| This dissertation is a study of the coral reefs in the Commonwealth of the Northern Mariana Islands (CNMI) that aims towards an understanding of the processes that influence coral community dynamics and reef development. The first chapter introduces CNMI's geological and environmental settings. It is hypothesized that geomorphological settings are an integral response of coral community growth throughout the Holocene, and in turn continue to influence present day community dynamics. This suggests reciprocity between geological setting and coral community types; the former influences the latter over short time intervals, while the presence of distinct coral communities generate the reef geomorphology over geological time scales. Naturally occurring and anthropogenic derived environmental gradients also act upon coral community structure and reef growth throughout the CNMI. The relative contributions of geomorphology and environment are examined throughout the dissertation. Initially, a methodological study that ensures data collection techniques accurately represent the community being surveyed, focusing upon a desired level of statistical power, is presented in Chapter II. Documenting the abundance of major benthic groups at relatively large spatial scales ensures a statistically sound baseline is established upon which change and appropriate management practices can be assessed over time. The greatest power of detecting a change in the benthos, at each site, within a feasible sampling period, was evident using 5 x 50 m random transects, extracting 60 frames per transect, and analyzing 5 data points on each frame. This optimal sampling strategy was tested at 23 locations and yielded 90% power of detecting a 20 to 30% relative change in dominant benthos abundance estimates. The third chapter uses these data collection techniques as part of a new habitat mapping approach applied to the Saipan Lagoon. Our approach involved the following steps: (1) demarcating habitats in the Saipan Lagoon using Moving Window Analysis (MWA); (2) testing habitat identifications with two, independent datasets, (3) digitizing habitats by spatially integrating statistically similar habitats, identified by MWA with ecological data, into a Geographic Information System (GIS), and (4) assessing the accuracy of the product map by ground truthing 348 validation points. MWA based mapping classified 16 habitat classes with a 77 accuracy, while traditional supervised classifications distinguished among 14 habitats with a 41% accuracy. Changes in the.lagoon since 1959 were calculated and included considerable declines in seagrasses, staghom Acropora, and Isopora and Porites dominated habitats that have been replaced by sand and carbonate rubble. Similar habitat development patterns were observed throughout the lagoon. Preeminent controls to habitat development include: (1) adjacent watershed size, (2) surface current velocities, and (3) lagoon size. Micro-controls, such as differing land use in the watershed alters the integrity of each habitat, but not the habitat's identity. Chapter IV seeks to explain patterns in outer reef slope coral community development. Multivariate tests found that modern coral assemblages were significantly related to a reefs geological and environmental setting. Four unique settings were distinguished: (1) typical consolidated Holocene reefs, (2) consolidated Holocene reefs of Rota Island, (3) unconsolidated Holocene reefs, and (4) Pleistocene reefs. Multiple regressions in each 'setting' found significant relationships between ecological reef measures (i.e., algae cover, coral diversity, coral recruitment, coral colony size and density, and coral cover) and environmental variables (i.e., watershed size, human population density, wave exposure, bathymetric slope, land use, and Crown-of-Thorn starfish outbreaks). The degree of influence of the environmental variables differed depending on reef 'setting'. A synthesis of significant findings regarding coral reef development in the CNMI is discussed in chapter V, including conclusions relevant to coral reef management and influential to policy. |
