I have a data set on the proportional composition of marine substrate for different locations which I would like to compare. For example, one replicate transect within a location may be 50% sand, 25% seagrass, 25% rubble (there are 14 categories).
In general, how does one analyse such conditional proportional data, since each value for each variable (e.g. % sand) is dependent upon the other proportions?
If these were independent proportions I would consider an ordination (e.g. NMDS) to examine clustering of replicate transects with respect to locations, but is this possible with conditional proportions? and if so how do I treat the proportions (standardisation, distance measure etc.)?
Additionally, I am considering multiple regression to test whether site characteristics (substrate composition and location) influence the density of fish (no. individuals/square metre). Is this possible? or can someone suggest a suitable alternative?
When researching this question all I could find was information about variables measured independently as proportions - no help there!