Data from: Growth, survival and mortality of juvenile and adult alien Conrad's false mussel Mytilopsis leucophaeata (Conrad,1831) (Mollusca, Bivalvia, Dreissenidae) in a brackish canal Journal of Shellfish Research 37(1): 1-9

Marinus van der Gaag, Gerard van der Velde, Frank P.L. Collas and Rob S.E.W. Leuven

Introduction: In this archive we share the data are presented from the study on growth, the survival and mortality of Mytilopsis leucophaeata in the North Sea canal (Noordzeekanaal) collected near Velsen (52.465800 North; 4.632216 East). This study on growth, survival and mortality 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 setup:

Sampling of water quality parameters: Monthly, water temperature (⁰C) and salinity of the North Sea Canal were measured, using a mercury thermometer and YSI model 33 S-C-T meter, respectively. Missing chlorophyll a data we derived from Servicedesk Data Data-ICT-Dienst Rijkswaterstaat, Delft for the North Sea Canal near Velsen. All physicochemical measurements were carried out in the surface water in the period 1989-1995. Salinity was measured in the period 1989-1993.

Collection of data from mussels in cages: Two stainless steel perforated cages (40 by 40 cm, height 15 cm, mesh size 2 mm, all mesh 30% of the surface) with nine perforated compartments measuring 13 x 13 cm in size were used. In each compartment 25 or 35 mussels of various size classes were put [shell lengths 2-4 mm (when present), 4-6 mm, 6-8 mm, 8-10 mm, 10-12 mm, 12-14 mm, 14-16 mm, 16-18 mm and 18-22 mm]. The cages were made heavier by attaching a tile (30x30x4.5 cm, weight 9.5 kg) to their underside. The cages were posted on the canal bottom, at a water depth of 75 cm in the shallow littoral zone under a jetty at the landing site of a ferry and attached by stainless steel cables to the jetty pole. Refreshment of water in the cages via flow through the numerous pores was guaranteed because of wind- and shipping- induced currents and by regularly cleaning of the cages to keep the pores open. Monthly the cages were taken out of the water to remove empty shells and dead mussels from their compartments, where after the cage was put into the water. At each monthly visit during the 1990 experiment, the shell length of each mussel was measured with a Vernier caliper (accuracy 0.1 mm). In the 1991 experiment, only the numbers of survived mussels were recorded monthly, and the dead ones and the empty valves were removed. In the 1992 and 1993 experiments, the monthly survival was recorded, and at several dates during the growing season, all shell lengths of the survivors in the cages were measured. During each visit, the cage was cleaned from fouling. Both cage experiments from 1990 (started June 14 and July 25) were used to generate combined data for analysis of growth (further mentioned combined experiments, or used as separate experiments named by their start date). In both experiments, the shell length was measured monthly. For the combined data, a correction was made for the mean growth between the two different starting days of the experiments. June 14 was used as starting date for the combined data. A distinction was made between summer growth (June 14 1990 up to August 23 1990) and overall growth (June 14 1990 up to January 16 1991).

Here we described the archived files:

2021_VanderGaag_Thesis_Mytilopsis_Chapter4_Mytilopsis_cage_experiments_.odt

Survival data collected from the cages posted on the stony bottom at Velsen in the North Sea canal, near the small jetty at the ferry landing stage. Date in DDMMYY Numbers for 2mm size classis Exp. = experiment %death = percentage died mussel in the preceding month bucket = closed nylon netting with 1 mm pores, placed in a compartment of the cage.

2021_VanderGaag_Thesis_Mytilopsis_Chapter4_NorthSeaCanal89_94.odt

Data collected at Velsen in the North Sea canal near the jetty at 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 Velsen Date in DDMMYY µg/l = microgram per liter µS/cm = micro Siemens/cm