Change in coral community at Lau Lau Bay

Lau Lau Bay contains some of the most diverse yet threatened reefs in the entire CNMI. The protected nature of the bay has allowed thriving reefs to develop over the past 5,000 years, resulting in an amazing, three dimensional reef structure today. Divers and fishermen alike value this type of reef structure because of its beauty and the fish habitat that it provides. The protection and isolation of the bay also means that it takes longer for these reefs to recover from disturbances, like typhoons and pollution, for example.

Upland burning and clearing for development, farming, and even hunting over the years has led to patches of exposed soil that only needs a rainstorm to bleed into Lau Lau Bay. Soil particles contain nutrients that wash into “nutrient free” coral reef waters. If the bleeding is not stopped, this change in the water quality changes the community structure (arrangement of plants and animals) of the living reef.

The CNMI Marine Monitoring Team has established two long-term sites since 2000 in Lau Lau Bay; however, we have also collected historical data from surveys that were undertaken in 1983 and 1991. Unfortunately, the trends are not good for the bay. At both sites there has been a large decrease in coral community evenness (an even amount of all species of coral and not dominance by just one species). Specifically, Lau Lau #2 shows the greatest loss of three dimensional corals (branching and massive) and an increase in Porites corals (all corals in the genus Porites). The watershed associated with Lau Lau #1 has less upland pollution washing down during each storm, and thus, the coral community has not yet changed this drastically.

So why is coral diversity important?

The importance of coral diversity can best be understood using the common flu as an example. When a flu passes through our population, not every individual gets sick because we are all different (we have a high diversity of genes). If we were all the exact same one, disease could wipe us all out and leave nothing behind. On a coral reef different species respond differently to disease and disturbance. This is one reason why a beautiful, diverse reef has evolved in Lau Lau Bay over the past 5,000 years. Because of upland pollution, we are decreasing coral diversity and making the living community all the exact same species. This can be very dangerous because if anything happens to this species, the entire reef is at risk.

This is only one reason why biological diversity is important. Diversity also creates habitats for animals to live (fish that we eat) and a beautiful site for our eyes. So it is extremely true that whatever we do on land can and does impact the ocean. Lau Lau Bay watershed restoration efforts that CRM and DEQ have or will soon start need public support and involvement for them to work. To learn more about CNMI’s coral reefs stay tuned to weekly articles right here, or contact us for more information. (Peter Houk)

Houk is a marine biologist at the Division of Environmental Quality.