Coral Reef Ecology - Lecture 12: Consequences of Coral Loss

Coral Reef Ecology - Lecture 12: Consequences of Coral Loss

Lecture Outline

  • Reliance on corals by fishes and vice versa

  • Responses of fishes to coral loss

  • Effects of coral loss versus structural collapse

  • Links to fisheries productivity

Further Reading

  • Pratchett, M.S. et al. (2008). Effects of climate-induced coral bleaching on coral-reef fishes: Ecological and economic consequences. Oceanography and Marine Biology: Annual Review, 46: 251-96.

  • Rogers, A., Blanchard, J.L., Mumby, P.J. (2018). Fisheries productivity under progressive coral reef degradation. Journal of Applied Ecology, 55(3): 1041-9.

Importance of Coral Families for Fish

  • Coral Families: Fish are categorized into various families that rely on corals:

    • Chaetodontidae (Butterflyfishes)

    • Pomacentridae (Damselfishes)

    • Gobiidae (Gobies)

    • Apogonidae (Cardinalfishes)

    • Labridae (Wrasses)

    • Acanthuridae (Surgeonfishes)

    • Blenniidae (Blennies)

    • Cirrhitidae (Hawkfishes)

    • Siganidae (Rabbitfishes)

    • Caracanthidae

    • Monacanthidae (Filefishes)

    • Scaridae (Parrotfishes)

    • Serranidae (Groupers)

    • Pomacanthidae (Angelfishes)

    • Pseudochromidae

    • Scorpaenidae (Scorpaenids)

  • Usage of Coral by Fishes:

    • Settlement: Coral serves as a crucial site for fish post-larval settlement.

    • Habitat: Coral provides shelter and breeding grounds.

    • Food Source: Many fishes rely on corals directly for sustenance.

Branching Corals

  • Key Coral Species: Importance of branching corals for fish feeding includes:

    • Acropora hyacinthus

    • Pocillopora damicornis

    • Montipora spp., among others.

  • Proportion of Bites: Data reveals that fish, particularly butterfly fishes, disproportionately rely on branching corals like Acropora and Pocillopora for feeding.

Fish Associations with Coral Colonies

  • Fish Species Diversity: Up to 12 species may be associated with a single coral colony, including numerous cryptic species, indicating complex interspecific relationships.

Feedback Mechanisms Between Fishes and Corals

  • Aeration: Fishes influence the environment around corals by enhancing water circulation.

  • Excretion of Nutrients: Fishes contribute to nutrient cycling through waste, ultimately benefiting coral health.

  • Regulation of Water Flow: Fish activities help modulate the flow of water, which can be beneficial for coral activities.

  • Defense Against Predators: Some fish provide protective benefits to corals.

  • Disease Resistance: Specific fish species can slow coral disease progression by altering the microbial communities around corals.

  • Reduction of Macroalgae: Certain fish contribute to lowering macroalgae levels, helping maintain coral dominance in reef ecosystems.

  • Increased Resilience of Bleached Corals: Some fish species play a role in boosting the resilience of corals subjected to bleaching.

Responses of Fishes to Coral Loss

  • Recent studies indicate significant shifts in fish communities following coral loss:

    • Coral-dwelling fishes: Exhibit declines in abundance, particularly obligate corallivores like many butterflyfish species.

    • Generalist vs. Specialist: Specialists that rely heavily on specific coral types face higher risks during coral loss episodes.

    • Specialist Fishes: Obligately dependent, only utilizing a limited number of coral species.

    • Generalist Fishes: More adaptable but still face challenges during coral loss episodes.

Susceptibility to Coral Loss

  • Variation in Responses:

  • Obligate corallivores show more pronounced declines compared to non-corallivores with increasing coral loss.

  • Data indicates that when coral cover decreases significantly (>90%), species richness and fish assemblages also decline due to loss of structural complexity.

Coral Loss versus Topographic Collapse

  • Structural Complexity: Loss of coral structures leads to compounded effects on fish species richness and abundance.

  • Critical Thresholds: The greatest effects on fish abundances tend to occur when coral cover drops below 10%, complicating the differentiation between coral loss and structural complexity loss.

Short versus Longer-term Responses to Coral Mass Bleaching

  • Most fish species decline in abundance following acute disturbances like mass-bleaching due to reductions in coral cover and habitat complexity.

  • Prolonged lower coral cover leads to ongoing adverse effects, with no significant compensatory increases in fish that might otherwise benefit from coral loss.

Economic Importance of Reef Fishes

  • Fishes are vital to coral reef ecosystems and the economies they support:

    • Economic significance roughly estimated at:

    • $5 million for the Great Barrier Reef (GBR)

    • $15 million in Indonesia

    • Higher estimates at $139 million (commercial) and $284 million (recreational).

Coral Trout and Fisheries

  • Coral Trout (Plectropomus spp.): Represents a key fisheries species in GBR:

    • Coral cover oscillations impact abundance, but mass bleaching shows mixed effects on specific species like P. leopardus.

    • While P. leopardus demonstrates some resilience, they can be affected by ocean warming.

Fisheries Productivity and Habitat Degradation

  • Degradation of reef habitats primarily results in declines in fisheries productivity. This decrease is attributed more to the loss of structural complexity than to coral loss alone.

  • Generally, larger species of carnivorous fishes may show increased mean body size with escalating habitat degradation, indicating some resilience to habitat losses.

Conclusions

  • Coral reliance among fish species reveals extensive dependencies, particularly with branching corals (e.g., Acropora, Pocillopora, and Stylophora).

  • Roughly 12% of coral reef fishes have obligate reliance on corals for their ecological needs.

  • Over 60% of reef fishes exhibit declines post-major disturbances that lower coral cover, illustrating the critical dependency on coral ecosystems for fish populations and broader ecological health.