Borneo’s robust corals: How they cope with the climate change and sedimentation pressures

Methods

Summary

We will measure a number of physical variables including ocean temperature, light levels, turbidity and sedimentation with calibrated sensors. Sediment traps will measure sedimentation rates throughout the dry (February-August) and wet (September- January) season. Water samples will complement the monitoring data. 

We will visually assess coral cover, coral diversity and disease prevalence using line transects with three replicates at two depths (5 m and 15 m) in each one of the four reefs we are studying. We will use photos from GoPro cameras to have a record for later coral identification. 

The coral coring team will use a pneumatic underwater drill system powered by scuba tanks. Drill holes will be plugged with underwater concrete plugs. 

Challenges

We are limited by rough weather and waves for the drilling and underwater surveys. We have planned ample time to enable the collection of replicates. 

Pre Analysis Plan

We aim to test if the coral reefs in the Miri-Sibuti Coral Reefs National Park are impacted by high sedimentation from the nearby rivers and/or rising ocean temperatures. To this aim we like to identify sites that are heavily impacted by sediments and control sites where no impact has been observed and learn from them about their capacity of surviving under unpleasant environments. Our colleagues at Curtin Sarawak Dive Club will assist us in the choice of reefs. The assessment of coral cover and diversity follows established protocols. The same holds for the coral tagging and physical parameter assessments. 

In terms of thermal stress from high ocean temperature we anticipate rather optimistic results since no bleaching observation has been reported for these reefs so far. Yet, it could also be due to under-reporting or missing research. 

The coral cores will be measured for their geochemical composition which will tell us how ocean temperatures and sediment delivery to the reefs has changed over long periods of time (>50 years). At the same time, we will be able to measure yearly growth rate, density and calcification of the corals and contrast these results with the geochemical data. The tagged coral genera from different reefs and depths will be collected during the second field trip and analyzed for their growth changes, the zooxanthellae density, chlorophyll a content and lipid content. All this will show how healthy and tolerant the corals are and how the different environmental conditions are affecting them.

All in-situ physical data, biological data and coral core data will be contrasted with publically available and local climate data to assess the relationship between coral diversity and cover with climate variability and change.