WK12: Ecology in Action: Managing threats in marine systems

Ecology in Action: Marine Systems and Island Interactions

Learning Objectives Review

  • Describing the modern scope of scientific inquiry in ecology.
  • Understanding differences in structure and function of different ecosystem types, especially Australian-centric examples and global examples.
  • Identifying drivers of diversity patterns.
  • Explaining limitations on energy flow in food webs and ecosystems.
  • Quantitatively describing patterns in populations and communities, including using data management programs like Excel.
  • Applying ecological sampling techniques and reporting on data.

The Science of Ecology

  • Natural history observations and real-world structure.
  • Postulating model hypotheses.
  • Predictions, experimental design, and data collection.
  • Testing hypotheses and predictions.
  • Confirmation leads to theory development for better explanation.
  • Failure provides feedback to refine understanding.
  • Focus on the application of ecological knowledge to solve problems, like conservation management and restoration.

Islands vs. Marine Systems

  • Islands:
    • Model systems: small, bounded, isolated, simplified
  • Marine Systems:
    • Vast, complex, continuous, interconnected
    • Difficult and expensive to study, often poorly understood.

Ashmore Reef: A Case Study

  • Location: Situated in Australian waters, south of Roti Island (Indonesia), about 35 km across.
  • Features: Four small islands totaling 54 hectares.
  • Vegetation: Low vegetation in the wet season, bare sand in the dry season.
  • History of Visitation and Exploitation:
    • Discovered by Rotonese in the 1700s.
    • Phosphate reserves (guano) harvested until the 1890s.
    • Seabird take documented from 1949-1980s.
    • Declared a marine reserve in 1983, with increasing enforcement in the 1990s.
    • Early 2000s: Primary location for asylum seeker arrivals, leading to a continuous presence of Australian Border Force vessels.
  • Threats to biodiversity: poaching, oil spills, and invasive species.

Citizen Science Contributions

  • Commercial bird watching tours since February 2000 provided island-wide and at-sea seabird surveys.
  • Experienced bird watchers collect and archive valuable data.
  • Data reveals 15 breeding species of seabirds with diverse families (frigatebirds, terns, tropic birds, shearwaters).
  • Diverse breeding strategies (surface, shrubs, burrows) and times of year (wet vs. dry season).
  • Diverse foraging strategies (close to shore, great distances, diving, surface feeding, kleptoparasitism).
  • Over 100,000 individual seabirds of these 15 species breed on these islands.

Seabird Numbers Example

  • Brown Boobies --> 8000 - 15000 pairs
  • Sooty Terns and Common Noddies --> 10000 - 60000 individuals.

Seabird Distribution and Population Trends

  • Shipboard sightings data informs at-sea distribution and foraging areas.
  • Data captures GPS location, species, count, date, and time.
  • Recent population trends show step changes in abundance in the late 1990s/early 2000s for species like brown boobies, masked boobies, and lesser frigatebirds.

Species Distribution Modelling

  • Understanding species-environment relationships.
  • Predicting distributions in unsurveyed areas.
  • Environmental layers used: bathymetric depth, chlorophyll A concentration (proxy for marine productivity), distance to coast, seabird slope angle (proxy for upwelling), and sea surface temperature.

Species distribution modelling example

  • Example: Common noddies are abundant within 30-50 km of island land masses.
  • Hutton's Shearwater: Mostly in inshore waters just inside the continental shelf.
  • Tahiti Petrel: Occupies deep pelagic waters (>200-300 meters).
  • Common Terns: Mostly coastal.
  • Red-footed Boobies: Constrained by breeding opportunities on islands and foraging distances.

Multi-Species Overlays and Seabird Species Richness

  • Identifying hotspots for particular species.
  • Example: Tahiti petrel, Bulwer's petrel, and Yuanan's petrel occur over deep pelagic waters, especially around the shelf slope area.
  • Terns and noddies occur near land.
  • Used for marine and conservation planning.
  • High species richness around Cartier, Ashmore Reef, Adele Island, and the Lassipede Islands due to productive marine waters and island breeding sites.

Trends in At-Sea Seabird Populations and Climate Variability

  • Analyzing changes in abundance of species over time (1999-2014/15).
  • Linking trends to climate variability using the Southern Oscillation Index (SOI) and Indian Ocean Dipole (IOD).
  • SOI and IOD are large-scale climatic indicators measured by sea surface temperature differences.

Montara Oil Spill (2009) and Subsequent Research

  • Largest oil spill in Australian history by surface area.
  • Millions of liters of oil released over three months.
  • Research questions: What were the impacts? Can we understand population trajectories? What are the at-sea needs of seabirds? What are the impacts of invasive species?
  • Seabird numbers continued to increase post-spill, potentially linked to environmental variation.

Seabird Species Responses to Montara Oil Spill

  • Common Noddies --> Increase after, eventual decline related to the environmental variation.
  • Sooty Turn --> Increase
  • Brown Booby --> Increase
  • Less Frigate Bird --> Increase

Red-Tailed Tropic Bird Tracking

  • Using GPS tracking and kernel density analyses to understand foraging areas.
  • Foraging trips average 2.8 days and 405 km.
  • Birds forage mostly to the North, Northwest, West, and Southwest, up to 150 km from the island.
  • Habitat suitability models used to identify optimal foraging areas based on surface temperature, chlorophyll a concentration, and bathymetry.
  • Montara oil spill was mostly to the East, potentially sparing tropic bird foraging areas.

PhD Programs on Frigatebirds, Boobies, and Terns

  • GPS tracking, diet samples, and blood samples used to understand ecology.
  • Great frigatebird tagged with a GPS logger and solar panel for long-term tracking, data downloaded automatically at base stations.

Frigatebird Sympatry

  • Jarod Diamond's hypothesis: High overlap in feeding habits between frigatebird species.
  • Rowan study compared lesser and great frigatebirds to understand niche partitioning.
  • Hypotheses tested:
    • Spatial separation in inshore vs. offshore waters.
    • Competition for prey in overlapping areas.

Frigatebird Tracking Results

  • Significant overlap in core foraging areas (72%) and home ranges (86%) between great and lesser frigatebirds.
  • Great frigatebirds occupied areas with slightly higher productivity and shallower depths.
  • Stable isotope analysis showed great frigatebirds forage at a higher trophic level closer to the coast, while lesser frigatebirds forage over deeper, pelagic waters.
  • Diet analysis revealed both species eat flying fish, but great frigatebirds also eat scad and trevally, while lesser frigatebirds eat big eyes.
  • Conclusion: Great frigatebirds exploit shallower, higher productivity waters and consume higher trophic order prey.

Flying Fish Abundance and Nesting Success

  • Flying fish abundance monitored via encounter rates from vessels.
  • Inshore waters had about a third as many flying fish as offshore waters.
  • Nesting success of lesser frigatebirds at inshore Adele Island was low (3% in 2013), linked to prey abundance fluctuations driven by sea surface temperature.

Frigatebird Migration Patterns

  • During the breeding season, frigatebirds are central place foragers.
  • In the non-breeding season, they undertake long journeys, including circumnavigating Borneo.

Seabird Census Techniques Via Drones vs Ground

  • Compared ground counts with drone counts for seabird populations.
  • Drone counts were consistently higher and more precise than ground counts.
  • High precision means more confidence in monitoring programs and better detection of real changes.
  • Recommendation to transition to drone counts for monitoring.

Tropical Fire Ants

  • Tropical fire ants (Solenopsis species) impact seabird chicks and turtle hatchlings.
  • They attack hatching chicks, kill ground chicks, and damage feet.
  • They also prey on turtle nests, impacting reproductive success of sea turtles.

Ant control methods:

  • Toxins: quick and effective but kill other invertebrates.
  • Insect growth regulator: fire ant-specific but slower and less effective.

Baiting experiments on islands.

  • Grey dotted line. --> Insect growth regulator.
  • Blue hatch line --> Toxins.

Ant Abundance and Management Strategies

  • Gridded islands with tuna lures to measure ant abundance (trace, small, intermediate, large, swarm).
  • West Island baited with insect growth regulator and toxins while East Island served as a control.
  • Baiting significantly reduced ant numbers after the first treatment.
  • Models developed to determine the amount of toxin needed for eradication.
  • Model results: Insect growth regulators alone didn't eradicate the ants. Combining one toxic baiting event gave probability of eradication of 41%.
    • To achieve a high probability of success, 8-9 toxic baiting events is required, paired with insect growth regulator events.

Other Threats at Ashmore Reef

  • Ongoing oil and gas exploration presents a future threat of oil spills.
  • New program with CSIRO to focus on ecosystem recovery, addressing weeds, tropical fire ants, and house mice.

Applied Ecology Takeaways

  • Ecology involves basic inquiry through application.
  • Experiments are not always possible, often relying on comparisons.
  • Ecology is complex, with steps implemented in variable orders.

Reminder

  • SETU assessments are open.
  • No exam practice question for this lecture, but review the Christmas Island lecture for ecology in action examples.