philly wrote:I realize this is a 3 dimensional unit to a 2 dimensional unit of measurement, but is there a formula??
It's not a conversion question.  A formula can probably be constructed, but it depends on many different things.  Without knowing your problem in details nobody will be able to help you.  
See 
http://sergey.gershtein.net/blog/2006/1 ... -foot.htmli have a ratio of plankton/dm cubed : fish/m squared
If you know the depth of the layer where both fish and plankton live, you could convert 
plankton/dm cubed into 
plankton/dm squared by muliplying the value by the depth of the layer in dm.  Then you'll only need to convert dm squared into meters squared here: 
http://www.convert-me.com/en/convert/area