Invasion
Invasion Description
1st record; Monaco, near Oceanographic Museum/Monaco/Mediterranean Sea (1984)
Caulerpa taxifolia is a cosmopolitan tropical species. The Mediterranean strain, is identical to a strain of C. taxifolia kept in many public and private aquaria (Jousson et al. 1993; Jousson et al. 2000) and is closely related to a wild population from Moreton Bay, Australia. In 1984, plants of this species were found growing in the sea, adjacent to the Oceanographic Museum of Monaco. By 1996, C. taxifolia had spread through much of the Eastern Mediterranean, from Croatia to Spain (Meinesz 1999). On the Mediterranean coast of France, between Monaco and Toulon, C. taxifolia reached its maximum extent, in 2007, but by 2009 showed regression, with many colonies in decline, and no new ones established. The causes of the regression are unclear, and are not simply connected to low winter temperature (Meinesz 2010; Turan et al. 2011). A similar decline was observed along the adjacent Ligurian coast of Italy from 2008 to 2013 (Montefalcone et al. 2015).
Geographic Extent
St. Cyprien/France/Mediterranean Sea (1991 Monaco, near Oceanographic Museum/Monaco/Mediterranean Sea (1984, Meinesz et al. 2001); St. Cyprien/France/Mediterranean Sea (1991, Meinesz et al. 2001); Mallorca, Balearic Islands/Spain/Mediterranean Sea (1992, Meinesz et al. 2001); Imperia/Italy/Ligurian Sea (1992, Meinez et al. 1999); Tuscany south of Leghorn/Italy/Ligurian Sea (2000, Ceccherelli et al. 2002, 43j28V24W N and 10j19V42W E)
Vectors
| Level | Vector |
|---|---|
| Probable | Aquatic Plant Shipments |
Regional Impacts
| Ecological Impact | Competition | |
| When the invasive form of Caulerpa taxifolia, began to spread from the vicinity of the Oceanographic Museum in Monaco, it began to replace native macroalgal and seagrass communities, with seaweeds of various height and structure were transformed into monospecific Caulerpa meadows (Verlaque and Fritayre 1994; Meinesz 1999). In particular, the seagrass Posidonia oceanica showed decreases in leaf number and thickness, and signs of necrosis when beds were invaded by C. taxifolia (Meinesz and Hesse 1991; Boudouresque et al. 1995). However, a later analysis suggests that while C. taxifolia increases its growth rate in the presence of P. oceanica, it was unable to outgrow the seagrass (Pergent et al. 2009). Caulerpa taxifolia was also reported to replace the seagrass Cymodocea nodosa. (Meinesz and Hesse 1991; Boudouresque et al. 1995). However, invasion of Posidonia oceanica by C. taxifolia was likeliest when the meadows were already disturbed and degraded and had patches of bare substrate (Montefalcone et al. 2010; Glasby 2013). (Meinesz and Hesse 1991; Boudouresque et al. 1995). Once established inside a P. oceanica, C. taxifolia affected the growth of the seagrass, causing it to produce vertical, rather than horizontal shoots, limiting the recovery of the seagrass (Molenaar et al. 2009). | ||
| Ecological Impact | Habitat Change | |
| Caulerpa taxifolia colonized hard and soft substrates along the Mediterranean coast of France, replacing native macroalgal communities on rocky substrates and seagrass (Posidonia oceanica) meadows. Species richness of invertebrate taxa was not greatly affected, but total abundances of several groups, particularly amphipods and mollusks, were reduced, compared to uninvaded sites (Bellan-Santini et al. 1996; Francour et al. 2012). A fish community in a C. taxifolia bed had similar species richness, but a lower abundance than in a seagrass (Cymdocea nodosa) bed (Relini et al. 1998). In another survey, using commercial fishing gear, Relini et al. (2001) found higher species richness and abundance in C. taxifolia beds compared to seagrass beds, but some commercially valuable larger species were absent in C. taxifolia beds. An unusual response to the habitat change caused by C. taxifolia was an increase in frequency of green color patterns in the fishes Symphodus ocellatus, Symphodus roissali and Coris julis (Labridae, Wrasses), all of which can control their coloration, adapting to a deep green background (Arigoni et al. 2002). | ||
| Ecological Impact | Food/Prey | |
| Caulerpa taxifolia was found to be a poor food for the sea urchin Paracentrotus lividus. Consumption was much smaller than with native algae, and the animals had diminished righting behavior and loss of spines (Boudouresque et al. 1996). Among the few animals known to consume C. taxifolia are native saccoglossan sea slugs, Oxynoe olivacea and Lobiger serradifalci, which normally feed on the native C. prolifera. These organisms were studied as potential biocotrol organisms. Due to their low abundance and grazing rate, they would have to be cultured and released in large numbers (Thibaut and Meinesz 2002). Lobiger serradifalci turned out to damage and fragment C. taxifolia so much that it contributed to its reproduction (Zuljevic et al. 2001). Foodwebs of dead meadow areas colonized by C. taxifolia have reduced diversity and abundance of native macroalgae, especially turf and encrusting species, increasing organic matter and sulfide levels, as well as microbial activity in the sediments (Deudero et al. 2014). | ||
| Ecological Impact | Toxic | |
| Caulerpa taxifolia, like other Caulerpa, produces a wide range of compounds (notably caulerpenyne, caulerpicine) which discourage grazers (Meinez and Hesse 1991). These compounds defend against grazers and epiphytes, and also competing macroalgae. Extracts from C. taxifolia inhibited growth of the brown alga Cystoseira barbata f. aurantia and Gracilaria bursa-pastoris(Ferrar et al. 1997) In toxicity tests, caulerpenyne proved toxic to sea urchin embryos, while another compound, 20,11 epoxy caulerpenyne was toxic to mouse embryos (Lemee et al. 1993). Toxicity assays with human cells (skin cells, primary cultures of melanocytes and keratinocytes, immortalized keratinocytes, and bone marrow cells) suggested that toxic effects on humans are minimal (ParentMassin et al. 1996). | ||
| Ecological Impact | Trophic Cascade | |
| Dense mats of Caulerpa taxifolia have negative effects on a bottom-feeding fish (Striped Red Mullet, a goatfish, Mullus surmuletus), limiting the access to prey and decreasing foraging success (Longepierre et al. 2005). | ||
| Economic Impact | Aesthetic | |
| Caulerpa taxifolia replaced diverse seaweed and invertebrate communities with monotonous, uniform meadows, affecting diving and tourism (Meinesz 1999). A successful control campaign was carried out in the waters around the Parc National de Port-Cros, an island near St. Tropez, using groups of 30-60 volunteer divers doing annual surveys and removals, since 1994. However, this must be considered a small-scale pilot program. By 2010, C. taxifolia was no longer seen in the park's waters, although this may have been part of the general decline in the Mediterranean (Meinesz et al. 2010). | ||
| Economic Impact | Fisheries | |
| Caulerpa taxifolia interferes with fisheries in two ways. (1) The dense masses of fronds clog nets and other fishing gear. (2) Some commercially important fishes (Pagellus erythrinus, Pagrus pagrus, and Solea lascaris) are scarce in Caulerpa beds (Relini et al. 2001). | ||