Invasion History

First Non-native North American Tidal Record: 2000
First Non-native West Coast Tidal Record: 2000
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Caulerpa taxifolia was first described from the Virgin Islands in 1802 and has been considered a species with a wide native range in tropical waters of the Atlantic, Pacific, and Indian Oceans (Meinesz and Hesse 1991; Meinesz et al. 2001; Guiry and Guiry 2016). One strain of this plant has been widely used as an ornamental plant in public and private aquaria. The invasive strain, which is widely used in the aquarium trade, has spread into subtropical and warm-temperate waters and is genetically distinct from tropical populations. This strain appears very similar to native populations from Moreton Bay, near Brisbane (Queensland), Australia (Jousson et al. 1998; Weidenmann et al. 2002; Schaffelke et al. 2002; Meusnier et al. 2004).

In 1984, Caulerpa taxifolia was first found growing in waters adjacent to the Oceanographic Museum in Monte Carlo, Monaco. By 1996, C. taxifolia had spread along much of the Western Mediterranean coast from Croatia to Spain (Meinesz 1999; Meinesz et al. 2001). By 2006, it had reached Turkey, in the eastern Mediterranean (Cevik et al. 2007). Other invasions were seen in other parts of the world. In Notojima, Japan, two colonies were seen about 5 m from an aquarium discharge pipe in 1992 and 1993, but they disappeared in the winter of 1994 (Komatsu et al. 2003). In 2000, colonies were discovered in California in Agua Hedionda Lagoon, Carlsbad and Huntington Harbor, southern CA (Jousson et al. 2000, Kaiser 2000). A multi-agency eradication program was started immediately and both populations were successfully eradicated (Williams and Schroeder 2004; Anderson 2005). Other invasions, in the Southern Hemisphere, have been more difficult to control. Caulerpa taxifolia spread from its native range in northern Australia to estuaries and lagoons in New South Wales and South Australia by 2002-2004 (Millar 2004; Wiltshire et al. 2010). Possible vectors included recreational boating, fishing gear, and aquarium transfers (Schaffelke et al. 2002; Glasby and Gibson 2007).

Since the Mediterranean and Californian invasions, attempts have been made to monitor and/or regulate the distribution and sale of Caulerpa spp. in the aquarium trade. In 1999, the US Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) placed the aquarium strain of C. taxifolia on the Noxious Weed List (Walters et al. 2006). Surveys from California in 2001-2002 showed that seven of 50 aquarium stores sold C. taxifolia and 26 sold one or more species of Caulerpa (Zaleski and Murray 2006). In 2001, California prohibited sale of C. taxifolia and eight other Caulerpa species (Walters et al. 2006). A later survey, in 2006, found that out of 43 California stores 23 sold Caulerpa spp. and 4 sold C. taxifolia, although probably not the invasive strain (Diaz et al. 2012). Surveys of Florida stores and US-UK Internet retailers in 2003-2005 found that 25 of 47 aquarium stores sold Caulerpa spp., as did 90 online sites located in the US and UK. Fourteen species of Caulerpa were obtained, including one non-invasive strain of C. taxifolia. The 'aquarium' strain of C. taxifolia was not found. However, the Caulerpa species in this survey were frequently misidentified by retailers and included some potentially invasive species (Stam et al. 2006; Walters et al. 2006). The international nature of the aquarium trade, and its acceleration by the Internet, increases the risk of Caulerpa and other marine invasions, and creates a challenge for regulators and conservationists (Padilla and Williams 2004).

North American Invasion History:

Invasion History on the West Coast:

In June 2000, divers mapping seagrass beds in California (CA) embayments discovered a patch of an unusual seaweed in Agua Hedionda Lagoon, Carlsbad, San Diego County, CA (Kaiser 2000; Anderson 2005). It was quickly identified as Caulerpa and genetic sequences of California specimens were compared with the Mediterranean strain of C. taxifolia (Jousson et al. 2000). In July 2000, populations were discovered in ponds connected to Huntington Harbor, Orange County, CA. A multi-agency eradication program (Southern California Caulerpa Action Team, SCCAT) was started almost immediately after the discovery, with the first control programs beginning with 17 days after the first discovery in Agua Hedionda Lagoon, using chlorine bleach, injected under PVC plastic sheets spread out over the seabed (Williams and Schroeder 2004; Anderson 2005). Laboratory tests indicated that bleach was effective at killing Caulerpa at the doses used in the field. Although the program was initially subject to some controversy (Dalton 2000), the method proved effective and no plants were found after November 2002. In late 2005, SCCAT declared that eradication was successful (Anderson 2005). The overall cost of the eradication program was $7 million dollars (Anderson 2007). A ban was imposed on the sale of Caulerpa taxifolia and 8 other Caulerpa spp., but in 2006, 53% of aquarium stores surveyed sold species of Caulerpa and 4 stores sold C. taxifolia (Diaz et al. 2012). While the ban is imperfect, and difficult to enforce, no other Caulerpa invasions have occurred in California waters (Anderson 2007).

Invasion History Elsewhere in the World:

In 1984, Caulerpa taxifolia was first found growing in waters adjacent to the Oceanographic Museum in Monte Carlo, Monaco. It initially occupied 1 m-2. By 1989, it covered 1 hectare and had survived several winters. A scientist, Alexandre Meinesz, identified the alga in 1989 and reported the occurrence to the Museum, the French and Monaco governments, and the press. The initial responses of the museum and the governments were denial of responsibility for the introduction, and of the likelihood of any negative impacts. The identity and origin of the alga was disputed (Olsen et al. 1998). Consequently, the opportunity for eradication was lost, and the seaweed, dubbed 'Killer Algae' by the press, began to spread rapidly (Meinesz 1999). Genetic studies found that this invasive, cold-tolerant form of Caulerpa taxifolia was observed in an aquarium in Stuttgart, Germany, and distributed to several public aquariums, including the Oceanographic Museum (Jousson et al. 1998). Further studies showed that the likely source of the 'aquarium strain' was the coastal waters around Queensland, Australia (Jousson et al. 2000; Weidenmann et al. 2002).

In July 1990, C. taxifolia was first detected in French waters at Cap Martin, and by September, it had spread 150 km west to Toulon (Meinesz et al. 2001). By 1992, it had reached the Balearic Islands, Spain and Imperia, Italy, on the Ligurian Sea (Meinesz et al. 2001). By 1993, it had spread to Sicily and the Straits of Messina (Meinesz 1999). Colonies of C. taxifolia also appeared in Croatia, on the Adriatic Sea in 1992-1994 (Meinesz 1999; Meinesz et al. 2001; Pecarevic et al. 2013). In 2000, it was discovered in Sousse, Tunisia (Meinesz et al. 2001), although this population was genetically distinct and may represent a separate invasion (Meusnier et al. 2004; Jousson et al. 2013). In 2010, a population of C. taxifolia was found at a Turkish naval base in Izmir, Turkey, the first record in the Aegean Sea (Turan et al. 2011). Overall, the pattern of invasion of C. taxifolia has been quite patchy. On the Mediterranean coast of France, between Monaco and Toulon, C. taxifolia reached its maximum extent around 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 et al. 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).

Another Indo-Pacific species, Caulerpa cylindracea (=C. racemosa var. cylindracea), was first collected in the Mediterranean off Libya in 1990, and now occurs from Turkey and Greece to Spain and Algeria, and now occupies a much greater area than C. taxifolia (Montefalcone et al. 2015). The two species co-occur, but it is unclear whether competition with C. cylindracea is involved in the decline of C. taxifolia (Piazzi et al. 2003; Montefalcone et al. 2015).

The invasive form of Caulerpa taxifolia is apparently derived from populations in or near Queensland, Australia, and has a genotype very similar to those of specimens from Moreton Bay, near Brisbane (Weidenmann et al. 2002; Schaffelke et al. 2002; Meusnier et al. 2004). Prior to the year 2000, C. taxifolia was known in New South Wales, only form Lord Howe Island, far offshore. In 2000, it was found in Fishermans Bay, South Australia; Gunnamatta Bay, Victoria; and Port Hacking, Lake Conjola, and Jervis Bay, New South Wales. It may have been established in these estuaries for 5 to 15 years (Millar 2000). By 2004, C. taxifolia was known from five more estuaries north and south of Sydney (Millar 2004). In 2002, C. taxifolia was discovered in the West Lakes-Port River estuary, near Adelaide, South Australia. The population was eradicated from the lakes, but persisted in the lower estuary (Wiltshire et al. 2010, Burfeind et al. 2013). The genetic diversity of the New South Wales and South Australia populations suggest multiple introductions by multiple vectors included recreational boating, fishing gear, and aquarium releases (Schaffelke et al. 2002; Glasby and Gibson 2007).

In Notojima, Japan, in central Honshu, on the Sea of Japan, two colonies of Caulerpa taxifolia were seen about 5 m from a public aquarium discharge pipe in 1992 and 1993, but they disappeared in the winter of 1994, probably due to low winter temperatures. Genetic tests confirmed that these plants belonged to the invasive aquarium strain. A survey of Japanese public aquariums found that 16 of 51 sites had cultured or exhibited C. taxifolia. The authors recommended that aquarium culture and sale of C. taxifolia be avoided (Komatsu et al. 2003).


Description

The thalli of green algae of the genus Caulerpa lack cell walls and consist of tubular filaments. They are coenocytic, meaning that chloroplast scan move through the whole thallus, making it the equivalne of a cell witn muti[le nuclei. They have horizontal stolons or rhizomes, anchoring rhizoids, and erect photosynthetic branches. The interior of the thallus is reinforced by filamentous ingrowths of wall material, called trabeculae, which gives it a firm texture. The erect branches can have the form of blades, divided fronds, or bunches of globular or shield-like structures. The blades of Caulerpa taxifolia and its relatives (e.g. C. mexicana) are called pinnae, resembling feathers, branching from the stolon in opposite fashion, tapered at the base, and rounded at the tip. The pinnules (branchlets) are also opposite and curved. The rhizoidal filaments are separated by less than 1 cm along the stolon and are 1-10 cm long. Fronds can reach 62 cm in length and the stolons can reach 60-100 cm in length, including branches. Caulerpa taxifolia is a genetically diverse species or species complex, widely distributed in the subtropics and tropics of the Atlantic, Pacific, and Indian Oceans. This description is based on: Bold and Wynne 1978; Meinesz and Hesse 1991; Schneider and Searles 1991; Meinesz 1999; Meinesz et al. 2001; and Guiry and Guiry 2016.

At least three genetically defined strains of Caulerpa taxifolia have been introduced outside their native range. This account is focused on the widespread aquarium-released form of Australian and Indo-Pacific origin (1), established in the Mediterranean Sea (Meinesz 1999; Jousson et al. 1998; Jousson et al. 2000) and southeast Australia (Millar 2004), and eradicated in California and Japan (Jousson et al. 2000; Komatsu et al. 2003). (2) A morphologically and genetically distinct form, C. t. var. distichophylla, also of Australian origin, has been introduced to Turkey and Italy (Jongma et al. 2013). (3) Another genetically distinct form, of unknown origin, has been found in Tunisia (Meusnier et al. 2004; Jongma et al. 2013). Introduced populations, in several southeast Australian estuaries, include multiple genotypes, indicating multiple introductions from northern Australia, possibly (but not definitely) including the Mediterranean-aquarium strain (Schaffelke et al. 2002). Genotypes on the Australian coast appear to divide into two incipient species, a coastal ecotype, that gave rise to invasive genotypes, and an oceanic form associated with clear waters near coral reefs (Meusnier et al. 2004).

Given the geographical range and genetic variety of Caulerpa taxifolia, the identity of the invasive form was fiercely debated. One early hypothesis was that it was a form of C. mexicana, first collected in the eastern Mediterranean in 1939 and probably introduced via the Suez Canal from the Red Sea. Genetic studies confirmed its identity as C. taxifolia, its origins from an aquarium population and its likely origin from populations in the vicinity of Queensland, Australia (Jousson et al. 1998; Olsen et al. 1998; Jousson et al. 2000; Famá et al. 2002; Weidenmann 2002). The invasive Mediterranean strain is distinguished by features of a ribosomal DNA gene and can be detected by a PCR (polymerase chain-reaction) test (Famá et al. 2002).

The invasive form of Caulerpa taxifolia received the moniker 'algue tueuse' (Killer Algae) in the French press as they reported the spread of the seaweed, its impacts, and the controversy over the source of its introduction to the Mediterranean. Although the alga is inedible to many invertebrates, and so is destructive to ecosystems, it is not directly dangerous to humans. 'Killer Algae' is the title of a book by the biologist Alexandre Meinesz, giving a personal account of his experiences during these events (Meinesz 1999).


Taxonomy

Taxonomic Tree

Kingdom:   Plantae
Phylum:   Chlorophycota
Class:   Chlorophyceae
Order:   Caulerpales
Family:   Caulerpaceae
Genus:   Caulerpa
Species:   taxifolia

Synonyms

Fucus taxifolius (Vahl, 1802)
Caulerpa pennata (J.V.Lamouroux, 1809)

Potentially Misidentified Species

Caulerpa mexicana
Native to the western Atlantic - Georgia to Brazil. Introduced into the eastern Mediterranean Sea via the Suez Canal (Schneider and Searles 1991; Guiry and Guiry 2016).

Caulerpa taxifolia var. distichophylla
Caulerpa taxifolia var. distichophylla is considered a genetically distinct but conspecific variety, native to Australia. The fronds are slender, up to 40 mm tall and 1-2 mm wide. It has been introduced to Sicily, Turkey (Levantine coast), Malta, Cyprus, and Greece (Jongma et al. 2013; Schembri et al. 2015; Aplikioti et al. 2015; Chefaoui and Varela-Alvarez 2018).

Ecology

General:

Sexual reproduction is uncommon in the genus Caulerpa, but is known in at least one population of C. taxifolia, from the exposed outer coast of Queensland, Australia. Thalli of this sexually reproducing population can be monecious or dioecious (Wright 2005; Phillips 2009). However, invasive populations of C. taxifolia have been reported to reproduce only asexually, either by expansion of the patch by the growing stolon, or by fragmentation (Ceccherelli and Cinelli 1999; Wright 2005). There is, however, some indirect evidence for sexual reproduction and hybridization in the derivation and breeding of invasive populations (Meusnier et al. 2004; Phillips 2009). Invasive populations in southeastern Australia had smaller fronds and stolons than native populations in Mooreton Bay, Queensland, but achieved greater density and biomass, including a higher density of fragmented fronds (Wright 2005). In the Mediterranean, dispersal of drifting fragments by currents, and human transport of fragments by hull fouling, fishing gear, or other means are the major mechanisms of spread (Belsher and Meinesz 1995; Ceccherelli and Cinelli 1999).

Caulerpa taxifolia was widely thought of as an exclusively tropical alga, so its survival in Mediterranean winters, at 10-12°C was unexpected. A temperature of 15.0-17.5°C is required for growth, with maximal growth at 28°C (Komatsu et al. 1997). The upper lethal temperature is 31°C, suggesting a large potential range for the Mediterranean population (Komatsu et al. 1997). It was thought that the 'aquarium strain' may have been accidentally selected for cold tolerance (Meinesz and Hesse 1991; Komatsu et al. 1997; Meinesz 1999). However, native populations from subtropical Moreton Bay, Queensland, Australia have temperature-survival and growth characteristics similar to introduced populations from the Mediterranean and southeast Australia (Chisholm et al. 2000; Glasby and Gibson 2007; Chefaoui and Varela-Alvarez 2017). In southeastern Australia, C. taxifolia is confined to shallow coastal lagoons and estuaries, and does not occur on the open coast. However, it stops growing below 22 PSU, and salinities below 20 PSU are lethal (West and West 2007). Sudden transfers to a salinity of 10 PSU will kill C. taxifolia in 180 min. and deliberate lowering of salinity to this level is a possible method of eradication in small, confined lagoons (Theil et al. 2007). In the Mediterranean, C. taxifolia occurs at salinities of 38-40 PSU (Turan et al. 2011). Although this alga is rare or absent in intertidal areas, large clumps of C. taxifolia could survive out of the water for ~24 hours, especially when shaded or moist, raising the possibility of transport on ropes and anchors of recreational boats(West et al. 2007).

Mediterranean C. taxifolia is capable of growing at very low light levels, 27 µE m-3s-1, although growth was best at 88-356 µE m-3s-1, all at 25°C. Weak light favors lengthening and branching of the fronds. At a wide range of temperature (20-30°C), light levels (27-356 µE m-3s-1) and photoperiods (10:14, 12:12 and 14:10 h L:D) isolated fragments produced new fronds and stolons within 10 days (Komatsu et al. 1997). The capability for growth at low light explains the occurrence of plants at depths up to 55 to 99 m although it is most abundant at 5-25 m (Meinesz and Hesse 1991; Belsher and Meinesz 1995).

Invasive populations of Caulerpa taxifolia grow in harbors, lagoons, and open coasts, on sandy, rocky, muddy bottoms, and seagrass beds (Posidonia oceanica and Cymodocea nodosa), in the Mediterranean Sea (Meinesz and Hesse 1991). Introduced populations in southeastern Australia are confined to semi-enclosed lagoons (Millar 2002; Glasby 2013; Burfeind et al. 2013), as were the two eradicated populations in southern California (Williams et al. 2012). In Australian lagoons, C. taxifolia's incursions into seagrass meadows (of Posidonia oceanica and Zostera capricorni) mostly occur in disturbed and bare areas (Glasby 2013). In Huntington Harbor, California, populations of Widgeon Grass (Ruppia maritima) were greatly reduced during the Caulerpa invasion. Similar negative effects were observed on Eelgrass (Zostera marina) in Agua Hedionda Lagoon, before the eradication of C. taxifolia (Williams et al. 2002). In the Mediterranean, recruitment of C. taxifolia was better in dead mats of P. oceanica than in bare sand, probably because of the lower near-surface current velocity and the richer nutrients from the dead seagrass (Infantes et al. 2011).

Caulerpa taxifolia, like other Caulerpa, produces a wide range of compounds (notably caulerpenyne and caulerpicine) which discourages fish and invertebrate grazers (Meinez and Hesse 1991). Caulerpa was not an adequate diet for the Mediterranean sea urchin Paracentrotus lividus (Boudouresque et al. 1996). In Australia, several herbivorous organisms, including a fish (Girella tricuspidata), an amphipod (Cymadusa setosa), and a sea hare (Aplysia dactylomela) strongly preferred other algae as food. A polychaete, Platynereis dumerilii antipoda, did survive well while feeding on C. taxifolia, but fed at higher rates on other algae (Gollan and Wright 2006). In toxicity tests, caulerpenyne proved toxic to sea urchin embryos, while another compound of caulerpenyne was toxic to mouse embryos (Lemée et al. 1993). One of the few groups of organisms feeding on Caulerpa spp. are specialized saccoglossan sea slugs. Two native Mediterranean sea-slugs, Oxynoe olivacea and Lobiger serradifalci, feed on native Caulerpa prolifera, but have low feeding rates and low recruitment on C. taxifolia (Thibaut and Meinesz 2000).

Competitors:

Caulera cylindracea

Trophic Status:

Primary Producer

PrimProd

Habitats

General HabitatGrass BedNone
General HabitatRockyNone
General HabitatMarinas & DocksNone
General HabitatUnstructured BottomNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone


Tolerances and Life History Parameters

Minimum Temperature (ºC)10Experimental, survival but no growth at 10-12 C, growth began at 15 to 17 C (Komatsu et al. 1997; Chisholm et al. 2000); Field (Mediterranean, Gacia et al. 1996)
Maximum Temperature (ºC)31.5Experimental (Komatsu et al. 1997); 35 C. Field (Mediterranean, Gacia et al. 1996)
Minimum Salinity (‰)20Field (Lake Conjola, New South Wales) and lab. No growth below 22.5 PSU (West and West 2007)
Maximum Salinity (‰)40Mediterranean Sea, Turkey (Turan et al. 2011)
Maximum Length (mm)1,000Total length of a stolon including branches (Meinesz and Hesse 1991)
Minimum Height (mm)50Meinesz and Hesse 1991, height of a frond was 50-100, at 5-10 cm.
Maximum Height (mm)620Meinesz and Hesse 1991, height of a frond in deep water, below 10 m.
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

The invasive form of Caulerpa taxifolia has been listed as one of the '100 Worst Invaders' for the Mediterranean Sea (Streftaris and Zenetos 2006), Europe (DAISIE 2009) and the world at large (Invasive Species Specialist Group of the World Conservation Union 2016). This alga's dramatic spread in the Mediterranean, the initially chaotic response from governments and the press, and Caulerpa's far-reaching impacts on marine communities and food webs helped raise the awareness of scientists and policy-makers on the issue of biological invasions (Boudouresque et al. 1995; Meinesz 1999; Anderson 2007; Glasby 2013). In particular, the Caulerpa invasion led to increased scrutiny of public aquaria and the private aquarium trade (Diaz et al. 2012; Stam et al. 2006). The invasion also spurred coastal managers to develop strategies for rapid response, with emphasis on eradication (Thresher and Kuris 2004; Locke and Hanson 2009). In the Mediterranean Sea, the areal extent of the invasion reached its peak in 2007, and it has since disappeared from some of the colonized areas (Meinesz et al. 2010). However, a new population was established in Izmir Bay, Turkey in 2010 (Turan et al. 2011). As C. taxifolia declined, another non-native, C. cylindracea (formerly known as C. racemosa, or C. r. var. cylindracea), invaded the Mediterranean in 1990 and now occupies a much large area of the seacoast than C. taxifolia (Boudouresque and Verlaque 2002; Montefalcone et al. 2015). The cause of the decline of C. taxifolia is unclear (Meinesz et al. 2010), although in some cases C. cylindracea can out-compete C. taxifolia (Piazzi and Ceccherelli 2002).

Economic impacts

Aesthetic- The 'aquarium strain' of C. taxifolia provides attractive foliage in home and public aquaria, and has qualities that make it desirable for aquaria, including tolerance to low light, low temperature, and resistance to grazing by herbivorous fish (Meinesz 1999). Consequently, it has been widely sold in the aquarium trade, together with other species of Caulerpa (Stam and Olsen 2006; Zaleski and Murray 2006; Smith et al. 2010; Walters et al. 2006). After the California invasion and eradication, C. taxifollia was officially declared to be a 'Noxious Weed' by the US Department of Agriculture, and banned from sale. California banned the sale of C. taxifollia, and several morphologically similar species (C. mexicana, C. sertulariodes, C. ashmeadii, C. floridana, C. cupressoides, and others that are considered invasive C. racemosa, C. scalpelliformis, C. verticillata) (Walters et al. 2006). These bans appear to have been partially effective, but the sale of algae over the Internet makes the prevention of illegal sales difficult (Walters et al. 2006; Williams et al. 2015).

Eradication- The cautionary story of the Caulerpa invasion in the Mediterranean, and some other successful eradications (Thresher and Kuris 2004), helped prompt a rapid, organized response to the discovery of C. taxifolia in southern California. The fortuitous discovery of the alga during a survey of Eelgrass (Zostera marina) was helpful, as was the small size of the colonies, and the estuaries to be treated. The eradication of Caulerpa taxifolia in Agua Hedionda Lagoon and Huntington Harbor, using plastic sheets and chlorine bleach, cost US$ 7.6 million for eradication (Kaiser 2000; Anderson 2005; Anderson 2007). Motivations for the eradication program included biotic integrity of native seaweed and seagrass, recreational value (diving, boating, fishing), and coastal property values. The affected lagoons do not support commercial fisheries and the probability of extensive spread in the open coast is unlikely. The Mediterranean and California invasions, as well as the Atlantic Lionfish invasions, have led to increased scrutiny and regulation of the aquarium industry, including surveys of Caulerpa spp. being sold in California, Florida, New Zealand, and Brazil (Stam and Olsen 2006; Zaleski and Murray 2006; Smith et al. 2010; Walters et al. 2006; Smith et al. 2010; Williams et al. 2015; Torrano-Silva et al. 2013).

Biological control was studied as a possible means to reduce outbreaks of C. taxifollia in the Mediterranean. This alga, like others of its genus including native Mediterranean species, concentrates a wide range of compounds (notably caulerpenyne and caulerpicine) which renders it inedible to most grazers. Two native saccoglossan sea slugs (Oxynoe olivacea and Lobiger serradifalci) were observed to eat C. taxifollia, though at very low rates. Mass rearing would be required to control the invasive alga (Thibaut and Meinesz 2000). An exotic saccoglossan, Elysia subornata, from the Caribbean was found to graze C. taxifollia at higher rates, but would not survive Mediterranean winters (Thibaut et al. 2001).

Fisheries- The dense growths of C. taxifolia in the Mediterranean have interfered with fishing gear by clogging nets (Meinesz 1999). The effects on populations of commercial fishes, due to changes in habitat and food webs, is more difficult to determine, but some fishes appear to have reduced abundance in C. taxifollia beds (Relini et al. 2000; Longepierre et al. 2005).

Ecological Impacts

Competition- In the Mediterranean, southeastern Australia, and California lagoons, the invasive form of Caulerpa taxifolia was found to invade and at least partially replace native macroalgal and seagrass communities (Meinesz and Hesse 1991; Boudouresque et al. 1995; Williams and Grosholz 2002; Glasby 2013). However, many of the invaded sites are experiencing disturbances from other sources as well, including weather, boats, and fishing gear (Meinesz et al. 2001; Turan et al. 2011; Glasby 2013). The California lagoons were highly disturbed, and in the case of Huntington Harbor, more or less artificial (Williams and Grosholz 2002; Anderson 2005). In Australian lagoons, C. taxifolia colonized cleared areas within meadows of the seagrass Posidonia australis, and persisted but did not replace the seagrasses (Glasby 2013). However, once established, C. taxifolia tends to resist displacement. Chemical compounds from C. taxifolia inhibited growth of the native Mediterranean brown alga Cystoseira barbata f. aurantia and Gracilaria bursa-pastoris (Ferrer et al. 1997). The effects of these compounds on seagrasses is less clear, since some (e.g. Posidonia oceanica) produce their own defensive compounds (Pergent et al. 2008). However, C. taxifolia, once established in a colony of the Mediterranean seagrass Posidonia oceanica, can affect the growth of the seagrass, causing it to produce vertical, rather than horizontal shoots, limiting the recovery of the seagrass. This is probably due to chemical compounds released by C. taxifolia (Molenaar et al. 2009).

Habitat Change- Caulerpa taxifolia invasions in the Mediterranean, Australia, and California, have replaced diverse macroalgal and seagrass communities with a uniform community of fern-like fronds, with few epiphytes. Caulerpa taxifolia's defensive chemical compounds prevent most epibionts from attaching and discourage most grazers (Meinesz and Hesse 1991; Ferrer et al. 1997). In the Mediterranean, total abundances of several groups of epifauna, particularly amphipods and mollusks were reduced, compared to uninvaded sites (Bellan-Santini et al. 1996; Francour et al. 2009). In New South Wales estuaries, the abundance of epifauna was correlated with C. taxifolia, suggesting greater use of the plants as shelter, but the abundance of infauna was negatively correlated (McKinnon et al. 2009; Gribben et al. 2013). Compared to seagrass beds, dense growths of C. taxifolia reduce water movement, and increase the accumulation of silt and organic detritus (Galluci et al. 2012). In Australia, negative effects on infauna have been noted, due to the accumulation of detritus containing deterrent compounds, and prone to hypoxia and the release of hydrogen sulfide (Tanner et al. 2013; Bishop and Kelaher 2013). Effects on an Australian bivalve (Anadara trapezia) were mixed, with negative effects of sediment hypoxia partly offset by reduced predation (Byers et al. 2010; Wright et al. 2012; Gribben et al. 2013). Effects on fishes are complex and are often species-specific, reflecting differing responses of their invertebrate prey (Relini et al. 1998; Relini et al. 2000; York et al. 2006).

Food/Prey- Caulerpa taxifolia is chemically defended by a variety of organic compounds and is inedible or toxic for most marine herbivores. Unlike most algae and seagrasses, it also has few or no epiphytes, which further decreases feeding opportunities for herbivores (Meinesz and Hesse 1991). Chemical compounds from C. taxifolia can also inhibit the growth of adjacent macroalgae (Ferrer et al. 1997). Experiments with a variety of herbivores, including sea urchins, amphipods, polychaetes, sea hares, and fishes, indicate that it is avoided or is inadequate for growth (Boudouresque et al. 1996; Davis et al. 2005; Gollan and Wright 2006). There are a few saccoglossan sea slugs which are Caulerpa specialists, including the Mediterranean natives, (Oxynoe olivacea and Lobiger serradifalci), which normally feed on C. prolifera, but will graze on C. taxifolia at low rates (Thibaut and Meinesz 2000). Detritus from C. taxifolia, reduced the abundance and species richness of infaunal communities, possibly because of deterrent chemical compounds (Tanner 2011).

Toxicity- Caulerpa taxifolia, like other members of its genus, produces a wide range of compounds (notably caulerpenyne, caulerpicine) which discourage grazers, epiphytes, and competing macroalgae (Meinesz and Hesse 1991; Ferrer et al.1997). The extent to which these cause mortality or illness in animals is unclear. In toxicity tests, caulerpenyne proved toxic to sea urchin embryos, while another compound caulerpenyne compound was toxic to mouse embryos (Lemée et al. 1993). One concern was that toxins from C. taxifolia might be passed to humans by consuming herbivorous fish (Salema Porgy, Sarpa salpa), which has been known to accumulate algal toxins (Meinesz and Hesse 1991). However, toxicity assays with human cells suggested that toxic effects on humans would be minimal (Parent-Massin et al. 1996).

Regional Impacts

NEP-VIPt. Conception to Southern Baja CaliforniaEconomic ImpactAesthetic
The eradication of Caulerpa taxifolia in southern California, using plastic sheets and chlorine bleach cost US$ 7.6 million for eradication (Anderson 2005; Anderson 2007). Motivations for the eradication program included biotic integrity of native seaweed and seagrass, recreational value (diving, boating, fishing), and coastal property values. The affected lagoons do not support commercial fisheries, and the probability of an extensive spread on the open coast is unlikely.
MED-IINoneEcological ImpactCompetition
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).
MED-IINoneEcological ImpactHabitat 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).
MED-IINoneEcological ImpactFood/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).
MED-IINoneEcological ImpactToxic
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).
AUS-XNoneEcological ImpactCompetition
In experiments, Caulerpa taxifolia colonized cleared areas within meadows of the seagrass Posidonia australis, and persisted but did not replace the grass. Effects on another seagrass, Zostera capricorni were harder to interpret, because of the decline of Z. capricorni in both experimental and control plots (Glasby 2013),
AUS-XNoneEcological ImpactHabitat Change
Effects of Caulerpa taxifolia on benthic communities were complex and sometimes contradictory. Overall, the dense physical structure of the C. taxifolia beds, increases deposition of silt and organic material, and reduces water movement, contributing to anoxia in the sediments, to a greater degree than found in native seagrass beds (Posidonia oceanica, Zostera capricorni ). Caulerpa taxifolia beds had similar meiofaunal species richness to native seagrass beds, but had many species absent in the seagrass sediments (Galluci et al. 2012). The bivalve Anadara trapezia had somewhat reduced predation in C. taxifolia beds, due to shelter, but had reduced health and predator resistance, due to anoxia, sulfide, and bacteria (Byers et al. 2010). Recruitment of A. trapezia was good, probably due to lack of predation, but reproductive output of females were reduced (Gribben and Wright 2006a; Gribben and Wright 2006b; Gribben et al. 2009; Gribben et al. 2013). In response to hypoxia in the sediments in C. taxifolia beds, A. trapezia altered its behavior, emerging from the sediment (Wright et al. 2010), but also showed morphological adaptations (shell morphology, gill mass, and palp mass), possibly due to natural selection (Wright et al. 2012).

Overall, the composition and abundance of the epifauna was positively associated with C. taxifolia biomass, but abundance of infauna was negatively correlated (McKinnon et al. 2009; Gribben et al. 2013). Benthic communities receiving high doses of detritus from plots colonized by C. taxifolia had reduced abundance of deposit-feeding animals, after 4 months of incubation, compared to those receiving equal doses of seagrass detritus (P. oceanica or Z. capricorni). The C. taxifolia detritus is especially prone to develop hypoxia, compared to the seagrass detritus (Bishop and Kelaher 2013).

Fish abundance was similar, but species diversity was reduced in Caulerpa taxifolia beds compared to seagrass beds. Gobiid fishes were more abundant in C. taxifolia, but sygnathids (seahorses and pipefishes) and monacanthids (filefies) were reduced (York et al. 2006).
AUS-XNoneEcological ImpactFood/Prey
In Australia, several herbivorous organisms, including a fish (Girella tricuspidata), an amphipod (Cymadusa setosa), and a sea hare (Aplysia dactylomela strongly preferred other algae to Caulerpa tiaxifolia as food. A polychaete, Platynereis dumerilii antipoda did survive well while feeding on C. taxifolia, but fed at much higher rates on other algae (Gollan and Wright 2006). Extracts of C. taxifolia added to agar disks, had weak negative effects on the feeding of snails and fishes (Davis et al. 2005). Detritus from C. taxifolia, added to sediment, reduced the abundance and species richness of infaunal communities, possibly because of deterrent chemical compounds (Tanner et al. 2010).
NEP-VIPt. Conception to Southern Baja CaliforniaEcological ImpactCompetition
Before its eradication, Caulerpa taxifolia greatly reduced the abundance of Widgeon Grass Ruppia maritima in Huntington Harbor and Eelgrass (Zostera marina) in Agua Hedionda Lagoon (Williams and Grosholz 2002).
NEP-VIPt. Conception to Southern Baja CaliforniaEcological ImpactHabitat Change
The Caulerpa taxifolia adversely affected seagrass beds (Widgeongrass Ruppia maritima) in Huntington Harbor and Eelgrass (Zostera marina) in Agua Hedionda Lagoon, nursery areas for fishes and invertebrates (Williams and Grosholz 2002). The eradication program had an even larger, but temporary effect, killing much of the benthic biota. However, some benthic invertebrates and eelgrass seeds survived the chlorine treatment (Anderson 2005).
P023_CDA_P023 (San Louis Rey-Escondido)Economic ImpactAesthetic
The eradication of Caulerpa taxifolia in southern California, using plastic sheets and chlorine bleach cost US$ 7.6 million for eradication (Anderson 2005; Anderson 2007). Motivations for the eradication program included biotic integrity of native seaweed and seagrass, recreational value (diving, boating, fishing), and coastal property values. The affected lagoons do not support commercial fisheries, and the probability of an extensive spread on the open coast is unlikely. Agua Hedionda Lagoon is the larger of the two areas, ca. 150 ha compared to about 2 ha for the affected ponds in Huntington Harbor, so most of the economic impact of the invasion and eradication occurred in Agua Hedionda (Williams and Grosholz 2002; Anderson 2005).
P023_CDA_P023 (San Louis Rey-Escondido)Ecological ImpactCompetition
Before its eradication, Caulerpa taxifolia greatly reduced the abundance of Eelgrass (Zostera marina in Agua Hedionda Lagoon (Williams and Grosholz 2002).
P023_CDA_P023 (San Louis Rey-Escondido)Ecological ImpactHabitat Change
The Caulerpa taxifolia adversely affected seagrass beds (Eelgrass, Zostera marina in Agua Hedionda Lagoon), nursery areas for fishes and invertebrates (Williams and Grosholz 2002). The eradication program had an even larger, but temporary effect, killing much of the benthic biota. However, some benthic invertebrates and Eelgrass seeds survived the chlorine treatment (Anderson 2005).
P050San Pedro BayEconomic ImpactAesthetic
The eradication of Caulerpa taxifolia in southern California, using plastic sheets and chlorine bleach cost US$ 7.6 million for eradication (Anderson 2005; Anderson 2007). Motivations for the eradication program included biotic integrity of native seaweed and seagrass, recreational value (diving, boating, fishing), and coastal property values. The affected lagoons do not support commercial fisheries, and the probability of an extensive spread on the open coast is unlikely. The two affected ponds in Huntington Harbor were only 1.2 ha each, compared to Agua Hedionda Lagoon, ca. 150 ha compared to about 2 ha for so most of the economic impact of the invasion and eradication occurred in Agua Hedionda (Williams and Grosholz 2002; Anderson 2005).
P050San Pedro BayEcological ImpactCompetition
Before its eradication, Caulerpa taxifolia greatly reduced the abundance of Widgeon Grass Ruppia maritima in Huntington Harbor (Williams and Grosholz 2002).
P050San Pedro BayEcological ImpactHabitat Change
Caulerpa taxifolia adversely affected seagrass beds (Widgeon Grass Ruppia maritima) in Huntington Harbor nursery areas for fishes and invertebrates (Williams and Grosholz 2002). The eradication program had an even larger, but temporary effect, killing much of the benthic biota. However, some benthic invertebrates survived the chlorine treatment (Anderson 2005).
MED-IINoneEcological ImpactTrophic 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).
MED-IINoneEconomic ImpactAesthetic
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).
MED-IINoneEconomic ImpactFisheries
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).
AUS-VIINoneEcological ImpactHabitat Change
Caulerpa taxifolia in the Port River-Barker Inlet estuary, South Australia, supported a much greater (4-9X) abundance of epifauna than a native seagrass bed (Zostera capricorni, with ophiuroids (brittle stars), in particular being more abundant in C. taxifolia. Infauna was slightly less abundant in the Caulerpa bed than in the Zostera bed (Tanner 2012).
MED-VIINoneEcological ImpactHabitat Change
Sediments covered by Caulerpa taxifolia had greatly reduced abundace and dviersity of meiofauna, in comparison with beds of the native seagrass Posidonia oceanica (Cvitkovic et al. 2017).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
MED-II None 1984 Def Estab
MED-III None 1993 Def Estab
MED-IV None 1993 Def Estab
MED-VII None 1994 Def Estab
NEP-VI Pt. Conception to Southern Baja California 2000 Def Extinct
AUS-XII None 0 Native Estab
AUS-X None 2000 Def Estab
NWP-4a None 1992 Def Failed
P050 San Pedro Bay 2000 Def Extinct
P023 _CDA_P023 (San Louis Rey-Escondido) 2000 Def Extinct
SP-IV None 0 Native Estab
AUS-VII None 2002 Def Estab
MED-VI None 2010 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude

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