Ecosystem resilience in the Caribbean


Image: One of the threats to a healthy Caribbean ecosystem - a lionfish photographed by Alex Zeni

 

 

During our time in Guadeloupe the team noticed a considerable number of fish traps along reefs adjacent to coastal towns and developments. These traps are designed to lure the fish into a 0.5m x 2m metal frame where they become caught and can be retrieved at a later time. The traps can be a navigation hazard for boats, they can also have a detrimental effect on the balance of coral reef ecosystems. Unfortunately, these balance shifts have been evident on the majority of the reefs where traps have been present. The team has also observed many reefs dominated by macro algal species (such as Dictyota sp) instead of reef building corals, such as the Elkhorn coral (Acorpora palmata).

 

A balanced ecosystem

If we think of a coral reef as a fully functioning metropolitan city, we know the city requires certain services in order to maintain and sustain the well-being of its citizens. For instance, a city needs (amongst many more) the range of services provided by gardeners, garbage collectors and doctors to continue to function in a healthy and effective manner. Without these essential services the power lines and infrastructure would soon become overgrown, the streets rancid and citizens plagued by disease and illness. 

One of the most important services for a coral reef is that of the gardener; on a coral reef this service is called herbivory. In a well-balanced coral reef ecosystem, macro algae is often controlled by herbivorous animals, which include the parrot and surgeon fishes, as well as various sea urchins grazing on the reef’s algae which gives corals their competitive edge in occupying space and continuing to grow. Herbivory is an essential service required to maintain healthy ecosystem resilience and resistance to natural and human impacts.

A well-balanced ecosystem has high resilience to various impacts including, hurricanes, anchor damage, coral bleaching and disease. However, the slower growth rate of coral (in comparison to algae) means corals are unable to recover faster than macro-algal species, which can move into the vacant space caused by the impact. If an impact is too severe or long in duration, macro algae will not only take over empty space, but also start to smother live corals. This process is commonly referred to as a phase-shift, which occurs when a coral-dominated reef shifts to become an algal-dominated reef, and essentially signifies the death of a coral reef. The reef is unable to recover without mitigation or assistance to enable the coral to re-establish over areas dominated by macro-algae.

 

No more hiding places

Apart from being an extremely valuable tourism asset, coral reefs offer high complexity and diversity, which in turn provides refuge for high-value economic species that algal dominated reefs cannot support. This lack of protection can often lead to excessive predation, which leads to an ecosystem that is unable to sustain itself.

 

Hurricanes & Lionfish in the Caribbean

The Caribbean experiences an annual hurricane season, which can often result in damage to coral reefs, caused by powerful and regular storms. In a healthy ecosystem, reefs are resilient and have the capacity to recover relatively quickly, however there have been two major long-term impacts throughout the Caribbean over the last two decades, which have led to phase shifts of many coral reefs in the region. Firstly, an outbreak of a disease affecting a dominant herbivorous urchin known as Diadema antillarum killed off massive numbers of the species (Lessios et al, 1984). Secondly, the mortality of elk-horn and stack-horn corals, and the invasion of the Indo Pacific lion fish (Pterois volitans and Pterois miles) somewhere between the mid 80’s to mid 90’s, introduced a voracious predator that has had serious impacts on Caribbean reef fish. These impacts, alongside overfishing pressure, ocean acidification and coastal development, have led to a serious decline in ecosystem resilience in Caribbean reefs.  

A marine biologist by the name of Professor Bob Steneck has documented this decline in his blog (http://bobsteneck.blogspot.com/) showing Caribbean reefs of the Lesser Antilles being dominated by beautiful Acropora sp species such as Elkhorn and Staghorn's in the 1970’s, to now being dominated by algal species such as Dictyota sp. Professor Steneck and our lead scientist Dr Manuel Gonzalez Rivero are currently working on  a collaboration with their findings in the Caribbean.

The benefit of MPA's

Fortunately, during our surveys, we were able to visit Marine Protected Areas such as the Cousteau Marine Reserve in Guadeloupe. Areas like this show with out a doubt, the advantages of taking one or more of the above threats out of the ecosystem, such as fishing or habitat degradation through coastal hardening. They offer a glimpse of hope that if we can provide more protection, and change our habits to reduce to rate of climate change, our reefs may be able to recover.

 

References:
Lessios, H. A., Robertson, D. R., & Cubit, J. D. (1984). Spread of Diadema mass mortality through the Caribbean. Science, 226(4672), 335-337.
Peter J. Mumby, John D. Hedley, Kamila Zychaluk, Alastair R. Harborne, Paul G. Blackwell (2005). Revisiting the catastrophic die-off of the urchin Diadema antillarum on Caribbean coral reefs: Fresh insights on resilience from a simulation model.
Morris, Jr., James A. and Whitfield, Paula E. (2009) Biology, ecology, control and management of the invasive Indo-Pacific lionfish: An updated integrated assessment. Beaufort, NC, NOAA/National Ocean Service/Center for Coastal Fisheries and Habitat Research,(NOAA Technical Memorandum NOS-NCCOS, 99)

 

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