A Big Picture for the Big Island

by Megan Joyce and Amanda Dillon
red_pencil_urchin

Red slate pencil urchin (Heterocentrotus mamillatus)

The ocean off the west coast of Hawai‘i Island is home to an especially vibrant marine ecosystem. This coastal region is teeming with bright fish, sea urchins and shellfish, green sea turtles, spinner dolphins, whales, manta rays, and coral reefs. West Hawai‘i has the largest expanse of intact and actively growing coral reef in all of the main Hawaiian Islands[1]. This wide array of flora and fauna makes West Hawai‘i incredibly important for marine biodiversity but also particularly vulnerable to the pressures of an increasing human population, coastal development, fishing, pollution, and climate change.

It is a daunting task to balance the impacts of human activities on land and in the sea with the effects of a changing climate and ocean on the marine ecosystem. For resource managers to effectively regulate and protect these dynamic ecosystems, they need greater insight on the myriad pressures that impact ecosystem health. Ecosystem-based management links the pressures of society to the ecological system, focusing on the whole instead of the parts. While each piece is significant in its own right, putting them together provides a view of the broader and interwoven ecosystem—the big picture.

Kahalu‘u by Christine Shepard

The west coast of Hawai‘i Island, Kahalu‘u (Photo courtesy of Christine Shepard, Coral Cove Imagery LLC ©)

With this ambitious goal in mind, Dr. Jamison Gove and a team of collaborators set out to evaluate the status of the marine ecosystem off the west coast of Hawai‘i Island. Community members, scientists, and resource managers came together to determine the primary pressures on the ecosystem and the indicators of marine ecosystem health. Pieces of this integrated ecosystem puzzle range from social indicators (e.g., fishing, population growth, and wastewater input) to biological indicators (e.g., numbers of reef fish and coral disease) to climate and ocean indicators (e.g., sea level rise, ocean temperature, and coral bleaching). The research team used these indicators to portray a “big picture” of West Hawai‘i in the recently published West Hawai‘i Integrated Ecosystem Assessment: Ecosystem Trends and Status Report.

Key findings of the report:

  • The population of Hawai‘i Island has increased by 320% in the last 56 years, increasing pressures that threaten the region’s marine environment.
  • More than 85% of onsite wastewater disposal in West Hawai‘i occurs via cesspools, where waste receives no treatment prior to disposal, resulting in pollution of nearshore marine environments.
  • From 2003–2014, mean fish length, an indicator of adult reef fish size, showed a decreasing trend in West Hawai‘i.
  • Herbivorous (plant-eating) fishes, which are important for coral reef ecosystem resilience, have declined in biomass across West Hawai‘i in the past 12 years.
  • Total fish abundance has shown an increasing trend while juvenile yellow tang, which comprise ~85% of the total aquarium fish catch, increased approximately 3–4 fold.
  • From 2003–2014, hard coral cover declined by nearly one third in the North and has remained relatively constant over the same time period in the South.
  • In 2015, an estimated 40-80% of corals bleached in the West Hawai‘i region.
  • Annual rainfall has been at or below the long-term average in the past 15 years while the intensity of short-term events has increased.
  • Sea-level is expected to rise 0.48 m (1.57 ft) from present day levels by 2100.
bleaching

Coral bleaching was widespread in West Hawai‘i in 2015. This photograph shows a bleached cauliflower coral (Pocillopora damicornis).

Although the report compiles many relevant indicators used to help track changes in the ecosystem of West Hawai‘i, some gaps remain. The evaluation of information and development of ecosystem indicators is an ongoing process. Nevertheless, this interdisciplinary report highlights the connections across different components of West Hawaii’s marine ecosystem—providing an important “big picture” context as we move toward ecosystem-based management in the region.

 

[1] Jokiel PL, Brown EK, Friedlander A, Rodgers K, Smith WR (2004) Hawai‘i coral reef assessment and monitoring program: Spatial patterns and temporal dynamics in reef coral communities. Pacific Science 58:159-174.
This entry was posted in Ecosystems and Oceanography and tagged , , , , , , , , , , , , , , , , , , , , , . Bookmark the permalink.