Coral Reef Dynamics and Marine Reserves in the Great Barrier Reef

Introduction

  • Topic: Tracking coral reef community dynamics and the effects of no-take reserves on inshore reefs in the Great Barrier Reef Marine Park.

  • Presenter: Maya Srinivasan, James Cook University.

Lecture Outline

  • Background and Early Work

  • The Inshore Island Fringing Reef Monitoring Program

  • Latest Results (2022-2024)

    • Coral trout: long-term trends and marine reserve effects.

    • Coral cover: long-term trends and the effects of coral bleaching, flooding, and cyclones.

  • Population Connectivity of Coral Reef Fishes

Benefits of Marine Reserves

1. Protect Exploited Species

  • Increased Numbers and Sizes

    • Target fish species' numbers and sizes greater within reserves compared to outside.

  • Spill-Over Effect

    • Adults move from reserves to fished areas, enhancing local fisheries.

  • Juvenile Supply

    • Reserves provide juveniles to surrounding fished areas.

2. Biodiversity Conservation

  • Protected Species and Habitats

    • Focused protection of threatened species and their habitats is vital.

  • Enhanced Resilience

    • Resilience provides the ability of reefs to withstand stress or recover from disturbances.

Marine Reserve Effects

  • Increase in Large Herbivorous Fish

  • Decline in Algae

  • Increase in Coral Cover and Diversity

  • Increase in Large Carnivorous Fish

  • Decline in Invertebrates and Small Reef Fish

  • Decline in Algal-Associated Organisms

Limitations of Marine Reserves

  • Are Marine Reserves Enough?

    • Evidence suggests reserves may promote resilience to various threats like COTS outbreaks and coral bleaching.

Great Barrier Reef Marine Park Overview

  • Size and Scope

    • Covers $344,400 ext{ km}^2$.

    • Contains over $3,500$ reefs and $900$ islands & cays.

  • History

    • The Great Barrier Reef Marine Park Authority (GBRMPA) established in 1975 under the GBR Marine Park Act.

    • Received World Heritage status in 1981.

  • Management Zoning

    • Implemented in the 1980s, rezoned in 2004.

    • Approximately $33 ext{ ext{%}}$ of area protected within no-take marine reserves (Green Zones).

Marine Park Zoning Plans

  • Zoning before Implementation (2003)

    • Less than $5 ext{ ext{%}}$ of the area designated as no-take zones.

  • Post-Zoning (2004)

    • Approximately $33 ext{ ext{%}}$ of the area designated as no-take zones.

Effects of Line Fishing Experiment (1995-2000)

  • Conducted by Mapstone et al., 2004, to assess impact on reef health.

Inshore Island Fringing Reef Monitoring Program

  • Established in 1999 to:

    • Examine the effects of marine park zoning.

    • Track changes in reef fish and benthic communities over time.

  • Participants: David Williamson (GBRMPA), Garry Russ (James Cook University).

  • Long-Term Locations:

    • Whitsunday Islands (since 1999)

    • Palm Islands (since 2000)

    • Keppel Islands (since 2002)

    • Magnetic Island (since 2004)

  • New Locations since 2022:

    • Turtle Group

    • Frankland Islands

    • Family Islands

    • Cumberland Islands.

Monitoring Process

  • Total Monitoring Sites: $145$ sites across $38$ islands.

  • Includes fished areas and no-take marine reserves (green zones).

  • Methodology:

    • Underwater Visual Census (UVC) assessing fish and benthic communities.

    • Conducting five $50 ext{ m}$ transects per site.

Surveys and Metrics Captured

  • Most comprehensive in-situ survey methodology detailing:

    • Fish species richness

    • Fish density and biomass

    • Coral cover and benthic complexity.

Coral Cover and Fish Richness Results (2022 - 2024)

Coral Cover(%):

  • Coverage varied across sites with distinct metrics for each year.

Fish Richness:

  • Variations noted between green zones and fished zones.

Long-Term Trends - Coral Trout Biomass

  • Consistency of biomass higher in green zones than in fished areas.

  • Effects_Size Range: from $1.5$ to $3$ in various reserves post-rezoning.

Trends in Size Structure

  • Discrepancies in size structure noted between green zones and fished reefs.

  • Lower proportions of fish under Minimum Legal Size (MLS) in green zones.

  • Shift towards larger individuals noted over the two decades post-rezoning.

Fishing in Green Zones

  • Surveyed $30$ sites regarding fishing line presence; results analyzed for impact between 2012 and 2014.

Coral Cover Long-Term Trends

  • Impacts documented from coral bleaching, cyclones, and floods.

Cyclone Debbie (2017)

  • Significant damage recorded in both coral and fish populations post Cyclone Debbie.

Population Connectivity

  • Tracking Larval Dispersal:

    • Essential for understanding connectivity between habitats.

    • Utilized juvenile DNA microsatellite profiles for tracking dispersal vectors.

  • Findings:

    • Connectivity noted from green zones to fished areas, ensuring replenishment of fish stocks.

Implications and Conclusions

  • Key takeaways include:

    • Consistent higher biomass in no-take zones compared to fished reefs.

    • No discernible effect of no-take marine reserves on coral cover.

    • Green zones act as self-replenishing units that are interconnected, providing ecological benefits to adjacent fished reefs.

Summary Statistics on Fish and Larval Supply

  • Data summarizing juvenile contributions to reefs and fisheries from green zones, emphasizing the ecological importance of well-managed no-take areas.

Statistical Data:

  • Significant increases in fish populations in green zones (e.g., larger fish producing significantly more offspring).

  • Metrics on larval dispersal capabilities of fish adults and implications for reef connectivity.