Publication Date:
2024-05-16
Description:
The invasive alien false mussels Mytilopsis leucophaeata cochleata and Dreissena polymorpha (Dreissenidae) have established populations in the North Sea canal in the Netherlands that connects the harbours of Amsterdam with the North Sea. The favourable
and unfavourable salinity ranges of both species were earlier studied in long-term outdoor mesocosm experiments. Their occurrence in salinity gradients in estuaries or canals connecting seaways to freshwater harbours provides information on their salinity
tolerance under field conditions. By the combination of laboratory experiments and
field data using the same source population a high predictability can be expected for
establishment of the gradients facilitated by constructions. The reliability of experimentally derived salinity-tolerance limits for both dreissenid species was tested using
data on their distribution in a salinity gradient of the littoral zone along the North Sea
canal. The mussels used for the survival experiments in mesocosms were also collected
from this canal. Favourable salinity ranges for adult survival in the mesocosms were
0.2 – 17.5 for M. leucophaeata cochleata and 0.2 – 6.0 for D. polymorpha. Unfavourable salinities were outside these ranges and led to high and fast mortality of these
species. Mytilopsis leucophaeata cochleata was present over nearly the whole length of
the North Sea canal with the highest densities close to the sea sluices where also the
highest salinities and water temperatures were measured. Their densities in the canal
decreased gradually at larger distances from the sea. Dreissena polymorpha co-exists
with M. leucophaeata cochleata at the east end of the canal with low salinity due to
the influence of freshwater of the river Rhine. The occurrence of D. polymorpha was
restricted to a salinity below 4 and M. leucophaeata cochleata only occurred at a salinity above 1.5 (maximum value measured in the canal 9.2). Shorter salinity gradients
with lower salinity ranges provided additional information on the co-existence of both
species. Co-existence was observed at a salinity range of 1.5–3.3 (own data), 1.0–3.5
(Van Couwelaar and Van Dijk 1989), both in the North Sea canal, and 0.2–2.8, in the Canal through Voorne (Janssen and Janssen-Kruit 1967). These data correspond with
studies of both species by Walton (1996) in the Hudson River (salinity range 0–3).
Found salinity ranges in the North Sea canal for both species match with the tolerance
results obtained by mesocosm experiments. A new invading dreissenid mussel Dreissena rostriformis bugensis and a mytilid Ischadium recurvum occur in the North Sea canal
since 2006 and 2012, respectively. Competition between recent and earlier invaders is
likely when salinity tolerances are similar. It has already been observed that D. rostriformis bugensis outcompetes D. polymorpha under freshwater conditions (Bij de Vaate
et al. 2014; Matthews et al. 2014). Ischadium recurvum has the potential to colonize
large parts of the canal and to be a strong competitor of M. leucophaeata cochleata
(Goud et al. 2019). Since January 2022, the new ‘Zeesluis IJmuiden’ with the biggest
locks in the world is in use, affecting the probability of population establishment of
new introduced and invasive alien mussel species.
Keywords:
co-existence
;
dark false mussel
;
densities
;
distribution
;
Dreissenidae
;
North
;
Sea canal
;
salinity
;
water temperature
Repository Name:
National Museum of Natural History, Netherlands
Type:
info:eu-repo/semantics/article
Format:
application/pdf