An annual report by the Broadscale Environmental Monitoring Program (BEMP, 2017/2018) recorded temporal changes in the prevalence of V. gibba in southern Tasmania, where it increased significantly between 2009 and 2013, with reduced densities apparent in 2017. The report attributed these fluctuations to ‘boom and bust’ cycles that are a common characteristic of many introduced species.

V. gibba is considered an important indicator species in multiple respects, such as of sedimentary instability (Solis-Weiss et al., 2004), sedimentation rate (Cosentino and Giacobbe, 2006), and is particularly prevalent during hypoxic, and after anoxic, crises (Hrs-Brenko et al., 1994). Hiscock et al., (2005) considered this species resistant to severe hypoxia.

Varicorbula gibba is native between Norway and the Mediterranean, and was introduced to Australia where it was first recorded in Port Phillip Bay, Victoria (Coleman and Sinclair, 1996).

After its initial introduction to Port Phillip Bay, Victoria, the species was believed to be introduced to the Derwent Estuary, Tasmania, via domestic shipping from Port Phillip Bay in 1996 (Derwent Estuary Program, 2008). Shells of the species were found in Port Adelaide, South Australia, in 2008 (Wiltshire et al., 2017). Follow up surveillance has not detected them since Wiltshire, pers. comm., 2021)

V. gibba is the only non-native Corbulidae to have become established in Australia (Lamprell and Healy, 1998).

It inhabits the shallow sublittoral zone to depths of around 140 m, where it is a shallow burrower in thick muddy sand with coarse elements, to which it attaches itself by means of a byssus. V. gibba is relatively immobile and is sedentary (Yonge, 1946).

V. gibba is a small bivalve mollusc with a maximum size of around 15-20 mm. It has two unequal valves: the smaller left valve fitting into the larger right valve. The right valve has well-developed, flat, concentric ridges which are widely spaced, whereas the left valve has finer, closely set, raised ridges. Umbones on both valves are high and curved, and there is a single, well defined cardinal tooth in each valve. The colour of the shells is usually cream/white with brown patches or bands.