ENVR101 Marine Ecosystems of Aotearoa

Marine Ecosystems in Aotearoa

Recap of Terrestrial Biodiversity

  • New Zealand has high endemism due to its biogeographical history and isolation from Gondwana.
  • Tectonic and volcanic activity created diverse climates, promoting speciation.
  • Human settlement impacted biodiversity through invasive species. There is an ongoing debate on whether vicariance or dispersal is more responsible for endemism levels.
  • Only 25% of native vegetation remains, making it a biodiversity hotspot.
  • Reptiles are the most threatened group, facing extinction due to predation and habitat destruction.

Marine Ecology and Conservation

  • Robert Payne's experiments showed the impact of removing top predators (starfish) on ecosystems, leading to the concept of keystone species.
  • Overfishing of crayfish and snapper led to kina barren ecosystems. The Hauraki Gulf Marine Park has struggled with conservation due to continued commercial fishing.
  • Crayfish are functionally extinct in much of the Gulf; snapper populations have significantly declined.
  • Recommendations include establishing marine reserves, halting trawling and dredging, and controlling sedimentation.

Marine Reserves

  • New Zealand has 44 marine reserves, covering less than 10% of its coastline.
  • Types of marine reserves vary in their restrictions on fishing activities.
  • The exclusive economic zone (EEZ) is 15 times the land size and has high species diversity.

Marine Biodiversity

  • High marine endemism is due to biogeographical history, ocean currents, and underwater features.
  • Warm currents from Australia mix with cold Subantarctic waters, creating rich microbe environments.
  • Seamounts, methane seeps, hydrothermal vents, and canyons (like the Kaikoura Canyon) support high biodiversity.

Marine Zones

  • Intertidal zone: exposed at low tide, submerged at high tide.
  • Continental shelf: shallower waters with kelp forests and coral reefs.
  • Pelagic realm: open water column inhabited by fish, whales, and dolphins.
  • Photic zone: where sunlight penetrates.
  • Aphotic zone: deep, dark water where light does not penetrate.
  • Mesophotic zone: twilight zone between 30-150 meters.

Species Diversity

  • Significant regional variation due to temperature differences (6°C from north to south).
  • High diversity of sea stars, mollusks, and crustaceans.
  • Black corals occur in shallow waters in fjordland, unlike elsewhere in the world.
  • 14001400 species of fish with nearly 300300 endemic. Over 11001100 jellyfish species.
  • Nearly half the world's cetaceans are found in New Zealand waters.
  • Whale populations declined sharply with commercial whaling in the 1700s.

Deep Sea and Threats

  • New Zealand has a remarkable number of sponge. A mass sponge bleaching event in fjordland (2022) decimated sponge populations due to a marine heat wave.
  • Sedimentation, fecal bacteria, and microplastics threaten marine ecosystems. 67% of beach trash is plastic.
  • Bycatch and overexploitation contribute to population declines. 12%12\% of stocks were overfished or depleted in 2023 and 5 fish stocks actually collapsed in the period. Recreational fishing amounts to millions in catch.
  • Size limits for fishing are a strategy to combat overfishing.

Conservation Status and Climate Change

  • The latest environment report indicates many indigenous marine mammals and invertebrates are threatened.
  • Oceans are capturing carbon emissions and excess heat, leading to ocean acidification and warmer waters.
  • Increasing acidity threatens coral reefs. Marine heat waves are becoming more frequent and intense.

Summary

  • Overharvesting of keystone predators has devastating effects.
  • Marine reserves work with proper implementation and local input.
  • New Zealand has high marine endemism due to isolation and diverse underwater topography.
  • Climate change, land use, overfishing, bycatch, and pollution threaten marine biodiversity.