010. The study found that following the 1982-83 bleaching event coral fish densities varied little over the sampling period of 30 year,s however there was a sharp response in recovery when coral cover recovered between 0 and 20%, waning after 20% recovery. They propose that fish diversity was related to the diversity and availability of food and shelter resources which also followed this parabolic trend. Following coral reef degradation and coral rubble transformation, the presence of cryptic invertebrates increases which, according to this article, provides prey for fish consumers, allowing populations to bounce back and recover.

The rather positive outlook of the previous article is contrasted by a study by Brooker et al published last year which much like what was explained in a short lecture in a previous post stresses the danger of local level extinctions of marine species. This article raises awareness to the local extinction of the corallivorous reef fish Oxymonacanthus longirostris following an intense mass bleaching event. They found that this extinction was due to loss of a key prey species Acropora millepora (Am) despite overall coral cover remained high. Further to this they found that the fish chose to feed on the bleached coral as opposed to alternative unaffected species in an experimental test that compared their feeding habits with healthy Am, bleached Am, and healthy Acropora noblilis (An). The continued selection of Am, regardless of condition, suggests that even when bleached Am either is a superior resource or that inherent preferences persist despite changing conditions. This article makes me reflect on the findings of the previous article that solely looks at the response of invertebrate feeding fish and those that don't have such a specified diet. As discovered with this article, responses are clearly more complex when corallivorous species are considered and/or those with behavioural inflexibility.

The third and final article in this review emphasises the role of structural complexity and the difference between coral mortality and eventual coral erosion. Ecologically driven coral mortality (for example the introduction of coral eating sea stars in this case) differs significantly from climate driven events (post Tropical cyclone) which normally induces complete skeletal erosion in the coming years/decades. When the latter occurs, a lack of structure significantly impacts the ability of fish species to survive, which has implications for short term studies on fish species response, as more significant responses are seen on longer timescales. The results of this article highlight the ability of disturbance type to influence rate at which structural complexity declines post mortality and therefore the impacts on reef associated fish species. The results from this article bears significance as it highlights that climate driven as opposed to ecologically driven changes are most detrimental, but also emphasises the value and need for long term studies.

While all of these articles produce interesting (and sometimes conflicting results) I think scale is an important constraint to the applicability of the results. Obviously it is incredibly difficult and resource consuming to produce a long term metaanalysis of coral reef and fish response to global bleaching events at a number of sites. I hope that as scientists and academics scramble to the sites where this year's bleaching event is impacting, there are collaborative efforts to look at differences (or indeed similarities) between sites.

COP21 cartoon

A rather fitting cartoon to summarise some of the aspects I mentioned in my previous post, referencing the concerns of sinking Pacific Island Countries. Lifebuoys and hooks won't be enough for our planet, lets hope over the coming days some substantial and constructive agreements can be made.

source: Politicalcartoons.com

COP21 - Don't forget the oceans!

Though not entirely relevant to the focus of my blog, it feels only right to make some comments about the United Nations COP21 discussions that are currently being held in Paris. Articles relating to oceans express concern that the negotiations are largely ignoring the vital resources that oceans provide. When you do some general reading around the negotiations the same discussions/focus on climate reparations, carbon tax, liabilities etc. dominate much of the commentary. The general lack of attention to marine and fisheries in the agenda for discussion has been stressed by various fisheries and conservation experts. Indeed, as highlighted by RFI, the World Ocean Day which was held by COP21 organisers was resigned to an area outside the registered-only badge area, exemplifying the muted role concerns over oceans will play over the course of the negotiations. East African researchers and activists have particularly stressed the importance of consideration of oceans and in particular coral reefs in sustaining the coastal economy of many countries.

In the negotiations themselves, on the 5th of December environmental leaders from the Pacific Islands were stressing the importance of the oceans to their countries, as they could suffer most from sea level rice, ocean acidification and indeed the degradation of coral reefs. Pressing for the target of a maximum 1.5 C increase, the Prime Minister of Tuvalu stresses the issue is not merely academic, for pacific islands like Tuvalu, it is a matter of life and death. 

Further to this, marine biologists have attended COP21 with the premise that in order to save our coral reefs we need to halt climate change immediately. The reasons listed in a Huffington post article outline they will become softer due to acidic waters, less diverse as less species will be able to thrive, less appealing due to proliferation of algae, less able to feed us, provide less protection from coastal erosion and less economic benefit from tourism. Marine biologists lament the fact that at best we could commit to 1.5 degree Celsius increase where other countries could still lead to a 6 degree increase. To avoid significant damage to corals, a cap on total carbon emissions would be needed, and this isn't even being considered at the negotiations.

So, from the marine perspective COP21 does not seem to hold ocean environments as a key concern and point of discussion. This is extremely worrying for the pacific islands as its not a matter of future impacts, it is a matter of now. Though oceans don't feature prominently on the agenda, one could argue severe impacts on the oceans can be mitigated by efforts to reach agreements on elements that do feature high up on the agenda, whilst it seems that this sphere is being neglected, the benefits of large scale multilateral agreements would most likely trickle down to the oceans.