Shellfish filter the water column to get food. Several factors in the water, such as temperature, salinity, suspended solids and food availability, affect the uptake of particles from the water and thus the growth and condition of shellfish. These factors can vary greatly in an estuary or bay. Measurements in breeding plots in the Wadden Sea show significant differences in growth rates in mussels.
To read more about this see: https://schelpdieren.com/2023/10/30/ruimtelijke-karakterisering-van-specifieke-voedselparameters-in-de-waddenzee/