Hi Estelle,

 

Your project sounds interesting. I think the existing MGET tool for simulating larval dispersal could be useful. Although this tool was originally applied to coral larvae it can be used for other taxa providing you are willing to ignore some of the behaviors of those animals that might cause them to disperse in a different way.

 

The tool has a three-step process, as shown on page 13 of this presentation.

 

1.    Create the simulation: here you provide rasters that define the extent of the study area and the spatial resolution of your analysis (the raster cell size). These rasters specify which cells that contain reefs, the IDs of those reefs, the proportion of the cell that contains reef vs. water, and a water mask.

 

2.    Load currents into the simulation: here you specify which currents dataset you want to use, as well as a start date and end date of currents data to download. At the moment, the tool in MGET only provides access to the Aviso geostrophic currents, although we have developed private versions that give access to Pacific ROMS (from NASA JPL) and HYCOM.

 

3.    Run the simulation: here you pick a start date to release larvae and specify the duration of the simulation, usually the larval PLD. The simulator disperses the larvae using Eulerian advection/diffusion. As output you receive a time series of rasters showing the density of larvae throughout the study area at each interval (you can configure the interval). This is suitable for creating animations. You also receive a connectivity matrix in the form of a shapefile that shows lines between the centroids of the reefs with an attribute showing the dispersal potential between the two. This dispersal potential is expressed as the maximum density of larvae released from reef A that were found to be suspended over reef B during the lifetime of the simulation.

 

To know more about the scientific details of this, please consult the following paper written by my colleague Eric Treml, who leads the larval dispersal research:

 

Treml, E.A., P.N. Halpin, D.L. Urban, and L.F. Pratson (2008). Modeling population connectivity by ocean currents, a graph-theoretic approach for marine conservation. Landscape Ecology 23: 19-36. doi:10.1007/s10980-007-9138-y.

 

To use the existing tool, I believe you must have an ArcView license. I do not think you need an ArcInfo license. But you do need to install the MATLAB Component Runtime (MCR). This is available for free here.

 

What is the schedule for your project? If it is not due for a while, you may be interested in some enhancements we’ve developed. These will be introduced into MGET in the next few months, once a new manuscript has been submitted. These enhancements include:

 

·         Addition of larval behavior parameters including: precompetency period, mortality, settlement, and vertical migration

·         Fully mass-balanced tracking of dispersal. The final output will change from maximum larvae density to the cumulative larvae settled, which is a more realistic measurement of the connectivity between reefs.

·         A advection/diffusion method that provides a higher degree of numerical stability and accuracy

·         Access to more currents datasets than Aviso

 

We have not incorporated other oceanographic parameters into the simulation yet. We have discussed the idea of using SST as a constraint on mortality and settlement. Eric has done some research on that but we do not plan to incorporate it as an option in the tool until sometime in the future.

 

You are welcome to contact us with questions. I included Eric’s email address in my response.

 

Best regards,

 

Jason