Intertidal vermetid reef as a shelter for invasive bivalves in a tropical bay

Abstract

Vermetid reef building species play an important role as ecosystem engineers modifying the physical environment, creating microhabitats and affecting local hydro-sedimentary patterns. We explore the association of native vermetid reefs (Petaloconchus varians) with the invasive bivalves Isognomon bicolor and Leiosolenus aristatus. We also examined the different utilization of the reef habitat, since L. aristatus is a boring species, comparing their population structure on sheltered and exposed rocky shores. Ten sites (five sheltered, five exposed) were sampled at Ilha Grande Bay (Rio de Janeiro, Brazil). I. bicolor and L. aristatus were the most frequent with mean densities of 20,000 (±3400) and 2100 (±600) ind.m2, respectively. There were no significant differences (t = 1.41; p = 0.17) between sheltered and exposed sites in relation to the densities of I. bicolor. However, there were significant differences (t = 3.14; p = 0.03) in relation to the densities of L. aristatus, with higher values at exposed sites. Mean size of both species was significantly (p < 0.01) higher in sheltered areas where the vermetid weight was significantly higher (t = 2.36; p = 0.02). Although native vermetid reefs act as a shelter for both invasive bivalves on sheltered and exposed rocky shores, they prevent the growth of I. bicolor which reaches smaller sizes in relation to populations outside of the reefs. Our results indicate that the two invasive bivalves might be differently affected by hydrodynamic processes.

Mediterranean spreading of the bicolor purse oyster, Isognomon bicolor, and the chicken trigger, Malleus sp., vs. the Lessepsian prejudice

“…In south Brazil, moderate wave exposure and availability of heterogenous steep rocky substrates (Whorff et al, 1995;Domaneschi & Martins, 2002) and rock crevices (Moyses, 2005;Zamprogno et al, 2010), seem to be important for the invasive success of I. bicolor, which preferentially settles inside biogenic secondary substrates (Rocha, 2002). Such observations, as well as suggested associations in invaded environments with native macroalgae (López & Coutinho, 2010) and vermetid reef habitat (Breves & Junqueira, 2017), substantially agrees with our sampling data. This habitat preference suggests that I. bicolor, despite the high invasiveness, cannot be considered a pioneering species in substratum colonization (Rocha, 2002) and does not display a clear opportunistic behaviour (Benthotage et al, 2020).…”

“…This invasive species, which in Brazilian coasts has caused profound changes in the native rocky coast communities reaching densities up to 800 individuals/100 cm 2 (Magalhães, 1999;Rapagnã, 2004;Breves-Ramos et al, 2010), was locally responsible for reducing 50% of the native barnacle population, Tetraclita stalactifera Lamarck, 1818 (López, 2003), and probably competes with Perna perna (Linnaeus 1758), an edible mussel of commercial interest (Rapagnã 2004;Breves-Ramos et al, 2010). In this respect, the observation that this invasive species does not settle on bare substrate, appearing only at late succession stages (Rocha, 2002), is not reassuring, and thereby represents a potential threat for protected species and habitats, such as the Mediterranean vermetid reefs (Milazzo et al, 2016), whose analogues in Brazilian waters are competing with I. bicolor colonization (Breves & Junqueira, 2017).…”