Data from: Temperature dependent larval occurrence and spat settlement of the invasive brackish water bivalve Mytilopsis leucophaeata(Conrad, 1831) (Dreissenidae) Journal of Sea Research 87: 30-34

M. van der Gaag, G. van der Velde, S. Wijnhoven, S. Rajagopal

Introduction In this archive the data are presented from the study of the larvae and spat of Mytilopsis leucophaeata in the North Sea canal (noordzeekanaal) collected near Velsen (52.465800 North; 4.632216 ast). This study of the larvae is a part of the study to obtain more insight in the autecology and life history of M. leucophaeata in relation to important environmental factors, which is the aim of the thesis.

Experimental set-up for larvae and spat study Physical and biological measurements Water temperature (°C) was measured with a thermometer to the nearest 0.1 °C. Salinity (Practical Salinity Scale) was measured by a YSI model 33 S-C-T salinity meter. Chlorophyll a (µg l-1) was measured (collected at side and analyzed in the laboratory) according to procedures described by Parsons et al. (1984). These parameters were measured monthly in the surface water.
Collection of larvae Larvae were collected monthly using a plankton net (diameter 29 cm, length 54 cm, mesh size 45 µm), which was drawn by a ferry across the whole width (275 m) of the canal during the 1989-1992 period. The plankton samples were fixed by adding formaldehyde to the canal water until a concentration of 0.8 % had been reached, transported to the laboratory in jars, and stored until analysis. Three larval subsamples were counted with a Sedgwick-Rafter counting cell. Average values were used to calculate the densities of larvae per cubic metre of water. Collection of spat from PVC panels Spat settlement we studied using 2 mm thick PVC panels (14.3 x 35 cm). Each settlement panel we placed in a 70 cm long PVC tube (open at both sides, diameter 14.3 cm) to create a less turbulent environment and to protect the panel from scouring and damage caused by large waves due to ships and storms. Both sides of the panel within the tube could be colonized (combined surface area 900 cm2). The tube containing one panel for colonization, we attached with a stainless steel cable to the jetty near the ferry at a depth of about 75 cm, and we laid it down on the stony bottom, on February 22 1989. Each month, the one month exposed panel was collected and replaced by a new in the period February 22 1989 until August 23 1990. A similar second tube with a panel we laid out on 5 April 1990 and this exposure experiment lasted until 28 August 1991. Individuals we counted in the laboratory on 16-900 cm2 of panel area depending on the density of the spat, and we expressed them as numbers per square metre. Removed PVC panels, we cleansed of overgrowth, and we reused on the next sampling date. Here we describe the archived files:

2021_VanderGaag_Thesis_Mytilopsis_Chapter3_Panels_out_.odt

Bal = Amphibalanus improvisus, Rit = Rhithropanopeus harrisii

2021_VanderGaag_Thesis_Mytilopsis_Chapter3_NorthSeaCanal89_94.odt Mytilopsis leucophaeata data collected from the stones on the stony bottom, in the North Sea canal, at Velsen, near the jetty at the ferry landing stage in the period 1989-1992. date = MMDDYY l = shell length in mm h = shell height in mm 2021_VanderGaag_Thesis_Mytilopsis_Chapter3_DaylengthTemperatureSalinityChlorophyllMytilopsisLarvaeSpat89-92.ods

Spreadsheet with collected larvae and spat of Mytilopsis leucophaeata in the North Sea canal near the ferry in Velsen in the period 1989-1992. Other collected data are day length, water temperature, salinity and chlorophyll a.

2021_VanderGaag_Thesis_Mytilopsis_Chapter3_sta-tistical_calculations_with_SAS_Mytilopsis_data_on_Stones.odt

Statistical output from the SAS program PROC TABULATE of the monthly collected data of Mytilopsis leucophaeata from the stones near the jetty in Velsen in the period 1989-1992. Length = shell length in mm Std = Standard deviation N = number of mussels collected Max = maximum shell length Min = minimum shell length