The marine aquarium trade in South Africa: a vector for alien invasive species?

Abstract

Biological invasions are increasingly recognized as a primary threat to biodiversity. Global transport and trade play an important role in the movement of alien species around the world, and as transport and trade have intensified over the decades, so too has the number of alien species introductions. As preventing the introduction of harmful species is a more cost-effective and efficient method to managing biological invasions, it is imperative that scientific studies are aimed at identifying the pathways responsible for introductions. The marine aquarium trade is an ever-growing business globally and only up until recently has been identified as a major pathway for the introduction of alien species. Except for the notorious cases of the invasive lionfish, Pterois volitans, and seaweed, Caulerpa taxifolia, the role of the aquarium trade towards the introduction of alien marine organisms has been largely unevaluated. With popularity rising for the marine aquarium hobby in South Africa, it is of concern that the trade remains predominantly unregulated. This study aims to investigate the risk posed by the marine aquarium trade as a pathway for the introduction of alien invasive species in South Africa.

One such vector examined in this study is live rock: any type of rock or dead coral skeleton encrusted with, and containing within its crevices, a wide variety of marine organisms, including colourful sessile invertebrates and encrusting algae. A combination of morphological and DNA barcoding molecular identifications, based on the phylogenetic inference of mitochondrial cytochrome c oxidase subunit 1 (COI) and internal transcribed spacer region (ITS) sequence data, was used to assign identifications to 174 taxa harvested from imported Indonesian and Kenyan live rock. Of the 6 diverse phyla identified, one alien species was flagged as harmful due to its successful invasion of other ecosystems in the world: the glass sea anemone Aiptasia pulchella. Non-target DNA amplification of live rock associated taxa exposed the coral pathogenic bacteria Vibrio spp., further suggesting that the marine aquarium trade is also a pathway for the introduction of pathogens. A second component of the study involved the assessment, via formal survey, of the role that pet stores and hobbyists play in the introduction and transmission of marine organisms around South Africa. Irresponsible aquarium pest disposal methods and informal trading pathways were revealed highlighting the need for an education intervention to promote responsible aquarium ownership skills. The third part of the study entailed a national stock inventory of marine aquarium traded fish and revealed that the number of species traded is vast (n = 228) and that 60 % are alien to South African waters. Although the strength of this vector was not defined, this study confirms that the marine aquarium trade is a pathway for the introduction of alien and potentially invasive organisms and serves as the foundation for future research into marine aquarium trade vectors in South Africa. The findings and conclusions presented here should be considered by biosecurity monitoring and management initiatives.