A Two-year study of coral recruitment and sedimentation in Asan Bay, Guam

Minton, Dwayne; Lundgren, Ian; Pakenham, Anna

Coral reefs on Guam are heavily impacted by numerous terrestrial activities. One of the most significant threats to their long-term health and persistence is sedimentation resulting from poor land management practices. Sediments are known to adversely impact at all life history stages. Due to their inherent fragility, coral larvae and newly settled recruits are the most susceptible to elevated sediment loads. Site specific management of adult coral populations may not ensure long-term persistence of coral reefs; instead, managing important demographic processes may be a more effective strategy for conserving coral reef ecosystems. Asan Bay, Guam, which contains a unit of War in the Pacific National Historical Park, has extensive nearshore coral reefs that have been heavily impacted by terrestrial-derived sediments. Recruitment was monitored in Asan Bay along a sediment gradient using both PVC and terra cotta plates to determine baseline recruitment levels and to investigate a possible correlation between sedimentation and recruitment. Plates were deployed for 3 month intervals for 2 years to examine temporal trends. Coral recruitment in Asan Bay was low; only 34 recruits were collected during this 2-year project, with Pocillopora spp. recruits the most common. Recruits from the family Poritidae and Acroporidae were also collected. No correlation between recruit density and sediment collection rate was observed, but settlement patterns of recruits on plates suggested light, not sediments (directly) or predation, was the primary factor affecting settlement patterns in Asan Bay. Preliminary investigations using fluorescence photography supported laboratory findings that suggest coral larvae are failing to settle, and are not experiencing post-settlement mortality. Reasons for the inhibition of larval settlement are unclear, but are most likely associated with local and regional factors, all of which will need to be addressed to achieve effective coral reef conservation in Asan Bay.

A Two-year study of coral recruitment and sedimentation in Asan Bay, Guam

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