Caribbean fish decline in the wake of coral collapse?

Posted on April 25, 2009 by ovehblog

A new study in Current Biology (some really interesting coral related stuff being published there lately) by Michelle Paddack and colleagues (Paddack et al 2009) documents a region-wide decline in reef associated fish in the Caribbean. The authors conducted a meta-analysis on a substantial amount of fisheries-independent, time-series data on Caribbean fish densities. Fish densities seem to have been pretty stable from the mid-50s until the mid-90s, to then exhibit significant negative rates of change during the past 10 years. What is striking is the generality of the decline that has occured the past decade, across the whole region (see figure below)

Recorded declines in fish densities across five Caribbean sub-regions 1996-2007

Differences in fished and non-fished species were non-significant. This leads the authors to speculate that fishing is not the main driver of these changes (although certainly it plays a part). Rather, as has been documented in the western Indian Ocean, these changes in fish communities could be a response to the substantial losses of coral cover which have occurred in the Caribbean the past decades. A wicked problem, primarily for managers and communities dependent on fisheries, is that changes in fish communities seem to manifest themselves as a form of “degradation debt” – that is, there is a substantial time-lag between changes in the underlying benthic community and the response of fish communities.

Resilient ‘super reefs’ a priority for conservation efforts

Posted on April 24, 2009 by ovehblog

picture-354
ScienceDaily, 23rd April 2009

The Wildlife Conservation Society announced today a study showing that some coral reefs off East Africa are unusually resilient to climate change due to improved fisheries management and a combination of geophysical factors. WCS announced the results of the study at the International Coral Reef Initiative (ICRI), which is meeting this week in Phuket, Thailand.

The study, published in the online journal Aquatic Conservation: Marine and Freshwater Ecosystems, provides additional evidence that globally important “super reefs” exist in the triangle from Northern Madagascar across to northern Mozambique to southern Kenya and, thus, should be a high priority for future conservation action.

Authors of the study include Tim McClanahan and Nyawira Muthiga of the Wildlife Conservation Society, Joseph Maina of the Coral Reef Conservation Project, Albogast Kamukuru of the University of Dar es Salaam’s Department of Fisheries Science and Aquaculture, and Saleh A.S. Yahna of the University of Dar es Salaam’s Institute of Marine Sciences and Stockholm University’s Department of Zoology.

The study found that Tanzania’s corals recovered rapidly from the 1998 bleaching event that had wiped out up to 45 percent of the region’s corals. Along with monitoring Tanzania’s reefs, WCS helps coral conservation in this region through training of park staff in protected areas.

The authors attribute the recovery of Tanzania’s coral reefs due in part to direct management measures, including closures to commercial fishing. Areas with fishery closures contained an abundance of fish that feed on algae that can otherwise smother corals, while the few sites without any specific management measures remain degraded; one site had experienced a population explosion of sea urchins—pests that feeds on corals.

Continue reading →

Doom and Boom on a Resilient Reef: Climate Change, Algal Overgrowth and Coral Recovery

Posted on April 22, 2009 by ovehblog

Our lab has just published a new paper in PLoS ONE, detailing the interactions of coral and algae on the Great Barrier Reef, and uncovered just how resilient some reefs can be following coral bleaching events. The southern end of the Great Barrier Reef was exposed to extended periods of high sea surface temperatures in the end of 2006, resulting in extensive coral bleaching across the Keppel Islands throughout January 2006. Following the bleaching event, a single species of fleshy macro-algae (Lobophora) overgrew the coral skeletons, causing high rates of mortality throughout the second half of 2006. But, by February 2007, corals were rapidly recovering due to an unusual seasonal dieback of the macro-algae, and astonishing regenerative capabilities of the dominant branching Acroporid corals – almost twice the rate of offshore corals on the northern Great Barrier Reef.

What is unusual about the Keppel Islands story is threefold: first, that corals recovered within months to years (reversal of macro-algae dominated reefs often takes decades), second, recovery of the corals occurred in the absence of herbivory (traditionally assumed to be the ‘driving factor’ in macro-algal phase shifts), and third, that corals recovered through asexual (regenerative) capacities rather than reseeding of reefs by larval recruitment. Understanding the processes that drive recovery following disturbances is critical for management of coral reefs, and the Keppel Islands example shows that managing local stressors (overfishing and water quality) helps reefs bounce back from global stressors such as coral bleaching events. PLoS One is an open-access journal, so the article is free to read – click on the link below, and feel free to rate and comments on the paper. Congratulations Guillermo et al!

Guillermo Diaz-Pulido, Laurence J. McCook, Sophie Dove, Ray Berkelmans, George Roff, David I. Kline, Scarla Weeks, Richard D. Evans, David H. Williamson, Ove Hoegh-Guldberg (2009 Doom and Boom on a Resilient Reef: Climate Change, Algal Overgrowth and Coral Recovery. PLoS ONE 4(4): e5239. doi:10.1371/journal.pone.0005239

The worlds most overpopulated coral reef?

Posted on April 21, 2009 by ovehblog

I remember seeing a fascinating presentation by Mahmood Riyaz on the reef slope failure of this coral reef at the ICRS conference in Florida last year – how the atoll rim was cracking due to the sheer amount of construction and concrete. Welcome to Male, the capital of the Maldives, where >100,000 people are crammed ontop of a coral reef atoll only 1.7km in length. The Maldives have been hit hard in recent years, collectively lost over 2/3 of it’s coral following the 1998 bleaching event. In addition, being such a low lying country is likely to be problematic given the projected sea level rises, so the Maldivian government is proposes a carbon neutral approach by 2020, and is even considering diverting some of the billion dollar tourism profits to purchase a new homeland. The photo above doesn’t do justice to the population density on such a tiny atoll – check the satellite images on google earth.

Parrotfish in Swedish fishmarkets

Posted on April 8, 2009 by ovehblog

Svenska Dagbladet, Swedens second largest daily newspaper, recently ran a story on the appearance of parrotfish in Swedish fishmarkets. Parrotfish can be likened to lawnmowers of the reef, and keep algae from smothering coral reefs.

Parrotfish sold for 269 SEK/kg at a Swedish fishmarket. Photo courtesy of Jerker Lokrantz/Azote

Parrotfish are not known to be an essential part of the Scandinavian kitchen, so one wonders what they are doing being flown halfway across the world to a country that has enough tasty seafood to satisfy its needs? When contacted by reporters store managers claimed that distributors would recomend parrotfish as a colourful species that would certainly attract buyers. They also explained that they did have policies regarding the sale of red-listed species, but that parrotfish do not appear on any such lists (WWF and IUCN). This is problematic, as models and observation suggest that the levels of parrotfish biomass required to safeguard reefs against algal domination, are probably much higher than those that would classify them as being red-listed.

And this doesn’t seem to be a one-off incident. Two PhD-students from Stockholm University, Jerker Lokrantz and Matilda Thyresson, are currently following up reports of large (several tons) shipments of parrotfish from Vietnam arriving to Sweden via the Netherlands. This whole story really illustrates the challenges facing marine resource management in the face of rapid exploitation driven by a globalized market, as highlighted by Berkes et al in the 2006 Science article “Globalization, Roving Bandits, and Marine Resources“.

“Macro-algal dominated coral reefs: shake that ASS”

Posted on March 26, 2009 by ovehblog

In recent years, coral reefs have been hit hard by an array of anthropogenic impacts – coral bleaching, coral disease, overfishing and eutrophication to mention but a few – resulting in significant declines in coral cover and species diversity. One of the classic examples of coral reef decline was discussed by Terry Hughes in a 1994 article in the journal Nature, entitled “Catastrophes, Phase Shifts and Large-Scale Degradation of a Caribbean Coral Reef”. Hughes concluded that the synergistic impacts of overfishing, hurricane damage and disease resulted in a ‘phase shift’ from a coral dominated ecosystem (52% coral cover, 4% algal cover) to a macro-algal dominated ecosystem (2% coral cover, 92% algal cover). Similar examples of phase-shifts from coral to macroalgal dominated ecosystems have been observed across the Caribbean region, throughout the Eastern-Pacific, Indian Ocean and on the Great Barrier Reef.

Whilst macro-algal dominated reefs and phase shifts have recieved considerable attention in the scientific literature, a recent paper questions the role and driving factors of such ‘alternative stable states’ (ASS), and implicates the dominance of several other organisms that take rise following the loss of coral cover.

First establishing that a ‘phase shift’ must result from a decline of coral and subsequent increases in an other ‘alternative’ organism that must last for a significant period of time (in this case >5yrs), Norström et al conducted a survey of the literature to determine exactly what alternative organisms were dominant on reefs following a phase shift.

The authors argue a timely point that phase shifts associated with coral reefs are not exclusively coral – macroalgal shifts, and often result in shifts to ‘other’ states, including ‘soft coral’ dominance (corallimorphs and octocorals), sponges and urchin dominated states.

One of the key findings of the research suggests that whilst these different alternative states are common, the factors driving the shift may be considerably different. Whilst macro-algal states are driven by ‘top down’ factors (a loss of herbivorous fish or urchins through overfishing or disease), soft coral and sponge states are more closely associated with ‘bottom up’ factors (declining water quality).

Site specific examples of phase shifts in coral reefs: a) Israel, b) Seychelles, c) Belize

Site specific examples of phase shifts and the persistence of alternative stable states in coral reefs: a) Israel, b) Seychelles, c) Belize

So what does it take to ‘shake that ASS’? (Alternative Stable State, of course). Once a coral reef has shifted to an alternative stable state, simply removing the stressor that triggered the shift might not be sufficient to produce recovery back to a coral dominated state – partly due to feedback mechanisms, or a longer-term decline in environmental conditions.