Shell mass, biomass, condition and reproductive state of the invasive bivalve Mytilopsis leucophaeata (Conrad, 1831) (Dreissenidae)Journal of Shellfish Research 39(2): 433-439Marinus van der Gaag, Gerard van der Velde, Frank P.L. Collas & Rob S.E.W. LeuvenIntroductionIn this archive, we share the data of the measurements of shell mass, biomass, condition and reproductive state of Mytilopsis leucophaeata collected in the North Sea canal near Velsen, together with physical and chemical parameters and chlorophyll a values from the sampling point. This study aimed to analyze data on shell dimensions (length and height), calci- and periostracum mass and biomass. Information on such data and the relation between the condition and reproduction of M. leucophaeata was not available. This information is useful for the conversion of shell length data to mass data. The onset and development of spawning can be determined based on changes in biomass in relation to environmental conditions. This information is a part of the thesis with the aim to obtain more insight in the autecology and life history of Mytilopsis leucophaeata in realation to important environmental factorsExperimental set-upSampling of water quality parametersWater temperature during 1989-1994 ranged from 2.9 - 26.1 0C, chlorophyll a from 1 - 67 µg l-1. Salinity in the canal ranged in the period 1989-1992 from 3.2 – 9.0. Chloride values of 1993 and 1994 were obtained from waterbase (Rijkswaterstaat 2019). By multiplying the chloride value from km 2 with 1.80655, salinity values were calculated. These values ranged from 1.2 to 6.8.Collection of musselsIn the period 1989 - 1992 at least 250 individuals were collected on a monthly basis. Shell length and shell height were measured of all sampled individuals (N=12,551) using a Vernier callipers with an accuracy of 0.1 mm.In the period 1993-1994 samples were taken from the littoral zone for biomass measurements (Number of individuals = 2,225).The samples were brought to the laboratory where they were stored alive in plastic bags at 4 0C. The shell was carefully brushed to clean it from debris and separated the flesh from the shell after. Both were dried in a stove at 60 ˚C for 48 hours. A desiccator, filled with silica gel in the bottom bin, was used during cooling down the material to room temperature. Shell and flesh were weighed separately using a Mettler Toledo analytical balance. To determine the ash weight and shell weight the dried and weighed shell and flesh were put separately in pieces of heated cleaned aluminium foil and were heated in a furnace at 550 0C for 24 hours. Mean periostracum weight was determined for 32 shell doublets by subtracting the total weight of all shells from the total weight of the heated shells.In the period May 26 - December 21 1993, 1,505 individuals were collected for measuring shell weight, dry flesh weight and total dry weight. For these individuals the relation between shell length (mm) and shell weight (mg), between shell length and dry flesh weight (mg), and between shell length and total dry weight (mg) (shell plus flesh) was determined. At May 26 1993, 126 mussels were used to study the relation between shell length and flesh dry weight (DW), ash weight (AW) and ash-free dry weight (AFDW), respectively.Gonad Squash Preparation and Gonad IndexMussels were collected, and were prepared on a fortnightly basis for analyses of their gonadal condition. Forty mussels were used belonging to the 12-13 mm size class. In the laboratory, these mussels were stored at 4 0C in a plastic bag pending further examination. The shell length of each individual was measured and the shells opened by slicing the posterior adductor muscle. Gonadal tissues showed to be invading the whole body tissue, filling the mantle lobes, mesosoma and outer surface of the digestive glands. Males are distinguishable by the milky white gonads; females have bright orange and brick red gonads.The reproductive stage of mussel population was assessed using gonad squash preparations based on the methods described by King et al. (1989). This method is not so time consuming and provides sufficient and trustful information. The numerical ranks are valued following King et al. (1989): 0 – resting, 1 – immature and/or spent, 2 – developing and/or spawning, 3 – ripe and/or redeveloping. The gonad index (GI) used to express the gonad cycle is determined as follows:Number in each stage x numerical ranking of the stage x 100GI = -------------------------------------------------------Number of animals in the stageCondition indexThe changes in dry flesh weight of M. leucophaeata in 1993 and 1994 were studied based on additionally collected individuals (22 months x 20 mussels) with a mean standardized shell length of 12.5 mm (range 10.8 – 13.5 mm). Mussels build up biomass to grow and to develop their gonads and will have a lower biomass after spawning.Based on the measured dry flesh weight and dry shell weights during the period May 26 1993 - December 21 1993 the condition index of 2,225 individuals could be calculated using the formula of Walne & Mann (1975):Dry flesh weight (mg) x 1000Condition Index (CI) = ------------------------------ Dry shell weight (mg)Here we described the archived files2021_VanderGaag_Thesis_Mytilopsis_Chapter6_MeasurementsMytilopsis.odtdate in MMDDYY2021_VanderGaag_Thesis_Mytilopsis_Chapter6_Mytash_Scan_Raju93-94.pdfData from mussels collected at Velsen in the North Sea canal near the ferry landing site at the north side. Dry flesh weight (in mg) is estimated in the period 1993-1994 together with the SE (standard error). Used are 20 animals per date in the size length-class of 10-14mm2021_VanderGaag_Thesis_Mytilopsis_Chapter6_North_Sea_Canal_89_94.odtData from mussels collected at Velsen in the North Sea canal near the ferry landing site at the north side in the period 1989-1994, and in summer 1994 at the power plant Hemweg in Amsterdam and the UNA power plant in Velsenµg/l = microgram per literµS/cm = microSiemens/cm2021_VanderGaag_Thesis_Mytilopsis_Chapter6_Mytilopsis_data.odtMytilopsis leucophaeata data collected from the stones on the stony bottom, in the North Sea canal, at Velsen, round the jetty at the ferry landing stage in the period 1989-1992.date = MMDDYYl = shell length in mmh = shell height in mm