Mangroves reduce the vulnerability of coral reef fisheries to habitat degradation
Year Published:
2019
Study Number:

117

Country:
Australia
Author:

Alice Rogers, Peter J. Mumby

Abstract:

Despite general and wide-ranging negative effects of coral reef degradation on reef communities, hope might exist for reef associated predators that use nursery habitats. When reef structural complexity is lost, refuge density declines and prey vulnerability increases. Here, we explore whether the presence of nursery habitats can promote high predator productivity on degraded reefs by mitigating the costs of increased vulnerability in early life, whilst allowing for the benefits of increased food availability in adulthood. We apply size-based ecosystem models of coral reefs with high and low structural complexity to predict fish biomass and productivity in the presence and absence of mangrove nurseries. Our scenarios allow us to elucidate the interacting effects of refuge availability and ontogenetic habitat shifts for fisheries productivity. We find that low complexity, degraded reefs with nurseries can support fisheries productivity that is equal to or greater than that in complex reefs that lack nurseries. We compare and validate model predictions with field data from Belize. Our results should inform reef fisheries management strategies and protected areas now and into the future.

Main Results and Conclusions:
  • Mangrove nursery habitats are critically important for the health and survival of reef fish offspring.
    • “When reef structural complexity is lost, refuge density declines and prey vulnerability increases.”(1)
    • “As the human population continues to grow, the food security and livelihoods of millions of people in tropical coastal communities depends on the continued productivity of coastal fisheries. For many, coral reef fish provide a major source of dietary protein, as well as livelihoods, a way of life, and cultural identity [1,2]. Yet, climate change and local anthropogenic pressures are causing varying degrees of degradation to coral reefs [3–6].”(1)
    • “While loss of reef habitat quality is a significant concern, it is not the only driver of reef fish productivity. The presence of nursery habitats, such as mangroves and seagrass beds, can enhance the biomass of multiple fish species [12–15].”(1)
  • Mangroves add habitat complexity to the ecosystem, which benefits species trying to survive on degraded reefs. 
    • “Our models predict that the biomass of both predators and herbivores responds more strongly to habitat complexity than to nursery availability (Fig 1; 60%–65% increase in predators with high complexity, 61%–70% increase in herbivores).”(3)
    • “However, a striking result is that mangrove access more than offsets the deleterious impacts of habitat degradation on fisheries productivity for this guild. In other words, the increased productivity resulting from nursery availability is such that degraded reefs with mangroves have equal or greater productivity than healthy reefs without (Fig 3A).” (4)
    • “The predicted impact of nurseries on productivity is greater than their impact on biomass, for which patterns are mostly driven by habitat complexity. Not surprisingly, the apparent disparity occurs because of growth and turnover.”(4)
  • With the immense amount of coral reef loss right now because of climate change, using mangroves as nurseries is more important than ever in countering these losses. 
    • “Here, we present both theoretical and empirical support for the conclusion that mangrove nurseries have the capacity to reduce the vulnerability of coral reef fisheries to ongoing and future habitat degradation.”(8)
    • “Yet, the protection and restoration of mangrove habitats should remain a priority as part of the battle to mitigate climate change impacts on coral reefs and their functioning.”(8)
    • “We predict that biomass on degraded reefs will be lower than on healthy reefs, and this has significant implications for ecosystem functioning and the multitude of services aside from fisheries that coral reefs support [34,35].”(8)
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 ecosystem function are defined by management strategy. Front Ecol Environ. 12: 324-9.
 https://doi.org/10.1890/ 130296.

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(2)FAO. The state of world fisheries and aquaculture 2016. Contributing to food security and
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(12)Harborne, A.R., Nagelkerken, I., Wolff, N.H., Bozec, Y.M., Dorenbosch, M., Grol, M.G.G.
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(13)Nagelkerken, I., Roberts, C.M., van der Velde, G., Dorenbosh, M., van Riel, M.C., Cocheret
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(5)Ortiz, J.C., Wolff, N.H., Anthony, K.R.N., Devlin, M., Lewis, S., Mumby, P.J. 2018. Imparied
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(6)Perry, C.T., Alvarez-Filip, L., Graham, N.A.J., Mumby, P.J., Wilson, S.K., Kench, P.S., et al.
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(35)Rogers, A., Harborne, A.R., Brown, C.J., Bozec, Y.M., Castro, C., Chollett, I. etl al. 2015.
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