densely overgrown with massive corals and corymbose
Acropora. Areas with large thickets of Acropora formosa
still occur but cover is dramatically reduced since the
1940s (about 20% of the lagoon shifted from coral and
sea grass cover to sand, Houk and van Woesik, 2008).
Toward the center of the lagoon, coral growth becomes
increasingly sparse as cover by sandy sediment increases.
Rocky outcrops with low coral cover and increasingly high
algal cover toward the land as well as small patch reefs
occur irregularly in the lagoon. Dense sea grass beds have
also been reduced in size (Houk and van Woesik, 2008).
General geology of the southern Marianas –
volcanics and limestones
Guam, at the southwestern end of the West Mariana
Ridge, was volcanically active from 32 to 20 Ma
Mariana Islands, Coral Reef Geology, Figure 4 Stages of Holocene reef growth on Guam from Randall and Siegrist (1988). It is clearly
visible how strongly the morphology of present-day reef growth is determined by early Holocene reef growth.
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