A Better Understanding of Coral Reef Ecosystems

Pelagic predators such as these barracuda, Sphyraena qenie, are part of the coral reef ecosystem in the U.S. Line Islands (NOAA Photo by Kevin Lino).
A team of scientists have embarked from Hawai'i on a three-month survey of coral reef ecosystems at Johnston Atoll, the U.S. Phoenix Islands, the islands of American Samoa, and the U.S. Line Islands in the tropical Pacific Ocean. The overarching objective is to better understand the coral reef ecosystems of these areas, many of which are seldom explored. The research expedition is part of a regular monitoring program, conducted by the Coral Reef Ecosystem Division (CRED), headquartered in Honolulu, Hawai'i. The expedition is supported by NOAA's Coral Reef Conservation Program and involves extensive cooperation among NOAA scientists and research partners, including the University of Hawaii Joint Institute for Marine and Atmospheric Research (JIMAR), the U.S. Fish and Wildlife Service, San Diego State University, and the Papahānaumaokuākea Marine National Monument.

The research expedition will be carried out from February 27 to May 24, 2012 aboard the NOAA ship Hi'ialakai. Under the leadership of Chief Scientists Dr. Jill Zamzow, Dr. Bernardo Vargas-Angél, and Jamison Gove, a diverse team of researchers will be conducting multidisciplinary coral reef ecosystem surveys, assessing the status of fishes, corals, algae, marine invertebrates, and the oceanographic conditions in which these organisms exist. The scientific data collected during the three-month research expedition will enable informed and effective implementation of ecosystem-based management and conservation strategies for coral reef ecosystems, helping to ensure their protection for generations to come.

Wednesday, November 3, 2010

What’s Shaping Kaua`i’s Coral Reefs?

by Courtney Couch 

We set sail last Tuesday for Kaua`i and Ni`ihau with several new scientists and crew members (including myself) and hopes for continued good weather. Kaua`i is the oldest of the Main Hawaiian Islands (approximately 5.1 million years old) and one of the most geologically complex islands. Since it is situated further west out of the shelter of the other islands, a large portion of Kaua`i’s coastline is battered by persistent strong trade winds and heavy swell. These factors together with the heavy rainfall have etched spectacular landscapes of precipitous valleys and ridges along the windward coasts. The leeward coast of Kaua`i is comprised of arid cliffs and gradual slopes of tan and red soil. Although the leeward coast is protected from the brunt of the trade winds, Kaua`i’s small size (1/7th the size of the Big Island) and its round shape, allows the winds to wrap around the island. We experienced these conditions first hand this week. Immediately following our departure from Pearl Harbor the trade winds started to pick up.  By the time we reached Kaua`i, the winds along the west coast were sustained at 15 knots with gusts to 30 knots, and this was on the leeward side of the island! Most days since then have been a challenge to find regions that are safe enough to launch the small boats, conduct our fieldwork, and retrieve the boats at the end of the day. 
Rough seas along West Kaua`i. Photo by: Courtney Couch
 As you may expect, these environmental conditions have dramatically shaped the coral reef ecosystems surrounding these islands. I spend all of my time researching coral health and disease along the leeward side of the Big Island, so the MHI RAMP cruise has been a unique opportunity to see the myriad of factors shaping coral reef structure on other islands. On the leeward reef slopes of the Big Island, you generally see dense Porites compressa beds as far as the eye can see.  The lower wave action due to deeper water along this coastline facilitates growth of this fragile species, which provides important habitat for many reef fish and invertebrates. Kaua`i’s leeward reefs are a different story. Many of the leeward study sites are comprised of flat algal covered pavement, bolder and small patches of consolidated reef. On the windward coast, reefs are primarily composed of flat pavement, rubble and boulders covered with low profile coral colonies. Overall, Kaua`i’s coral communities are sparser, comprised of smaller colonies and dominated by the more wave tolerant genera such as the pocilloporids and montiporids. So where has all the coral gone? 

Kaua’i’s older age plays a large role the overall reef structure. As Kaua`i moves further away from the hotspot that the Big Island currently resides over, it moves into higher latitudes less favorable for coral growth. The slow erosion of the land and reefs also generates sand and together with the high wind and wave action can act like sand paper and scour the substrate. Wave action is arguably one of the most significant factors shaping reef structure in Hawai`i.  High wave action prevents the development of fragile species and large colonies that can be easily broken off the substrate. Heavy rainfall along the windward coasts also transports large amounts of sediment onto the reefs reducing water clarity necessary for coral growth. Along the leeward coast of Kaua`i agricultural and residential development has facilitated sedimentation events during infrequent large rainfalls. These events blanket the reefs with fine red silt than can smother coral and reduced light. 
Coastal erosion along West Kaua`i. Photo by: Courtney Couch
While many of Kauai’s reefs no longer have the structural complexity and coral cover that the Big Island now has, it does have flora and fauna not commonly found on the Big Island. While Kaua`i lacks vast stretches of coral like we see on the Big Island, there is quite a diversity of algae (limu).  My dive buddy is a phycologist (limu expert) and frequently finds uncommon species, which is very exciting for him, and very educational for us.  From a coral biologist’s perspective South Kaua`i does have unique coral communities. We found one of the largest populations of Pocillopora eydouxi I have ever seen. This beautiful species can reach up to 100 cm in diameter and its intricate branches serve as a refuge for a range of fish and invertebrates.
Pocillopora eydouxi colonies provide important habitat for reef fauna. Photo by: Courtney Couch
At a site not too far away we also encountered an unusually high number of cryptic coral species such as Leptoseris incrustans, Leptoseris tubulifera, Leptoseris papyracea, and Cosinaraea wellsi.  As for fish, Kaua`i and especially Ni`ihau still have large curious predators such as uku and `omilu and kahala that come to see what you are all about on the dives.   However, none of the teams saw more than a couple of sharks here and there, which was surprising.  Where there is complexity (a lot of vertical relief of the substrate), there are nice aggregations of fish, and they typically are much larger up here.  
Antipathes sp. found along South Kaua`i. Photo by: Courtney Couch
Even with the less than ideal weather conditions, the scientists and crew aboard the Hi`ialakai have successfully completed our surveys around Kaua`i, Ni`ihau and West O`ahu.  With two days left in the second leg, we are ready for the last segment of the cruise, South Moloka`i.




 






 
Posted by NOAA CRED at 8:42 AM

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)