Filtration and respiration of filter-feeding marine invertebrates are linked through allometric power-law functions.

Filter feeding in marine invertebrates is a secondary adaptation where the filtration rate (F) that provides the food energy to cover the respiration (R) increases with increasing body dry weight (W), and therefore it may be suggested that the exponents in the equations F=a1Wb1 and R=a2Wb2 have, during evolution, become near equal, b1≈b2, ensuring that the F/R-ratio=a1/a2 is nearly constant. Based on published data, we verify the hypothesis of equal allometric power-law exponents and test to what degree the F/R-ratio may be used to characterize various adaptations to filter feeding. The available b-values for very different taxonomic groups of filter feeders (bivalves, ascidians, crustaceans, polychaetes, jellyfish) covering 8 decades support in most cases the hypothesis of b1≈b2. For obligate phytoplankton filter feeders where b1≈b2 the F/R-ratio was used to estimate the critical phytoplankton biomass below which the animal would starve. However, if the food-particle retention efficiency is not constant during an animal's ontogeny the F/R-ratio may change according to the size range of particles being captured at the specific stage of development.