Gracilaria vermiculophylla

Invasion History

First Non-native North American Tidal Record: 1979
First Non-native West Coast Tidal Record: 1979
First Non-native East/Gulf Coast Tidal Record: 1998

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General Invasion History:

Gracilaria vermiculophylla is native to the Northwest Pacific, including the coasts of Japan, Korea, China, and Vietnam. It was first described from Hokkaido, Japan in 1956, by H. Ohmi (Rueness 2005; Guiry and Guiry 2016). Agarophyton species are widely cultured as a source of agar (Israel et al. 1999; Rueness 2005; Hommersand and Freshwater 2009) and there are a large number of studies reporting their physiology and growth characteristics. Species of the genera Gracilaria and Gracilariopsis are extraordinarily difficult to identify morphologically and molecular analyses are resulting in extensive revisions of their taxonomy and distribution (Gurgel and Frederiq 2004; Bellorin et al. 2004; Rueness 2005; Saunders 2009). Since 2000, G. vermiculophylla has been identified from the Eastern Pacific, near Ensenada, Mexico (Bellorin et. al. 2004); Elkhorn Slough, California (Rueness 2005); and British Columbia (Saunders 2009). In the Eastern Atlantic, it is known from Sweden to Spain (Rueness 2005), and in the Western Atlantic it ranges from Georgia to New Hampshire (Gurgel and Frederiq 2004; Rueness 2005; Tyler et al. 2005; Nettleton et al. 2013). Some of the invasion sites in Europe were near areas of Magallana gigas (Pacific Oyster) cultivation (Rueness 2005). The vast majority of introduced populations have genetic signatures similar to those of plants from northwest Japan, indicating their probable transport with Pacific Oysters (Crassostrea gigas) from that region. Secondary transport by currents, boat fouling, and ballast water has resulted in secondary introductions and genetic mixing (Krueger-Hadfield et al. 2017).

North American Invasion History:

Invasion History on the West Coast:

The full range of Gracilaria vermiculophylla on the West Coast of North America is unknown, as is the date of introduction, owing to confusion with G. pacifica and other similar species (Aguilar-Rosas et al. 2014; Kathy Ann Miller, personal communication). It was first reported from specimens collected in 1979 in Ensenada, Mexico and identified by molecular methods (Bellorin et al. 2004). The first specimens from US waters were collected in Elkhorn Slough, California in 1994 (Goff et al. 1994, cited by Bellorin 2004; Rueness 2005). RNA sequences were found to be nearly identical with Japanese G. vermiculophylla (Rueness 2005). In 2006-2008, specimens were collected at Bamfield and Courtenay on Vancouver Island, and at Port Moody on the British Columbia mainland near Vancouver, again identified through molecular methods (Saunders 2009). Additional collections were made in 2013-2015 from Tomales Bay, Bodega Bay, and Puget Sound and identified as G. vermiculophylla (Krueger-Hadfield et al. 2017). Possible vectors of introduction to the West Coast include hull fouling, ballast water, and Pacific Oyster transplants.

Invasion History on the East Coast:

Geacilaira vermiculophylla was probably introduced to the Atlantic Coast of North America some time before the year 2000. To date, the earliest reported collection is from 1998 at Hog Island Bay (identified as 'G. aff. tenuistipitata) on the Atlantic Coast of Virginia (Gurgel and Frederiq 2004). In Hog Island Bay, just north of the mouth of the Chesapeake Bay, G. vermiculophylla was collected in 1999 (Gurgel and Frederiq 2004). Large blooms of Gracilaria spp had been observed in Hog Island Bay for some years previously (Tyler et al. 2005; Thomsen et al. 2005). In 2000, in Masonboro Sound, North Carolina an unidentified Gracilaria sp. was reported fouling nets and covering intertidal mudflats. By 2002, this alga was causing problems in power plants in the Cape Fear estuary and was distributed over a wide salinity range (Thompson 2002 personal communication). Reports of G. vermiculophylla fouling fishing gear were also widespread (Freshwater et al. 2006). By 2004, it ranged from the south side of Cape Fear (Brunswick County) to Beaufort and Bogue Sound, Carteret County, NC (Freshwater et al. 2006). The vectors of introduction to this region are not clear. Few transplants of Pacific oysters (C. gigas) were made in this area. During World War II, extensive aquaculture of Graciliaria sp. for agar was undertaken in North Carolina, but the cultured seaweed was presumed to be a native species, recently described as G. hummi, (Hommersand and Freshwater 2009). Deliberate transplants of G. vermiculophylla from Asian waters were unlikely under wartime conditions. This alga could have been introduced by ship fouling or ballast water, sometime after the war, and unrecognized due to its similarity with Gracilaria tikvahiae and Gracilariopsis longissima ('Gracilaria verrucosa'). However, G. vermiculophylla gametes survive only briefly in the water column, and adult plants are rare in hull fouling. Alternatively, it could have been introduced with some of the scattered official or unofficial and unsuccessful plantings of Pacific Oysters (Crassostrea gigas)on the East Coast in the 1950s-1970s (Krueger-Hadfield et al. 2017). Genetic analyses suggest that G. vermiculophylla had two separate introductions during this period, one that stayed confined to southern New England, while the other spread north to Great Bay, New Hampshire, and south to Georgia (Krueger-Hadfield et al. 2017).

Subsequent studies, using genetic methods, found that G. vermiculophylla has become widespread on the East Coast of North America, south to Wassaw Sound, Georgia (Byers et al. 2012; Kollars et al. 2015) and north as far as Great Bay, New Hampshire (Thomsen 2004; Thomsen et al. 2005; Thomsen and McGlathery 2006; MacIntyre et al. 2011; Nettleton et al. 2013). It was found to be abundant in the York River, Virginia in 2007 (Johnson and Lipcius 2012) and elsewhere in the Chesapeake Bay (James Norris, 2005, personal communication). The extent of G. vermiculophylla's growth in Chesapeake Bay, Delaware Bay, and other Northeastern US estuaries is unknown, owing to the need for molecular identification. The difficulty of identification also makes documentation of its spread difficult. Specimens in South Carolina and Georgia were collected in 2009, where mats of the alga covered mudflats that historically lacked macrophytes (Byers et al. 2012). In 2000-2003, G. vermiculophylla was collected along the southern Gulf of Maine, from Provincetown, Massachusetts to Dover, on Great Bay, New Hampshire (Nettleton et al. 2013).

Invasion History Elsewhere in the World:

The earliest reported collection of Gracilaria vermiculophylla in Europe was in the Netherlands in 1980. Blooms of a red alga were observed in Oostvoornse Meer, a lagoon in the Rhine Delta near Rotterdam. Specimens taken in 1994 were identified as G. vermiculophylla by molecular methods (Rueness 2005; Stegenga and Karremans 2015). Another early collection was in 1985, in the Ria de Aveiro lagoon, Portugal (Abreu et al. 2011). As in North America, this invasion was initially unrecognized, because of its similarity to native species. By 2004, this seaweed was known from many coastal and estuarine sites from the Oslofjord, Norway to the Bahia a Coruna, Spain, and the Ria Formosa, Portugal (Ruenss 2005). It continued to spread to new areas, including Northern Ireland in 2012 (Nunn and Minchin 2013), and the Baltic Sea coasts of Denmark and Germany in 2003-2007 (Thomsen et al. 2007; Hammann et al. 2013). In 2006-2009, G. vermiculophylla was found in lagoons of the Po Delta and in the Venice Lagoon, on the northern Adriatic Sea (Sfriso et al. 2012; Munari et al. 2015). Gracilaria  vermiculophylla has spread south from Europe to lagoons on the Atlantic coast of Morocco, where it was first collected in 2002 (Guillemin et al. 2008).

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Description

The genus Gracilaria formerly contained 100+ species, many of which are morphologically similar, but also highly variable (Bold and Wynne 1978; Schneider and Searles 1991). This genus has been subdivided to include two new genera , Agarophyton and Crassa, and a revived genus Hydropuntia, considered to represent three separate lineages (Gurgel et al. 2018). An extensive new moleculr analysis of the genus found that this species cluster within the genus Gracilaria, aas Gracilar vermiuclophylla (Lyra et al. 2021)  Algae of the tribe Gracilarieae generally arise from a disc-shaped holdfast and have a bushy, densely branched thallus, composed of long, thin, cylindrical branches. Gracilaria vermiculophylla has 3-orders of lateral branches, either alternate or unilateral. The branches are tapered towards the tips. The two major phases in the life cycle, diploid tetrasporophytes and haploid gametophytes are morphologically similar. Both stages are marked with reproductive structures, called sporangia, which appear as small bumps on the branches. Agarophyton vermiculophyllum thalli can reach ~100-2000 mm in length, with branches about 5 mm in diameter. The plants are dark-red to reddish brown, but sometimes greenish or black. Identification of G. vermiculophylla requires detailed microscopic examination and/or molecular methods. This description is based on: Bellorin et al. 2004, Rueness 2005, Thomsen et al. 2005,  Freshwater et al. 2006, Saunders 2009, Sfriso et al. 2012, and Nettleton et al. 2013 and Lyra et al. 2021).

 

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Taxonomy

Ecology

General:

Gracilaria vermiculophylla has become widespread in a range of estuarine habitats from cold-temperate to subtropical climates, and tolerates highly variable salinity, light, air exposure, and nutrient levels (Rueness 2005; Thomsen et al. 2005; Thomsen et al. 2007; Sfriso et al. 2012). In experiments, this alga tolerated exposure to 5-34°C with 80-100% survival, and tolerated salinities from 5 to 60 PSU (Yokoya et al. 1999; Kim et al. 2016). Good growth was seen at 10 to 30°C and 10-45 PSU (Yokoya et al. 1999-Japan; Kim et al. 2016-New England). Rueness (2005), working with populations from Brittany, France found optimal growth at 20°C and 10 PSU. Differences in light and other culture conditions makes comparisons difficult, but clearly a. vermiculophyllum is well adapted to estuarine conditions. In Yokoya et al.'s experiment, growth occurred over the range of light intensities tested, from 20 to 100 µE m-3s-1, with the greatest growth at the highest irradiance (Yokoya et al. 1999). Nejrup et al. (2013), found similar patterns with low growth rates at 5°C at all light levels, a slight reduction in growth at 30°C, and growth rates leveling off between 100 and 250 µE m-3s-1. Gracilaria vermiculophylla has several mechanisms protecting its cells from ultraviolet light, which may partially explain its survival in shallow water, and tolerance of air exposure (Roleda et al. 2012). It can also tolerate five months of darkness at 8°C, even when partially dehydrated (Nyberg et al. 2009), and burial for a week in sediments (Thomsen et al. 2009). Gracilaria vermiculophylla is capable of rapidly taking up inorganic nitrogen compounds, even at very high environmental concentrations, (600 µMN) enabling rapid growth and competition with other species (Abreu et al. 2011). It is also capable of taking up dissolved organic nitrogen (urea, amino acids) (Tyler et al. 2005). Gracilaria vermiculophylla requires relatively high nutrient concentrations to sustain rapid growth, but has high nutrient storage capacity, which may permit to continue growing through warm seasons (Pedersen and Johnsen 2017).  Introduced populations of Gracilaria vermiculophylla have shown a rapid evolutionary shift, with increasing tolerance of heat and cold, and low salinity, as shown by common-garden experiments, comparing native G. vermiculophylla rom Asia with invading populations (Sotka et al. 2018).

Gracilaria vermiculophylla is known mostly from estuarine habitats, often in shallow water, including intertidal marshes and mudflats, seagrass beds, and systems receiving freshwater inflows and high nutrient inputs (Rueness 2005; Thomsen et al. 2009; Abreu et al. 2011; Byers et al. 2012; Cacabelos et al. 2012). It grows attached to shells and stones, but also grows in large mats of drifting fragments (Hu and Lopez-Bautista 2013). In mudflat habitats from Virginia to Georgia, it grows attached to the mud chimneys of the polychaete Diopatra cuprea (Thomsen et al. 2005; Byers et al. 2012; Kollars et al. 2016). In Brittany, it is frequently associated with the introduced Spartina maritima (Smooth Cordgrass) (Surget et al. 2107). As a densely branched, fast-growing algae, G. vermiculophylla supports a wide range of grazers and epibiota. In Japan, the amphipods Grandierella japonica and Monocorophium uenoi lived on G. vermiculophylla and grazed on epiphytic diatoms growing on the algae (Aikins and Kikuchi 2002). In Virginia, Georgia, and Sweden, A. vermiculophylla is inhabited by large numbers of red algae, amphipods, isopods, and snails, feeding on the epiphytic algae and to a lesser extent on the seaweed (Nyberg et Gl. 2009; Byers et al. 2012; Wright et al. 2014). Experiments in Europe suggest that G. vermiculophylla is not a preferred food for the amphipod Gammarus locusta, the isopod Idotea baltica, and the Common Periwinkle Littorina littorea (Jensen et al. 2007, cited by Hu and Lopez-Bautista 2013; Weinberger et al. 2009; Nejrup et al. 2013). Non-native colonies of G. vermiculophylla (from Germany) produced compounds that reduced settlement of fouling organisms in native region (Japan) and, to as greater extent, in non-native waters in Germany. The groups that were most effected were diatoms, and other red algae (Wang et al. 2017).

Consumers:

Periwinkles, isopods, amphipods

Trophic Status:

Primary Producer

PrimProd

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Habitats

General Habitat	Grass Bed	None
General Habitat	Coarse Woody Debris	None
General Habitat	Unstructured Bottom	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Low Intertidal	None

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Life History

In its native range, Gracilaria vermiculophylla has a complex life cycle with two morphologically somewhat similar life-cycle phases, a diploid tetrasporophyte and a haploid gametophyte (Bold and Wynne 1978; Rueness 2005; Kollars et al. 2015). Female plants are poorly branched, strongly wrinkled, and thick in their lower portion, while male plants are more finely branched and produce spermatia in shallow depressions, which appear as numerous pale dots on the thallus (Sfriso et al. 2012). A third stage, the carposporophyte, developed only within a specialized branch of the female thallus, the cystocarp. The blades of the tetrasporophytes are covered with asexual tetrosporangia. The tetrasporangia divide into a fourfold (cruciate) pattern to produce tetraspores. The tetraspores are released, and settle, and grow into gametophytes (Bold and Wynne 1978). Tetrasporophytes are morphologically similar to male gametophytes (Sfriso et al. 2012).  In its introduced habitats, the life cycle of algae or flowering plants  is often modified, which is consistent with a rule, called 'Baker's Law', which states that asexual life-cycle stages tend to predominate in invading populations. North American and European populations consist largely of diploid populations reproducing by fragmentation (Krueger-Hadfield et al. 2016). Introduced populations of G, vermiculophylla have larger thalli, more resustant to breaking or tearing, compared to popualtiomns in Japan (Murren et al. 2022).  he seasonality of reproduction and recruitment is unclear, but in temperate climates (Virginia, North Carolina, France, Venice, Portugal), coverage and/or biomass of G. vermiculophylla increases rapidly in March or April and persists until November or December (Freshwater 2006; Thomsen 2007; Abreu et al. 2011; Sfriso et al. 2012; Surget et al. 2017). Populations in Portugal reproduce year-round, but spores did not germinate below 5°C (Abreu et al. 2011). In addition to sexual reproduction, G. vermiculophylla reproduces rapidly by fragmentation, with fragments as small as 1 mm (Abreu et al. 2011; Surget et al. 2017).

Morphology of the thallus of Gracilaria vermiculophylla varies with the nature of attachment.  On South Carolina mudflats, most thalli were attached to worm-tubes, and few to hard substrates.  Worm-attached and free-living thalli were sexually reproductive, mostly in summer (Krueger-Hadfield et al. 2023).

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	5	Lowest tested, Yokoya et al. 1999; Kim et al. 2016, Experimental
Maximum Temperature (ºC)	34	Kim et al. 2016, Experimental.
Minimum Salinity (‰)	5	3 weeks survival, at 0.7 (Rueness 2005; Weinberger et al. 2008), but poor recovery after exposure below 5 PSU, in experimental and field (Nejrup and Pedersen 2012).
Maximum Salinity (‰)	60	Highest tested, Yokoya et al. 1999
Minimum Length (mm)	100	Rueness 2005
Maximum Length (mm)	2,000	Rueness 2005
Broad Temperature Range	None	Cold temperate-Tropical
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

The geographical range and impacts of Gracilaria vermiculophylla are probably underestimated because of its similarity to native species and the need for molecular identification. Nonetheless, the ability of G. vermiculophylla to develop dense populations in brackish estuaries and to grow on exposed intertidal mudflats has resulted in its quick expansion and growing abundance. In some cases, it has replaced or partially replaced native algal and seagrass communities, as well as interfered with fisheries, and fouled power plant intake screens (Rueness 2005; Freshwater et al. 2006; Thomsen et al. 2007; Byers et al. 2012; Cacabelos et al. 2012; Stiger-Pouvreau and Thouzeau 2015). Growth rates of G. vermiculophylla from Long Island Sound were lower than those of native G. tikvahiae at 20-29°C, but much higher at 34°C. Gracilaria vermiculophylla also maintains higher nitrogen concentrations than G. tikvahiae (Gorman et al. 2017).

Economic Impacts

Fisheries- Agarophyton vermiculophyllum is abundant in Hog Island Bay, Virginia where it contributes to large blooms of drift algae which can cover oyster and shellfish beds (Thomsen et al. 2005). These drift algae are assumed to be unpleasant aesthetically, especially when washed up on shore. The extent of this alga's abundance and distribution in Chesapeake Bay proper is unknown. This alga interferes with commercial fishing by clogging nets and turtle excluder devices in NC waters (North Carolina Sea Grant 2005; Freshwater et al. 2006). In 2009, 'hairballs' of algae, tentatively identified as this species (by Karen McGlathery), clogged crab nets in Tangier Sound, lower Chesapeake Bay (Bay Weekly 2009).

Industry- Agarophyton vermiculophyllum was causing problems at the Brunswick Nuclear Power Plant near Wilmington, North Carolina: "It creates problems for us by severely clogging plant intake screening." (Thompson 2002, personal communication; Freshwater et al. 2006).

Ecological Impacts

Competition- Agarophyton vermiculophyllum has rapidly developed dense populations in estuaries in North America from Virginia to Georgia, and in Europe, from Sweden to Portugal. It has been replacing native seaweed and seagrass populations (Rueness 2005; Thomsen et al. 2007; Byers et al. 2012; Cacabelos et al. 2012). In Virginia and the Chesapeake Bay region it has been a component of sporadic blooms of drift algae. Ulva lactuca and G. vermiculophylla together form 80% of the macroalgal biomass in Hog Island Bay (Thomsen et al. 2005; Tyler et al. 2005). This alga was reported to be highly invasive in the Cape Fear estuary, NC (Thompson 2002, personal communication; Freshwater et al. 2006), and is a potential competitor with native algae. In Sinaloa, Mexico, G. vermiculophylla was the dominant macroalga during the rainy season and the dominant, or even the only species, at some locations (Pinon-Gimate et al. 2008). One unusual competitive feature in Northwest Atlantic estuaries is mediated by a native snail, Ilynassa obsoleta, which seems to prefer this alga for egg-laying, discouraging grazing by herbivores (Guidone et al. 2014).

Impacts on seagrasses are a special concern, given their global importance. In the Ria de Aveiro, Portugal, masses of G. vermiculophylla have overgrown and smothered the native intertidal Dwarf Eelgrass Zostera noltei (= Nanozostera noltii), depriving the seagrass of light and reducing its growth (Cacabelos et al. 2012). Modelling indicates that G. vermiculophylla competes with the seagrass Zostera marina (Nyberg 2007), although field experiments suggest that the effects may be variable (Martinez-Luscher and Holmer 2010; Thomsen et al. 2013).

Habitat Change- Reported habitat impacts of G. vermiculophylla have been widely varied. These include modifying existing plant communities, such as seaweed and seagrass communities, attracting different groups of epibionts, and creating new habitat in relatively barren mudflat communities. This seaweed is regarded as an important ecological engineer (Byers et al. 2012). As discussed under 'Competition', attached plants and drifting masses of algae can potentially smother and shade eelgrass beds (Nyberg 2007; Martinez-Luscher and Holmer 2010; Cacabelos et al. 2012; Thomsen et al. 2013).

Agarophyton vermiculophyllum provides densely branched habitat and refuge from predation for sessile invertebrates and algae. In Danish estuaries, it creates habitat for a diverse fauna and other attached algae, but excessive growth can also contribute to anoxia (Nyberg 2007; Nyberg et al. 2009; Thomsen et al. 2013). In Chesapeake Bay, patches of G. vermiculophylla offer refuge from predation for small Blue Crabs (Callinectes sapidus), partially compensating for the decline of seagrasses in the Bay (Falls 2008; Johnston and Lipcius 2012).

In intertidal mudflat habitats, it creates structured, vegetated habitat. From Virginia to Georgia, G. vermiculophylla has formed colonies attached to the protruding tubes of the polychaete Diopatra cuprea, creating extensive masses of finely branched vegetation in formerly bare habitat (Thomsen et al. 2005; Byers et al. 2012; Kollars et al. 2016). In Virginia coastal bays, fouling of tubes by the alga caused high mortality among the tubeworms (Berke et al. 2014), but in South Carolina and Georgia estuaries, the worms actively added G. vermiculophylla, and at some times and sites, the added seaweed enhanced the polychaete's growth, probably by attracting prey (Kollars et al. 2014). The seaweed colonies were heavily colonized by invertebrates, especially snails and amphipods (Byers et al. 2012; Wright et al. 2014).

Food/Prey- By growing rapidly and providing a large organic biomass, this algae provides a potential food source, including acting as a substrate for edible epiphytes and microbes, and is likely a large addition to the detrital food web. It is also a major absorber and recycler of nutrients in estuaries (Thomsen et al. 2009; Byers et al. 2012; Gulbransen and McGlathery 2013). However, deterrent chemical compounds prevent many herbivores, including snails and amphipods, from consuming this seaweed directly (Nylund et al. 2011; Byers et al. 2012; Nyberg et al. 2009; Hammann et al. 2013; Wright et al. 2014). However, another study, using Ampithoe valida, and many populations of G. vermiculophylla from locations in the Northwest Pacific (native), Northeast Pacific, Northwest Atlantic, and Northeast Atlantic found no difference in palatability between native and introduced populations of G. vermiculophylla. The evidence for rapid evolution of anti-herbivore compounds in introduced populations of this alga seems to be equivocal (Bippus et al. 2018).

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