DOI: 10.17026/dans-xnd-jscx
title: Data from: Salinity as a barrier for ship hull related-dispersal and invasiveness of dreissenid and mytilid bivalves

description: Data from: Salinity as a barrier for ship hull related-dispersal and invasiveness of dreissenid and mytilid bivalvesMarine Biology 163: article 147Marinus van der Gaag, Gerard van der Velde, Sander Wijnhoven, Rob S.E.W. LeuvenIntroductionIn this archive the data are presented from the study of the salinity tolerance of the benthic stage of Conrad’s false mussel, Mytilopsis leucophaeata (Conrad, 1831) (Dreissenidae). The salinity tolerance of M. leucophaeata was compared with the zebra mussel, Dreissena polymorpha polymorpha (Pallas, 1771) (further referred to as D. polymorpha) (Dreissenidae), and the blue mussel, Mytilus edulis edulis L., 1758 (further referred to as M. edulis) (Mytilidae). This part of the study was performed in outdoor mesocosms at the Radboud University in Nijmegen in the period 1991-1995. The salinity tolerance study is a part of the thesis: Conrad’s false mussel (Mytilopsis leucophaeata) (Dreissenidae), biology of an early invader in the Netherlands. The aim of the thesis is to obtain more insight in the autecology and life history of M. leucophaeata in relation to important environmental factors.Sampling sitesMussels were collected from the North Sea canal (Noordzeekanaal) and The IJ, at sampling locations with different salinities. M. edulis was collected from the North Sea, on the outside of sluices near Velsen (salinity 17 PSU) (52.461464 North; 4.554730 East), M. leucophaeata was collected inside the sluices in the North Sea canal (salinity 6 PSU) (52.465800 North; 4.632216 East) and D. polymorpha was collected from Lake IJ opposite Amsterdam’s central railway station (salinity 1.5 PSU) (52.382355 North; 4.902987 East).Experimental set-up for salinity tolerance studiesThree long-term experiments were carried out with D. polymorpha, M. leucophaeata and M. edulis. Twelve outdoor concrete tanks (length 150 cm, width 80 cm, height 60 cm) served as mesocosms and were buried in the ground (depth 50 cm). The mesocosm inner walls were lined with PVC. The ground between the mesocosms was paved with concrete slabs to prevent plant growth. The mesocosms were covered with a frame with chicken wire to prevent leaf litter and terrestrial animals falling into the tanks.Mussel survival was equated to tolerance and studied in a salinity gradient. The salinity gradient was created by varying salinity concentration over the series of mesocosms and prepared by mixing water collected outside - (salinity 17 PSU) and inside the sluices (salinity 6) of the North Sea canal, with fresh water collected near Nijmegen from the Waal River, the main distributary of the Rhine River in the Netherlands. The water was not filtered before use. Salinity higher than 17 PSU were produced by mixing sea water from outside the sluices with 10 % river water and adding Mediterranean Sea salt produced for sea aquarium use.During the experiments, salinity was checked weekly using an YSI model 33 S-C-T meter. Salinity levels were kept stable by adding sea salt after periods of rain, or tap water after periods of evaporation at high temperatures. The measured deviation from the initial salinity was always less than 10%. The water temperature was measured weekly with a mercury thermometer. In each mesocosm, a small air compressor and a bubble stone maintained the oxygen content. The air bubbles caused constant mixing of the water in the mesocosm.The mussels were stocked in nylon nettings of size 30 x 15 cm, mesh size 1 mm; in most cases 24 mussels belonging to several size classes were added per netting (3 specimens per size class). This was done to ensure that all mussels were present at the same depth and are exposed in this way to similar conditions and for a practical reason, viz. that all mussels could easily be taken out of the water and studied. Each nylon netting was marked with a number and was attached to the chicken wire covering with a rope located in the center of the mesocosm and allowed to hang freely in the water at a depth of approximately 25 cm. Depending on the number of test species in the mesocosm (i.e., one, two or three species), two, four or six nets hung in a mesocosm, respectively. The lengths of all mussel shells were measured before they were used in the experiment with a Vernier caliper with an accuracy of 0.1 mm. The mussels were not marked individually. To mimic ship transport, the mussels were not acclimated before they were exposed to the salinities in the mesocosms thus were added after collection in the field directly to the mesocosms. No food was added to the mesocosms, so that mussels were dependent on sources of nutrition initially present and spontaneously developed plankton in the water.In the first experiment that occurred in 1991-1992, the salinity gradient consisted of the 12 mesocosms containing salinities of 0.5, 1.7, 3.2, 6.0, 7.0, 8.5, 10.0, 12.0, 14.0, 17.0, 20.0 and 30.0 PSU after mixing. In the second experiment of 1992-1995, the salinity gradient consisted of 12 mesocosms with salinities of 0.2, 2.0, 4.0, 7.5, 9.0, 10.5, 13.0, 15.0, 17.5, 30.0, 36.0 and 40 PSU after mixing, to which all three bivalve species were exposed, except for 36 PSU which was not used for D. polymorpha and 40 which was only used for M. edulis. In the third experiment occurring in 1993-1995, the salinity gradient consisted of 11 mesocosms with salinities of 0.2, 2.0, 4.0, 6.0, 7.5, 9.0, 10.5, 13.0, 15.0, 17.5 and 30.0 PSU after mixing to which D. polymorpha and M. leucophaeata were exposed. The nettings were opened every week for inspection. Individuals that were still alive were counted, put back into the nettings and hung back in the mesocosms. Empty shells and dead mussels identified by their open shells were removed and counted, their shell lengths measured and the date when death was established was recorded. Subsequently water temperature and salinity were measured. The salinity of the water in each mesocosm was adjusted to the initial level when necessary, as described previously. Analyses were carried out using length of the survivalperiod, water temperature and numbers of dead and living mussels to calculate survival percentages. The influence of mussel size on species survival capacity was also analyzed.Mussels and size classesThree long-term experiments were carried out with the three bivalve species. During the three experiments, the selected shell length classes of D. polymorpha were 4-5, 6-7, 8-9, 10-11, 12-13, 14-15, 16-17, and 18-26 mm. In the experimental periods 48 individuals were added per mesocosm, distributed over two nettings. During the three experiments, the selected shell length classes for M. leucophaeata were 4-5, 6-7, 8-9, 10-11, 12-13, 14-15, 16-17, and 18-23 mm. In the experimental periods 48 individuals were added per mesocosm, distributed over two nettings.During experiment two (1992-1995) also nine size classes were selected for M. edulis that, for the most part, differed by 3 mm (4-7, 8-11, 12-15, 16-19, 20-23, 24-27, 28-31, 32-35 and 36-49 mm) resulting in a total of 54 M. edulis individuals per mesocosm distributed over two nettings.Here we describe the archived files:2021_VanderGaag_ThesisMytilopsis_Chapter2_Mytilopsis(august1991).odsSurvival of Mytilopsis leucophaeata in mesocosms in the period 1991 – 1992.Date in DD/MM/YYYYWatertemp = water temperature in degrees Celsius in the mesocosm0,5S = Number of survived mussel at the salinity of 0,5S (= 0.5 permillage)Days = number of days after start of the experiment0,5-17,0S = summed number of survived mussels in all salinities%N = percentage of survived mussels alive from start date.2021_VanderGaag_ThesisMytilopsis_Chapter2_Dreissena(august1991).odsSurvival of Dreissena polymorpha in mesocosms in the period 1991 – 1992.Date in DD/MM/YYYYWatertemp = water temperature in degree Celcius in the mesocosm0,5S = Number of survived mussel at the salinity of 0,5S (= 0.5 permillage)0,5-6,0S = summed number of survived mussels in salinity-range 0.5 – 6.0%N = percentage of survived mussels (0.5 – 6.0) alive from start date.Days = number of days after start of the experiment2021_VanderGaag_ThesisMytilopsis_Chapter2_Mytilopsis(october1992).odtSurvival of Mytilopsis leucophaeata in mesocosms in the period 1992 – 1994.Date in MMDDYY‰ = permillage salinity in mesocosmExperiment start with measurements of exact shell length(in mm)/size class: 2 nettings(a, b)/mesocosm (salinity permillage)2021_VanderGaag_ThesisMytilopsis_Chapter2_Dreissena(october1992).odtSurvival of Dreissena polymorpha in mesocosms in the period 1992 – 1994.Date in MMDDYY‰ = permillage salinity in mesocosmExperiment start with measurements of exact shell length(in mm)/size class: 2 nettings(a, b)/mesocosm (salinity permillage)Availability of small sized mussels was too low to fill all the nettings.At salinities higher than 6.0‰ only the number of mussels is given.2021_VanderGaag_ThesisMytilopsis_Chapter2_Mytilus(october1992).odtSurvival of Mytilus edulis in mesocosms in the period 1992 – 1994.Date in MMDDYY‰ = permillage salinity in mesocosmExperiment start with measurements of exact shell length (in mm)/size class: 2 nettings(a, b)/mesocosm (salinity permillage)Mortality mussels at salinities 0.2 – 9.0 and salinity 40+ was finished within 14 days. Shell length measuring was not interesting because of no growth in that short period.2021_VanderGaag_ThesisMytilopsis_Chapter2_Mytilopsis(april1993).odtSurvival of Mytilopsis leucophaeata in mesocosms in the period 1993 – 1995.Date in MMDDYY‰ = permillage salinity in mesocosmExperiment starts with measurements of exact shell length (in mm)/size class: 2 nettings(a, b)/mesocosm (salinity permillage)2021_VanderGaag_Thesis_Mytilopsis_Chapter2_Dreissena(april1993).odtSurvival of Dreissena polymorpha in mesocosms in the period 1993 – 1995.Date in MMDDYY‰ = permillage salinity in mesocosmExperiment start with measurements of exact shell length(in mm)/size class: 2