Limnoithona tetraspina

Invasion History

First Non-native North American Tidal Record: 1993
First Non-native West Coast Tidal Record: 1993
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Limnoithona tetraspina was described from Tsung-ming Island, China, in the Yangtze River Delta (Orsi and Ohtsuka 1999). The extent of its range in Asia is not known, but we have not found reports of this copepod from interior fresh waters, so we are treating it as a marine species for database and mapping purposes. In 1993, it was collected in San Francisco Bay, California, where it now ranges from salinities of 0 to at least 30 PSU (Bollens et al. 2011).

North American Invasion History:

Invasion History on the West Coast:

In September 1993, Limnoithona tetraspina was collected at Chipps Island, California, at the head of Suisun Bay. By July-August 1994, it had largely replaced L. sinensis in the San Francisco estuary (Cohen and Carlton 1995; Orsi and Ohtsuka 1999). It has become the numerically dominant copepod in the low-salinity zone of the estuary, from Antioch, in the Delta to Martinez, at Carquinez Straits (Bouley and Kimmerer 2006), and was the third most abundant copepod in San Francisco Bay proper (Bollens et al. 2011). In 1997-1999, it ranged through San Francisco Bay proper, from San Pablo Bay to the South Bay, primarily during periods of heavy river flow and low salinity (Bollens et al. 2011).

In 2003, three specimens of L. tetraspina were found in the Grays River, Washington and Trojan power plants on the Columbia River, Oregon (Sytsma et al. 2004). In 2005, this copepod was found in the tidal portion of the Columbia River from Astoria (River Km 8) to near Oak Point, Washington (R Km 75) in low abundances (200-600 m-3), but was not found further upstream (Cordell et al. 2008; Dexter et al. 2015).

Limnoithona tetraspina was found in transpacific ballast water aboard ships arriving in Puget Sound, but in much higher quantities in ships from the West Coast (Cordell et al. 2008; Lawrence and Cordell 2010). Invasions of other West Coast estuaries are possible.

Invasion History Elsewhere in the World:

In August 2009, Limnoithona tetraspina was first collected in the Shat al Arab estuary, Iraq, at the head of the Persian Gulf, and was later collected at salinities of 1.7-4.7 PSU and temperatures of 27-28 PSU. It is presumed to be a ballast water introduction here (Mohammed et al. 2014).

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Description

Limnoithona tetraspina has a shield-shaped prosome and four tapering thoracic segments. The final thoracic segment is conical and truncated, bearing the much reduced P5 swimming legs (pereiopods). The urosome is slender, consisting of four segments (Barroso do Abiahy et al. 2007).

The adult female has a short rostrum, which projects ventrally. The forehead is rounded dorsally. The cephalosome is partially fused with the first thoracic (leg-bearing) segment. There are short triangular lateral extensions at the posterior border of the cephalosome. The first and second urosome segments are fused, resulting in a 4-segmented urosome, swollen anteriorly. On the first urosome segment, there is a knob near the genital opening with 1 long and 1 short seta. The length of the caudal rami is 5 X the length, and each ramus is armed with one outward seta near the base and 5 setae at the tip. From the outward side inward, the first seta is shortest, setae 2 and 3 are plumed and longer, with 3 being the longest. The antennule consists of 11 free segments. The body length is ~0.55 mm (n=3, Barroso do Abiahy et al. 2007). The female, like other Oithonidae, often carries two symmetrical egg masses attached to the genital segment.

The adult male lacks a rostrum, while its forehead is rounded dorsally. The cephalosome is partially fused with the first thoracic (leg-bearing) segment. The male has short triangular lateral extensions of the posterior border of the cephalosome. Its urosome consists of five segments. The genital segment is swollen anteriorly. The length of the caudal rami is 4.5X the width, with setae like that of the females. The antennules are symmetrical and digeniculate (2 hinged joints) with 17 segments. The body length is approximately 0.38 mm (n=4, Barroso do Abiahy et al. 2007).

The copepodite and naupliar stages of this copepod have not been described. Morphology and development should be somewhat similar to that described for Oithona brevicornis by Uchima (1979).

In a redescription of L. tetraspina, Barroso do Abiahy et al. (2006) moved the genus Limnothona to the family Cyclopettidae, based on a morphological analysis.

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Taxonomy

Ecology

General:

Planktonic cyclopoid copepods mate in the water column. Males use their modified antenules to grasp the female and transfer spermatophores to the female's genital segment. Female cyclopoid carry eggs in two symmetrical clusters under the abdomen (Barnes 1983). Eggs hatch into nauplii which go through six stages. The first stage, NI, has 3 pairs of appendages and is unsegmented- each molt has additional appendages and/or more differentiation of segments. The sixth stage (NVI) molts into a first copepodite stage (CI), with the basic form of the adult, and fully differentiated feeding structures, but with only two pairs of swimming legs, and only one urosomal segment. The copepod goes through five additional molts, with increasing numbers of swimming legs, urosomal segments, and sexual differentiation. The sixth (CVI) stage is the male or female adult (Uchima 1979). In L. tetraspina, overall development in the laboratory under food-rich conditions was about 22 days at 18 C for females, and 20 days for males, but development was slower, with individual stages taking much longer, when nauplii or copepodites were fed natural food assemblages (Gould and Kimmerer 2010).

Limnoithona tetraspina is characteristic of estuarine waters (Orsi and Ohtsuka 1999). We do not know if it can complete its life cycle in nontidal fresh water. Adult and juvenile cyclopoid copepods feed raptorially, seizing particles, and may be carnivorous or omnivorous, feeding on algae, ciliates, rotifers, and copepod nauplii (Barnes 1983). Limnoithona tetraspina feeds primarily on ciliates and flagellates, while not significantly grazing diatoms or dinoflagellates (Bouley and Kimmerer 2006; Gifford et al. 2007; York et al. 2014).

Food:

Ciliates, motile phytoplankton

Trophic Status:

Omnivore

Omni

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Habitats

General Habitat	Unstructured Bottom	None
Salinity Range	Limnetic	0-0.5 PSU
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Planktonic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	4	Field, Columbia River estuary (Bollens et al. 2012)
Minimum Salinity (‰)	1	Field records: Orsi and Ohtsuka 1999
Maximum Salinity (‰)	30	Field records: Bollens et al. (2011) reported L. tetraspina occurring at up to 30 PSU, while Bouley and Kimmerer (2006) and Orsi and Ohtsuka (1999) gave its salinity range as 1-10 PSU.
Maximum Duration	24	Hatching to adult, 18 C, laboratory (Gould and Kimmerer 2010)
Minimum Length (mm)	0.4	Adult female (n=4, do Abiahy et al. 2007)
Maximum Length (mm)	0.6	Adult female (n=3, do Abiahy et al. 2007)
Broad Temperature Range	None	Warm-temperate-Subtropical
Broad Salinity Range	None	Oligo-Polyhaline

General Impacts

Ecological impacts

Competition: Limnoithona tetraspina appears to have largely replaced a previous introduction of L. sinensis in the low-salinity region of the San Francisco estuary (Orsi and Ohtsuka 1999), and the Columbia River. However, interactions between the two species have not been studied. In the San Francisco estuary, L. tetraspina may have been favored by its greater tolerance of brackish water (Ferrari and Orsi 1984; Bouley and Kimmerer 2006).

Food/Prey: Currently, the partial replacement of larger copepods by L. tetraspina may be adversely affecting larval fishes. The small size of L. tetraspina deters visual predators, while the nutritional composition of these copepods may be poorer, since flagellates and ciliates lack the high-quality lipids found in the diatoms eaten by calanoid copepods (Winder and Jassby 2011). For example, the endangered Delta Smelt (Hypomesus transpacificus) selectively prefers larger copepods, based on feeding experiments (CALFED Science Program 2009, research by Lindsey Sullivan).

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Regional Impacts

P090	San Francisco Bay		Ecological Impact	Competition
Competition- Limnoithona tetraspina appears to have largely replaced a previous introduction, L. sinensis in the low-salinity region of the San Francisco estuary (Orsi and Ohtsuka 1999), and in the Columbia River, as well. However, interactions between the two species have not been studied. In the San Francisco estuary, L. tetraspina may have been favored by its greater tolerance of brackish water (Ferrari and Orsi 1984; Bouley and Kimmerer 2006).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
Competition- Limnoithona tetraspina appears to have largely replaced a previous introduction, L. sinensis in the low-salinity region of the San Francisco estuary (Orsi and Ohtsuka 1999), and in the Columbia River, as well. However, interactions between the two species have not been studied. In the San Francisco estuary, L. tetraspina may have been favored by its greater tolerance of brackish water (Ferrari and Orsi 1984; Bouley and Kimmerer 2006).
NEP-IV	Puget Sound to Northern California		Ecological Impact	Competition
Competition- Limnoithona tetraspina appears to have replaced a previous introduction, L. sinensis, in the low-salinity region of the Columbia River estuary. Limnoithona sinensis was collected in the Columbia River in 1979-1980 surveys, but only L. tetraspina was found in 2003 (Sytsma et al. 2004).
P260	Columbia River		Ecological Impact	Competition
Competition- Limnoithona tetraspina appears to have replaced a previous introduction, L. sinensis, in the low-salinity region of the Columbia River estuary. Limnoithona sinensis was collected in the Columbia River in 1979-1980 surveys, but only L. tetraspina was found in 2003 (Sytsma et al. 2004).
P090	San Francisco Bay		Ecological Impact	Food/Prey
Food/Prey- Currently, abundances of L. tetraspina relative to large copepods may be adversely affecting Delta Smelt (Hypomesus transpacificus), which selectively prefer larger copepods, based on feeding experiments (CalFed Science Program 2009, research by Lindsay Sullivan; Slater et al. 2014) The effects of introduced copepods are additionally complex, because of the varying size of the life-stages, and the interaction of different species of fish predators (Sullivan et al. 2016).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Food/Prey
Food/Prey- Currently, abundances of L. tetraspina relative to large copepods may be adversely affecting Delta Smelt (Hypomesus transpacificus), which selectively prefer larger copepods, based on feeding experiments (CalFed Science Program 2009, research by Lindsay Sullivan) The effects of introduced copepods are additionally complex, because of the varying size of the life-stages, and the interaction of different species of fish predators (Sullivan et al. 2016).
CA	California		Ecological Impact	Competition
Competition- Limnoithona tetraspina appears to have largely replaced a previous introduction, L. sinensis in the low-salinity region of the San Francisco estuary (Orsi and Ohtsuka 1999), and in the Columbia River, as well. However, interactions between the two species have not been studied. In the San Francisco estuary, L. tetraspina may have been favored by its greater tolerance of brackish water (Ferrari and Orsi 1984; Bouley and Kimmerer 2006)., Competition- Limnoithona tetraspina appears to have largely replaced a previous introduction, L. sinensis in the low-salinity region of the San Francisco estuary (Orsi and Ohtsuka 1999), and in the Columbia River, as well. However, interactions between the two species have not been studied. In the San Francisco estuary, L. tetraspina may have been favored by its greater tolerance of brackish water (Ferrari and Orsi 1984; Bouley and Kimmerer 2006).
CA	California		Ecological Impact	Food/Prey
Food/Prey- Currently, abundances of L. tetraspina relative to large copepods may be adversely affecting Delta Smelt (Hypomesus transpacificus), which selectively prefer larger copepods, based on feeding experiments (CalFed Science Program 2009, research by Lindsay Sullivan) The effects of introduced copepods are additionally complex, because of the varying size of the life-stages, and the interaction of different species of fish predators (Sullivan et al. 2016)., Food/Prey- Currently, abundances of L. tetraspina relative to large copepods may be adversely affecting Delta Smelt (Hypomesus transpacificus), which selectively prefer larger copepods, based on feeding experiments (CalFed Science Program 2009, research by Lindsay Sullivan; Slater et al. 2014) The effects of introduced copepods are additionally complex, because of the varying size of the life-stages, and the interaction of different species of fish predators (Sullivan et al. 2016).

References

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