Invasion History

First Non-native North American Tidal Record: 1968
First Non-native West Coast Tidal Record: 1981
First Non-native East/Gulf Coast Tidal Record: 1968

General Invasion History:

The hydrozoan Maeotias marginata is native to the Black Sea and the Sea of Azov (Naumov 1969), and is considered to be part of the 'Sarmatic' cnidarian fauna (named for an ancient sea and an early tribe of the region) (Naumov 1969; Mills and Sommer 1995). Other widespread invaders of this fauna are Cordylophora caspia, Moerisia spp., and Blackfordia virginica. The medusa of M. marginata was first discovered in canals in the Netherlands in 1762 and again in 1889 (Mills and Rees 2000). These occurrences apparently represent a very early introduction by shipping. We do not know if M. marginata is still present in the Netherlands. In 1896, M. marginata (as M. inexspectata or M. inexpectata) was described from its native region, the Black Sea, by Ostroumoff (Naumov 1969).

Maeotias marginata became widely introduced in the 20th century. Medusae were collected in the Chesapeake Bay in 1968 (Calder and Burrell 1969); the Edisto River, South Carolina in 1972 (Burrell and Joseph 1974); Loire estuary, France in 1972 (Denayer 1973); the Suisun Marsh, San Francisco Bay in 1981 (Mills and Sommer 1995); Fujian, China (Xu et al. 1985); and the Baltic Sea, Finland in 1990 (Vainola and Oulasvirta 2002). The medusa is limited to brackish waters, ~4-15 PSU, but tolerances of the polyp are unknown (Mills and Sommer 1995; Rees and Gershwin 2000).

North American Invasion History:

Invasion History on the West Coast:

On the West Coast, Maeotias marginata has only been observed in brackish parts of the San Francisco Bay estuary system. Field notes of conservation agencies suggest that it may have been seen in Suisun Slough as early as 1959 (Rees and Gershwin 2000), but the first definitive collection of the medusa was in 1981, in Suisun Marsh (Schroeter 2008). In 1992, it was collected in the Petaluma River (Mills and Sommer 1995), and later in the Napa River (Mills and Rees 2000), the Suisun Slough, and near Chipps Island in Suisun Bay (Lia McLaughlin 2003, IEP newsletter http://www.water.ca.gov/iep/newsletters/2003/IEPNewsletter_fall2003_mar23.pdf). Analysis of plankton survey records indicates a trend of increasing abundance in Suisun Marsh from 1981 to 2005 (Schroeter 2008).

Invasion History on the East Coast:

Maeotias marginata was collected from the Pamunkey River, Virginia, a York River tributary of Chesapeake Bay, in October and November of 1968, and September of 1970 (Calder and Burrell 1969; Calder 1972). We are not aware of later records of Maeotias marginata in the Chesapeake Bay, but this may reflect limited studies of hydromedusae since then. In 1972, Maeotias marginata was collected at the junction of Intracoastal Waterway and South Edisto River (Burrell and Joseph 1974). Again, we do not know of more recent records here or elsewhere on the East Coast. However, the hydroids are unlikely to be detected without a specific sampling effort, owing to their small size (0.1 mm) and their occurrence on detritus (Rees and Gershwin 2000).

Invasion History Elsewhere in the World:

As noted above, the medusa of M. marginata was first discovered in canals in the Netherlands in the 18th century, and was recorded again in 1889 (Mills and Rees 2000). This medusa tolerates freshwater for several days, which may aid in its invasion of canal systems (Mills and Rees 2000). Later appearances of this species are very spotty. One medusa was captured in the Loire estuary, France in 1971 (Denayer 1973). In 1999, numerous medusae were seen in the Väinameri region of the Estonian Baltic (Väinölä and Oulasvirta 2002). This medusa has also been reported from China, in the Jiulong River Estuary, near Xiamen (Xu et al. 1985). The spotty appearance of medusae may reflect very sporadic production by the very small and inconspicuous polyps, as in the related Craspedacusta sowerbii (Freshwater Jellyfish) (Acker and Muscat 1976).


Description

The hydroid stage of Maeotias marginata is very small (~0.1 mm height), lacks tentacles, and develops directly from eggs. The hydranth bears large transparent nematocysts oriented around the presumed mouth. The hydroids have been observed only in culture, and have not been detected in the field (Rees and Gershwin 2000; Wintzer et al. 2011a). Hydroids in a culture dish adhered to detritus and other hydroids, not to the glass of the dish. The hydroid illustrated as M. inexspectata (=marginata) in Mills and Sommer (1995) actually belongs to Moerisia sp. (Mills and Rees 2000; Rees and Gershwin 2000).

The medusae have a roughly hemispherical umbrella, with four radial canals. They are released at about 1 mm in diameter, and initially have four tentacles and radial canals, as well as a well-developed ring canal. Mature medusae have the four radial canals but develop up to 60 smaller centripetal canals per quadrant, and over 500-600 tentacles. Each tentacle arises from a bulb with a deep reddish-brown ocellus. As the medusa matures, it acquires statocysts, arranged in three rows along the umbrella margin. The medusae grow up to 50 mm diameter and ~25-30 mm high. The umbrella is clear in younger medusae, but opaquely white, with pinkish or brownish color around the rim of the bell in adults. The manubrium reaches almost to the mouth of the bell, and has its margins elongated into four frilly lips. The four main radial canals are draped with hanging folds of gonads. When extended, the tentacles exceed the diameter of the bell. (Description from: Naumov 1969; Denayer 1973; Mills and Sommer 1995; Mills and Rees 2000; Rees and Gershwin 2000; Bouillon et al. 2004)


Taxonomy

Taxonomic Tree

Kingdom:   Animalia
Phylum:   Cnidaria
Class:   Hydrozoa
Subclass:   Hydroidolina
Suborder:   Limnomedusae
Family:   Olindiidae
Genus:   Maeotias
Species:   marginata

Synonyms

Maeotias inexpectata (Mayer, 1910)
Maeotias inexspectata (Ostroumoff, 1896)
Medusa marginata (Modeer, 1891)
Olindias inexpectata (Naumov, 1969)

Potentially Misidentified Species

Moerisia sp.
A polyp of Moerisia sp. in the San Francisco estuary was erroneously identified as that of Maeotias marginata by Mills and Sommer (1995) (Mills and Rees 2000; Rees and Gershwin 2000).

Ecology

General:

Maeotias marginata has a conspicuous planktonic medusa stage, and a small obscure hydroid stage. Hydroids have only been described from San Francisco Bay, in culture (Mills and Rees 2000), and have not been studied in the field. The hydroids were attached to bits of detritus in the bottom of culture dishes, but did not attach to the glass. Feeding was not observed, and polyps did not grow in culture (Rees and Gershwin 2000). Presumably, benthic or zooplankton prey would be stung and captured by nematocysts near the mouth and ingested. Polyps are presumed to bud asexually to produce new polyps, and also to bud off medusae, but these processes have not yet been described.

Medusae appear in the plankton at about 1mm in diameter, and feed on zooplankton, including barnacle larvae, copepods, crab zoeae, copepod eggs, and tanaids (Mills and Sommer 1995; Schroeter 2008). In the San Francisco estuary, the medusae fed primarily on calanoid copepods (65%), barnacle nauplii (14%), cyclopoid copepods (14%), and corophiid amphipods (4%) (Wintzer et al. 2011c). The medusae appear to be heavier than water, and remain close to the bottom, with occasional bouts of upward swimming (Mills and Sommer 1995). In the field, they pulse to the surface, flip over, and slowly sink, with extended tentacles (Rees and Gershwin 2000). Medusae in Mills and Sommer's (1995) San Francisco estuary study were all male, but in 1996, Rees and Gershwin (2000) collected some females, and were able to observe the development of fertilized eggs, which metamorphosed directly into small polyps (Rees and Gershwin 2000). Many aspects of the life cycle remain poorly understood.

Food:

Copepods, barnacle nauplii, crab zoeae

Trophic Status:

Carnivore

Carn

Habitats

General HabitatUnstructured BottomNone
General HabitatGrass BedNone
Salinity RangeMesohaline5-18 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone


Tolerances and Life History Parameters

Maximum Temperature (ºC)27Field, Suisun Marsh (Schroeter 2008)
Minimum Salinity (‰)0.9Field observations of medusae (Mills and Sommer 1995; Schroeter 2008), but up to 10 days of survival of medusae in fresh water. (Mills and Rees 2000) Salinity tolerance of polyps is unknown.
Maximum Salinity (‰)15Experimental observations of medusae (Mills and Sommer 1995), (Mills and Rees 2000) Salinity tolerance of polyps is unknown.
Minimum Dissolved Oxygen (mg/l)2.8Field, Suisun Marsh (Schroeter 2008)
Minimum Reproductive Temperature11.3Field Temperatures for medusae (Calder and Burrell 1969; Denayer 1973; Mills and Sommer 1995)
Maximum Reproductive Temperature27Field Temperatures for medusae (Calder and Burrell 1969; Denayer 1973; Mills and Sommer 1995)
Maximum Width (mm)50Medusa width (Naumov 1969; Mills and Sommer 1995; Mills and Rees 2000)
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneMesohaline

General Impacts

Maeotias marginata, together with other introduced hydrozoans in brackish estuaries (Moerisia spp., Cordylophora caspia, Blackfordia virginica), has the potential to alter planktonic food webs through predation on zooplankton. Most estuaries have few or no native brackish-water hydrozoans (Calder 1972; Calder 1976; Rees and Gershwin 2009).

Ecological Impacts

Competition- In Suisun Marsh, M. marginata medusae overlap with larvae of Morone saxatilis (Striped Bass) and could be competing with them for food. Maeotias marginata is a possible competitor with larval fishes, particularly economically important Striped Bass (Morone saxatilis) and endangered Delta Smelt (Hypomesus transpacificus) (Schroeter 2008; Wintzer et al. 2011b; Wintzer et al. 2011c). Temporal and dietary overlap was greatest with Delta Smelt, and introduced Threadfin Shad (Dorosoma petenense), but minimal with Morone saxatilis and threatened Longfin Smelt (Spirinchus thaleichthys) (Wintzer et al. 2011c). Predation on fish larvae occurred, but at a very low rate, less than 1% of food contents (Schroeter 2008; Wintzer et al. 2011c).

Regional Impacts

P090San Francisco BayEcological ImpactCompetition
Potentially, M. marginata sp. is a competitor with larval fishes, particularly economically important Striped Bass (Morone saxatilis) and endangered Delta Smelt (Hypomesus transpacificus) (Schroeter 2008; Wintzer et al. 2011b; Wintzer et al. 2011c). Temporal and dietary overlap was greatest with Delta Smelt, and introduced Threadfin Shad (Dorosoma petenense), but minimal with Morone saxatilis and threatened Longfin Smelt (Spirinchus thaleichthys) (Wintzer et al. 2011c).
NEP-VNorthern California to Mid Channel IslandsEcological ImpactCompetition
Potentially, M. marginata sp. is a competitor with larval fishes, particularly economically important Striped Bass (Morone saxatilis) and endangered Delta Smelt (Hypomesus transpacificus) (Schroeter 2008; Wintzer et al. 2011b; Wintzer et al. 2011c). Temporal and dietary overlap was greatest with Delta Smelt, and introduced Threadfin Shad (Dorosoma petenense), but minimal with Morone saxatilis and threatened Longfin Smelt (Spirinchus thaleichthys) (Wintzer et al. 2011c).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
MED-X None 0 Native Estab
MED-IX None 0 Native Estab
NEA-II None 1762 Def Failed
B-VII None 1999 Def Estab
NEA-IV None 1971 Def Unk
NA-ET3 Cape Cod to Cape Hatteras 1968 Def Estab
CAR-VII Cape Hatteras to Mid-East Florida 1972 Def Estab
NEP-V Northern California to Mid Channel Islands 1981 Def Estab
NWP-3a None 1985 Def Estab
M130 Chesapeake Bay 1968 Def Estab
P090 San Francisco Bay 1981 Def Estab
S090 Stono/North Edisto Rivers 1972 Def Estab
P093 _CDA_P093 (San Pablo Bay) 1992 Def Estab
B-X None 2012 Def Unk
NEA-V None 2002 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
31007 Mills and Sommer 1995) 1992 1992-01-01 Petaluma River Def 38.1104 -122.4874
33867 Rees and Gershwin 2000 1998 1993-01-01 Napa River (San Francisco Bay Def 38.1092 -122.4858

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