Preferences of the Ponto‐Caspian amphipod Dikerogammarus haemobaphes for living zebra mussels

Abstract

A Ponto-Caspian amphipod Dikerogammarus haemobaphes has recently invaded European waters. In the recipient area, it encountered Dreissena polymorpha, a habitat-forming bivalve, co-occurring with the gammarids in their native range. We assumed that interspecific interactions between these two species, which could develop during their long-term co-evolution, may affect the gammarid behaviour in novel areas. We examined the gammarid ability to select a habitat containing living mussels and searched for cues used in that selection. We hypothesized that they may respond to such traits of a living mussel as byssal threads, activity (e.g. valve movements, filtration) and/or shell surface properties. We conducted the pairwise habitat-choice experiments in which we offered various objects to single gammarids in the following combinations: (1) living mussels versus empty shells (the general effect of living Dreissena); (2) living mussels versus shells with added byssal threads and shells with byssus versus shells without it (the effect of byssus);(3) living mussels versus shells, both coated with nail varnish to neutralize the shell surface (the effect of mussel activity); (4) varnished versus clean living mussels (the effect of shell surface); (5) varnished versus clean stones (the effect of varnish). We checked the gammarid positions in the experimental tanks after 24 h. The gammarids preferred clean living mussels over clean shells, regardless of the presence of byssal threads under the latter. They responded to the shell surface, exhibiting preferences for clean mussels over varnished individuals. They were neither affected by the presence of byssus nor by mussel activity. The ability to detect and actively select zebra mussel habitats may be beneficial for D. haemobaphes and help it establish stable populations in newly invaded areas.

The impact of zebra mussel (Dreissena polymorpha) periostracum and biofilm cues on habitat selection by a Ponto-Caspian amphipod Dikerogammarus haemobaphes

“…Gammarids can discriminate between shells with intact and varnished (i.e. artificial) surfaces, preferring the former (Kobak & _ Zytkowicz, 2007;Kobak et al, 2009), but they did not distinguish between varnished shells and those devoid of periostracum in our study, showing that the attractant was completely eliminated with the periostracum removal.…”

“…As the gammarids did not respond to mussel activity, viz. valve movements and byssus production (Kobak & _ Zytkowicz, 2007;Kobak et al, 2009) and did not discriminate between biofilmed and cleaned living mussels (this study), we can conclude that the specific cue must be associated with the periostracum.…”

“…Thus, the presence of biofilm affects gammarids, but its quality, associated with particular surface types, does not. Therefore, the biofilm quality could not be responsible for the gammarid preferences for zebra mussel shells, observed by Kobak & _ Zytkowicz (2007) and Kobak et al (2009).…”

“…Previous studies have shown that the varnish is neutral to gammarids, i.e. neither attracts nor repels them (Kobak & _ Zytkowicz, 2007;Kobak et al, 2009). Like other substratum types, the varnished shells were either coated with the old biofilm (#6) or devoid of it (#7).…”

“…In the present study, we intended to find the source of a cue attracting D. haemobaphes to living dreissenids and their shells. Previous research has shown that this cue is likely associated with the shell surface (Kobak & _ Zytkowicz, 2007;Kobak et al, 2009), but its exact nature has not been determined. We hypothesized that two potential attractant sources were possible: (1) the biofilm developing on shells, which is possibly different from those growing on other surfaces and/or (2) the outer proteinaceous shell layer, the periostracum.…”