Effects of Ficopomatus enigmaticus ecosystem‐engineered habitat structure on population parameters of the amphipod Melita palmata : A NIS‐NIS interaction study

Abstract

The variability of some population (demo) parameters of the gammarid amphipod Melita palmata was associated with contrasting habitat structures created by the non‐indigenous reef‐builder polychaete Ficopomatus enigmaticus in the Mar Chiquita coastal lagoon (37°40 S, 57°23 W, Argentina). Sampling of M. palmata was conducted biweekly during the reproductive period in F. enigmaticus reefs and sediment from reef‐free areas, accounting for the vertical distribution and the presence/absence of macroalgae. Males, females (non‐ovigerous and ovigerous), and juveniles are present in both reefs and sediment, but the abundance of M. palmata is several orders of magnitude higher in reefs. Reefs? M. palmata population (demo) displays variations in: (a) abundance, (b) mean size, and (c) proportions of demographic categories. In reefs, females show a higher proportion of ovigerous specimens and a female‐biased sex ratio, contrasting the 1:1 ratio observed in sediment. Individuals are more abundant in the surface layer covered with macroalgae in reefs (small sizes) and macroalgae or valves in sediment. The association of M. palmata to F. enigmaticus reefs drives its permanency in the system, enhancing its reproductive potential via different reproductive traits and habitat use, with a reduced potential to spread to marginal areas.