Assessing marine bioinvasions in the Galapagos Islands: implications for conservation biology and marine protected areas

The Galapagos Islands are recognized for their unique biota and are one of the world's largest marine protected areas. While invasions by non-indigenous species are common and recognized as a significant conservation threat in terrestrial habitats of the Archipelago, little is known about the magnitude of invasions in its coastal marine waters. Based upon recent field surveys, available literature, and analysis of the biogeographic status of previously reported taxa, we report 53 non-indigenous species of marine invertebrates in the Galapagos Islands. Forty-eight (90.6%) of these species are newly reported or newly recognized as introduced, a nearly ten-fold increase from the five species previously recognized as nonindigenous. Of these 48 species, 30 (62.5%) were newly discovered in surveys commenced in 2015. Ascidians (11 species), bryozoans (10), polychaetes (9), and hydroids (8) account for 38 (71.7%) of the introduced species. Our analyses further detected 33 cryptogenic invertebrate and algal species and one littoral vascular plant. Most taxonomic groups remain to be assessed for the presence of non-indigenous species. Importantly, the recent field surveys were restricted predominantly to one habitat (harbor biofouling) on two islands, further suggesting that introduced species richness for the Galapagos Islands may be considerably higher. Most of the introduced species treated here were likely brought to the Galapagos by ships. While we presume that most if not all of the many thousands of vessels arriving in the Galapagos Islands since the 1500s had marine animals and plants attached to their hulls, we hypothesize that the general absence in the Islands of extensive shoreline structures (in the form of wharves, docks, pilings, and buoys) until the last half of the 20th century may have constrained extensive colonization by fouling species. The proliferation of shoreline structures may have both provided expanded habitat for non-indigenous species that had earlier colonized natural substrates, as well as having facilitated a 20th and 21st century wave of new invasions in the Galapagos Islands. Our results represent the greatest reported increase in the recognition of the number of invasions for any tropical marine environment in the world. This work suggests that the number and potential ecological impacts of nonindigenous species in tropical marine and maritime habitats may be substantially underestimated in other regions of the world. Our study demonstrates that tropical marine invasions deserve significant attention, not only in a biogeographical, historical, and ecological context, but also from a management perspective, especially in the Galapagos and other high-value conservation areas.