coralreefecologylab

Climate change is happening at a rate alarmingly faster than at any other time in Earth’s past. Genetic adaptations in corals haven’t kept up with the rapid pace.

Coral thermal thresholds (the temperature they can withstand) have not changed over the past 20 yrs but bleaching and mortality have increased. This means that corals are not changing rapidly enough to prevent bleaching. As corals lose their symbionts which provide their, color the outer tissues become transparent and the white skeleton beneath becomes visible. This is referred to as bleaching.

Coral thermal thresholds (the temperature they can withstand) have not changed over the past 20 yrs

Since the 1980s, regional bleaching events have occurred on coral reefs throughout the world with increasing frequency and increasing geographic extent. As a result, almost every coral reef region in the world has now suffered extensive stress or mortality.

Source: www.noaanews.noaa.gov

Until recently, the Hawaiian Islands had escaped widespread bleaching events where high mortality occurred. However, in 2014 and 2015, Hawai‘i experienced unprecedented widespread bleaching and mortality. Most islands reported well over half of the corals exhibiting signs of paling and bleaching and subsequent death. The continued increase in global temperature due to anthropogenic production of CO2 from fossil fuels and other human induced emissions means that future bleaching events will be increasingly more severe and frequent.

These coral bleaching events highlighted several science and management needs. It will be critical to establish a baseline to determine what is there before the bleaching then we can monitor the extent of the bleaching and mortality. With this information, we can then identify places where corals are more resilient so we can determine why these species and sites are more resistant to temperature effects.

These coral bleaching events highlighted several science and management needs.

A simple and easy field method of determining the severity of bleaching is the comparison of different shades of color over time and between sites and corals. The only existing color card to make this assessment was developed in 2002 for Australian corals. It has been used extensively throughout the world including for Hawaiian corals, but the shades are not fully representative of corals in regions beyond Australia. Our Hawaiian Ko‘a (coral) card will represent the colors of the major species of Hawaiian corals as they lose their symbionts. It allows more precise measurements through a gradient of shades in the commonly recognized system of degrees. This allows transfer of information about the color without referencing the card. For example, if a corals color starts at 10o and is assessed at 50o a month later we know precisely how much color it has lost.

There is a growing need in Hawai‘i for such a tool as more scientists, students, community members, and resource managers become involved in monitoring of the changes taking place on our reefs.

* The Coral Watch coral health chart developed in 2006 by the University of Queensland, Australia to determine extent of coral bleaching.

** A preliminary representation of the Hawaiian Ko‘a Wheel a color reference card currently under development to assess coral health and bleaching.

The Hawaiians understood the importance of corals to the preservation of the people and its ecological connectivity to the ecosystem. The Kumulipo, the Hawaiian creation chant, recants the creation of Po’ele and Kumulipo. The first living organism to be created was the coral. “Hanau ka uku ko’ako’a, Hanau kana, he ‘ako’akoa puka”. Born was the coral polyp, born was the coral. From coral all other marine organisms were brought forth signifying the vital importance of corals.

To develop the card is not as simple as it appears. We are using professional underwater photographers to assure natural colors and uniform consistency. They will establish the initial range of healthy corals and photograph coral fragments at each stage of bleaching.

We are conducting laboratory trials with different species of corals. We increase temperatures slowly and take samples of each colony as the colors change.

To understand what is happening to the corals physiologically as they bleach, we take pulse-amplitude modulation (PAM) measurements.

From each fragment we extract and measure the chlorophyll a content using a spectrophotometer which measures the reflectance or transmittance at a certain wavelength. This will tell us the concentration chlorophyll as it relates to color.

We are counting the hundreds of zooxanthellae (the tiny single celled algae that have a symbiotic relationship with the corals) that provide color in corals and are reduced as bleaching progresses. Originally developed to count blood cells we use a hemocytometer to determine the symbiont densities in coral. This will give us a link from cell counts to color.

We all know that the “ridge to reef” paradigm has become a familiar management theme throughout the Pacific and for centuries has been a central element in the native Hawaiian management scheme known as the ahupua‘a system.

This view of Hawaiian land division and resource management combined watersheds, streams, and coastal regions as integral interacting components of an ecosystem. In this holistic view, the sustainability of watershed and nearshore resources were recognized as being related to human practices on land, which today is a central premise in ecological science. The Hawaiians understood what they did on land would affect their fishing.

The Hawaiians understood that what they did on land would affect their fishing.

However, there was no quantitative data until recently in Hawai’i to verify this linkage on a large scale. So why did we believe so strongly that this relationship was valid, that the watersheds affected the reefs? Well, it’s because there have been links established on a small scale, such as on the south shore of Moloka’i, where a clear connection between poor land practices was correlated with poor reef condition. But we have also worked in regions that we didn’t find that link. There really was no data on a statewide scale to examine this relationship and validate a connection. In order to see if there really is a connection we needed a large scale data on the watersheds and on the reefs (there are 580 watersheds).

The watershed data came from University of Hawai’i researcher Mike Kido and we used our reef data from our Coral Reef Assessment and Monitoring Program (CRAMP). We developed a watershed and a reef index and compared them to see if there really is a link between the two. We looked at over 60 biological and environmental factors, such as water motion and coral cover, to see which were most important in influencing coral reef communities. The same was done for the watersheds to develop an index of watershed health and reef health. What we found was an overall significantly positive correlation between the watersheds and the reefs. So the healthier the watershed, the healthier the reef.

“What we found was an overall significantly positive correlation between the watersheds and the reefs. So the healthier the watershed, the healthier the reef.“

This provided the first quantitative statewide evidence to support the long standing assumption that there is a significant overall relationship between the condition of watersheds and the condition of adjacent coral reef communities in Hawai‘i. Not surprising.

What is interesting is that the relationship was strongest for shallow sites on south-facing shores but diminished as you traveled west and east around each of the islands. In addition, as you get to the north facing coasts we found no statistically significant relationship at all between the watersheds and the reefs. High surf conditions along the north shore increase local wave driven currents and flush watershed-derived materials away from nearshore waters. Consequently, reefs in these locales are less vulnerable to the deposition of transported land derived materials. Also, since the south shores of the islands have less wave energy, this is where the most development initially occurred so you have more degraded watersheds on the south shores.

We conducted field verification of this model. We needed to be able to go to a new site and determine whether it fit this pattern. We also had a very small sample size on north shores, preventing validation of the watershed/reef correlation. So we did this on Kaua‘i. We added north and south facing reefs in 4 categories of watershed health (excellent which is depicted in blue, good, fair, and poor which is colored red). This wasn’t as easy as it sounds. We couldn’t find excellent watersheds on the south shores of any of the islands except in a few rare exceptions that we couldn’t use (such as Waimea on Kaua’i where a huge watershed drains into a small area that has little reef structure and is not surrounded by good watersheds). We added 49 stations at 8 sites, one in each index health category on the south shore and one in each index health category on the north shore.

With this validation data we found the same pattern. Shallow south shores are impacted more heavily by watershed impacts than north facing reefs.

“Shallow south shores are impacted more heavily by watershed impacts than north facing reefs.”

There are however some factors that can override this watershed/reef relationship, such as heavy fishing pressure or sand scour, but the general pattern is clear. We can now predict reef health from watershed health in certain regions.

“We can now predict reef health from watershed health in certain regions.”

We can evaluate reefs, predict reef health from watershed health, and improve and coordinate conservation and resource management of the entire ahupua‘a. We are now developing an interactive map that shows each of the 580 watersheds and their connection to the reef.

This can tell managers where restoration efforts in the watershed will be most effective in protecting the reefs. We also found that watersheds need not be pristine for adjacent reefs to contain high coral cover. Thus, watersheds may not need to be fully restored to pristine natural conditions to support thriving coral reef communities in adjacent marine waters.

Map showing (a) watershed health indices (WHI), (b) reef health indices (RHI), and (c) the difference between RHI and WHI for watersheds on the islands of Ni‘ihau and Kaua‘i. In the lower map (c), negative numbers indicate watershed health is greater than reef health and positive numbers indicate reef health is greater than watershed health.

Author: coralreefecologylab

Coral Reef Color Card

Ridge to Reef