Caribbean fish decline in the wake of coral collapse?

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 … Continue reading Caribbean fish decline in the wake of coral collapse?

Resilient ‘super reefs’ a priority for conservation efforts

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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.

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Using the internet as an early warning of ecological change

A recent paper out in Frontiers in Ecology and the Environment  (Galaz et al 2009) identifies novel and fascinating ways on how to capture looming ecological crises. The basic problem addressed by the authors is this: The six billion people on Earth are changing the biosphere at unprecedented rates. Ecosystems tend to respond to such … Continue reading Using the internet as an early warning of ecological change

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

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.

asdasdWhilst 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.

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