Regenerating a coral reef

In my last post I mentioned some of the challenges facing reefs and reef fish, particularly overexploitation and habitat degradation. Although these issues affect reef fish in different ways, they can work in tandem to intensify conservation problems. The good news is that we have better insight into how to lessen or even remove some of these challenges. The bad news is that, in some cases, the odds are stacked against the fish.

Some species of fish will only settle on reefs with adequate habitat quality. Photo by J Maragos and courtesy of USFWS.

Some species of fish will only settle on reefs with adequate habitat quality. Photo by J Maragos and courtesy of USFWS.

As I said before, fisheries don’t exploit all species equally– some fish species are more prized than others. When fishing selectively removes fish that fill certain roles, we can see a cascading effect throughout the ecosystem. Raymundo et al. (2009) found that coral within protected areas showed less evidence of disease, perhaps because fishing in other areas preferentially removed the predators which controlled smaller coral-eating fish. Another study recommended switching from spear gun- and trap-based fishing to line fishing because lines catch a smaller proportion of the fish that help with coral recovery rather than slowing it (Cinner et al. 2009). Why is it important to limit coral disease and damage? Based on research by Feary et al. (2007), degraded coral habitats can create a self-reinforcing trend in which fish larvae are less likely to settle on degraded coral, so there are fewer fish to maintain ecosystem function, so the reef degrades more, so fewer fish larvae settle…and so on.

Are there things we can do, aside from altering fishery practices to improve reef habitats? Yes, although we are still figuring out our best strategies. According to research in Indonesia, creating stable rock platforms for larval coral to colonize led to greater coral recruitment in areas which had been damaged by blast fishing (Fox et al. 2005). However, it was important to maintain rock stability over the long term, since strong currents could move things around, so working over large areas at a time might be the best course of action. Graham et al. (2013) recommended using extreme weather events, such as massive rain inputs or cyclical cold spells, as catalysts for action so that we take advantage of natural events to start removing invasive fish species or algae that smothers coral. It is important, however, to recognize that the reefs we end up with may not be exact replicas of what they once were. Research on the Great Barrier Reef found that, 13 years after a bleaching event, while the roles that fish species filled were the same as before the bleaching, some of the species themselves had been replaced- rather than being restored, the reef had regenerated in a slightly different form (Bellwood et al. 2012).

And the reality is that climate change will continue to push fish outside of their comfort zone. I mentioned the problem of ocean acidification in my last post- it turns out that there’s a lot more going on there than you might expect. Research on clownfish has found that fish exposed to the acidity levels expected by 2100 had trouble distinguishing good habitat from bad because they couldn’t read the olfactory cues (Munday et al. 2009) and engaged in riskier behavior which led to higher mortality rates (Munday et al. 2010).

So, while we can make some adjustments to support reef fish populations, other factors may be moving beyond our control. What can we, as individuals, do to help these organisms and the ecosystems they inhabit? That’s what I’ll look into for my final post of the month.

Works cited:

Bellwood, D.R., A.H. Baird, M. Depczynski, A. González-Cabello, A.S. Hoey, C.D. Lefèvre, and J.K. Tanner. 2012. Coral recovery may not herald the return of fishes on damaged coral reefs. Oecologia 170:567–573.

Cinner, J.E., T.R. McClanahan, N.A.J. Graham, M.S. Pratchett, S.K. Wilson, and J.-B. Raina. 2009. Gear-Based Fisheries Management as a Potential Adaptive Response to Climate Change and Coral Mortality. Journal of Applied Ecology 46:724–732.

Feary, D.A., G.R. Almany, M.I. McCormick, and G.P. Jones. 2007. Habitat Choice, Recruitment and the Response of Coral Reef Fishes to Coral Degradation. Oecologia 153:727–737.

Fox, H.E., P.J. Mous, J.S. Pet, A.H. Muljadi, and R.L. Caldwell. 2005. Experimental Assessment of Coral Reef Rehabilitation Following Blast Fishing. Conservation Biology 19:98–107.

Graham, N.A., D.R. Bellwood, J.E. Cinner, T.P. Hughes, A.V. Norström, and M. Nyström. 2013. Managing resilience to reverse phase shifts in coral reefs. Frontiers in Ecology and the Environment 11:541–548.

Munday, P.L., D.L. Dixson, J.M. Donelson, G.P. Jones, M.S. Pratchett, G.V. Devitsina, K.B. Døving, and D.M. Karl. 2009. Ocean Acidification Impairs Olfactory Discrimination and Homing Ability of a Marine Fish. Proceedings of the National Academy of Sciences of the United States of America 106:1848–1852.

Munday, P.L., D.L. Dixson, M.I. McCormick, M. Meekan, M.C.O. Ferrari, D.P. Chivers, and D. Karl. 2010. Replenishment of fish populations is threatened by ocean acidification. Proceedings of the National Academy of Sciences of the United States of America 107:12930–12934.

Raymundo, L.J., A.R. Halford, A.P. Maypa, A.M. Kerr, and D.M. Karl. 2009. Functionally Diverse Reef-Fish Communities Ameliorate Coral Disease. Proceedings of the National Academy of Sciences of the United States of America 106:17067–17070.