Dikerogammarus water is over 13oc. A study conducted by

Dikerogammarus villosus

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Charlee mcmanus | Ecology of freshwaters | 22/12/17

Species
ecology

Life cycle and reproduction

During D.
Villosus reproduction the male carry the females by taking hold of them
prior to them molting. Once the female has shed, copulation takes place. At
this point the females and males can be seen swimming together in their pairs
and are difficult to separate. Once mating is completed the male releases the
female and the female carries the embryos in a pouch until hatching. When D. villosus are juveniles they hatch at lengths ranging between 1.8
– 4.7mm, at 6mm’s in length they reach sexual maturity. Maturity can be reached
in as little as a month providing the water temperature is 20oc.
According to a study by Devin. Et al (2004) during water temperatures of 5.5 –
10.5oc females can grow between 2.2 – 2.9 mm per month while males
in the same temperature grow only 1.3 – 1.6 mm per month. However, in warmer
waters of 14.5 – 22oc both sexes can grow 2.6mm in two weeks. From
the point in which female D. Villosus reach
maturity they can reproduce throughout the year providing the temperature of
the water is over 13oc. A study conducted by Devin. Et al. (2004)
found that there where 3 breeding peaks. The first peaks were during mid-April,
followed by August and then finally in mid-October. Female D. Villosus are also able to produce up to 200 offspring per peak
however in most cases less than 50 offspring are produced.

Habitat

Within the United Kingdom and throughout Europe D. villosus inhabit both fresh and
brackish waters including canals, rivers and lakes. D. villosus can also be found in vegetation and amongst rocks
within lakes and rivers. Furthermore, D.
villosus can adapt and tolerate different water temperatures and salinity
levels. A study conducted by M. c. M. Bruijs. Et al concluded that D. villosus can withstand a wide range
of temperatures ranging from 5oc – 20oc and that D. villosus are also able to adapt to
varying levels of salinity. In the experiment conducted by M. c. M. Bruijs. Et
al the D. villosus could not
survive in salinity of 25%, however they were able to survive at 10% and after
10 days they had adapted to be able to withstand salinity levels of 20%. Furthermore
D. villosus are also able to survive
outside of water bodies, studies have shown that they are able to survive
inside the shell clusters of zebra mussels on the sides of boats for at least 6
days (Martens and Grabow 2008) and that they are able
to survive for up to 6 days in roots and piles of macrophytes outside of water
bodies (Rewicz et al). Another study conducted by B?cela-Spychalska et al.
(2013) concluded that D. Villosus are
even able to survive between 3-5 days within folds of diving suits that are
moist.

Feeding habits

D. villosus are an omnivorous
predator whom will prey upon a variety of invertebrates including Dragon and
mayfly nymphs, Chironomids, leeches, isopods and aquatic bugs. Furthermore,
killer shrimp have been known to prey upon fish eggs and even juveniles. D. villosus kill their prey by biting
into them and shredding them prior to eating. It has also been observed that D. villosus also kill and injure prey
needlessly without feeding on them.  D. villosus have the capability to have
a more damaging effect on prey communities than predators such as fish, as
unlike fish they are similar in size to their prey and can penetrate prey
shelters thus leaving no hiding places. although D. Villosus are predators they are also able to feed on microalgae,
carrion and detritus. Microalgae is efficiently consumed by D. villosus during their juvenile stage
prior to them reaching maturity. furthermore, a study conducted by Platvoet et
al. 2006 was able to confirm that D.
villosus lacked mouthparts with any morphological specializations thus
concluding that D. villosus where
able to feed on varying food sources

Predators

Known predators of D.
Villosus are varying fish species including trout, perch and the ell. Furthermore
D. Villosus have also been known to
kill and eat each other.

Solutions

Since the first sighing of D. Villosus in September 2010 both natural England and the
environment agency within the UK have been working together to minimize the
chance of the species spreading throughout other water bodies. The first
solution to the problem was to minimize the spread as quickly as possible. The
environment agency thus led an extensive investigation into Grafham
reservoir.  The investigation concluded
that the species had not yet spread to any waters leading from the contaminated
sight or in any nearby waters. However even though there was not a spread of
the invasive species the first brief also states that water surveys will be
conducted throughout the UK to pin point any other areas in which contain the
invasive species. Furthermore, a risk assessment was created by natural England
and the environment agency, due to the risk assessment measures where put into
place in Grafham whereby boaters and anglers that use the reservoir where to
abide by stricter biosecurity measures, such as the “wash down and clean off”
facilities on site. This measure was put into place to minimize the spread of D. Villosus.

Following the briefing note in 2010 a further 4
briefing notes where created regarding the spread of D. Villosus within the UK. Since the first sighting in 2010 within
Grafham reservoir, Cardiff bay and Eglwys Nunydd in south wales were also
reported to have the invasive species within the area during 2010. Furthermore,
another site in Norfolk broads (Barton broad) was also reported to have D. Villosus during 2012. The final
briefing note published in 2012 encouraged and is further advertising the “check,
clean, dry” scheme which was established in briefing note 4. The “check, clean,
dry” poster is posted throughout the UK in vulnerable areas.

Briefing note 5 also states that the scientific and
technical advice group or STAG has also provided expert advice on how to manage
the D. Villosus invasion and has also
been conducting research. A study of the implications D. Villosus will have on biodiversity in the UK was studied by Cambridge
University and supported by the university of Leeds and Queens university in
Belfast, the study was funded by the Esmee Fairbairn foundation and natural
England, this study researched the parasites that may be carried by the species
and if the species can be affected by such parasites.

Another solution was to use suitable disinfectant
substances to further improve current biosecurity measures. Defra commissioned
CEFAS to investigate into this in 2012. The disinfectants that where to be used
where to be safe and effective for use in field. The aim of the use of
disinfectants was to use them on a large scale to completely eradicate or to
even control the current populations of D.
Villosus in the UK. It was believed that the use of disinfectants along
with the conclusion from a study funded by Defra’s water framework directive
regarding the introduction pathways of D.
Villosus would result in effective control of the invasive species.

In 2012 a final eradication report was published by
CEFRAS that listed multiple different methods of eradication of the invasive
species D. Villosus. Some of the
methods where to physically remove them through trapping, by modifying the
habitats in which D. Villosus inhabit
by removing rocks or adding chemical or electrical barriers. Biological
controls where also suggested through adding known predators and parasites,
furthermore male sterilization and the use of semiochemicals where also
suggested as viable means of controlling the population.

However along with D.
Villosus came a parasite. The microsporidian Cucumispora Dikerogammari was able to follow the invasive species to
the UK. Cucumispora Dikerogammari is
a parasite that invades the muscles of the host, it then quickly reproduces and
eventually kills the host due to the number of parasites reproduced. Although
this could be a viable solution to the control of the D. Villosus population in the UK there is concern that the
parasite may also cause harm to the native species within such water bodies. A
study that was conducted by Bacela-Spychalska, K. et al investigated the
effects of the parasite Cucumispora Dikerogammari
on activity levels and the appetite of D.
Villosus. The study found that infected D.
Villosus at a late stage of infection where more active than the early
stage infected. When bloodworms where added to the experiment both the infected
and non-infected ate the bloodworms, however the infected ate much less than
the healthy D. Villosus. The fact
that infected D. Villosus are more
active is a benefit as the parasite is dependent on cannibalism. Cannibalism is
common in D. villosus so by the
infected being more active the chances of it being eaten by another D. Villosus is higher. Thus, causing the
parasite to continue infecting and killing the invasive species.

Conclusion.

In conclusion D.
Villosus have the capability to be severely damaging to the native species of
the UK due to there ability to reproduce very efficiently, the fact that there
is a limited number of predators and their ability to adapt to varying water
temperatures and salinity levels. Although D.
Villosus seem to be the model for invasive species they do have flaws. By
using effective biosecurity measures to control the spread and continuing
research into D. Villosus there is a
possibility that the invasion can be controlled and eventually eradicated from
UK waters.   

References.

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