Does rock type account for variation in mussel attachment strength? A test with Brachidontes rodriguezii in the southwestern Atlantic

Jorge L Gutiérrez,Lorena P Arribas,María Bagur,M Gabriela Palomo

doi:10.1186/s10152-018-0514-6

Abstract

Mussel attachment strength varies in space and time, frequently in association with variations in wave exposure. Yet, it remains uninvestigated whether different rock types can contribute to variation in mussel attachment. Here we compared the attachment strength of the mussel Brachidontes rodriguezii between soft and hard intertidal rock substrates that are typical of coastal Buenos Aires Province, Argentina: Pampean loess cemented by calcium carbonate and orthoquartzite, respectively. Overall comparisons of mussel attachment across natural platforms of either rock type (10 loess sites and 4 orthoquartzite sites) indicated stronger mussel attachment to orthoquartzite. However, mussel attachment strength did not differ when compared across natural loess platforms and introduced orthoquartzite blocks (i.e., groins and revetments) occurring within the same site. Mussels attaching to loess showed more byssal threads than those attaching to orthoquartzite at the same site. These findings suggest, first, that rock type does not influence mussel attachment strength in our study system, secondly, that overall differences in mussel attachment strength with rock type across natural platforms in our study range are due to confounding influences of co-varying factors (e.g., wave exposure) and, finally, that mussels can increase byssus production to counteract potential substrate failure when attaching to soft, friable rock. The latter likely explains the ability of mussels to maintain relatively stable cover across rocks of contrasting hardness.

Highlights

Sessile and low-mobile organisms inhabiting rocky shores and reefs rely on their morphology and adhesion mechanisms to withstand wave action [1]
The difference between the mean mussel attachment strength of mussels in orthoquartzite and loess was significantly higher than the expected if sites are randomly assigned to each rock type (Fig. 2, Table 2)
Substrate failures were far more common and can either be attributable to adhesive plaque detachment, breakdown of the basal rock substrate, or adhesion to loose particles

Summary

Introduction

Sessile and low-mobile organisms inhabiting rocky shores and reefs (e.g., algae, barnacles, mussels, gastropods, echinoids) rely on their morphology and adhesion mechanisms to withstand wave action [1]. Just a few studies on algae have addressed relationships between organismal attachment strength and substrate type in rocky shores and reefs [9, 13, 14] They suggest that algal attachment is generally weaker on soft relative to hard substrates. Gutiérrez et al Helgol Mar Res (2018) 72:10 strongly to hard (granite, sandstone) than soft rock (limestone), and that thalli attached to soft rock are more often dislodged due to substrate failure (vs breakage at the stipe-thallus junction or thallus). This suggests that the probability of kelp dislodgement increases with decreasing substratum hardness and increasing friability (i.e., the potential of rocks to break and disaggregate into smaller pieces). It remains unclear whether they can do so in response to rock friability so as to counteract potential substrate failure

Methods

Results

Conclusion