Caprella mutica

Invasion History

First Non-native North American Tidal Record: 1973
First Non-native West Coast Tidal Record: 1973
First Non-native East/Gulf Coast Tidal Record: 1998

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General Invasion History:

Caprella mutica is native to the Northwest Pacific. It was first described from Peter the Great Bay, Russia, by Schurin in 1939, and was subsequently found from the Kurile Islands and Akkeshi Bay in Hokkaido Japan (Ashton 2006) south to the Bohai Sea (Laoning Province) and Jiazhou Bay (Shandong Province) in China (Huang 2001). This caprellid has been introduced to the East (Delaware-Newfoundland) and West coasts (California-Alaska) of North America, Europe (from Spain to Norway and Germany), and New Zealand. Caprellids are capable of long-distance dispersal on floating seaweeds or other objects, but ballast water, ship fouling, and the culture of Pacific Oysters (Crassostrea gigas) are likely vectors for the transport of C. mutica to different regions of the world. Many of the occurrence records are associated with aquaculture facilities and other man-made structures, such as breakwaters, marinas, and oil platforms (Platvoet et al. 1995; Willis et al. 2004; Ashton 2006; Page et al. 2006; Ashton et al. 2007; Cook et al. 2007).

North American Invasion History:

Invasion History on the West Coast:

In 1973, Caprella mutica (initially reported as C. acanthogaster) was collected at Field's Landing, in Humboldt Bay, California (Martin 1977, cited by Carlton 1979, Marelli 1981, Boyd et al. 2002). In 1977, it was collected near Oakland in San Francisco Bay (Marelli 1981) and now ranges throughout the South and Central Bay (Cohen et al. 2005). It has been collected at many locations in California, including Elkhorn Slough (in 1978, Marelli 1981), San Diego Bay (in 2001, Fairey et al. 2002, reported as C. acanthogaster), Morro Bay, Channel Islands Harbor, Port Hueneme, Los Angeles-Long Beach Harbors, San Diego Bay (Cohen et al. 2002; Fairey et al. 2002), and oil platforms off Santa Barbara (Page et al. 2006). To the north, it was first collected in Coos Bay, Oregon in 1983 (Carlton 1989; Wonham et al. 2005), Puget Sound, Washington in 1998 and Victoria, British Columbia in 1995 (Cohen et al. 1998; Cohen et al. 2001; Frey et al. 2009). Later it was found to range much farther north, including the Queen Charlotte Islands and Prince Rupert, British Columbia (Frey et al. 2009), and Ketchikan to Kachemak Bay, and Dutch Harbor, in the Aleutian Islands. The timing of this northern invasion is not clear- the earliest Alaskan record is from Sitka in 2001 (Ashton et al. 2008). Pre-existing populations or natural range extensions are conceivable, but extensive collections of caprellids were made in Alaska in the 19th century (US National Museum of Natural History 2012), and in British Columbia in the 20th century (Frey et al. 2009). Potential vectors for C. mutica's transport to the West coast include transplants of Pacific Oysters (Crassostrea gigas), hull fouling, and ballast water.

Invasion History on the East Coast:

The earliest collection of Caprella mutica on the East Coast of North America was in 1998 in Brundenel, on Prince Edward Island, Canada, in the Gulf of St. Lawrence (Locke et al. 2007; Turcotte and Sainte Marie 2009). In 2000, in a survey of southern New England harbors, Caprella mutica was collected in many locations from Gloucester, Massachusetts, south to Newport, Rhode Island. A subsequent survey in 2003 extended the range north to Freeport, Maine, and south to Mystic, Connecticut (MIT Sea Grant 2003). In 2013, established populations of C. mutica were found in the Indian River Inlet, Delaware and Ocean City Inlet, Maryland (Macarena Ros, personal communication, 2013). This caprellid was also collected in Passamaquoddy Bay, New Brunswick, Canada (in 2002, Ashton 2006), Placentia Bay on the south shore of Newfoundland (in 2010, Fisheries and Oceans Canada 2011), and at several more locations in the Gulf of St. Lawrence, including Chaleur Bay (in 2003) and the Magdalen Islands, Quebec (in 2005, Turcotte and Sainte Marie 2009).

Invasion History Elsewhere in the World:

Caprella mutica was first reported in European waters from a surge barrier in Zeeland, and Burghsluis, Netherlands, on the Eastern Scheldt estuary, where it was named as a new species C. macho (Platvoet 1995). In 1999, it was found near a salmon farm in Oban, on the west coast of Scotland (Willis et al. 2004), the Shetland Islands and in Austevoll, Norway (Skifterik 2001; Ashton 2006; Cook et al. 2007). This caprellid is now known from much of the coast of Northwestern Europe, from Le Havre, France (on the English Channel) to Helgoland, Germany (on the North Sea), including the Channel Coast of England, the east and west coasts of Scotland, and the west and east coasts of Ireland (Tierney et al. 2004; Buschbaum and Gutow 2005; Ashton 2006; Arenas et al. 2006; Ashton et al. 2007; Cook et al. 2007; Schückel et al. 2010).

In the Southwest Pacific, Caprella mutica is established near Timaru and Lyttleton on the South Island of New Zealand (Willis et al. 2009).

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Description

Caprellid amphipods have a greatly modified body form, when compared to more familiar gammarid amphipods. The body is elongated (giving rise to the name 'skeleton shrimp'), though the abdomen is compressed. The head is partly fused with the first thoracic segment (called Pereonite 1 in amphipods). The head bears a pair of long antennae 1, somewhat shorter antennae. The 1st antennae (A1) have a 3-segmented peduncle, tipped by a flagellum with multiple segments. The 2nd antennae (A2) may be fringed with long setae, and have 3-4 segments in the peduncle, and a shorter flagellum, usually of 2 segments. A mandibular palp of several segments is present in some genera, arising between the antennae, but this is absent in Caprella. There is a small pair of gnathopods, with small grasping claws, with a movable finger (Gnathopod 1) on Pereonite 1. Pereonite 2 bears a much larger pair of gnathopods (Gnathopod 2), which may have conspicuous spines or setae. Pereonites 3 and 4 usually have round or club-shaped gills, while in most species, including Caprella, pereiopods are absent. Pereopods 5, 6, and 7 are roughly equal and hook-like, for climbing and attachment, with 6 segments. Females develop oostegites, plates which form a brood pouch. Males are usually larger than females of the same species. Females and immature males can be hard to identify to species level. (Description from: Barnes 1983; Watling and Carlton, in Carlton 2007).  

Caprella mutica males can grow up to 35 mm, while females grow up to 15 mm (MarLin 2006). Paired dorsal and lateral spines on pereonites 3 to 7 increase in number and size with maturity. Mature males can often be distinguished from other caprellids by naked eye. Immature specimens may only have small paired dorsal spines on pereonite 5. Live specimens of both sexes are bright orange to red in color, with the brood pouch of the female being pale white with dark red dots (Platvoet et al. 1995). There are a number of morphological differences between male and females. Females have no setation on the first and second pereopods, but do have dorsal and lateral spines on pereonites 3 to 7. The pereonites and Gnathopod 2 of females are greatly shortened compared with those of the males. Mature females are distinguished by the developing oostegites and brood pouch. (See further descriptions from: Platvoet et al. 1995; Ashton 2006; MarLin 2006; and Watling and Carlton, in Carlton 2007)

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Taxonomy

Ecology

General:

Life History – The males are large and slender, armed with larger gnathopods, probably an adaptation to compete for females and to guard themselves during molting. The embryos are brooded by the female in an egg-pouch formed by large plates (oostegites) on the 3rd and 4th pereionites (Turcotte and Sainte Marie 2009). Development is direct, with the newborn juveniles having the general form of adults. Females reach maturity at Instar VII (the 6th molt), an average of 53 days after birth (cultured at 14⁰C). The average lifespan was 90-120 days with most females producing two broods before death (Cook et al. 2007). However, estimated brooding time and lifespan varies greatly in the field, with varying temperature and food conditions (Turcotte and Sainte Marie 2009). The importance of maternal care in C. mutica is unclear (Boos et al. 2011). In culture, newborn juvenile C. mutica may cling to the females after birth, and remain nearby for several days, but disperse within a week. Brooding females and females with newborns are more likely to fight with males than non-reproducing females (Matthews 2008). The population cycle is strongly seasonal in the Sea of Japan and in Chaleur Bay, Quebec, with peaks of reproduction in spring (April-May) and summer (June-August), and two generations per year (Turcotte and Sainte Marie 2009). In Scotland, with somewhat higher winter temperatures, (minimum of 7⁰C) reproduction occurred year-round, but populations peaked in July-August (Ashton 2006). In culture, C. mutica was able to reproduce at 4-26⁰C, but reproduction was optimal at 16⁰C and impaired at the upper and lower limits (Boos et al. 2011).

Ecology – Caprellids can feed in a variety of ways, including filtering small particles from the water, browsing on small filamentous algae, scraping tissue from large algae, scavenging, and predation (Turcotte and Sainte Marie 2009). Caprella mutica appears to be capable of using all these modes of feeding, which may contribute to its success as an invader (Cook et al. 2007, Turcotte and Sainte Marie 2009; Cook et al. 2010; Best et al. 2013). The high abundance of C. mutica found around salmon farms may be due to direct consumption of salmon feed, as well as feeding on enhanced densities of phytoplankton stimulated by nutrients from the aquaculture operation (Boos et al. 2011). It has been found clinging to vegetation, hydroids, bryozoans, and manmade structures (ropes, nets, etc.) (Ashton 2006; Willis et al. 2004; Maciejeski 2008). It tolerates wide ranges of temperature, 2 - 25⁰C, and salinities as low as 11 PSU in the field in the northern Sea of Japan (Schevchenko et al. 2004, cited by Turcotte and Sainte Marie 2009). In laboratory experiments, the temperature range was similar, 2-26⁰C, but the lower salinity limit was higher at 15 PSU. It showed little mortality at the highest salinity tested, 40 PSU (Ashton et al. 2007). In North Sea, off Netherlands and Belgium, C. mutica was dominant on intertidal and floating artificial substrates, in waters with high densities of suspended particulate matter, and less than 17 m depth, while the native C.linearis dominated on fixed, subtidal substrates in deeper water (Coolen et al. 2016). Caprella mutica appears to have sufficient tolerance and flexibility of habitat, feeding, and life history to colonize much of the world's temperate waters (Ashton 2006; Boos et al. 2011). 

Food:

Phytoplankton, seaweed, detritus

Consumers:

Fishes

Competitors:

Caprella californica, Caprella linearis

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Coarse Woody Debris	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
General Habitat	Vessel Hull	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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Tolerances and Life History Parameters

Minimum Temperature (ºC)	-2	Based on field distribution, laboratory animals tolerated 2 C, lowest tested (Ashton 2006)
Maximum Temperature (ºC)	28	Experimental, 48 h LT 50 (Ashton 2006)
Minimum Salinity (‰)	14.6	Experimental, 48 h LC 50, reduced activity below 18 ppt (Ashton 2006)
Maximum Salinity (‰)	40	Experimental, highest tested (Ashton 2006)
Minimum Reproductive Temperature	4	Lowest tested (Ashton 2006). Hatchlings maintained at 4 C died after 4 months (Boos et al. 2011), but winter hatchlings probably would survive a normaly seasonal cycle with spring warming.
Maximum Reproductive Temperature	20	Highest tested (Boos et al. 2011)
Maximum Length (mm)	50	Nihsimura 1995, males, in Japan, cited by Cook et al. 2007
Broad Temperature Range	None	Cold temperate-Warm temperate
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

In its invaded range, Caprella mutica has achieved extraordinary densities, especially on man-made structures. Studies of its economic and ecological impacts are limited, but observations indicate that C. mutica can affect aquaculture operations, displace native caprellids, and affect the feeding of native fishes (Ashton 2006; Page et al. 2007; Shucksmith et al. 2009; Turcotte and Sainte Marie 2009).

In Price Edward Island, Canada, high densities of caprellids (C. mutica and C. linearis) were shown to inhibit the settlement of the tunicate Ciona intestinalis (Collin and Johnson 2014). Since the tunicate appears to be locally invasive, and interfering with mussel aquaculture, there may be a potential for biocontrol by encouraging caprellid populations (Collin and Johnson 2014).

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Regional Impacts

NEP-VI	Pt. Conception to Southern Baja California		Ecological Impact	Food/Prey
On oil platforms off Santa Barbara, the caprellid community was dominated by Caprella mutica, which was a major component of the diet of a native fish, the Painted Greenling (Oxylebius pictus), which was very abundant at the platform (Page et al. 2007).
P065	_CDA_P065 (Santa Barbara Channel)		Ecological Impact	Food/Prey
On oil platforms off Santa Barbara, the caprellid community was dominated by Caprella mutica, which was a major component of the diet of a native fish, the Painted Greenling (Oxylebius pictus), which was very abundant at the platform (Page et al. 2007).
NEA-III	None		Ecological Impact	Competition
In laboratory experiments in Scotland, C. mutica displaced the native caprellids C. linearis and Pseudoprotella phasma from natural (hydroid) and artificial habitat (plastic mesh) patches on fouling plates. Displacement of C. linearis occurred even when the density of the native was 10X that of C. mutica (Shucksmith et al. 2009).
NEA-III	None		Economic Impact	Fisheries
Mussel farmers observed reduced settlement of spat during periods where C. mutica was most abundant; however a causal connection could not be confirmed (Ashton 2006).
NA-S3	None		Economic Impact	Fisheries
Field and laboratory work (unpublished) indicates that high densities of C. mutica interfere with settlement of mussel spat (Turcotte and Sainte Marie 2009).
NA-S3	None		Ecological Impact	Competition
On fouling plates, high densities of Caprella mutica and the cryptogenic C. linearis inhibit the settlement of the tunicate Ciona intestinalis, which is locally invasive in the Gulf of St. Lawrence. One possible mechanism is physical disturbance or chemical avoidance of caprellids by settling tunicate larvae (Collin and Johnson 2014).
NA-S3	None		Ecological Impact	Predation
A negative correlation between newly settled tunicates (Ciona intestinalis) and caprellids (C. mutica and C. linearis) on fouling plates in Prince Edward Island estuaries may be the result of predation by caprellids on the larvae. While the two caprellids were equally abundant, C. mutica's larger size suggests that it made the largest contribution to the interaction (Collin and Johnson 2014).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Predation
In Bodega Harbor, caging experiments and feeding trials showed that Caprella mutica was a significant predator on recruits of Ciona intestinalis (Rius et al. 2014).
P112	_CDA_P112 (Bodega Bay)		Ecological Impact	Predation
In Bodega Harbor, caging experiments and feeding trials showed that Caprella mutica was a significant predator on recruits of Ciona intestinalis (Rius et al. 2014).
P090	San Francisco Bay		Ecological Impact	Competition
Caprella mutica was less tolerant of low salinity (LC50 of 17-21 PSU) than C. californica (LC50 of 16 PSU), and died out more quickly after low-salinity events in San Francisco Bay, but recolonized more rapidly due to faster maturity and higher fecundity (Desmet 2011).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
Caprella mutica was less tolerant of low salinity (LC50 of 17-21 PSU) than C. californica (LC50 of 16 PSU), and died out more quickly after low-salinity events in San Francisco Bay, but recolonized more rapidly due to faster marity and higher fecundity (Desmet 2011).
CA	California		Ecological Impact	Competition
Caprella mutica was less tolerant of low salinity (LC50 of 17-21 PSU) than C. californica (LC50 of 16 PSU), and died out more quickly after low-salinity events in San Francisco Bay, but recolonized more rapidly due to faster marity and higher fecundity (Desmet 2011). , Caprella mutica was less tolerant of low salinity (LC50 of 17-21 PSU) than C. californica (LC50 of 16 PSU), and died out more quickly after low-salinity events in San Francisco Bay, but recolonized more rapidly due to faster maturity and higher fecundity (Desmet 2011).
CA	California		Ecological Impact	Food/Prey
On oil platforms off Santa Barbara, the caprellid community was dominated by Caprella mutica, which was a major component of the diet of a native fish, the Painted Greenling (Oxylebius pictus), which was very abundant at the platform (Page et al. 2007).
CA	California		Ecological Impact	Predation
In Bodega Harbor, caging experiments and feeding trials showed that Caprella mutica was a significant predator on recruits of Ciona intestinalis (Rius et al. 2014)., In Bodega Harbor, caging experiments and feeding trials showed that Caprella mutica was a significant predator on recruits of Ciona intestinalis (Rius et al. 2014).

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