Allometric relationships in feeding and digestion in the Chilean mytilids Mytilus chilensis (Hupé), Choromytilus chorus (Molina) and Aulacomya ater (Molina): A comparative study

Abstract

As a first attempt to explain the functional basis of the co-occurrence of three sympatric species of native mussels frequently found at the cold-temperate coasts of Chile, we tested the existence of potential morpho-functional differences operating at the feeding and digestive levels of Mytilus chilensis, Choromytilus chorus and Aulacomya ater. Clearance rate (CR (l h–1)), gill area (GA: mm2), dry weight of labial palps (WLP: mg), gut contents (GC: mg), weight of digestive gland (WDG: mg), specific (mg of maltose or tyrosine mg prot−1h−1) and total (mg of maltose or tyrosine digestive gland−1h−1) amylase, cellulase, laminarinase, xylanase and protease activities were measured in different size individuals of the three species collected from Corral Bay (Chile). Hydrolytic activity of digestive extracts towards natural substrates elaborated from different macrophyte was also tested for the 3 species. No significant differences between species were found for mass-exponents (b) scaling CR (b=0.744) and GA (b=0.803). However, size-specific CR and GA were found to vary between species, ranking as follows: M. chilensis>C. chorus>A. ater. WLP fitted to an inter‐specific common function (b=0.77). Regarding digestive parameters, no significant inter‐specific differences were found between mass-exponents for GC (b=0.434), WDG (b=1.067) and total enzyme activities (common b ranged from 0.904 to 1.212), except total amylase which was significantly higher in A. ater (b=1.838). Specific activities of digestive enzymes were size-independent except A. ater amylase, which increased with body-size, and protease in the three species which decreased with size. For a common body-size, GC and carbohydrase activities were significantly higher in M. chilensis than in C. chorus and A. ater. Inter‐specific differences were found in the composition of carbohydrase pool: amylase was the prevalent enzyme in M. chilensis (up to 44.5% of total carbohydrase) whereas the three carbohydrases had a similar contribution in C. chorus and A. ater. Sugar release from vascular plants was significantly higher in C. chorus.