Caulerpa prolifera

Invasion History

First Non-native North American Tidal Record: 2021
First Non-native West Coast Tidal Record: 2021
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Caulerpa prolifera has a wide native range in the warm-temperate-tropical western and eastern Atlantic, the Mediterranean Sea, and the Indo-Pacific (Guiry and Guiry 2021). In the Western Atlantic, it ranges from North Carolina to central Brazil (Alphin,et al. 1997; Brayner et al. 2008; Carneiro, et al. 2019; Cocentino et al. 2021; US National Museum of Natural History, Department of Botany, 2021; Global Biodiversity Information Facility 2021). In the Eastern Atlantic, it ranges from the Gulf of Cadiz, Spain to the Canary Islands (Guiry and Guiry 2021). It was described by Forsskål, from Alexandria, Egypt, in 1775, as Fucus prolifer, and redescribed by Lamoreaux in 1809 (Boisset et al. 2015). Caulerpa prolifera is found through the Mediterranean Sea, from Spain and Morocco to the Black Sea and Egypt (Gallardo et al. 1993). In the Indo-Pacific, it is found from Tanzania to China, Palau, and Fiji (Guiry and Guiry 2021; US National Museum of Natural History, Department of Botany, 2021). Genetic comparisons show that Western Atlantic populations were distinct, and East Atlantic and Mediterranean populations show a lack of genetic connectivity. Mediterranean populations were more closely related to Indo-Pacific populations, suggesting past or present gene flow (Varela-Alvarez et al. 2015).

Caulerpa prolifera shows a pattern of range expansions or fluctuations at the edges of its range. It was first reported from the Azores in 2013, on Sao Miguel and Faial Islands, but the authors considered natural dispersal possible, by the Gulf Stream (Cacabelos et al. 2015). This alga was was established in the Spanish (eastern) part of the Gulf of Cadiz, but was found in the Ria Formosa in 1805 and 1847 but did not become established in the Ria Formosa until 2011. Genetic evidence suggested that the new population was introduced from the Mediterranean (Cunha et al, 2015; Parreira et al. 2021). In addition, C. prolifera has also been spreading through the Suez Canal (Hegazi 2006; Gab-Alla 2007). 

Caulerpa prolifera is well established on the East Coast of North America, south of Cape Hatteras, and in the western Gulf of Mexico (Guiry and Guity 2021; US National Museum of Natural History, Department of Botany, 2021). However, the first collection in Texas occurred in the Laguna Madre in 1998 (Strenth 2001).

On the California West Coast in 2021, a diver noticed extensive growths of an unfamiliar seaweed near China Cove, near the mouth of Newport Bay, California (Paglia 2021; Ritchie 2021). A survey revealed that it was about 200 m² of C. prolifera covering 1.2 hectares of Bay bottom. After a systematic survey, in July 2021 divers used suction hoses to discharge plants into a filtration bag with 1mm mesh and the algae fragments were filtered out, while the water was returned to the harbor. Surveys will be continued after the eradication efforts to detect any remaining plants (Southern California Caulerpa Action Team, 2021). The public is discouraged from collecting or touching the algae as it is extremely prone to breaking up into small reproductive fragments, and is advised instead to photograph it and send the pictures to local agencies (Southern California Caulerpa action team, 2021). The probable vector for introduction in West Coast waters is the marine aquarium industry/hobby market. After the introduction and eradication of the invasive form of Caulerpa taxifolia in Agua Hedionda Lagoon and Huntington Harbor, the state of California banned C. taxifolia and 9 other species, including C. prolifera.

North American Invasion History:

Invasion History on the West Coast:

In April, 2021, a diver noticed extensive growths of an unfamiliar seaweed, near China Cove, near the mouth of Newport Bay, California (Paglia 2021; Ritchie 2021). An initial survey in April 2021 indicated that there were about 200 m² of C. prolifera, spread over 1.2 hectares of Bay bottom, including rooted patches and loose clumps, and plants attached to drifting algae. Caulerpa prolifera is extremely prone to breaking up into small, reproductive fragments, so the public is discouraged from collecting or touching the algae, and advised just to photograph it, and send the pictures to local agencies. Swimming and boating in the infested area is discouraged (Southern California Caulerpa Action Team 2021). Because of strong currents and wave action the methods used to eradicate another species C. taxifolia, such as covering the bottom with plastic and pumping chlorine underneath, was not feasible. In addition, hand removal of C. prolifera alone lead to fragmentation. After a systematic survey, in July 2021 divers instead used suction hoses to discharge plants into a filtration bag with 1mm mesh and the algae fragments were filtered out, while the water was returned to the harbor. Surveys will be continued after the eradication efforts to detect any remaining plants (Southern California Caulerpa Action Team, 2021).  In September 2023, C. prolifera was seen by a diver near Coronado Cays, San Diego. Another eradication program is planned (California Department of Fish and Wildlife 2023).
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The probable vector for introduction is the marine aquarium industry/hobby market. In surveys of California aquarium stores in 2001–2002 and again in 2005–2006, C. prolifera was found in 6% of 43–50 aquarium stores surveyed (Zaleski and Murray 2006; Diaz et al. 2012). After the introduction and eradication of the invasive form of Caulerpa taxifolia in Agua Hedionda Lagoon and Huntington Harbor, the state of California banned C. taxifolia and 9 other species, including C. prolifera. In general, the ban on the sale of Caulerpa spp. was found to be relatively ineffective. Caulerpa spp. are difficult to identify, and sales on the internet and informal trading among aquarists make it difficult to control the use of Caulerpa spp. or their disposal into natural waters (Dias et al. 2012).

Invasion History Elsewhere in the World:

Caulerpa prolifera is native to the eastern end of Mediterranean Sea, but has been spreading rapidly through the Suez Canal, reaching the Bitter Lakes, near the Red Sea end of the canal (Hegazi 2006; Gab-Alla 2007).

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Description

Caulerpa prolifera is a green alga from family Caulerpaceae. Caulerpa prolifera grows in the form of a long stolon spreading across sediments or rocks with stipes supporting leaf-like blades (thalli). Genus Caulerpa thalli lack cell walls and consist of tubular filaments. They are coenocytic, meaning that chloroplasts can move through the whole thallus, making it the equivalent of a cell with multiple 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 of Caulerpa spp. grow on a stipe, above the stolon, and can have the form of blades, divided fronds, or bunches of globular or shield-like structures (Schneider and Searles 1991). The blades of Caulerpa prolifera are leaf-like, elongated and ellipsoid, with smooth edges. Fronds range from 30 to 150 mm, and 3–15 mm width (Schneider and Searles 1991). The size, shape, and spacing of the blades can vary with environmental conditions, with larger, longer, and more widely spaced blades in shade, and closer, smaller, and rounder blades in bright sun (Collado-Vides 2002). Caulerpa prolifera is monophyletic throughout its range (Fama et al. 2002). A genetic boundary was seen between Mediterranean and Atlantic populations, but with a closer affinity between Mediterranean and Indo-Pacific populations (Varela-Alvarez et al. 2015).

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Taxonomy

Ecology

General:

Caulerpa prolifera grows in the form of a long stolon spreading across sediments or rocks with stipes supporting leaf-like blades. The stolon produces many adhesive rhizoids which attach it to surfaces or sand grains (Friedlander et al. 2006). Caulerpa thalli lack cell walls so chloroplasts and nutrients can move freely through the whole colony. Sexual reproduction is uncommon in the genus Caulerpa. However, reproduction by fragmentation is very frequent in Caulerpa prolifera. In experiments, only fragments that included stalk and stolon produced near rhizoids (Smith and Walters 1999).

Caulerpa prolifera's native range runs from warm-temperate climates (Mediterranean Sea, southeastern North America) to the tropics (Savva et al. 2013; Guiry and Guiry 2021; US National Museum of Natural History, Department of Botany 2021). A temperature of 13–33 °C is required for growth, with maximal growth at 28°C. The upper limit for growth is 33°C, suggesting a large potential range (Savva et al. 2013). Caulerpa prolifera is reported to range into the Black Sea, with a salinity of ~18 PSU (Gallardo et al. 2013), and has been reported from the Suez Canal (Gab-Alla 2007). Caulerpa prolifera occurs on rocky, sandy, and muddy bottoms, often in seagrass beds. In some locations C. prolifera appears to coexist with seagrasses in a stable relationship, while in others, C. prolifera appears to displace the native grasses. In Tampa Bay, C. prolifera rapidly colonized experimentally disturbed areas in beds of the native seagrass Halodule wrightii, (Shoal Grass) and could replace it if disturbance persists (Stafford and Bell 2006). Caulerpa prolifera has lower light requirements than H. wrightii and can grow in deeper or more turbid waters, but the two species can coexist in undisturbed habitats (Taplin et al. 2005). In other habitats, C. prolifera can replace native seagrasses (Hegazy 2008; Tuya et al. 2013).

Food:

Consumers:

Competitors:

Culerpa taxifolia, other macroalgae

Trophic Status:

Primary Producer

PrimProd

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Habitats

General Habitat	Grass Bed	None
General Habitat	Unstructured Bottom	None
General Habitat	Canals	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None

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Life History

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	13.5	Savva et al. 2018
Maximum Temperature (ºC)	33.1	Savva et al. 2018
Minimum Salinity (‰)	18	Based on occurrence in Black Sea
Maximum Salinity (‰)	43	Field, Suez Canal, Gab-Alla 2007
Minimum Width (mm)	3	Schneider and Searles 1991
Maximum Width (mm)	15	Schneider and Searles 1991
Minimum Height (mm)	30.5	Leaf plus stalk (Schneider and Searles 1991)
Maximum Height (mm)	151	Leaf plus stalk (Schneider and Searles 1991)
Broad Temperature Range	None	Warm-Temperate-Tropical
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

Caulerpa prolifera is an important habitat former in its native range, stabilizing sediment, and providing shelter for many organisms, but its chemical defenses limit its role as a food source for herbivores. In many parts of its wide native range it appears to coexist with many species of seagrasses. However, disturbance can lead to increasing dominance by C. prolifera (White 1988; Stafford and Bell 2008; Tuya et al. 2013). These concerns and the invasion and eradication of C. taxifolia have led to the rapid development of an eradication plan in California (Southern California Caulerpa Action Team 2021).

Competition- Caulerpa prolifera is a colonial seaweed whose stolons can spread rapidly over soft bottoms, creating dense thickets of leafy blades. On one hand, these growths can stabilize sediment and create habitat for many organisms. However, Caulerpa spp. can contain toxic compounds, and are indigestible for many herbivorous organisms, and can replace angiosperm seagrasses like Halophila, Halodule spp., Cymadoce spp., Posidonia, and Zostera marina, which are important food resources for herbivores as well as structural habitat features. Even within its native habitat, resource managers are concerned that human disturbance or other environmental changes will shift the balance towards dominance or replacement by C. prolifera (White 1988; Stafford and Bell 2006). In areas where it has recently invaded, it partially replaces native seagrasses. In the Suez Canal, C. prolifera has replaced the Red Sea native (Halophila stipulacea) and C. prolifera beds in the Suez supported a lower diversity and biomass of benthic invertebrates (Hegazi 2006; Gab-Alla 2007). In the Portuguese lagoon Ria Formosa, where C. prolifera was historically collected in the 19th century and then reappeared in 2011, beds of C. prolifera did not reduce overall diversity, but a couple of species, the gastropod Bittium reticulatum and a tanaid Apseudopsis formosus, were sharply reduced. In the Ria Formosa, Caulerpa prolifera has mostly colonized bare sediment, and so far has not replaced the native seagrasses Cymdocea nodosa and Zostera marina (Pareira et al. 2021). On the island Gran Canaria, C. prolifera extensively replaced C. nodosa. Removals of Caulerpa led to increased biomass and spread of the native seagrass (Tuya et al.2013).

Toxicity- Caulerpa prolifera, like other Caulerpa, produces a wide range of compounds which discourage microbial growth and invertebrate feeding, including those feeding on detritus (Box et al. 2010). There are some herbivores which specialize on Caulerpa; saccoglossan sea slugs, such as Ascobulla fragilis in Spain and Elysia cauze can tolerate the deterrent compounds (White 1988; Box et al. 2010).

Habitat Change- In April 2021, Caulerpa prolifera was reported by a diver near the mouth of Newport Bay, California. By May, the state had re-activated the Southern California Caulerpa Action Team, formed for the earlier eradication of C. taxifolia populations in Huntington Harbor and Agua Hedionda Lagoon in 2002. As with the earlier C. taxifolia invasion, C. prolifera is seen as a a threat to Eelgrass beds and associate invertebrate and fish communities. In May 2021, the Southern California Caulerpa Action Team developed an eradication plan, primarily using suction devices to remove the algae, with nets to capture any fragments. The earlier C. taxifolia eradications used chlorine, pumped under plastic sheets covering the bottom, as a method of eradication, but currents and boat activity made that impractical in Newport Bay The estimated total cost of the Phase I removal effort, including preliminary and post-removal surveys, could exceed $1 million (Southern California Caulerpa Action Team 2021).

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