Effects of the invasive macroalga Lophocladia lallemandii on the diet and trophism of Pinna nobilis (Mollusca: Bivalvia) and its guests Pontonia pinnophylax and Nepinnotheres pinnotheres (Crustacea: D)

Abstract

Pinna nobilis and its guests Pontonia pinnophylax and Nepinnotheres pinnotheres were sampled from Posidonia oceanica meadows invaded and non-invaded by the red alga Lophocladia lallemandii. Understanding the interactions among native and invasive species was the primary aim. Therefore, the effects of the invasive L. lallemandii on the percentage contribution of the food sources of P. nobilis and its guests and their trophic associations were investigated applying mixing models to the δ13C and δ15N stable isotopes. Isotopic analyses revealed that the guests of P. nobilis occupied a higher trophic level than their host, being the capacity for food selection the reason of this trophic increase. The invasion of L. lallemandii altered the percentage contribution of the food sources to the consumers diet. Whereas the percentage contribution of the food sources to the δ13C signatures did not really change, L. lallemandii produced variations in the percentage contribution to the δ15N signatures. This red macroalga represented one of the main food sources for P. nobilis, with a real contribution of 19.4% in the invaded meadows. Moreover, L. lallemandii slightly decreased the trophic level of the consumers. This study provides the first isotopic and trophic data for the pea crab N. pinnotheres.