The role of herbivory and fouling on the invasive green alga Caulerpa filiformis in temperate Australian waters

Abstract

The green macroalga Caulerpa filiformis is rapidly dominating algal assemblages in shallow subtidal regions along the New South Wales (NSW) coast. Given that invasive species are known for their competitive superiority, the interactions between C. filiformis and herbivores and fouling species was investigated and were compared with those co-occurring native species. Extensive field surveys were carried out to assess purported damage from herbivores, and co-occurrence of C. filiformis with herbivorous fish and invertebrate species. Signs of herbivory on C. filiformis were visible, and several common herbivorous invertebrates and fish co-occurred with the alga. Laboratory and field feeding assays with fresh algae indicated that generalist invertebrate herbivores such as Turbo torquatus did not consume C. filiformis, whereas herbivorous fish did consume C. filiformis but not in preference to other palatable algae. C. filiformis was fouled at similar concentrations and with similar epiphytic species to other co-occurring algae. Thus the ability of C. filiformis to deter herbivory and fouling by using biotic deterrents (both chemical and structural) is limited and unlikely to be the major factor driving its successful invasion into NSW habitats.

Effectiveness of the California State Ban on the Sale of Caulerpa Species in Aquarium Retail Stores in Southern California

“…Numerous other Caulerpa species, including C. racemosa subspecies, C. scalpelliformis, C. brachypus, and C. filiformis, have invaded other regions of the world (Davis and others 1997;others 2003, 2004;Jacoby and others 2004;Ruitton and others 2005;Cummings and Williamson 2008). In the previous study by Zaleski and Murray (2006), distributions of the 11 taxa found in aquarium retail stores included at least 8 that have geographic distributions extending into temperate waters.…”

“…Following the Mediterranean Sea invasion, the aquarium strain of C. taxifolia invaded Australian (Schaffelke and others 2002) and southern California waters (Jousson and others 2000) in 2000; California introductions resulted in the expenditure of over $7.7 million U.S. dollars for an apparently successful eradication effort (Merkel and Associates, Inc. 2006). Besides C. taxifolia, other Caulerpa species, such as various C. racemosa subspecies, C. scalpelliformis, C. brachypus, and C. filiformis, have invaded numerous locations, including the Mediterranean Sea, Australia, and Canary Islands (Davis and others 1997;others 2003, 2004;Jacoby and others 2004;Ruitton and others 2005;Cummings and Williamson 2008); the vectors for these introductions are unclear.…”

Beyond the border: Effects of an expanding algal habitat on the fauna of neighbouring habitats

“…An asterix in the x-axis labels indicates a significant difference between isolated and edge habitats. be a deterrent to marine invertebrates (Paul et al, 2001) and C. filiformis is a low preference food for local marine herbivores (Cummings and Williamson, 2008;Davis et al, 2005). Close proximity to chemically-deterrent plants in the terrestrial environment (Atsatt and O'Dowd, 1976), and macroalgae in marine environments (Pfister and Hay, 1988) can result in associational resistance, where a palatable plant is less likely to be detected by herbivores when surrounded by an unpalatable plant.…”

“…in the Mediterranean, Tuya et al, 2014;V azquezLuis et al, 2008). Species of Caulerpa produce an array of non-polar secondary compounds (caulerpenynes, Paul et al, 2001) that result in tissues from this species being low preference foods for most marine herbivores (Cummings and Williamson, 2008;Davis et al, 2005). Secondly, the fauna associated with macrophytes is known to be influenced by the spatial arrangement of habitat patches.…”

Relationships between the spread of Caulerpa filiformis and fish communities on temperate rocky reefs

“…This generally occurred during rapid visual counts as we came closer to these fishes causing them to actively hide, a well‐known behaviour documented across underwater visual census techniques (Dearden et al ., ). Some fish herbivores do consume C. filiformis in the field (Cummings & Williamson, ), however, this data was based on bite marks and it is unknown whether actual consumption occurred.…”