Download Sponge ecology and coral reef phase shifts in Indonesia Dr James

IH270: Sponge ecology and coral reef phase shifts in Indonesia
Dr James Bell, Victoria University of Wellington, New Zealand
Coral reefs are among the most biodiverse ecosystems in the world but it is estimated
globally that 60% of reefs are threatened by local-scale human activities, including coastal
development, overexploitation, invasive species, and pollution, in addition to global-scale
impacts of climate change and ocean acidification. The Indo-Pacific region is a global hotspot
of marine diversity for most major taxa and encompasses 75% of the world’s coral reefs;
however, despite the high overall marine diversity found in the Indo-Pacific, the majority of
past research on the overexploitation and degradation of coral reefs has focused on
scleractinian corals and fish. In contrast, the impacts of degradation on other important
groups of reef organisms, the subject of this project, have been relatively poorly studied.
While there are a large range of impacts that environmental degradation has on reefs, one
of the most controversial is the occurrence of ‘phase shifts’, which can be defined as a
change in the equilibrial community in response to a persistent change in environmental
conditions. Although phase shifts from coral to algal dominated systems have received the
most attention, they are not the only trajectory that coral reefs may follow after declines of
coral and herbivorous fish. This project is uniquely different to other current coral reef
research in that it focused in the potential for coral reefs to undergo changes from coraldominated systems to sponge-dominated systems. Understanding the causes and
consequences of such phase shifts is critically important for coral reef management, as these
changes can have profound effects on reef ecosystem function. For example, the diverse
functional roles of sponges on coral reefs mean changes in their distribution and abundance
patterns have the potential to affect overall reef ecosystem functioning, particularly through
their trophic relationships with other organisms.
There is some evidence that a phase shift to a sponge dominated reef community has
occurred at the most degraded sites in the Wakatobi. This project will specifically document
the spatial variation in the abundance and diversity (using a morphological surrogate) of
sponges across sites in the Wakatobi, and assess the variation in total sponge abundance,
and that of key sponge species across environmental gradients in the Wakatobi. If indeed a
change to a sponge dominated community has occurred there is likely to be significant
impacts on the way the reef system functions. This project will also examine if there is any
evidence for indirect effects of this shift to a sponge dominated community, such as changes
in the proportion of sponge feeding species and likely impacts on water column trophic
interactions, which could be assessed through a modeling approach.
Given the expected declines in coral abundance in response to climate change and ocean
acidification effects, there is every possibility that sponge-dominated reefs might become
more abundant in the future, and this project will begin to assess how such reefs might
function and if they can support similar levels of fish biomass and productivity as coraldominated systems.
Further Reading:
Bell, J. J., & Barnes, D. K. A. (2002). Modelling sponge species diversity using a morphological
predictor : a tropical test of a temperate model. Journal for Nature Conservation, 10(1), 4150.
Bell, J. J. & Smith, D. (2004) Ecology of sponge assemblages (Porifera) in the Wakatobi region,
south-east Sulawesi, Indonesia: Richness and abundance. Journal of the Marine Biological
Association of the United Kingdom, 84, 581-591.
Bell, J.J. (2008) Functional roles of marine sponges. Estuarine and Coastal Shelf Science 79:
341-353.
Bell, J.J. (2007). The use of volunteers for conducting sponge biodiversity assessments and
monitoring using a morphological approach on Indo-Pacific coral reefs. Aquatic
Conservation: Marine and Freshwater Ecosystems 17, 133-145.
Bell, J.J. (2007). Contrasting patterns of species and functional composition for coral reef
sponge assemblages. Marine Ecology Progress Series 339, 73-81
Dudgeon SR, Aronson RB, Bruno JF, Precht WF (2010) Phase shifts and stable states on coral
reefs. Mar Ecol Prog Ser 413:201-216
Hughes TP, Graham T, Jackson JBC, Mumby PJ, Steneck RS (2010) Rising to the challenge of
sustaining coral reef resilience. Trends in Ecology & Evolution 25, 633-642
Norström, A., Nyström, M., Lokrantz, J., & Folke, C. (2009) Alternative states on coral reefs:
beyond coral–macroalgal phase shifts. Marine Ecology Progress Series, 376, 295-306.
Perea-Blázquez, A., Davy S.K., Bell, J.J. (2012) Energy flow from the pelagic environment to
the benthos through sponge assemblages. PLoS ONE 7(1): e29569.