Ruben van Hooidonk is a PhD student at Purdue University Climate Dynamics Prediction Lab where he studies the effects of climate change on coral reefs under the supervision of assistant professor Matthew Huber.
Research Interests

Research Interests

 

Coral reefs are one of the most species-rich ecosystems on earth and studies estimate that reefs provide a habitat for 10% of all species on earth (Reaka-Kudla, 1997). Moreover, the combined monetary value of coral reef resources such as food, tourism, and protection from coastal erosion provided by coral reefs is estimated at about $375 billion each year (Constanza, 1997; Bryant et al., 1998). Human activities such as coastal development, destructive fishing practices (dynamite, cyanide, dredging), overexploitation of resources, marine pollution, increased atmospheric carbon dioxide concentrations, and land-use related runoff  threaten fifty-eight percent of worldÕs coral reefs (Bryant et al., 1998).  Increasing ocean temperatures threaten reefs as well; increased temperatures lead to coral bleaching, and bleaching causes mass mortality (Brown and Suharsono 1995) and  is projected to occur annually on reefs in most tropical oceans in 30-50 years (based on a doubling of carbon dioxide levels by 2100, Hoegh-Guldberg-1999).

        

Tropical cyclones damage coral reefs by wave action, by a decrease in salinity, by an increase in nutrients, and by an increase in sedimentation rates on a reef (Rogers, 1990; McCook 1999). These impacts can physically damage corals, cause stress on corals, and bury corals. The total impact of a tropical cyclone on coral reef ecology has not been studied extensively and the impact on deep (30-40m) reefs has received almost no attention from marine biologists (Bak, 2005).

 

These impacts must also be considered in relationship to increasing ocean temperatures. The current increase in ocean temperatures (Barnett et al., 2005) could lead to an increase in tropical cyclone intensity (Trenberth, 2005; Emanuel, 2003), increased intensity can lead to more wave action, more resuspended sediment, and more runoff. The effects of increased intensity of TCs and increased precipitation following a tropical cyclone on coral reefs are not known.

Another area to consider is coral bleaching, tropical cyclones, by reducing SST in their cold wakes, might have a beneficial effect on coral reefs as well. As tropical cyclones need warm water to form, tropical cyclones are prone to occur near areas where conditions are favorable to coral bleaching. Vertical mixing during a tropical cyclone transports deep cool water to the surface, and thus cooling the coral reef vecinity, and possibly ending or preventing a thermal bleaching event. This effect of tropical cyclones has yet to be quantified.

 

A significant lack of data hinders current knowledge of the impact of tropical cyclones on coral reefs, and because tropical cyclone regimes might be changing, a growing need exists to fill this gap in our knowledge.

 

In order to address these gaps in our understanding we will (1) quantify the effects of tropical cyclones on reef ecology, and (2) use these data to predict the impact of tropical cyclones on coral reefs in a globally warming world.

 

 

Current research

 

To quantify historical TC impact on bleaching events, remote sensing SST data, from NOAA OISST, TMI and the ERA-40 data set will be analyzed. Bleaching thresholds (temperature anomalies and duration of anomalies until bleaching is likely to occur) will be calculated for coral reef areas. The analysis of SST data obtained from the datasets, a month before, during and after a TC passes within 100km of a reef, will make it possible to quantify the influence of TCs on bleaching conditions. This analysis will show how many times a TC has reduced sea temperature below bleaching thresholds at all global reef locations. Temperature loggers will be placed in situ to confirm  the temperature effect. Field observations using video transects will assess the amount of bleaching before and after the TC. 

 

We will test our hypothesis that TCs end conditions favorable to bleaching compared to the null hypothesis that states that all bleaching conditions are ended for other reasons than TCs. 

 

Diseases

 

It is possible to detect run-off events using remote sensing products. We will use remote sensing to analyse the extend of run-off generated by TCs and see if this run-off has a spatial and temporal correllation to the occurrence of coral diseases. A dataset of coral disease occurrence in the Florida keys has been provided by Prof. J. Porter of UGA, enabling us to perform this analysis. Coral reefs will be inspected for diseases before and after a TC using SCUBA diving and established reef monitoring protocols.