Bivalve cultures provide habitat for exotic tunicates in southern Brazil

Rosana Rocha

doi:10.3391/ai.2009.4.1.20

Abstract

Commercial shellfish farming is increasing in Brazil to provide for the growing local and international markets. Shellfish (mussel and oyster) production in Brazil is greatest in the state of Santa Catarina where three sea ports with national and international commerce are sources of non-indigenous species (NIS) that have the potential to find suitable habitat in the shellfish farms. Here we describe the tunicate community associated with shellfish farms during the past 10 years. Survey results identified 17 species of which only one was native. Two were clearly introduced. Of the 14 species classified as cryptogenic, 10 were probably introduced. Tunicates become very abundant in farms and as a consequence farms require periodic cleaning of the shells as well as associated equipment. Styela plicata and Didemnum perlucidum are the most abundant and may become a threat to natural communities, but they are currently not found on natural substrates. Ciona intestinalis and Styela clava were not found in shellfish farms, even though C. intestinalis, at least, has been introduced many times in Brazil. We recommend that a public awareness program be developed to prevent colonization by C. intestinalis in the bivalve farms. Additionally, we emphasize that the diversity of possibly introduced species also requires close monitoring for rapidly expanding populations, since a diversity of life cycles and biological requirements also increases the probability of the appearance of a new pest.

Highlights

IntroductionBivalve farms (mussels and oysters) create complex novel substrates and communities due to the combination of bivalve shells and artificial substrates
Bivalve farms create complex novel substrates and communities due to the combination of bivalve shells and artificial substrates
The dynamics of colonization and use of shellfish farm substrates by tunicates suggest that shellfish farms are potential havens for introduced and possibly invasive species

Summary

Introduction

Bivalve farms (mussels and oysters) create complex novel substrates and communities due to the combination of bivalve shells and artificial substrates. Farms are usually located within calm bays and estuaries which are locations that provide high quality habitat for fouling organisms including introduced species. Farm structures are usually suspended and protected from predation by invertebrates and fish providing refuge for exotic organisms such as tunicates. Recent studies indicate that shellfish farms offer substrate and habitat for many exotic species (reviewed by McKindsey et al 2007). Tunicates are commonly an important part of the community associated with bivalves and while they do not compete with bivalves for food (Lesser et al 1992; Petersen 2007), they can compete for substrate space and may even cause bivalve mortality by growing over them (Igic 1972). Tunicates may often cause severe economic losses (LeBlanc et al 2003)

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