How to analyze relation between two independent scale variables and one common nominal variable?

I have three variables: Location (nominal, 4 classes); Density_settlement (scale, 5 values per class); Weight_plankton (scale, 4 values per class).

There are two datasets, one inlcuding Density_settlement and Location (4x5), the other including Weight_plankton and Location (4x4). There is no pairing between the Density and Weight of the plankton: Density is gathered through count of settlement, while Weight is defined through random sampling of ocean water. However, I do expect a relationship between both.

What is a good way to test this in R? I have tried to fit a GLM and correlation, but it does not seem to be appropriate.