The southern coast of Saipan contains several beautiful beaches where extensive reef development has occurred through time. Our monitoring program conducts surveys on the reefs adjacent to Obyan, Boyscout, and Coral Ocean Point beaches. These reefs are fortunate for their favorable environmental setting consisting of; 1) protection from prevailing NE swells (low exposure), and 2) adjacent, small watersheds consisting of raised limestone rock, with relatively low amounts of terrigenous sediments washing into the marine environment during storms. These environmental conditions have led to the development of lush, three-dimensional reef structures that exist today. The living reef (the top few centimeters of the reef structure) has been exposed to various natural disturbances over the years. These include large crown-of-thorns starfish populations (COTS) (1969, 1985, 1995, 2004-6) and frequent typhoons. The graph below shows a large decrease in coral cover at Obyan that was affiliated with the high COTS populations in 2004. However, we believe the reef to be resilient based upon the relatively high levels of coralline algae, which are the preferred substrate for new coral settlement, and large number of new coral recruits.

One major difference between Obyan and Boyscout is the degree of exposure to prevailing oceanic swells and currents. Boyscout is just south of Naftan point which provides greater protection from swells and enhanced isolation from currents running north to south. Isolation may explain why we see fewer coral recruits at Boyscout as compared with Obyan (see graph below), while lower exposure may help explain the prevalence of delicate branching Porites corals in recent years. Fragile Porites corals are not eaten by COTS and because boyscout beach is tucked into the cliffline clam seas prevail.

The graph on the left shows a directional change in the coral community is occurring at Boyscout. Note the decrease of most corals between 1987 and 2005, while Porites corals are increasing. The photo behind graph shows a rare incidence of coral competition as a dominant Porites coral is overgrowing a Goniastrea coral. In summary, we hypothesize that more frequent natural disturbance events followed by low recruitment rates yields ideal conditions for the dominance of Porites.

In contrast, the coral community at Obyan shows larger variability over the years. This is due to natural disturbances that selectively act against the larger, three-dimensional corals, followed by high recruitment rates to replace them (see recruitment graph above). As a result there are many corals with relatively large abundaces at any given time on Obyan's reefs (see graph on right).

THREATS TO REEF HEALTH: Recent threats to Obyan's reefs originate from runoff waters associated with the continuous widening of the secondary access road. Storm events have the ability to transport significant amounts of dredge material used to cap the secondary road into the marine waters. The DEQ and CRM non-point source pollution programs are currently working on the design plans for appropriate stormwater treatment infrastructure. Once completed, these plans will require support from the public and government in order to ensure the completion of this project before we document negative trends in reef health!

Looking for more indepth information? The marine monitoring program has more detailed information and reports available upon request.