To Save Coral Reefs, First Save the Mangroves

On the 30th December, just before the start of the new year aired the first episode in a new David Attenborough series on The Great Barrier reef. I watched this from home with my parents expecting to hear similar things to what I have been sharing on this blog and been learning about this past year or so, including from my studies in Los Angeles. I write this post because there was something very significant I learnt whilst engrossed in this documentary. At no point have I been aware of the importance of mangroves and how they provide refuge for many of the coral reef fish species whilst they are learning to adapt to their conditions, avoid predators and the adverse effects of climate change.

This led me to doing a little more investigating around the area, and it turns out that understanding of the significance of mangroves has only been a relatively recent thing. In fact, I was led to an article published in 2014 which appeared to first academic draw attention to the link, emanating from the discovery of Caroline Rogers of the USGS in Hurricane Hole, U.S. Virgin Islands where she discovered more than 30 species growing among the mangrove roots (4 of these threatened!). The article acknowledges mangroves as a novel natural refuge from climate change and points to the importance of mangroves as a conservation technique, especially relevant after various academics (see previous post) have found MPA's (Marine Protected Areas) ineffective. The article studied two major reef building corals (Colpopphyllia natans and Diplopia labyrinthiformis) that were growing in mangrove shaded and exposed (unshaded) areas noting the differences between them. The results found that C. Natans preferred living in areas shaded by mangroves and none of its colonies were bleached, whereas the exposed had been bleached. D. labyrinthiformis preferred unshaded areas, but bleached more significantly because of this, pointing to the significance of mangroves as a refuge for coral species adapting to climate change based on evidence from this particular location of study. This will definitely be an interesting aspect to monitor as we begin to understand more about the symbiotic relationship between corals, fish and the mangrove roots.

Also just to add, I would recommend readers watch the first episode of the new David Attenborough and take a look at the second episode which is due to air tomorrow. The programme uses a submersible to capture recording of activity at night, which is now technologically possible, and ecologically extremely interesting. Furthermore the programme aims to look at the most pristine areas of the Great Barrier Reef. So, for a good insight into the beauty of Coral Reefs, their significance, relevance to indigenous cultures and for the threats posed to them, I recommend readers give the episodes a watch. I will certainly be paying attention to any new things I can learn, and if there is more discussion on the threats to coral reef fish species.

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.

Climate driven regime shifts vs rebound potential

Conditions under which coral reefs show resilience and regenerate from bleaching events or dramatically shift in state to less diverse and productive algal states are not well known in ecology yet. This is a severe drawback if one wants to investigate the impacts of climate change and associated bleaching events on coral reef fish. As I have come to understand and explain through previous posts, the potential for coral reef fish to survive bleaching events depends on the frequency and severity of these events. There are also a wide range of biological and behavioral factors that influence this, such as the specificity of diet, range and distribution of these species. We already know that a loss of coral cover significantly impacts juveniles that rely on cover to survive and evade predators.

A letter published to Nature this year by Graham et al., one of the leading researchers on this issue looks to understand the dynamics by which a >90% loss of coral cover can lead to both recovery and  a shifting of regime, two completely different responses. And these two different reef responses translate to two distinctive fish species responses, with a return to predistrubance structure on recovering reefs yet becoming significantly and progressively altered on those that shifted regimes. Using a 17 year dataset the paper assesses the long term ecosystem dynamics of 21 reef sites across Seychelles, the most severely affected area by the 1998 el Nino.

Figure 1. Response or recovery of coral reef assemblages post disturbance (source: Graham et al.,2015)

Results from the study found 12 of 21 sites recovered but this was laboured over the first 7-10 years, speeding up after this period as local recruitment levels increased. The main point to take from the paper is that a trajectory towards recovery occurred when reefs were structurally complex and in deeper water. In these area juvenile corals and herbivorous fish populations were high and nutrient loads low. This is interesting as it suggests a level of symbiotism between coral reef fish and coral reefs; while the fish species rely on the reef for protection and for survival, the coral species depend on the herbivorous fish species to recover. Whilst the paper does give an interesting insight into reef responses to disturbance it is important to remember this was only one rather local study, there could be significant regional differences in factors that influence such response.

Endangered Coral Reef Fish

Below is an introduction to some of the endangered fish species that rely on coral reef cover, it is important to dedicate a post to this so to highlight the beautiful species that are at risk, illuminating the main concerns of this blog. This list has been adapted from a study that assesses the IUCN Red List of Threatened Species focussing specifically on the US Pacific Islands. It is important to mention that the species listed below are IUCN classified as "endangered", "vulnerable" and/or NOAA "species of concern." Notably, there are many more species that are listed as "near threatened" or "decreasing" in population.


Common Name: Sharptooth Lemon Shark
Family: Carcharhinidae
Species Name: Negaprion acutidens
Range: wide ranging, native to Indian Ocean and western Central Pacific
Justification: Narrow habitat range, heavily overfished
IUCN classification: Vulnerable


Common Name: Threadfin Butterflyfish
Family: Chaetodontidae
Species Name: Chaetodon flavocoronatus
Range: endemic to western Pacific
Justification: very limited range
IUCN classification: Vulnerable


Common Name: Tawny Nurse Shark
Family: Ginglymostomatidae
Species Name: Nebrius ferrugineus
Range: Indo-Pacific
Justification: Heavily fished, narrow habitat range
IUCN classification: Vulnerable


Common Name: Humphead Wrasse
Family: Labridae
Species Name: Cheilinus undulatus
Range: Tropical Indo Pacific
Justification: valued economically, heavily overfished, 50% pop decline in past 20 yrs
IUCN classification: Endangered
NOAA specie of concern


Common Name: Manta Ray
Family: Mobidulae
Species Name: Manta alfredi
Range: wide but sparsely distributed and fragmented Pacific, Atalantic, Indian oceans
Justification: used for medicene, low reproductive output, specific resource needs
IUCN classification: Vulnerable


Common Name: Green Humphead Parrotfish
Family: Scaridae
Species Name: Bolbometopon muricatum
Range: wide range
Justification: overfished, extinct in some localities
IUCN classification: Vulnerable
NOAA specie of concern


Common Name: Squaretail Coral Grouper
Family: Serranidae
Species Name: Plectropomus areolatus
Range: Indo-Pacific, Red Sea, Southeast Asia
Justification: wide range but heavily fished, declined 30% over last 20 years
IUCN classification: Vulnerable


Common Name: Blacksaddled Coral Grouper
Family: Serranidae
Species Name: Plectropomus laevis
Range: large from East African Coast to central and Southern Pacific
Justification: targetting of juveniles by fishing
IUCN classification: Vulnerable


Common Name: Queensland Grouper
Family: Serranidae
Species Name: Epinephelus lanceolatus
Range: Indo-Pacific, locally rare but widely distributed
Justification: Fished heavily, cultural significance in China, reproductive difficulties
IUCN classification: Vulnerable


Common Name: Scalloped Hammerhead
Family: Sphyrnidae
Species Name: Sphyrna lewini
Range: circumglobal distribution in warm temperate and tropical seas
Justification: fishing
IUCN classification: Endangered


Common Name: Great Hammerhead
Family: Sphyrnidae
Species Name: Sphyrna mokarran
Range: large widely distributed, restricted to continental shelves
Justification: valuable in market so fished both intentionally and accidentally
IUCN classification: Endangered


Common Name: Zebra Shark
Family: Stegostomatidae
Species Name: Stegostoma fasciatum
Range: Indian, West and Central Pacific Oceans
Justification: overfishing
IUCN classification: Vulnerable


Some important points to take from this are:

• sharks make up the most of the endangered coral reef fish species
• there is very little overlap with the ideas shared in the lecture from my previous post
• fishing is the main cause of species endangering, very little reference to natural (climate driven) or biological reassons for population decreases