A Long-Term Paleoecological Record of Coral Reef Communities

Smithsonian Institution, Washington DC

Investigators

Abstract

ABSTRACT A Long-Term Paleoecological Record of Coral Reef Communities John M. Pandolfi Ear- 0105543 Reef coral communities living during the past 500 ka (thousand years) show remarkable persistence in taxonomic composition and diversity during multiple episodes of global climate change. In contrast, similar studies conducted over decadal time scales in living reefs show striking change and unpredictability with apparent dramatic and unprecedented decline during the past 30 years. This apparent paradox confounds attempts to predict the response of coral reefs to local and global environmental change. This research will investigate the taxonomic composition and diversity of coral communities, using a long term paleoecological record between 9000 and 6000 years before present (ybp) in the Holocene raised reef terrace along a 35 km segment of coastline of the Huon Peninsula, Papua New Guinea (PNG). The exposed fossil reef from the 3000-year Holocene interval preserves fossil assemblages before and after a clearly identifiable, narrowly dated, and widespread earthquake disturbance event. The 20 m high Holocene seacliffs contain a shallow fore-reef habitat that exquisitely preserves reef coral assemblages, and can be dated and sampled with a resolution within 150 years. This temporal framework, inaccessible in living reefs, corresponds well to the life history attributes of the long-living corals, and provides the key link between studies of older Pleistocene assemblages and modern studies at decadal time scales. Study of the PNG paleoecological record of coral reefs in the absence of significant human impact will document: 1) patterns in coral community structure every 150 years for 3000 years, including post-disturbance community re-colonization; and 2) the relationship between coral species distribution patterns through time and space and global climate and local environmental variation, during continuous sea level rise and variable Holocene sea surface temperatures. Ecological data will be gathered by conducting surveys measuring the abundance of reef coral species along 25-m transects representing similar age assemblages over a 35 km distance. Previous work differentiating the ancient habitats will be corroborated using sedimentology and composition of the coralline algal communities. A significant component of this research is to relate species distribution patterns through time and space to fluctuations in their environment. Thus, the Holocene reef environment will be characterized using 'paired' geochemical analyses (isotopic and trace element) of corals and mollusks. A detailed temporal sequence will be established for each of the sampled Holocene reef geological sections using abundant 14C (radiocarbon) age dates.