Hanauma Bay Carrying Capacity Study

Hanauma Bay Biological Carrying Capacity Study:

How much is TOO much?

Purpose

The goal of this study is to determine the relationship between human use of the Hanauma Bay Nature Preserve (HBNP) as measured by the number of users and levels of disturbance to marine life for the purpose of managing the number of park visitors at levels which protect and maintain the integrity of the Bay’s marine communities.

What is Carrying Capacity?

There are 4 main carrying capacity parameters:

Biological– How many people can snorkel at HBNP each day without disturbing coral, invertebrate and fish communities beyond repair?

Social– How close are people to each other on the beach or while snorkeling? Do they feel like their personal space is being invaded?

Physical– Based on square-footage, how many people can fit on the beach at HBNP? This is typically not the limiting capacity variable.

Facilities– How many people can the bathrooms, garbage cans, and maintenance crew’s support?

These first few years, we will be documenting the biological carrying capacity of HBNP. The first year documented how the carrying capacity related to corals.  Year 2 will focus on how both corals and reef fish are influenced by human interaction with the use of cage experiments.

The Consequences of Human Impact

High visitor levels at Hanauma Bay puts increased stress on the natural resources and marine life.  Each time someone steps on a “rocky surface” in the water, which is actually part of the living reef system, they are damaging these resources and limiting the availability of food and shelter for marine life which depend on the system for survival.  With over 3,000 visitors each day, improper stewardship becomes a very serious threat.  This is why staying off of the reef is so important.

The Experiment

How do we measure and determine carrying capacity?

We can find the answer by looking at…

Research in 2018/2019

  • Human Activity 
    • Where are the most popular areas to snorkel or wade?
      • Do we see more disturbance in those areas? Or, the same as low use areas?
  • Trampling
    • Dead coral skeletons were placed throughout HBNP, and their rates of breakage were documented over two sets of month long studies.

OLYMPUS DIGITAL CAMERA

  •  Sedimentation
    • Sediment Traps for deposition
      • Sediment that has been kicked up and deposited back onto the reef flat can fall on corals leading to smothering of tissue and/or energy-costly production of mucus to remove sediment, it also can cause scraping and lesions on corals referred to as sand scour.

PA180543.JPG

    • Secchi Disk for suspended
      • Sediment that has been kicked up and remains suspended in the water column can block light and thus decreases the ability for corals to utilize light during photosynthesis.

OLYMPUS DIGITAL CAMERA

  • Coral composition 
    • Inshore transects.
    • Long-term (CRAMP).

Research in 2019/2020

  • Cage Experiments
    • Cage treatments within HBNP will provide 3 different environments:
      1. Full cages provide a reef environment where humans and fishes are eliminated.
      2. Partial cages provide a reef environment where humans are eliminated, but grazing by fishes is still allowed.
      3. No-cage areas provide a reef environment where both influence of humans and fishes can be observed.
    • Within Cage treatments, the following will be documented for a period of 1 year to see how each may change in relation to human and fish influence…
      • Benthic composition – amount of algae and corals occupying the reef.
      • Coral growth rates (permits pending)
      • Coral breakage rates using dead coral skeletons.
      • Coral recruitment rates.

Screen Shot 2019-09-04 at 11.39.45 AM
Experimental plots (not drawn to scale) are located within all major sectors of Hanauma Bay: Backdoors, Keyhole, Channel, Witches Brew, and Offshore.  Each area has 4 sets of full cages (checkered boxes, 1 yd x 1 yd each), partial cages (dotted line boxes within roped enclosure), and no cage treatments (outside of roped off enclosure and not shown in inlay). Full cage and partial cage treatments are within a 4 yd by 4 yd area roped off to the public using floating safety pool lines and warning signs. Please do not enter roped-off research zones.

  • Coral composition and orientation
    • Inshore transects for benthic composition using photomosaics.
    • Coral bleaching and health surveys.
    • Long-term (CRAMP).