Volume 11, Issue 2 (2016)
published June 2016
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Research articles |
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Nikolas John Kaplanis, Jill L. Harris and Jennifer E. Smith
Distribution patterns of the non-native seaweeds Sargassum horneri (Turner) C. Agardh and Undaria pinnatifida (Harvey) Suringar
on the San Diego and Pacific coast of North America
(pp 111–124)
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Here we report the occurrence of the two non-native brown macroalgal species Sargassum horneri (Turner) C. Agardh and
Undaria pinnatifida (Harvey) Suringar in San Diego County and describe expansions in their ranges and new invasions
on the California and Baja California coasts. Both species have exhibited characteristics of successful invaders: establishing
in new areas, spreading locally, and persisting through multiple generations in areas that have been invaded. These species now
occur primarily in harbors, but have also invaded open coast sites, suggesting that they can invade areas with relatively high
wave action and with well-established native benthic communities. The rapid and uncontrolled spread of these species to date
has serious implications for their expansion along the west coast of North America. The ecological and economic consequences
of these invasions require further research.
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Bram D’hondt, Luc Denys, Wim Jambon, Roeland De Wilde, Tim Adriaens, Jo Packet and Johan van Valkenburg
Reproduction of Crassula helmsii by seed in western Europe
(pp 125–130)
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The amphibious plant species Crassula helmsii is a widely established and still-spreading alien
in various parts of Europe, where it is considered invasive as its dense swards stress the viability of local biota.
The species was considered to exclusively reproduce through vegetative means, until ex situ germination was recorded
from a single locality in Belgium. We assessed whether this seed viability holds on a wider scale, by testing
16 populations from The Netherlands, Belgium, northern France, eastern England and northern Germany in a greenhouse
germination experiment. Seedlings were observed from all populations but two, and from each of the five countries.
Although most fruits were lacking seeds and the inferred germination percentages were overall low, germinable seed
numbers are considerable given the high density of flowering stems. An in situ test revealed seeds to make it through
normal winter conditions without signs of physical damage and with retention of germinability. Our results suggest
that reproduction by seed is a relatively cryptic but widespread phenomenon throughout western Europe. The persistency
of seed banks requires further investigation. Nonetheless, these findings already challenge the efficacy of techniques
currently applied in C. helmsii control.
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Pieter Boets, Dimitri Brosens, Koen Lock, Tim Adriaens, Bart Aelterman, Joost Mertens and Peter L.M. Goethals
Alien macroinvertebrates in Flanders (Belgium)
(pp 131–144)
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Biological invasions of aquatic macroinvertebrates are gaining interest because of their potential
for significant ecological and socio-economic impacts (positive and negative). In the present study,
an inventory was made of the alien macroinvertebrates occurring in Flanders (northern Belgium) based
on extensive existing collections of biological samples and supplemented with our additional sampling
programs. Fresh and brackish waters as well as the Belgian coastal harbours, situated at the interface
of the marine environment, were investigated. Over 2,500 samples containing alien macroinvertebrates
were identified to species level, which allowed us to accurately map their distribution in Flanders.
Alien macroinvertebrates are widespread and abundant in many watercourses in Flanders. Four new
macroinvertebrate species for Flanders were discovered: Procambarus clarkii (Girard, 1852),
Echinogammarus trichiatus (Martynov, 1932), Synurella ambulans (F. Müller, 1846) and
Laonome calida Capa, 2007. Fifty-two alien macroinvertebrates were encountered in fresh and
slightly brackish surface waters, and 21 alien species were reported for the Belgian part of the North
Sea and its adjacent estuaries. Most alien macroinvertebrates collected were crustaceans and molluscs.
Alien species found in fresh and brackish water mainly originate from the Ponto-Caspian area and North
America; fewer species originated from Asia and South- and East-Europe. The major pathways were probably
shipping and dispersal through canals. Based on observations in neighbouring countries, several additional
species are expected to arrive in the near future. Follow-up work is needed to assess the ecological and
economic impacts of existing alien macroinvertebrates, and a monitoring program is needed to detect
new incoming species.
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Diana Teubner, Ann-Katrin Wesslein, Peter Browne Rønne, Michael Veith, Christian Frings and Martin Paulus
Is a visuo-haptic differentiation of zebra mussel and quagga mussel based on a single external morphometric shell character possible?
(pp 145–154)
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The sharp-angled (presence of an acute ridge) or rounded (absence of an acute ridge) transition of the ventral and dorsal shell surfaces
is the “key feature” for the distinction of Dreissena polymorpha and Dreissena rostriformis. However, up to now it has not been
possible to put this into a quantifiable framework. Therefore, the aim of this study was to develop a method, which (i) facilitates
the quantification of this feature as a morphometric parameter and (ii) to test whether the presence or absence of an acute ridge
can be used to distinguish the two species both in mathematical terms and under field conditions. We called the new parameter ‘angularity’ (An)
and developed a method for its quantification. An ≤ 3.3 and An ≥ 4.7 were the discriminant thresholds for quagga mussels and zebra mussels,
respectively. 3.3 < An < 4.7 did not allow for a clear distinction between species. Nevertheless, An is highly sensitive in morphometrically
discriminating both species: more than 96% of the mussels were correctly classified whereas less than 1% were falsely classified. We conducted
a visuo-haptic experiment in which we asked test persons to rate mussels according to their angularity (acute ridge present vs. absent).
Remarkably, our results revealed that all participants were well able to distinguish the species at an error rate of 8.4 %. Nevertheless,
even naïve persons who have no previous knowledge of dreissenid mussels can reliably select specimens of zebra and quagga mussels under
field conditions based on the angularity alone.
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Mark Wejlemann Holm, Jens Kristian Davids, Per Dolmer, Esbern Holmes, Thomas Theis Nielsen, Bent Vismann and Benni Winding Hansen
Coexistence of Pacific oyster Crassostrea gigas (Thunberg, 1793) and blue mussels Mytilus edulis Linnaeus, 1758 on a sheltered intertidal bivalve bed?
(pp 155–165)
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The invasive Pacific oyster, Crassostrea gigas Thunberg, 1793 was introduced in Denmark for aquaculture in the 1970s. Presently,
feral populations are found in many parts of the country, with the largest populations established on existing beds of blue mussel,
Mytilus edulis Linnaeus, 1758. This study was conducted in the Limfjord estuary, at Agger Tange, where C. gigas was introduced in 1972.
The study site is a large cluster of raised intertidal bivalve beds inhabited by C. gigas and M. edulis in a sheltered part of the estuary.
The two bivalves have some of the same living requirements, and as C. gigas have been present in the ecosystem for more than 40 years,
we hypothesize that the presence of C. gigas has altered the spatial and temporal distribution of M. edulis by inducing a niche separation.
The spatiotemporal development of the bivalve bed was determined using orthophotos. C. gigas and M. edulis were collected from the bivalve
bed, shell lengths were converted into biomass, which were interpolated to create biomass contours and combined with modelled topography of the bivalve
bed to study niche separation. The bivalve bed slowly extended northwards over a period of 11 years, where it also became more fragmented. The northern
part of the bed was composed of mussel mats on top of soft sediment. This area was dominated by M. edulis, while areas in the south were dominated
by C. gigas. In the southern part, the bivalve bed was composed of thick and compact sediment suggesting it represent the oldest part of
the bivalve bed. There were no differences in the conditions of C. gigas and M. edulis from old or newly established areas, and there were
no difference in the vertical distributions of the bivalve species. Thus, spatial and temporal separation of the two species is not pronounced at present,
and thus unable to explain why they seemingly coexist.
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Mattias Hempel, Rüdiger Neukamm and Ralf Thiel
Effects of introduced round goby (Neogobius melanostomus) on diet composition and growth of zander
(Sander lucioperca), a main predator in European brackish waters
(pp 167–178)
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We inspected diet and growth of zander Sander lucioperca, a main predator in North European brackish waters,
from the Kiel Canal, northern Germany, to analyse effects of the introduced round goby Neogobius melanostomus
as possible prey. Round goby represented the most important fish prey taxon in the zander diet in 2011–2013 with 21.8%
of relative importance index (RI) over all inspected specimens. In particular zander of total length ≥200 mm fed
heavily on round goby, at least in the warmer quarters (2nd and 3rd) of the years under study. RI for these
quarters was ranging from 10.4% to 52.1% for predator specimens of 200–399 mm and from 45.6% to 79.7% of RI
for specimens of ≥400 mm. In the colder quarters of the inspected years (1st and 4th), zander ≥400 mm showed a high
amount of cannibalism, with RI of young-of-the-year zander as prey ranging from 23.9% to 38.9%. The asymptotic
total length (L∞) of the zander, calculated by the von Bertalanffy growth equation, was 937 mm. In comparison with data
from 1995/1996, before the round goby invasion in 2006, zander from our study showed considerable differences in diet
composition. RIms herring and Pomatoschistus spp. decreased from 26% to 13.4% and
14.2% to 4.4%, respectively. RI of young-of-the-year zander as prey for larger zander increased from 1.2%
to 7.7% and round goby occurred as newly established prey taxon. Zander also showed faster growth and a better condition
factor. We assume that this development has the potential to enhance the situation of the local fisheries that
are strongly related to the catch of zander. In addition, abundance control of round goby seems to result from
the high predator abundance..
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Nils van Kessel, Martijn Dorenbosch, Jan Kranenbarg, Gerard van der Velde and Rob S.E.W. Leuven
Invasive Ponto-Caspian gobies rapidly reduce the abundance of protected native bullhead
(pp 179–188)
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Invasions by alien species may cause a decline in populations of vulnerable protected species through interference and resource competition.
During the last decade, four invasive goby species of Ponto-Caspian origin have displayed rapid dispersal in The Netherlands. High densities
of these species have been recorded in large rivers and hydrologically connected water bodies such as canals and floodplain lakes. In the River
Meuse, alien tubenose goby (Proterorhinus semilunaris), round goby (Neogobius melanostomus) and bighead goby (Ponticola kessleri)
occupy similar habitat to native, protected river bullhead (Cottus perifretum), i.e., coarse substrates with large pebbles, and groyne stones
and riprap that protect river banks against erosion and preserve river channels. In the years following the arrival in 2011 of N. melanostomus
in the River Meuse, a rapid decline in native C. perifretum average density from twenty to one individual per 100 m² was observed, most likely
due to predation and competition for shelter and/or food. C. perifretum density also declined at sites colonized by Ponticola kessleri
and/or Proterorhinus semilunaris only. However, when compared to sites where N. melanostomus was present, C. perifretum density
remained relatively high. Similar effects on other native benthic fish species may occur in the near future due to the presence of alien gobies.
Compliance with ecological status objectives relating to the European Habitats Directive and Water Framework Directive may not be achievable due
to the loss of protected and endangered native fish species in areas invaded by alien gobies.
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Andrée D. Gendron and David J. Marcogliese
Reduced survival of a native parasite in the invasive round goby: evidence for the dilution hypothesis?
(pp 189–198)
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With economic globalization, a growing number of exotic species are integrating into food webs outside
their historical range, giving rise to the development of novel associations between exotic hosts and
local parasites. Depending on the parasite’s ability to survive and undergo transmission, invasive exotic
hosts can act as sinks or reservoirs for native parasites, thus either decreasing or increasing their
overall abundance in indigenous hosts. Here we evaluate the relative host competence of the invasive
round goby (Neogobius melanostomus) for a native acanthocephalan species, Neoechinorhynchus
tenellus, in the Great Lakes – St. Lawrence River basin. The second most abundant helminth acquired
by the round goby, N. tenellus was found to die prematurely in this novel paratenic (transport) host.
On average, nearly half of the cysts found in gobies sampled at 14 localities contained dead and degenerated
cystacanths. Parasite remnants in hepatic tissues were surrounded by mast cells indicative of an innate
inflammatory host reaction. Conversely, cystacanths of N. tenellus were intact in johnny darters
(Etheostoma nigrum) and logperch (Percina caprodes), two co-occurring native paratenic hosts.
We conclude that the round goby is currently a poor host for N. tenellus relative to indigenous
counterparts. As such, this abundant exotic fish could act as a sink and impair the transmission of
N. tenellus, possibly resulting in parasite dilution in native fish competitors. The significantly
higher intensity and prevalence of infection in johnny darters at a goby-free locality supports this
hypothesis. However, this new host-parasite relationship might evolve with time toward an attenuation
of the goby immune defense reaction. Indeed, we found a negative correlation between the frequency
of cystacanth degradation and time since gobies established in a given locality, with the lowest
degeneration rate in the St. Clair River area where the round goby was first recorded in
the Great Lakes – St. Lawrence basin. The dilution effect, if it exists, could then be temporary.
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Benjamin J. Wegleitner, Andrew Tucker, W. Lindsay Chadderton and Andrew R. Mahon
Identifying the genetic structure of introduced populations of northern snakehead (Channa argus) in Eastern USA
(pp 199–208)
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With new introductions of invasive species occurring at an alarming rate, resource managers must be able
to rapidly determine the source of introduction if there is to be a chance of preventing further spread
or future invasions. The first North American populations of reproducing northern snakehead (Channa argus)
were detected in Maryland in 2002 and have continued to spread into new watersheds. We used four microsatellite
markers to describe genetic characteristics of four established C. argus populations in Eastern U.S.A.,
a collection of samples of unknown origin from a Chinatown market in Manhattan, New York, and of a C. argus
population of uncertain status in the Upper Hudson River. We aimed to determine the probable source
of the introduction of C. argus to the Upper Hudson River basin and to clarify the genetic structure
of C. argus populations in northeast U.S.A., overall. Results from population structure analysis infer
two distinct genetic groups among the specimens sampled. Measures of genetic distance suggest the C. argus
population in the Upper Hudson is most similar to the population in the Lower Hudson near Queens, NY. Results
conclude that the Potomac River and Chesapeake Bay basins represent one genetic population, which suggests
that introductions to the Chesapeake Bay were sourced from the Potomac population and/or that the Bay does not
represent a barrier to C. argus dispersal. Overall, our analysis provides evidence of multiple introductions
into U.S. waters and human mediated secondary spread from these founding populations.
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Vanessa Salete Daga, Tiago Debona, Vinícius Abilhoa, Éder André Gubiani and Jean Ricardo Simões Vitule
Non-native fish invasions of a Neotropical ecoregion with high endemism: a review of the Iguaçu River
(pp 209–223)
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The freshwater fish fauna of the Neotropics comprises one of the most diverse ichthyofaunas globally. The Iguaçu ecoregion of the Neotropics
includes about 100 described species, of which ≈70% are endemic and the majority of these are considered to be threatened with extinction.
As is the case in freshwaters worldwide, the Iguaçu ecoregion has been strongly impacted by a variety of factors, including urbanization,
agriculture, the construction of dams and the introduction of non-native species. There is, however, a paucity of information on fish invasions
and their impacts in the Iguaçu ecoregion. To address this knowledge gap an exhaustive literature review was conducted to determine the extent
of introductions, the main vectors of introductions and the major risks associated with the introduction of non-native fish into the Iguaçu ecoregion.
A total of 41 studies concerning non-native fish in the Iguaçu ecoregion were found, the majority (56.1%) from lists of species and first records
of non-native species; while 29.3% of the studies only mentioned possible negative impacts of non-native species and 14.6% of studies evaluated,
indirectly, the impacts of non-native species. The Iguaçu ecoregion has a long history of fish introductions, beginning with the first record
of the “common carp” Cyprinus carpio in 1944, and continuing to the recent record, in 2012, of Steindachnerina brevipinna. Since 1944,
29 non-native species have been introduced, 19 from different ecoregions of the Neotropics, and 10 introduced from other zoogeographic regions
(Ctenopharyngodon idella, C. carpio, Hypophthalmichthys molitrix, H. nobilis and Misgurnus anguillicaudatus
from Palearctic region; Clarias gariepinus, Oreochromis niloticus and Tilapia rendalli introduced from Ethiopian region,
and Ictalurus punctatus and Micropterus salmoides from Nearctic region). The main vector of introduction was aquaculture, with
the aquarium trade, baiting, sport fishing and stocking also playing roles. Studies indirectly investigating the establishment and spread
of the introduced species in the Iguaçu ecoregion found nine non-native species which were considered established. Moreover, studies evaluating
the impact of non-native species have investigated changes in the feeding habits of non-native species, suggesting competition with native species
for food resources, and the increase in the number of fish species introduced over time. The impacts of non-native fishes, often associated with
other environmental changes, such as the construction of dams and pollution in the Iguaçu ecoregion, may have severe consequences for the endemic
fish fauna, resulting in the further decline and potential extinction of native species.
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