Macroinvertebrate sampling

Macroinvertebrate sampling
To investigate diversity and abundances of other macroinvertebrates and their association with mussels, we collected a 2-min kick-sample with a standard square-framed
net (frame width: 25 cm, mesh size: 250 μm) within a 3-m
radius of the mussel quadrat at each of the 50 sites. We
sampled all available habitats in proportion to their occurrence following the protocol of Furse et al. (1981). All taxa
were identified to family level.
Filtration rate of individual mussels
To assess the importance of mussels as biofilters in
the lake, we measured filtration rates in the laboratory in
January 2010. The filtration rate of a mussel is defined as
the volume of water that passes through the mussel’s gills
per unit time and can be approximated as clearance rates,
i.e., the decrease in the concentration of chl a as phytoplankton is filtered out of the water (Coughlan 1969,
Riisgård 2001, McIvor 2004). We transported 20 randomly
selected specimens of each of the 2 mussel species (P.
caerulea and L. marginalis) to the laboratory in lake water at ∼20°C (approximate lake temperature at time of
collection) where we measured chl a clearance rates. We
allowed mussels to acclimatize to room conditions and
temperature of 21°C for ∼4 h. We placed each mussel
individually in a randomly selected beaker with 0.5 L of
algae-rich water collected from Ramna Lake (lat 23°44′
16″N, long 90°24′00″E), which had a chl a concentration
of 49.13 ± 12.42 μg/L and similar levels of organic and
inorganic pollution as Dhanmondi Lake (Razzak et al.
2012, Mokaddes et al. 2013). Three control beakers held
no mussels. We measured chl a concentration at the start
of the experiment and in each beaker after 1 h with a
fluorometer (Aquafluor Handheld Fluorometer). Care was
taken not to touch or otherwise disturb the mussels.
Shells showed no signs of periphyton growth