austropotamobius is a genus of crayfish in the family astacidae .

it contains three extant species , and one species known from fossils of barremian age : austropotamobius llopisi ( via , 1971 ) † austropotamobius italicus ( faxon , 1914 ) austropotamobius pallipes ( lereboullet , 1858 ) austropotamobius torrentium ( schrank , 1803 ) — stone crayfish

austropotamobius

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the river dove represents white - clawed crayfish austropotamobius pallipes in a high - quality , upland limestone river , in the north - east of the species’ uk range .
these four marl loughs in northern ireland have strong isolated populations of white - clawed crayfish austropotamobius pallipes . this site has been selected because of its hydrological isolation and the absence of crayfish plague from northern ireland .
the kent is a river of upland character in southern cumbria . densities of white - clawed crayfish austropotamobius pallipes are very high throughout much of the kent system ( particularly in the tributaries ) , perhaps higher than anywhere else in england .
the welsh river wye system is the best site known in wales for white - clawed crayfish austropotamobius pallipes . the tributaries are the main haven for the species , particularly at the confluences of the main river and the edw , dulas brook , sgithwen and clettwr brook .
craven in northern england supports strong populations of white - clawed crayfish austropotamobius pallipes in the limestone streams feeding malham tarn , and in malham tarn itself . this site is well - isolated and is therefore an important refuge , unlikely to be invaded by non - native crayfish species .
the eden is a river with high water quality that supports a large population of white - clawed crayfish austropotamobius pallipes in the northern part of its range in england . as with the river wye , the tributaries of the eden , especially those flowing off limestone , are of particular importance .
sites have been selected to provide representation over a wide geographical area . the sites selected are within parts of the country where the keeping of live non - native crayfish has ( since 1996 ) been prohibited except under licence , and where there are high - quality aquatic habitats and recent ( post - 1990 ) records of healthy , recruiting austropotamobius pallipes
justification : austropotamobius torrentium has been assessed as data deficient . while this species is relatively widespread across europe it is undergoing significant declines throughout much of its range . however , rates of decline have not been quantified and therefore this species cannot be assessed under criterion a . further research on rates of decline is urgently needed before an accurate assessment of conservation status can be made .
this lowland site in central england represents white - clawed crayfish austropotamobius pallipes in standing water . this 1 ha marl pit holds a very large population , estimated at 50 , 000 . although crayfish plague outbreaks have occurred in the midlands , this waterbody is isolated from river systems and is a good example of a ‘refuge’ site in an important part of the species’ former range .
the wensum is a chalk - fed river in eastern england , and is an eastern example of riverine white - clawed crayfish austropotamobius pallipes populations . as with most of the remaining crayfish populations in the south and east of england , the threats from non - native crayfish species and crayfish plague are severe . designation of the river as a sac provides as much protection as can be afforded to such vulnerable populations .
austropotamobius pallipes has a wide distribution throughout europe . it was previously thought that the western limit of the species range was in portugal ( though it is now thought to be extinct there ) , but is now northwestern spain . montenegro is the easterly limit , whilst spain and scotland are the southerly and northerly limits respectively . its distribution is restricted in austria , corsica , germany , lichtenstein and montenegro ( souty - grosset et al . 2006 ) .
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and an italian species for which the name is being discussed . the italian species is thought to be comprised of a number of subspecies , though this depends on the author . both the italian form and
füreder , l . , gherardi , f . , holdich , d . , reynolds , j . , sibley , p . & souty - grosset , c .
bradley , p . , palmer , m . , foster , j . , hefti , d . , hutchings , a . , machino , y . , maguire , i . , pugh , m . , schulz , h . , sket , b . , wilson , n . , soulsby , a . - m . , batchelor , a . , dyer , e . , whitton , f . , livingston , f . , milligan , h . t . , smith , j . , lutz , m . l . , de silva , r . , mcguinness , s . , kasthala , g . , jopling , b . , sullivan , k . & cryer , g .
) has been assessed as endangered under criterion a2ce . in the last ten years this species is suspected to have undergone a decline of somewhere between 50–80 % based on presence / absence data available for england , france and italy . the situation in these countries is thought to be similar to that of the other countries in its range for which there is no population data . these global declines are largely attributed to the introduced crayfish ( e . g . , signal crayfish and red swamp crayfish ) and crayfish plague
, which are now found throughout this species entire range . this species is managed and protected by a number of international and national legislations , however these are limited in their capacity to prevent the further spread of non - native species . population monitoring is urgently required within some of the other countries for which no data was available to determine at what rate this species is being lost from aquatic systems .
england , wales , ireland , france and italy once held the greatest abundance of this species , however over the last 10 - 20 years this species has undergone significant declines in these countries and the greatest subpopulation is now found in ireland which is still free from the signal crayfish . the status of this species has recently been reviewed by holdich
: this species was recorded as present in livno and in boracko lake in the neretva drainage in 1895 and from gacko ( herzegovina ) and ljuta ( croatia ) in 1961 ( entz 1909 , karaman 1961 ) . these drainage systems are part of the adriatic drainage system .
: this species is reported from several localities including : vransko lake ( island of cres ) , near the towns of vica and gornjit kosinj , zrmanja , krupa , centina and krka rivers ( grube 1864 , bruina 1907 ) . this species has been eliminated from the main stem of the river nereta due to intensive draining and pollution ( gottstein
. 1999 ) . it has been described as native to croatia in the rivers belonging to the adriatic sea drainage ( i . maguire and g . klobučar pers . comm . 2009 ) . some populations on the south have disappeared ( the ljuta river , vrljika river ) but due to the enthusiasm of local people , before it became extinct , some crayfish were transferred to surrounding tributaries . it has not been detected in the krka and zrmanja rivers , but has been seen in some of the smaller tributaries . the main causes of disappearance are regulation of river banks and intensive agriculture ( pollution ) on the river banks ( i . maguire and g . klobučar pers . comm . 2009 ) .
: groombridge ( 1993 ) reports this species within the country , however machino says this report is a mistake ( y . machino pers . comm . 2009 ) .
: there has been much debate over the origin of this species within england . this species is now considered indigenous within this country following the recent work of holdich , palmer and sibley ( 2009 ) in which they found a number of records to suggest that this species has been present for at least 500 years and was certainly widespread and abundant prior to the introduction of signal crayfish and crayfish plague ( thomas and ingle 1971 , holdich and reeve 1991 ) . however , since the 1970s with the introduction of the signal crayfish (
) , this species has been undergoing significant declines in its range ( sibley 2003 , 2004 ) . this species is suspected to have undergone a 95 % decline within hampshire since the 1970s ( a . hutchings pers . comm . 2009 ) . data collected by the environment agency on presence / absence in southwest england , indicates that this species has undergone a decline of 31 % in 10 years ( occurred in 87 water framework directive subcatchments prior to 1975 , but was only found in 26 of these by the end of 2008 ) ( sibley , holdich and lane 2009 ) . rates of decline for the south west region were determined by mapping presence / absence in sub - catchment units , and provides greater resolution than that provided by mapping presence / absence in 10 km² grid cells ( p . sibley pers . comm . 2009 ) ; however this estimate is likely to underestimate true decline as many once dense subpopulations are rapidly disappearing ( p . sibley pers . comm . 2009 ) . a decline of greater than 95 % is suspected for the thames region ( g . scholey and a . ellis pers . comm . 2009 ) ; it was once present in all the major thames tributaries but now only eight of the 55 sub - catchments ( 97 . 9 % decline over a ten year period ) have any records for
, although a few small populations still exist in kent ( j . foster pers . comm . 2009 ) . east anglia has also undergone significant losses since the 1970s with a range contraction from 384 km of occupied river ( between 1970 - 2000 ) , to just 84 km post 2000 ( m . pugh pers . comm . 2009 ) . the situation in britain has recently been reviewed by holdich
. 1993 , changeux 1996 ) . attempts have been made to restock waterways which have been affected by the plague . the population numbers of this species are said to be declining significantly ( vigneux et al . 1993 , vigneux 1997 , changeux
. 2006 ) . this situation is similar to what is happening across much of france : in jura 60 % of known subpopulations have disappeared since 1989 ( ~ 37 % decline over a ten year period ) . numerous subpopulations have disappeared in 14 departments , with declines are occurring in 26 of the 92 departments ( c . souty - grosset pers . comm . 2009 )
: this species was first discovered in germany in 1989 where it is restricted to the south - west of the country ( holdich 2002 ) . the population numbers are declining ( h . schulz pers . comm . 2009 ) .
: o ' keeffe ( 1986 ) estimated a population density of approximately 37 , 000 adults in white lake ( 32 ha ) . matthews
. ( 1993 ) estimated a population density of over one million adults in lough lene ( 430 ha ) ; both these subpopulations have since disappeared . reintroductions have taken place and have been successful within white lake ( reynolds
. 2000 ) , however the lough lene subpopulation has since disappeared . crayfish plague is suspected to have caused these declines . matthews and reynolds ( 1995 ) estimated populations in blessington reservoir , co . wicklow , at 500 adults per 100 m of rocky shoreline , and o ' keeffe ( 1986 ) noted dense populations in lisheen streams nearby ; stream densities were up to 6 . 5 per m² . outbreaks of the plague in the 1980s caused losses in two catchments . since then , slow declines are suspected to be occurring in some parts of ireland ( j . reynolds pers . comm . 2010 ) .
in that area ( füreder and machino 1999a ) . a significant decline in the number of populations within liguria , piedmont , and tuscany has also been observed ( souty - grosset
. 2004 ) only seven of these populations remained representing an annual change of 58 % , or 99 . 5 % over 10 years . south tyrol is thought to be exhibiting some of the greatest declines in the abundance of this species .
: this species is both native and introduced within this country . in the danubian drainage it is said to be native ( its presence needs to be proved ) , but on the mediterranean side it is thought to be introduced ( y . machino pers . comm . 2009 ) .
is native to slovenia . this species ' subpopulations are low due to the impacts of the crayfish plague ( budhina 1989 , b . sket pers . comm . 2009 )
is uncertain . albrecht ( 1983 ) considers that it is not native to spain , due to a reference stating that this species was absent in 1642 . grandjean
. ( 2005 ) found low genetic variability in the spanish subpopulation , but with similarities to a subpopulation in italy . grandjean
. ( 2001a ) suggest that this could be due to anthropogenic introductions . alternatively , this could be due to a bottleneck during the pleistocene , and current subpopulations have arisen from a single refugium . spanish and italian subpopulations could be descended from an extinct intermediate population in france . however , gutiérrez - yurrita
to be indigenous to spain . according to records , it was abundant in the 1960s , but had become scarce and restricted to northern spain in the 1990s . alonso
. ( 2000 , 2001 ) state that less than 1 , 000 small subpopulations exist in northern and north - eastern spain . to attempt to reinstate this species , some areas are being subject to restocking . garcia - arberas and rallo ( 2000 ) state that this species is still located in areas of the basque country where it was thought to have gone extinct
: this species is native to switzerland , but is currently experiencing a strong recession ( d . hefti pers . comm . 2009 ) . it is typically found in western regions and alpine valleys , although its presence in montane lakes is thought to be as a result of introductions ( holdich 2002 ) . it is highly sensitive to crayfish plague (
) . this species is considered as ' highly endangered ' ( stucki and zaugg 2006 ) .
this is a freshwater species which can be found under submerged cobbles , rocks , logs , tree roots , and amongst fallen leaves in permanent water bodies such as canals , streams , rivers , lakes , reservoirs and water - filled quarries ( holdich 2003 ) . recently it has been found that
2006 ) . vertical banks and overhanging vegetation have been highlighted as important features in determining crayfish abundance ( naura and robinson 1998 ) . it may also be found in large numbers in waters dominated by
. 2006 ) . this species is intolerant to pollution and hydrological change . waters containing
. this species occurs in areas with relatively hard , mineral - rich waters on calcareous and rapidly weathering rocks . a study from western france ( trouilhé
population had a dissolved oxygen concentration as low as 4 . 93 mg / l , while water temperature rose above 20°c for several consecutive days during summer . nitrate concentrations were always found to be above 30mg / l . principal component analyses ( pca ) suggested that an increase of organic matter was a discriminant factor for the presence or absence of this species
it can live for more than 10 years , and usually reaches sexual maturity after three to four years . it will carry 20 - 160 eggs , but usually less than 100 ( holdich 2003 ) .
ary productivity , c ) cultural value – recreational fishing , education , heritage . crayfish are also an
portant food source to a range of species including otters , salmonids , and birds such as kingfishers ( kettunen and ten brink 2006 ) .
this species is not commercially harvested for food but may be taken incidentally , mistaken for the signal crayfish .
. 2009 ) . invasive crayfish are aggressive predators for food and habitat , and often prey upon the white - clawed crayfish . this species is also threatened by
or porcelain disease . it may be present in 10 % of a population without apparent harm , but problems may occur if a higher prevalence is reached ( holdich 2003 ) .
significant declines are occurring across much of this species range : approximately ~ 52 % decline over 10 years in england , ~ 52 % decline between 1995 and 2003 within france , and a 99 . 5 % decline estimated for a ten year period in the south tyrol region of italy . these countries once held the greatest abundance of this species ( thomas and ingle 1971 , holdich and reeve 1991
) are present throughout much of this species range . the situation in ireland is slightly less serious in that signal crayfish are not yet reported from here , however
is present and already driving slow declines . this species is estimated to have undergone a 50 - 80 % decline over a 10 year period over its global range . sibley ( 2002 ) has suggested that should the current trend in the decline of this species continue , it faces possible extinction in britain within 30 years .
it is important to note that though this species may appear to be numerous in areas , the degree of genetic variability may in fact be low . low intra - population genetic variability has been observed in croatia , france ( gouin
2008 ) , and portugal . in some populations ( e . g . in the basin of the river sieve in italy ) the absence of heterozygotes and a high level of inbreeding has been observed ( bertocchi
this species has been listed under the eu habitats directive annex ii and v and therefore requires the designation of special areas of conservation for its protection . it has also been listed under appendix iii of the bern convention .
in ireland , this species is protected by the european union ( natural habitats ) regulations 1997 . under this regulation , special areas of conservation ( sacs ) are designated where there are good populations of this species . this applies to all european countries .
within the united kingdom , a biodiversity action plan ( uk bap ) has been developed for this species : this seeks to maintain the current distribution of the species through a combination of restricting the spread of non - native crayfish and crayfish plague , as well as providing suitable habitat features ( uk biodiversity group 1995 ) .
. 1999 ) , although control may be achieved through trapping . some success has , however , been achieved in enclosed waters in
) has yet to be added to this act ( holdich and sibley 2009 ) .
this species is also indirectly affected by the eu water framework directive which seeks to achieve good ecological status of aquatic systems . there are a number of local community education programs that aim to inform local communities on identification of native and non - native species and the legal implications of removing these species from the wild . it is also protected by the wildlife acts ( since 1975 ) in ireland . non - native crayfish are prohibited by the fisheries acts within ireland ( j . reynolds pers . comm . 2010 ) .
this species has been reintroduced ( using hatchery reared individuals ) into a number of sites at which it was previously found ( rogers and watson 2007 ) . methodological approaches for re - introductions have been recently reviewed by souty - grosset and reynolds ( 2009 ) . the suitability of the target habitat , the stocking material and the stocking procedure itself are paramount during any reintroduction measure : apart from general water quality and structural parameters , a suitable habitat is ideally geographically isolated from other surface waters and human activities such as intensive fishing pressure and agricultural practices . genetics of stocking material must be considered . however , it is first essential to make sure that the target habitat is free of crayfish plague . analyses of experience gathered in various european countries indicate how difficult it is to get the best information as a basis for successful restocking and consequently the discussions recently conducted among european researchers and managers were aimed at achieving consensus and common strategies
within switzerland this species is regulated by the national swiss fisheries legislation and is deemed ' highly endangered ' . there is a closed fishing season of 40 weeks per year and minimum harvest size limit of 9 cm ( hefti and stucki 2006 ) .
population monitoring within countries for which trend information is lacking , is needed . further research within these countries , on the main drivers of decline is also required .
füreder , l . , gherardi , f . , holdich , d . , reynolds , j . , sibley , p . & souty - grosset , c . 2010 .
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füreder , l . , gherardi , f . & souty - grosset , c .
hefti , d . , kozubikova , e . , machino , y . , manko , p . , miron , l . , pârvulescu , l . , puky , m . , schulz , h . , sket , b . , zaikov , a . , soulsby , a . - m . , batchelor , a . , dyer , e . , whitton , f . , livingston , f . , milligan , h . t . , smith , j . , lutz , m . l . , de silva , r . , mcguinness , s . , kasthala , g . , jopling , b . , sullivan , k . & cryer , g .
there is no information on the population status of this species in this country .
this species is most abundant in austria and germany . in austria , there are 534 localities which are said to account for 46 % of all crayfish populations ( pöckl 1999 ) .
bulgaria : there are only a few small subpopulations of this species ( zaikov and hubenova 2007 ) . nothing is known on the status of this species in this country .
this species is thought to be reasonably well preserved in this country , however anthropogenic pressure on this species habitat is increasing and likely to be driving some declines in abundance . some parts of the population have also been significantly impacted by drought which has caused 95 % mortality in some streams ( i . maguire pers . comm . 2010 ) .
is a native species and occurs in springs and streams at higher elevations . even a co - existance of this species with
czech republic : it is unclear whether this species is native or introduced to this country . it has been found at varying densities in streams , but in a study by kozak
france : this species is considered to be close to extinction within this country ( collas , julien and monnier 2007 ) germany : this species is undergoing a decline however there no trend information is available ( h . schulz pers . comm . 2009 ) . greece : this species can be found in 11 out of the 50 prefectures ( koutrakis et al . 2007 ) . compared to the other 2 crayfish species found in greece , this species is believed to have undergone the greatest decline . however there is indication of recovery in some areas ( koutrakis et al . 2007 ) . hungary : this species is threatened by organic pollution and the spread of non - native crayfish species which has resulted in a decline in the population numbers ( p . miklós pers . comm . 2009 ) . italy :
the species is fragmented in its distribution . in the province of udine , 2 of the 3 populations recorded in 1995 have gone extinct in 2005 ( machino and füreder 2005 ) . there has been a strong decline in this species in northern italy ( füreder 2009 ) .
is already thought to have gone extinct in a tributary of lake ohrid ( koselska brook ) below rečica as a result of pollution ( y . machino pers . comm . 2009 ) .
slovakia : this species is rare in this country , but population numbers are thought to be stable at present ( p . manko pers . comm . 2009 ) . slovenia :
switzerland : this species is known from the eastern parts of switzerland where it is known to be in severe decline . it is considered to be ' highly endangered ' by the swiss national legislation on fisheries ( d . hefti pers . comm . 2009 ) . turkey :
2006 ) . female size at maturity has been observed at 4 . 61 cm ( total length ) ( i . maguire pers . comm . 2010 . recorded sizes for
ranged from 6 to 9 cm ( females ) and from 8 to 10 . 5 cm ( males ) ( laurent 1988 ) .
2002 ) . in germany , stone crayfish females may incubate 40 to 70 eggs ( laurent 1988 ) . the maximal number of eggs per female ( in croatia ) we found was 104 ( an average value was 53 . 56 ) ( maguire
declines in this keystone species are said to negatively impact both ecosystem structure and function within freshwater environments through loss of : a ) provisioning services – food production from fisheries , recreational fishing , b ) regulatory and support services – trophic cascades , water purification , nutrient cycling , primary productivity , c ) cultural value – recreational fishing , education , heritage . crayfish are also an important food source to a range of species including otters , salmonids , and birds such as kingfishers ( kettunen and ten brink 2006 ) .
2006 ) . this species is reported to be undergoing significant population declines in most of the countries in which it is known from , however no quantitative data on the rate of decline is available .
. 2006 ) . this species is also listed under appendix iii of the bern convention .
this errata version of this assessment has been published to correct a mistake in the status of the population in the czech republic , it is now labelled as native .
füreder , l . , gherardi , f . & souty - grosset , c . 2010 .
( errata version published in 2017 ) . the iucn red list of threatened species 2010 : e . t2431a121724677 .
the only freshwater crayfish native to the uk ( 3 ) , this species is olive - green to brown in colour and can reach up to 12 centimetres in length . the common name refers to the fact that the undersides of the claws are off - white to pinkish in colour . females tend to have wider abdomens than males , and males have larger claws . in males , the first two appendages are specialised ; they are used to place a sperm mass ( spermatophore ) underneath the female during mating ( 2 ) .
this crayfish tends to be nocturnal , emerging at night to feed on a broad diet consisting of detritus , animal matter and plants . it also occasionally indulges in cannibalism , particularly on individuals with soft cuticles following their moult ( 2 ) .
mating takes place in autumn ; the eggs develop whilst attached to the mother ' s abdomen , and the female overwinters with the eggs still attached to her . after the eggs hatch , the juveniles remain attached to the mother before becoming independent at the beginning of summer . during the first year of life , juveniles may moult more than seven times . after they reach maturity , however , there tends to be an annual moult ( 2 ) .
this crayfish was once widely distributed across europe , but has undergone a severe decline , and remaining populations are increasingly fragmented ( 2 ) . before 1980 this species was also widespread throughout britain and ireland ( 2 ) , but a large number of populations have since been lost ( 3 ) . it is currently still fairly abundant in central and northern areas of england ( 2 ) .
you can view distribution information for this species at the national biodiversity network atlas .
the freshwater white - clawed crayfish tends to prefer clear , well - oxygenated , alkaline water ( 2 ) and occurs in small streams , lakes , rivers , water - filled quarries and reservoirs ( 2 ) .
the freshwater white - clawed crayfish is classified as endangered ( en ) on the iucn red list ( 1 ) . listed in appendix iii of the bern convention , annexes ii and v of the ec habitats directive and protected under schedule 5 of the wildlife and countryside act 1981 ( 3 )
perhaps the most devastating factor affecting freshwater white - clawed crayfish at present is crayfish plague , a virulent fungal disease carried by the aggressive introduced species , the american signal crayfish ( pacifastacus leniusculus ) ( 4 ) . spores of this disease can be spread in the water , on wet equipment and on fish ( 2 ) . competition with introduced crayfish species has also affected our native crayfish ( 3 ) ; signal crayfish were first introduced to the uk in the 1970s and are now naturalised and breeding ( 2 ) . two other introduced species have become established ( 3 ) ; the narrow - clawed ( or turkish ) crayfish ( astacus leptodactylus ) and the noble crayfish ( astacus astacus ) ( 2 ) . pollution and river works are also likely to have affected the species ( 2 ) .
the freshwater white - clawed crayfish has been targeted as a priority for conservation under the uk biodiversity action plan ( uk bap ) . the species action plan aims to maintain the current distribution of the species through a combination of restricting the spread of non - native crayfish and crayfish plague , as well as providing suitable habitat features ( 3 ) . the environment agency has carried out research into potential methods of controlling the signal crayfish , and is currently investigating the use of pheromones to lure this introduced species into traps ( 5 ) . it is an offence under schedule 9 of the wildlife and countryside act to release the three introduced species of crayfish into the wild ( 3 ) .
there may be further information about this species available via the national biodiversity network atlas .
environment agency . ( 2001 ) freshwater crayfish in britain and ireland . the environment agency , bristol .
environment agency . ( 2001 ) preventing the spread of crayfish plague in the south west . environment agency , bristol .
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( of astacus pallipes lereboullet , 1858 ) lereboullet , a . ( 1858 ) . descriptions de deux nouvelles especes d ' ecrevisses de nos rivieres . memoirs de la societe des sciences naturelles de strasbourg . 5 : 1 - 11 , 3 plates . [ details ]
crandall , k . a . & s . de grave . ( 2017 ) . an updated classification of the freshwater crayfishes ( decapoda : astacidea ) of the world , with a complete species list . journal of crustacean biology . [ details ]
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lives in a diverse variety of clean aquatic habitats but especially favours hard - water streams and rivers . a major threat to the native white - clawed crayfish is posed by the introduction of non - native species of crayfish , which have been farmed in britain since the late 1970s . soon after this , crayfish plague ( a virulent disease caused by the fungus
) broke out and spread rapidly , causing drastic losses of native crayfish in rivers in england . it is believed that this disease was introduced and is spread by the most frequently farmed species , the north american signal crayfish
, a carrier of the disease . crayfish plague can be introduced into a waterbody not only by entry of signal crayfish but also by water , fish or equipment that has been in contact with signals . this greatly increases the risk to remaining white - clawed crayfish populations .
signal and other non - native crayfish are larger and more aggressive than the native species and are able to produce more young . consequently , the introduced species pose a threat not only because some are disease - carriers , but also through predation and competition with white - clawed crayfish . in britain , signal crayfish are now well - established in the wild . in northern ireland no crayfish farms have been established and crayfish plague is unknown , although it occurs in the republic of ireland ( holdich & reeve 1991 ; holdich & rogers 1997 ) . it is only in areas free of disease that white - clawed crayfish are likely to survive in the future .
a significant part of the eu resource is found in the uk and the republic of ireland , where is widespread .
is widespread in most parts of england and is common in parts of eastern wales . it is present in south - west northern ireland . a significant part of the eu resource is found in the uk , but the species is now seriously threatened over most of its range in britain .
populations free of crayfish plague . a number of these safe havens in the north of england have been selected , as they are away from the main outbreaks of crayfish plague . the sites selected cover a variety of habitats , including rivers , natural lakes , and some ‘refuges’ of artificial origin ( but within the natural geographical range of the species ) that contain large isolated populations with a good chance of remaining free of crayfish plague . the relatively low proportion of the total uk population contained within the sac series reflects the fact that many recorded populations are in areas vulnerable to crayfish plague .
while the sac series makes a contribution to securing favourable conservation status for this annex ii species , wider measures are also necessary to support its conservation in the uk . these include actions taken under the
many designated sites are on private land : the listing of a site in these pages does not imply any right of public access .


fusinus cretellai is a species of sea snail , a marine gastropod mollusk in the family fasciolariidae , the spindle snails , the tulip snails and their allies .

fusinus cretellai

buzzurro g . & russo p . ( 2008 ) . a new replacement name for fusus crassus pallary , 1901 . triton 17 : 7 page ( s ) : 7 [ details ]
( of fusus crassus pallary , 1902 ) pallary p . ( 1901 - 1902 ) . diagnoses de quelques coquilles nouvelles provenant du maroc . journal de conchyliologie . 49 : 226 - 228 , 314 - 315 . , available online at urltoken page ( s ) : 314 [ details ]
after more than 2 years of preparations , the diatombase portal is now officially launched . . . .
last week - on may 30 and 31st – 8 thematic experts on talitridae came together for the first time during a lifewatch - worms sponsored workshop . the workshop took place at the hellenic centre for marine research in crete , where it was organized back - to - back with the 8th international sandy beaches symposium ( isbs ) . the group focused on identifying relevant traits for the talitridae , and adding this data through the amphipoda species database . . . .
on 23 april 2018 , a number of editors of the world register of introduced species ( wrims ) started a three day workshop in the flanders marine institute ( vliz ) . these three days were used to evaluate , complete and improve the content of this worms thematic register ( tsd ) . . . .
the 2nd worms early career researchers and 3rd worms achievement award were granted respectively to françois le coze and geoff read . congratulations ! . . .
in 2018 , to celebrate a decade of worms ' existence , it was decided to compile a list of our top marine species , both for 2017 and for the previous decade . . . .
the scleractinian corals are now accessible though their own list portal . this world list contains over 1 500 accepted names of extant species and is one of the most complete existing resources for scleractinian taxa . . .
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version 43 . 0 went live 11 / 6 / 2018 - i hope that the majority of issues have been fixed . my email address is on the home page if you see anything wrong .
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gibraltar area . 2m deep , on rock , aguilas , murcia , spain . 16mm .
synonym : crassus pallary . 3m deep , under stone , aguilas . 15mm .
buzzurro g . & russo p . ( 2008 ) . a new replacement name for fusus crassus pallary , 1901 . triton 17 : 7
buzzurro & russo , 2008 . in : costello , m . j . ; bouchet , p . ; boxshall , g . ; arvantidis , c . ; appeltans , w . ( 2014 ) european register of marine species , accessed through pesi at
this work is licensed under a creative commons attribution - share alike 3 . 0 license
pesi is funded by the european union 7th framework programme within the research infrastructures programme . contract no . ri - 223806 . activity area : capacities . period 2008 - 2011 - website hosted & developed by vliz banner picture : gannet ( morus bassanus ( linnaeus , 1758 ) ) by karl van ginderdeuren - contact pesi
an average of about 1400 new marine species are described each year worldwide . a surprising high number of these are from european waters , which one might have assumed were so well studied that they contained no surprises . these new species include all phyla , from microbes such as bacteria up to vertebrates . the majority of newly described species are invertebrates , partly because the formal process of naming new bacteria lags far behind the rate of their discovery . bellow you can find a list of all european species which have recently been discovered by marbef researchers . [ 1 ]
here you can find links to initiatives which aim to provide lists and information on all species ( both marine and terrestrial ) .
heip , c . , hummel , h . , van avesaath , p . , appeltans , w . , arvanitidis , c . , aspden , r . , austen , m . , boero , f . , bouma , tj . , boxshall , g . , buchholz , f . , crowe , t . , delaney , a . , deprez , t . , emblow , c . , feral , jp . , gasol , jm . , gooday , a . , harder , j . , ianora , a . , kraberg , a . , mackenzie , b . , ojaveer , h . , paterson , d . , rumohr , h . , schiedek , d . , sokolowski , a . , somerfield , p . , sousa pinto , i . , vincx , m . , węsławski , jm . , nash , r . ( 2009 ) . marine biodiversity and ecosystem functioning . printbase , dublin , ireland issn 2009 - 2539
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didemnum vexillum , the carpet sea squirt , is a species of colonial tunicate in the family didemnidae .

believed to be native to the waters around japan , it has been reported as an invasive species in a number of places in europe , north america and new zealand .

it is sometimes given the nickname " d. vex " because of the vexing way in which it dominates marine ecosystems when introduced into new locations .

this bottom-colonizing tunicate can build over most substrates , including cobble , and grows over other organisms when it needs more room to expand .

its appearance has given rise to the common name marine vomit .

it was first described from new zealand as didemnum vexillum in 2002 by kott .

at the time , he thought he was describing a species new to science .

didemnum vexillum

invasive species - didemnum tunicate ( didemnum vexillum ) alaska department of fish and game .
didemnum vexillum ( colonial sea squirt ) ; habit , on a boat hull .
didemnum vexillum ( colonial sea squirt ) ; habit , taken from a boat hull .
didemnum vexillum ( colonial sea squirt sp ) ; overgrowing solitary tunicates ( ciona intestin ) .
recommendations for reducing the rate of spread and potential re - invasion of didemnum vexillum . report of the gb working group for d . vexillum ( 2011 )
marine nuisance species - species didemnum vexillum doi . usgs . woods hole coastal and marine science center .
automated detection of ncrnas in the draft genome sequence of a colonial tunicate : the carpet sea squirt didemnum vexillum .
until recently , the taxonomy of didemnum vexillum and forms referred to in the scientific literature and media as “ didemnum sp . ” and “ didemnum sp . a” has been in dispute . however , new morphologic and genetic studies of species of didemnum collected worldwide ( lambert , 2009 ; stefaniak et al . , 2009 ) have shown : 1 ) that the valid taxonomic name for “ didemnum sp . ” and “ didemnum sp . a” is didemnum vexillum kott ( 2002 ) , originally described from new zealand ; 2 ) that didemnum vestum kott ( 2004 ) , originally described from new hampshire , is a junior synonym of d . vexillum ; and 3 ) the region of origin of didemnum vexillum is most likely japan . we follow this taxonomy here .
didemnum vexillum is a compound ascidian ( tunicate or sea squirt ) and belongs to the family didemnidae ( kott , 2002 ) .
automated detection of ncrnas in the draft genome sequence of a colonial tunicate : the carpet sea squirt didemnum vexillum . - pubmed - ncbi
worldwide occurrences table download . kmz file ( didemnum vexillum , usgs ) , and open it in google earth to see locations of worldwide occurrences .
national exotic marine and estuarine species information system ( nemesis ) - didemnum vexillum smithsonian institution . smithsonian environmental research center . marine invasions research lab .
stephan g . bullard and robert b . whitlatch in situ growth of the colonial ascidian didemnum vexillum under different environmental conditions ( pp 275 - 278 )
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these pages are under development - if you would like to recommend management information to include here please contact us . first records in great britain of the invasive colonial ascidian didemnum vexillum . kate griffith , stephen mowat , rohan h . f . holt , kirsten ramsay , john d . d . bishop , gretchen lambert and stuart r . jenkins ( 2002 ) . didemnum vexillum – feasibility of eradication and / or control in holyhead marina . ccw contract science report no . 875 ( 2009 ) . the carpet sea squirt didemnum vexillum : eradication from holyhead marina . progress to october 2009 . rohan holt , ccw survey of a non - native ascidian ( sea squirt ) didemnum vexillum in holyhead harbour . ccw marine monitoring report no ( 2009 ) . assessment of the impacts of didemnum vexillum and options for the management of the species in england . project report for defra ( 2010 ) . maps indicating potential spread of didemnum vexillum in gb . developed with funding from defra , ccw and snh . for information on methods refer to the above report ( ' assessment of the impacts of didemnum vexillum and options for the management of the species in england ' ) .
lambert l , 2009 . adventures of a sea squirt sleuth : unraveling the identity of didemnum vexillum , a global ascidian invader . aquatic invasions , 4 : 5 - 28 .
nicole l . lengyel , jeremy s . collie and page c . valentine the invasive colonial ascidian didemnum vexillum on georges bank ― ecological effects and genetic identification ( pp 143 - 152 )
bullard sg ; whitlatch rb , 2009 . in situ growth of the colonial ascidian didemnum vexillum under different environmental conditions . aquatic invasions , 4 ( 1 ) : 275 - 278 . urltoken
genetic conspecificity of the worldwide populations of didemnum vexillum kott , 2002 ( pdf | 1 . 5 mb ) aquatic invasions ( 2009 ) volume 4 , issue 1 : 29 - 44 .
threat to native ecosystems , especially in the province of zeeland , as didemnum sp .
issg . 2007 . ecology of didemnum sp . the global invasive species database , urltoken
lambert , g . 2009 . adventures of a sea squirt sleuth : unraveling the identity of didemnum vexillum , a global ascidian invader . aquatic invasions 4 ( 1 ) : 5 - 28 .
we assessed the relative growth of didemnum vexillum under different environmental conditions . pouches containing pre - weighed d . vexillum colonies were deployed at three different depths and in three different salinity regimes for two weeks . upon recovery , colonies were reweighed to determine their change in biomass . d . vexillum grew fastest in shallow water ( 1 . 0 m ) and in high salinity areas ( 26 - 30 ppt ) .
lauren stefaniak , gretchen lambert , adriaan gittenberger , huan zhang , senjie lin and robert b . whitlatch genetic conspecificity of the worldwide populations of didemnum vexillum kott , 2002 ( pp 29 - 44 )
colonial tunicates ( didemnum lahillei ) attached to mussels in puget sound . photo by gretchen lambert
denny cm , 2008 . development of a method to reduce the spread of the ascidian didemnum vexillum with aquaculture transfers . ices journal of marine science , 65 ( 5 ) : 805 - 810 . urltoken
denny , c . m . 2008 . development of a method to reduce the spread of the ascidian didemnum vexillum with aquaculture transfers . ices journal of marine science advance access , p . 1 - 6
didemnum vexillum , also known as dvex or carpet sea squirt , is a colonial ascidian thought to originate from japan . it reproduces and grows quickly and is classed as an invasive non - native species .
mary r . carman , hannah m . allen and megan c . tyrrell limited value of the common periwinkle snail littorina littorea as a biological control for the invasive tunicate didemnum vexillum ( pp 291 - 294 )
kott , p . , 2004 , a new species of didemnum ( ascidiacea , tunicata ) from the atlantic coast of north america : zootaxa , v . 732 , p . 1 - 10 . [ description of didemnum vestum and comparison with d . vexillum and d . lahillei ] ( pdf format )
the invasive colonial tunicate didemnum vexillum has become widespread in new england waters , colonizing large areas of shell - gravel bottom on georges bank including commercial sea scallop ( placopecten magellanicus ) grounds . didemnum vexillum colonies are also fouling coastal shellfish aquaculture gear which increases maintenance costs and may affect shellfish growth rates . we hypothesized that d . vexillum will continue to spread and may affect shellfish larval settlement and survival . we conducted a laboratory experiment to assess interactions between larval bay scallops ( argopectin irradians irradians ) and d . vexillum . we found that larval bay scallops avoid settling on d . vexillum colonies , possibly deterred by the low ph of the tunicate’s surface tissue . the results of this study suggest that widespread colonization of substrata by d . vexillum could affect scallop recruitment by reducing the area of quality habitats available for settlement . we propose that the bay scallop can serve as a surrogate for the sea scallop in estimating the negative impact d . vexillum could have on the recruitment of sea scallops on georges bank .
colonial tunicates ( didemnum lahillei ) attached to mussel cages in british columbia . photo by gordon king
adventures of a sea squirt sleuth : unraveling the identity of didemnum vexillum , a global ascidian invader ( pdf | 1 . 5 mb ) aquatic invasions ( 2009 ) volume 4 , issue 1 : 5 - 28 .
the goal of this website is to assemble and communicate information on the distribution , ecology , and marine habitat impacts of the invasive colonial ascidian invader didemnum vexillum . researchers and others are encouraged to share their observations on these topics .
jeffery m . mercer , robert b . whitlatch and richard w . osman potential effects of the invasive colonial ascidian ( didemnum vexillum ) on pebble - cobble bottom habitats in long island sound , usa ( pp 133 - 142 )
. in the netherlands , gittenberger ( 2007 ) describes the subtidal snail , trivia arctica , as a generalist predator of colonial ascidians ( including d . vexillum ) and another predatory snail of the genus lamellaria which appears to feed solely on d . vexillum .
summary of the d . vexillum trnas genes . pie charts indicate the fraction of the different anti - codons within each isoacceptor family
citation : forrest bm , fletcher lm , atalah j , piola rf , hopkins ga ( 2013 ) predation limits spread of didemnum vexillum into natural habitats from refuges on anthropogenic structures . plos one 8 ( 12 ) : e82229 . urltoken
rhode island marine & estuarine invasive species site - didemnum tunicate narragansett bay research reserve . coastal training program .
alien species alert : didemnum vexillum kott , 2002 : invasion , impact , and control ( feb 2017 ; pdf | 1 . 67 mb ) international council for the exploration of the sea . see also : alien species alert for more information
stefaniak l ; lambert g ; gittenberger a ; zhang h ; lin sj ; whitlatch rb , 2009 . genetic conspecificity of the worldwide populations of didemnum vexillum kott , 2002 . aquatic invasions , 4 ( 1 ) : 29 - 44 . urltoken
laing , i . , bussell , j . and somerwill , k . ( 2010 ) assessment of the impacts of didemnum vexillum and options for the management of the species in england . project report for defra , uk . available at : urltoken
( of didemnum vestum kott , 2004 ) kott . 2004 . zootaxa 732 : 1 - 10 [ details ]
lambert , g . , 2009 , adventures of a sea squirt sleuth : unraveling the identity of didemnum vexillum , a global ascidian invader : aquatic invasions , v . 4 , no . 1 , p . 5 - 28 . ( pdf format )
coutts adm ; forrest bm , 2007 . development and application of tools for incursion response : lessons learned from the management of the fouling pest didemnum vexillum . journal of experimental marine biology and ecology , 342 ( 1 ) : 154 - 162 . urltoken
didemnum vexillum ( d . vexillum ) is a marine colonial tunicate . tunicates , in general , are commonly referred to as ascidians or sea squirts . d . vexillum is known as “carpet tunicate” because of its growth pattern , or “glove leather tunicate” due to the fact that it feels like soft , wet leather . in alaska , it is mostly referred to by its shortened scientific name , “d . vex” ; an apt nickname since it reflects the vexing way the species has been observed taking over marine ecosystems when introduced to new environments .
global invasive species database - didemnum spp . ( tunicate ) iucn . species survival commission . invasive species specialist group .
carpet tunicate , colonial ascidian , colonial sea squirt , didemnid , didemnum tunicate , marine vomit , whangamata sea squirt .
page c . valentine , mary r . carman , jennifer dijkstra and dann s . blackwood larval recruitment of the invasive colonial ascidian didemnum vexillum , seasonal water temperatures in new england coastal and offshore waters , and implications for spread of the species ( pp 153 - 168 )
kott , p . , 2002 , a complex didemnid ascidian from whangamata , new zealand : journal of marine biology association of the united kingdom , v . 82 , no . 4 , p . 625 - 628 . [ first description of didemnum vexillum ] ( pdf format )
introduced species remark in new zealand ( nation ) : didemnum vexillum is considered a major threat to new zealand ' s mussel industry because of its demonstrated invasiveness on artificial structures , and its ability to over - grow and smother mussels ( coutts and forrest 2007 ) . [ details ]
stefaniak , l . , g . lambert , a . gittenberger , h . zhang , s . lin , and r . b . whitlatch . 2009 . genetic conspecificity of the worldwide populations of didemnum vexillum kott , 2002 . aquatic invasions 4 ( 1 ) : 29 - 44 .
valentine pc ; carman mr ; dijkstra j ; blackwood ds , 2009 . larval recruitment of the invasive colonial ascidian didemnum vexillum , seasonal water temperatures in new england coastal and offshore waters , and implications for spread of the species . aquatic invasions , 4 ( 1 ) : 153 - 168 . urltoken
settlement plate ( 14x14 cm ) with the white encrusting d . vexillum colony on the top left of which a piece was collected in december 2009 for the genome analyses
( of didemnum vestitum kott , 2004 ) kott , p . ( 2004 ) . a new species of didemnum ( ascidiacea , tunicata ) from the atlantic coast of north america . zootaxa . 732 : 1 - 10 . [ details ] available for editors [ request ]
visit the control section of the response tab to find out what adf & g has been up to . we partnered with the smithsonian to investigate use of biocides to control didemnum vexillum in whiting harbor . we learned that in small enclosures salt and chlorine are effective agents to remove tunicate colonies from treatment areas .
in the northeast pacific , didemnum vexillum is most similar to other didemnid tunicates , including d . carnulentum ritter and forsyth , 1917 , d . albidium ( verrill , 1871 ) , trididemnum opacum ( ritter , 1907 ) , t . strangulatum ( ritter , 1901 ) , and t . alexi lambert 2003 .
stefaniak , l . , lambert , g . , gittenberger , a . , zhang , h . , lin , s . , and whiltlatch , r . b . , 2009 , genetic conspecificity of the worldwide populations of didemnum vexillum kott 2002 : aquatic invasions , v . 4 , no . 1 , p . 29 - 44 . ( pdf format )
introduced species remark in new zealand ( nation ) : d . vexillum is considered a serious and persistent fouling pest to their commercial shipping industry and ports ( coutts and forrest 2007 ) . [ details ]
morris ja jr ; carman mr ; hoagland ke ; green - beach erm ; karney rc , 2009 . impact of the invasive colonial tunicate didemnum vexillum on the recruitment of the bay scallop ( argopecten irradians irradians ) and implications for recruitment of the sea scallop ( placopecten magellanicus ) on georges bank . aquatic invasions , 4 ( 1 ) : 207 - 211 . urltoken
stefaniak , l . , zhang , h . , gittenberger , a . , smith , k . , holsinger , k . , lin , s . and whitlatch , r . b . ( 2012 ) determining the native region of the putatively invasive ascidian didemnum vexillum kott , 2002 . journal of experimental marine biology and ecology , 422 - 423 : 64 - 71 .
james a . morris , jr . , mary r . carman , k . elaine hoagland , emma r . m . green - beach and richard c . karney impact of the invasive colonial tunicate didemnum vexillum on the recruitment of the bay scallop ( argopecten irradians irradians ) and implications for recruitment of the sea scallop ( placopecten magellanicus ) on georges bank ( pp 207 - 211 )
didemnum vexillum has been introduced to the northeast pacific , and has been recorded at several sites from alaska to california . this species also has been collected from numerous locations around the world , including the northeast united states , northern europe and great britain , japan , and new zealand ( lambert 2009 ) . its native geographical range likely includes japan ( stefaniak et al . 2012 ) .
image shows predation by cushion stars , patiriella regularis , and sea urchins , evechinus chloroticus , on a large ( ∼20×35 cm ) fragment of didemnum . predation by these and / or other species was observed following fragment inoculation into beds of the macroalga carpophyllum flexuosum , and when settlement plates with fragments or pre - established didemnum colonies were placed on the seabed .
the carpet sea squirt ( didemnum vexillum ) is an unusual marine animal that lives in immobile colonies made up of thousands of tiny , genetically identical individuals ( 2 ) ( 3 ) ( 4 ) . the common name of this species comes from the way in which these colonies often grow as flat , carpet - like mats across the ocean floor ( 2 ) ( 3 ) ( 5 ) .
griffith , k . , mowat , s . , holt , r . h . f . , ramsay , k . , bishop , j . d . d . , lambert , g . and jenkins , s . r . ( 2009 ) first records in great britain of the invasive colonial ascidian didemnum vexillum kott , 2002 . aquatic invasions , 4 ( 4 ) : 581 - 590 .
the colonial ascidian didemnum vexillum , sea carpet squirt , is not only a key marine organism to study morphological ancestral patterns of chordates evolution but it is also of great ecological importance due to its status as a major invasive species . non - coding rnas , in particular micrornas ( mirnas ) , are important regulatory genes that impact development and environmental adaptation . beyond mirnas , not much in known about tunicate ncrnas .
colonies of didemnum vexillum exhibit a wide variety of morphological variants . where current velocity is low , they form long , ropey or beard - like colonies that commonly hang from hard substrates such as docks , lines , and ship hulls . where current velocity is high , they form low , undulating mats with short surficial appendages that encrust and drape rocky seabeds ( pebbles , cobbles , boulders , and rock outcrops ) .
settlement plates were positioned in face - up and face - down orientations , with suspended plates compared to uncaged seabed plates . all plates were exposed to an ambient larval supply from a suspended pontoon 2–3 m away , for a three month experimental duration . a ) . mean didemnum cover ( % cover ±1se ) on plates inoculated with didemnum fragments . b ) . mean density of didemnum recruits ( ±1se ) on plates subjected only to ambient larval supply . different letters ( a , b , c ) indicate significant differences as indicated by the permanova post - hoc t - test .
perspex plates were positioned in face - up and face - down orientations , with the seabed treatment including a cage and no cage comparison . all plates were exposed to larval recruitment from a floating pontoon approximately 25 m away , for a three month experimental duration . a ) . mean didemnum cover ( % cover ±1se ) on plates inoculated with didemnum fragments . b ) . mean density of didemnum recruits ( ±1se ) on plates subjected only to ambient larval supply . different letters ( a , b , c ) indicate significant differences as indicated by the permanova post - hoc t - test .
the exotics guide : non - native marine species of the north american pacific coast ( revised sep 2011 ) - didemnum sp . a san francisco estuary institute ; center for research on aquatic bioinvasions .
d . vexillum appears to be undergoing a rapid worldwide expansion , with most of the new records appearing in the past 10 – 15yrs . in all cases where it has been recorded as a new occurrence , it has undergone simultaneous population increases .
osman rw ; whitlatch rb , 2007 . variation in the ability of didemnum sp . to invade established communities . journal of experimental marine biology and ecology , 342 ( 1 ) : 40 - 53 . urltoken
( of didemnum vestum kott , 2004 ) bouchet , p . ; fontaine , b . ( 2009 ) . list of new marine species described between 2002 - 2006 . census of marine life . [ details ]
minchin d ; sides e , 2006 . appearance of a cryptogenic tunicate , a didemnum sp . fouling marina pontoons and leisure craft in ireland . aquatic invasions , 1 ( 3 ) : 143 - 147 . urltoken
in two separate experiments of three months duration , different substrata were exposed to ambient larval recruitment , with half of them also inoculated with a didemnum fragment . a ) mean didemnum cover ( % cover ±1se ) on bare settlement plates compared with plates that were pre - fouled with other sessile species . b ) . mean didemnum cover ( cm 2 ±1se ) on bare settlement plates compared with cobbles that were collected from the adjacent intertidal zone . in both experiments , substrata were suspended between 0 . 5 and 1 . 5 m deep . different letters ( a , b ) indicate significant differences as indicated by the permanova post - hoc t - test .
the present paper describes a range of experiments designed to examine processes that affect the establishment of didemnum on suspended and rocky subtidal habitats in new zealand’s marlborough sounds ( 41 o 13′s 174 o 07′e ; fig . 1 ) . based on experimental evidence , as well as field observations , we consider the potential for didemnum to establish in natural seabed habitats , and the role of reservoir populations on artificial structures in the spread and establishment of the species .
introduced species vector dispersal in united states part of the north atlantic ocean ( marine region ) : the specific vector of the d . vexillum introduction is uncertain although international shipping , local boat traffic , and / or shellfish imports are among the most likely sources . [ details ]
settlement plates were positioned in face - up and face - down orientations , with the seabed treatment including a cage and no cage comparison . all plates were exposed to an ambient larval supply from a suspended pontoon approximately 25 m away , for a two month experimental duration . a ) . mean didemnum cover ( % cover ±1se ) on plates inoculated with didemnum fragments . b ) . mean survival of didemnum ( % survival ±1se ) colonies on plates for which a colony cover ( mean ∼73 % ) was pre - established at the start of the experiment . different letters ( a , b , c ) indicate significant differences as indicated by the permanova post - hoc t - test .
assumed to be native to the waters around japan , and introduced to pacific northwest waters , didemnum vexillum is a colonial tunicate consisting of many small individuals called zooids . each zooid pumps water through its own siphon , filters out oxygen and feeds on small organisms such as phytoplankton , zooplankton , oyster and mussel larvae , and other suspended organic materials . it then discharges the filtered water and waste into a common space that is shared within a system of other zooids where it is discharged through a small pore . d . vexillum’s clear , firm , fleshy matrix consists of several systems of zooids linked together to form a contiguous mass colony that looks like a network of darkish leaf - like veins with pores . each zooid will have a consistent color with the rest of the colony . the color of a colony can range from yellow to orange to reddish brown . as the colonies grow they can smother out other stationary wildlife and filter feeders , including mussels and oysters . d . vexillum exudes a toxic substance onto its surface , preventing other species from fouling its exterior and discouraging predators .
the consistent failure of didemnum to establish in any of the seabed transplants , or on the face - up orientation of the no cage treatments , suggests that predators had relatively unlimited access . in contrast , colonies on face - up plates within cages persisted to a similar extent to that observed on suspended treatments , thus illustrating the invasion potential of didemnum in the absence of benthic predation pressure . such results are of interest , as a face - up orientation approximates a common scenario in which didemnum forms high - biomass colonies on suspended structures , which can slough off and provide a considerable supply of fragments to the adjacent seabed [ 30 ] . however , irrespective of whether didemnum propagules colonize suspended structures or the seabed , subsequent establishment and invasiveness on face - up surfaces may be less than face - down , and subject to a greater suite of limiting factors than predation alone , such as over - settlement by seasonal algae ( this study ) and smothering by sediment [ 44 ] .
didemnum revealed a greater ability to establish as a result of fragment inoculation than ambient larval recruitment . this was evident in experiments that compared different substrata ( see fig . 2 ) , and was also observed in the field during the blackwood and onahau bay experiments . in fact , at blackwood bay , the cover of didemnum resulting from ambient recruitment was not measurable by image analysis . the important role of fragments in the establishment of didemnum [ 43 ] and other colonial ascidians [ 56 ] has previously been recognized . natural fragmentation in the species arises from the tendril - like lobes that colonies often exhibit [ 57 ] , and fragments can remain viable for as long as four weeks when artificially kept in suspension [ 45 ] . although didemnum can reattach from fragments as small as 5×3 mm , survivorship increases with fragment size under field conditions [ 44 ] ; thus , relatively large fragments were used in the present study to maximize the likelihood that they would be viable and able to reattach .
the comprehensive annotation of the d . vexillum non - coding rnas provides a starting point towards a better understanding of the restructuring of the small rna system in ascidians . furthermore it provides a valuable research for efforts to establish detailed non - coding rna annotations for other recently published and recently sequences in tunicate genomes .
substratum type and the presence of an established fouling assemblage were unimportant as explanatory variables for the invasion success of didemnum . the species established equally well on settlement plates and cobbles , and was able to recruit to , and subsequently overgrow , cosmopolitan fouling taxa such as colonial ascidians and encrusting bryozoans . the latter finding is consistent with field observations and manipulative experiments from a number of localities world - wide , which indicate the ability of didemnum and other ascidians to overgrow other sessile organisms [ 16 ] , [ 18 ] , [ 54 ] , [ 55 ] . a single exception for didemnum is evident from a recent experimental study ( ∼10 weeks duration ) in long island sound , which suggested that invasion success was linked to the availability of unoccupied space [ 41 ] .
the combination of regional scale transplants , smaller spatial scale experiments , and associated field observations , provided compelling evidence that benthic predation is a key mechanism that limits didemnum ’s establishment in the natural cobble habitats of the study region . simultaneously , the widespread occurrence of the species in habitats that are elevated off the seabed ( see table 1 ) , is consistent with evidence for other sessile marine invertebrates that both anthropogenic and biogenic structures can provide a refuge from benthic predation [ 17 ] , [ 37 ] , [ 62 ] , [ 63 ] . however , most studies of didemnum and other colonial ascidians have shown that predation acts to reduce but not prevent establishment in natural habitats [ 36 ] – [ 38 ] , [ 40 ] . by contrast , the present study indicates that benthic predation may completely exclude didemnum from certain habitat types . this result is consistent with recent analysis showing that , unlike other didemnid ascidians that contain compounds that are thought to reduce predation [ 64 ] , didemnum does not contain potent secondary metabolites [ 26 ] .
in autumn 2008 at blackwood bay , didemnum establishment by fragments was poor compared with the previous summer ( fig . 5a ) , but was consistent with the fact that the persistence of pre - established colonies was simultaneously low ( fig . 5b ) . in the fragment inoculation experiment , a significant treatment×orientation interaction ( table 5a ) reflected the significantly greater didemnum cover on face - down suspended plates ( 6 % cover ) than in all other treatments in which cover was < 1 % ( fig . 5a , permanova , pair - wise comparison p < 0 . 05 ) . on no cage plates , no didemnum was recorded in the face - up orientation ( fig . 5a ) , nor did any pre - established didemnum persist in that orientation ( fig . 5b ) . by contrast , survival was significantly greater in seabed cage and face - down suspended treatments ( fig . 5b , permanova , pair - wise comparison p < 0 . 05 ) . whereas mean survival was comparable for the two orientations in the cage treatments ( 19 . 5±5 . 8 and 31 . 2±21 . 1 % for face - down and face - up plates , respectively ) , the face - up suspended plates became covered in a layer of filamentous algae and didemnum survival was poor ( fig . 5b ) .
valentine pc ; carman mr ; blackwood ds ; heffron ej , 2007 . ecological observations on the colonial ascidian didemnum sp . in a new england tide pool habitat . journal of experimental marine biology and ecology , 342 ( 1 ) : 109 - 121 . urltoken
in new zealand , aquaculture industries have spent $ 807 , 000 attempting to eradicate the species from economically important habitats such as mussel lines . the sea scallop , placopecten magellanicus , is regularly overgrown by d . vexillum in georges bank and in eastport , maine ( valentine et al . , 2007b ) . the impact of this species on biology of sea scallops and its ecological and economical impact on fishing is yet unknown , though studies suggest the presence of the species inhibits recruitment ( morris et al . , 2009 ) . ecological knowledge gained from studies on this and other similar species suggest that d . vexillum may become a permanent member of the community .
two transplant experiments were conducted in january 2008 ( austral summer ) to examine the regional - scale establishment potential of didemnum in the marlborough sounds ( table 2 ) . firstly , large colony fragments ( ∼100×200 mm ) were attached to cobbles and transplanted to subtidal cobble habitats along each of 11 transects ( 1–16 m depth , 10 m long , n = 102 in total ) in three main locations : ruakaka bay , blackwood bay and onahau bay ( fig . 1 ) . the transects were revisited over the following 24 hours , and after 1 month , and the presence / absence of didemnum colonies was determined .
secondly , fragments were transplanted into canopies of a fucoid macroalgal species ( carpophyllum flexuosum ) that didemnum had previously been observed to establish on ( see table 1 ) . it was hypothesized that the erect biogenic structure provided by the algal canopy would elevate didemnum from the seabed and provide a refuge from predation . two plots ( a treatment and reference plot ) of c . flexuosum were identified in each of two locations ( fig . 1 ) , each covering an area of at least 10×10 m at approximately 2 m depth . ten didemnum fragments ( ∼30×100 mm ) were transplanted into the treatment plots in each of four positions : ( i ) within canopy approximately 1 m from the seabed , ( ii ) within canopy at the base of the stipe of each c . flexuosum , ( iii ) within canopy on the seabed , and ( iv ) at the edge of each canopy on the seabed ( i . e . at the distinct boundary between the canopy and barren rock habitat ) . for each of the ten canopy transplants , fragments were attached to ten separate tagged c . flexuosum plants . the plots were revisited over the following 24 hours , and after 1 month , and the presence / absence of didemnum colonies was determined .
we provide here a comprehensive homology - based annotation of non - coding rnas in the recently sequenced genome of d . vexillum . to this end we employed a combination of several computational approaches , including blast searches with a wide range of parameters , and secondary structured centered survey with infernal . the resulting candidate set was curated extensively to produce a high - quality ncrna annotation of the first draft of the d . vexillum genome . it comprises 57 mirna families , 4 families of ribosomal rnas , 22 isoacceptor classes of trnas ( of which more than 72 % of loci are pseudogenes ) , 13 snrnas , 12 snornas , and 1 other rna family . additionally , 21 families of mitochondrial trnas and 2 of mitochondrial ribosomal rnas and 1 long non - coding rna .
in addition to these limiting factors , considerable small - scale variability was often evident within the same treatment ( e . g . among plates in the same treatment separated by only tens of centimeters ) , which was not always explainable by extrinsic factors such as differential predation pressure . this variability mirrors that previously observed across small spatial scales in the recruitment and establishment of didemnum and other ascidians [ 18 ] , [ 66 ] . such findings suggest a stochastic element to successful establishment that may in part be driven by inherent variability in didemnum ( e . g . differential viability of fragments from the same or different colonies ) .
transplants of didemnum fragments were conducted along 11 transects ( 1–11 ) across three main locations ( filled squares ) also used for small scale experiments : ruakaka bay ( 1–2 ) , blackwood bay ( 3–9 ) and onahau bay ( 10–11 ) . filled triangles indicate locations of fragment transplants into macroalgal ( carpophyllum flexuosum ) beds .
valentine pc ; collie js ; reid rn ; asch rg ; guida vg ; blackwood ds , 2007 . the occurrence of the colonial ascidian didemnum sp . on georges bank gravel habitat : ecological observations and potential effects on groundfish and scallop fisheries . j . exp . mar . biol . ecol , 342 : 179 - 181 .
within the past few years , the colonial ascidian species didemnum vexillum has been reported from many parts of the world and has drawn attention as a nuisance species because it reproduces rapidly and fouls marine habitats ( including shellfish aquacultures and fishing grounds ) , ship ' s hulls , and maritime structures . it has been reported from northern europe ( netherlands , france , ireland , northern ireland , wales , scotland , england , and italy ) , the u . s . east coast ( new jersey , new york , connecticut , rhode island , massachusetts , new hampshire , maine ) , offshore of new england on georges bank , the u . s . and canadian west coasts ( california , oregon , washington , british columbia , alaska ) , japan , and new zealand .
didemnum also failed to establish in the carpophyllum flexuosum transplant experiment . in the case of the seabed transplants ( adjacent to and at the edge of the c . flexuosum canopy ) , this result was consistent with the regional - scale transplant experiment , with predation on the fragments observed within the first day of the experiment . however , didemnum ’s failure to establish following transplant to the basal stipe of c . flexuosum , and especially the canopy , was contrary to our expectations . the seastar c . muricata was observed to consume one of the basal transplants , and one of the canopy transplants had t . smaragdus on it . one month later , neither the transplanted fragments nor their remains were visible .
didemnum vexillum colonies alter marine habitats and threaten to interfere with fishing , aquaculture , and other coastal and offshore activities . the colonies shown here are found on hard substrates that include dock structures and floats , wood and metal pilings , moorings and ropes , steel chain , automobile tires , polythene plastic , rock outcrops , gravel seabed ( pebbles , cobbles , boulders ) , and ship hulls . they overgrow organisms such as tunicates , sponges , macroalgae , hydroids , anemones , bryozoans , scallops , mussels , and oysters . where these colonies occur on the seabed , they likely cover the siphons of infaunal bivalves and also serve as a barrier between demersal fish and benthic prey . the colonies have been found at water depths ranging from intertidal to continental shelf depths of 65m ( 213 ft ) .
in the second experiment ( see table 2 ) , the cover of didemnum developing from ambient larval inoculation and fragments was compared between replicate ( n = 4 ) settlement plates and natural greywacke cobbles of comparable surface area , which were collected from the study site . the selected cobbles were devoid of visible macrofouling , and were centre - drilled so that they could be hung in a similar manner to the plates . plates and cobbles were suspended horizontally facing down ( 0 . 5–1 . 5 m depth ) for three months at ruakaka bay ( fig . 1 ) . the cover of didemnum was determined at the end of the three month deployment , and was expressed as surface area ( cm 2 ) to account for the differences in cobble sizes .
unlike the solitary tunicates , the colonial d . vexillum broods its larvae within the colony’s matrix , and then releases the planktonic larvae . the larvae are very short lived , likely settling onto a firm surface and near the point of origin , where it metamorphoses into a zooid an then buds off asexually to form a colony . however , fragments from a colony can survive indefinitely , reproducing asexually while drifting , or traveling within ship ballast water to colonize new areas .
the decline in establishment success of fragments in the autumn experiment at blackwood bay ( compared with summer ) was accompanied by poor survival of pre - established colonies at the time of the mid - winter cessation of the experiment . such findings are consistent with a seasonal decline in success due to decreasing water temperatures [ 61 ] , as opposed to a failure of the inoculation method . thus , even though didemnum can persist and still recruit until mid - winter in the study region [ 46 ] , the period of greatest risk for establishment and proliferation is clearly during warmer summer months . despite an apparent seasonal decline in invasion success in cooler months , the fact that didemnum still persists means that established populations will provide a reservoir from which extensive colonies may develop the following summer .
d . vexillum prefers protected marine waters and reproduces rapidly , fouling ship hulls , docks , piers and shellfish aquacultures . it can be found on any substrate , including gravel , seabed , metal , plastic , rope , fiberglass , wood , and even eelgrass and seaweeds . mature colonies in calm waters can appear as long , rope - like drippy , mats extending downward from where they are attached . it has been found from intertidal to over 200 feet depth . they do well in polluted waters .
a series of field caging experiments was undertaken to test the hypothesis that didemnum could establish on ( or survive transplant to ) the seabed , if benthic predation was reduced ( table 2 ) . the overall experimental design compared establishment success among settlement plates ( 20×20 cm ) that were deployed in two horizontal orientations ( face - up and face - down ) , and which were either : ( i ) uncaged on the seabed , ( ii ) fully caged on the seabed using a 10 mm stainless mesh screen ( to exclude larger predators ) , or ( iii ) suspended at comparable depths from adjacent suspended structures that were infected with didemnum . seabed cages and plates were attached to gridded ( 150×150 mm ) steel reinforcing mesh . previous studies in the region have shown that the cage design and method does not introduce experimental artefacts [ 44 ] .
management of d . vexillum has been restricted to attempts in new england ( j dijkstra and l harris , university of new hampshire , usa , personal communication , 2009 ) and new zealand ( coutts and forrest , 2007 ) . during their study , coutts and forrest ( 2007 ) examined a variety of eradication techniques and determined that regional eradication is unlikely , but eradication at small - scales may be possible . denny ( 2008 ) tested several chemical techniques and determined a 2 % bleach solution worked best . establishing monitoring programs is likely the most effective management strategy .
the fragment inoculation component of the caging experiment was repeated during april to june 2008 , covering a two month autumn to mid - winter period in new zealand . daily mean water temperatures of 13 . 1 to 17 . 1°c during the second experimental period were within the species optimal range [ 25 ] , [ 29 ] , and didemnum was still actively recruiting throughout this period . simultaneous with the fragment inoculation experiment , the persistence of pre - established didemnum colonies was assessed using the same experimental design ( n = 6 per treatment ) . for this component , the colonies were pre - established on settlement plates using fragments . the resultant colony cover on the plates at the beginning of the experiment ranged from 50 to 92 % ( mean 72 . 1 % ±1 . 7se ) and plates were randomly allocated across treatments . results were expressed as colony survival , reflected as the change in percentage cover at the completion of the experiment .
in the caging experiments , the establishment success of didemnum was greatest on suspended plates , from which benthic predators would have been completely excluded . where predation pressure was reduced by caging , didemnum fragment establishment and recruitment yielded broadly similar patterns to suspended treatments . greater recruitment to the face - down aspect of plates was consistent with the negative phototaxis exhibited by ascidian larvae immediately prior to settlement [ 61 ] , [ 65 ] . marked variability in establishment success in some caged treatments was evident ( see fig . 4 ) , which possibly reflected incursion into some cages of small predators ( in particular juvenile cushion stars , patiriella regularis ) that were not excluded by the 10 mm mesh . the low level recruitment and colony cover on uncaged face - down seabed plates was not anticipated , but likely reflects reduced predation pressure . the face - down orientation would have restricted predator access into the spaces among the cobbles , especially in the case of larger - bodied urchins and cushion stars .
bullard sg ; lambert g ; carman mr ; byrnes j ; whitlatch rb ; ruiz gm ; miller rj ; harris lg ; valentine pc ; collie js ; pederson j ; mcnaught dc ; cohen an ; asch rg ; dijkstra j ; heinonen k , 2007 . the invasive colonial ascidian didemnum sp . : current distribution , basic biology , and potential threat to marine communities of the northeast and west coasts of the united states . j . exp . mar . biol . ecol , 342 : 99 - 108 .
caging experiments were first conducted for three months ( 17 january –11 april 2008 ) during the recruitment peak at the study site in blackwood bay ( fig . 1 ) . seabed caged and uncaged plates were deployed at approximately 10 m depth , and arranged 25 m distance from a floating pontoon ( dimensions ∼2×4 m ) that had been pre - seeded with approximately 350 kg of reproductive didemnum [ 51 ] . uncaged plates were also suspended beneath the pontoon at a similar depth . a fragment of didemnum was attached to one set of plates ( n = 6 ) and colony percentage cover measured after three months . the ambient larval supply from the pontoon was simultaneously measured on an additional set of plates ( n = 3 suspended , n = 6 seabed caged and uncaged ) that were deployed for the same period , and involved counting the density of recruits in the laboratory using a binocular microscope . daily mean water temperature during the experiment were determined from hourly measurements with a tidbit v2 temperature logger , and ranged from 17 . 0 to 19 . 6°c .
colonial ascidians are hermaphroditic - they are both male and female at the same time - and reproduce sexually by broadcast spawning , and asexually by budding . d . vexillum broods larvae in the colony’s matrix . the larvae spend a few hours moving within the water current before settling on a firm surface . the larvae metamorphose into zooids that can then start a new colony . larval settlement happens at different times depending on a number of habitat parameters , such as water temperature . when lobes , sections of tunicate colonies , break off , they can drift in the water to a new site , resettle on hard substrate , and begin a new colony .
d . vexillum is likely to originate from japan ( lambert , 2009 ) and is now found in the northeast pacific ( british columbia to southern california ( cohen et al . , 2001 ; lambert , 2009 ) , northeast of the usa ( bullard et al . , 2007a ; dijkstra et al . , 2007a ) , new zealand ( coutts , 2002 ; coutts and forrest , 2007 ) , the netherlands ( lambert , 2009 ) , northwestern france ( lambert , 2009 ) , ireland ( minchin and sides , 2006 ; minchin , 2007 ) , england ( arenas et al . , 2006 ) and north wales ( usgs , 2009 ) .
a two - way repeated - measures analysis of variance ( rm - anova ) was used to test for differences through time in the percentage cover of didemnum on bare and pre - fouled plates at the ruakaka site . the experimental design included ‘inoculation’ ( two levels : fragments and recruits ) and ‘fouling’ ( two levels : bare and pre - fouled ) as fixed orthogonal factors . data from the substratum type experiment were analyzed using a two - way anova with ‘inoculation’ ( two levels : fragments and recruits ) and ‘substratum’ ( two levels : ‘plate’ and ‘cobble’ ) as fixed orthogonal factors .
during the summer of 2008 in blackwood bay , didemnum established a greater colony cover and recruited at greater densities on face - down plates compared to face - up ones ( orientation , p < 0 . 01 , table 4a , figure 4a ) . additionally , there was a significant treatment effect ( table 4a , figure 4a ) , with suspended plates having greater cover than the seabed no cage treatment ( permanova , pair - wise comparison p < 0 . 05 ) , but not the seabed cage treatment . on face - down plates , fragment inoculation led to 34 . 2 ( ±12 . 8 ) and 39 . 8 % ( ±17 . 9 ) mean cover in suspended and cage treatments , respectively , compared with 8 % cover ( ±3 . 4 ) on no cage plates . on face - up plates , didemnum failed to establish without caging , and cover was relatively low but comparable on suspended and caged plates . patterns in recruitment density largely mimicked the fragment inoculation patterns , with a significant effect of orientation and treatment ( table 4b , figure 4b ) . no recruits were recorded on the face - up plates unless they were caged or suspended ( fig . 4b ) .
a colonial tunicate , d . vexillum colonies consist of many small individuals called zooids , each about a millimeter in length , sharing a common tunic or matrix . zooids bodies are small , soft , and sac - like . tunicates are filter feeders that survive by eating detritus and plankton - tiny animals and plants that drift in the ocean . each zooid pumps water through its body , extracting food particles from the water and then , along with neighboring zooids , discharges the filtered water into a common space . the water leaves the colony from shared siphons . siphons appear as small pores in the surface of the tunicate . the siphons are clearly visible on solitary tunicates , and sometimes expel water when gently squeezed , thus the name “sea squirt” .
the experiment conducted in summer 2009 at onahau bay generally confirmed the importance of orientation , and the greater establishment ( fig . 6a ) and recruitment ( fig . 6b ) of didemnum in suspended compared with seabed habitats . in the fragment inoculation experiment , a significant treatment×orientation interaction ( table 6a ) indicated an orientation effect for suspended , but not seabed plates ( see fig . 6a , permanova , pair - wise comparison p < 0 . 05 ) . a similar general pattern was evident for larval recruitment ( fig . 6b ) , although significant effects of both treatment and orientation were detected ( table 6b ) .
d . vexillum is difficult to identify correctly with the naked eye because it looks like other didemnids , some of which are native to coastal alaska . it may be orange , pink , yellow , tan or cream in color . its surface has visible veins with small pores . the texture of the sea squirt is smooth , like firm gelatin and leathery rather than slimy . the colony may cling strongly to the surface on which it grows and can be difficult to pull off nets , lines and other fibrous materials . mature colonies can form large , pendulous lobes that resemble tendrils of dripping wax when growing on vertical substrate in the water column or in areas with low current velocity . when growing on the sea floor and in areas with high current velocity it forms low , undulating mats with short lobes .
while the results suggests a more important role for fragmentation in the initial stages of establishment , localized ambient larval recruitment may lead to a comparable level of establishment to fragments in the longer - term ( > 12 months ) [ 54 ] . thus , the apparent advantage in establishment by fragmentation may diminish over time . the findings highlight that despite the potential for dispersal in this species over scales of hundreds of meters and perhaps a few kilometers [ 51 ] , low level larval recruitment at the outer limits of the dispersal range may not immediately lead to the development of extensive new populations of didemnum , even on suspended artificial structures which generally appear optimal for establishment .
didemnum established equally well on settlement plates , irrespective of whether they were bare or pre - fouled ; however , inoculation with fragments led to a colony cover that was considerably greater than that arising from ambient recruitment alone ( fig . 2a ) . on pre - fouled plates , microscopical observation revealed new recruitment and colony growth on top of the existing fouling . after three months , plates inoculated with fragments had a mean colony cover of 59 . 2 to 78 . 3 % ( ±23 . 7 and 7 . 3 % , respectively ) compared with < 3 % cover on plates exposed to larval recruitment alone . hence , there was a statistically significant effect of inoculation type , which was consistent over time ( table 3a ) . in contrast , there was no overall effect of substratum , but the substratum effect was variable over time ( table 3a , substratum×month , p < 0 . 05 ) . even after one month , the didemnum cover resulting from fragment inoculation ( mean 36 . 3±6 . 1 and 18 . 3±1 . 6 % for bare and pre - fouled plates , respectively ) was already considerably greater than achieved from ambient recruitment . the comparison of plates and cobbles yielded a similar pattern , with significantly greater colony cover arising from fragment inoculation compared to larval recruitment , but no significant effect of substratum type ( fig . 2b , table 3b ) .