In situ method for measurements of community clearance rate on shallow water bivalve populations

Abstract

The ecological impact of a species is most often assessed by extrapolating laboratory results to nature. In the case of clearance rates of suspension feeding bivalves, the laboratory results are typically maximal clearance rates measured on single individuals at constant conditions. The legitimacy of such extrapolations has for long been questioned and the possible bias has been studied by performing field measurements. In such field measurements, the focus has been on the use of natural seawater (e.g., Bayne et al. 1977;Bayne and Widdows 1978;MacDonald and Ward 2009). In these studies, the bivalves were collected from its natural habitat, transported to a land-or ship-based experimental setup and clearance measured using ambient seawater. In other studies, the collected animals were introduced to experimental setups, which were placed in the field during measurements (e.g., Vismann 1990;Cranford and Hargrave 1994; Cranford and Hill 1999;Pouvreau et al. 2000). The latter three studies used the bio-deposit method (Iglesias et al. 1992), which allows for a fuller study of feeding, particle selection, and absorption rates at different ambient conditions. However, the studies focused upon the effect of ambient conditions at the level of individual bivalves. Many marine bivalves live at very high densities where interspecific and intraspecific interactions are most likely to occur. We strongly believe that including the aspects of population and inter-species interactions are needed if the ecological impacts of populations of suspension feeding bivalves are to be assessed. Several authors report in situ clearance rates based on algal concentration profiles above mussel beds and the reduction of seston concentration in near-bottom layers allows area grazing calculations (e.g., Dolmer 2000). To our knowledge, the aspect of population interactions has only been addressed by a few other researchers: Prins et al. (1996) has studied in situ grazing of a mussel bed by a 12 m long, 0.8 m width 'Benthic Ecosytem Tunnel' equipped with current speed monitor and battery driven water samplers, and Asmus and Asmus (1991) used the Sylt flume (20 ¥ 2 ¥ 2 m), which canalized the tidal water over a bed of Mytilus edulis L. AbstractAn open-top chamber was designed for measuring ambient community clearance rate on undisturbed bivalve populations in the field. The chamber was pressed 5-10 cm down in the sediment on the mussel bed. It holds approximately 30-40 cm water column equal to a volume of 43-77 L. It was provided with an air lift connected to a SCUBA diver pressure tank generating a continuous and gentle water circulation. This ensures a complete mixture of suspended particles, and thereby, a maximum filtration by the bivalves. An in situ fluorometer was mounted to record plant pigment reduction due to mussel clearance in real-time. To calibrate the in situ fluorometer triplicate water samples were obtained initially in each of the bivalve filtration measurements. The water samples were filtrated, extracted, and later analyzed fo...

Physiological responses of female and male black-lip pearl oysters(Pinctada margaritifera)to different temperatures and concentrations of food

“…Means are presented with standard error (5 < n < 10). Hansen et al 2011), but few of them examine gender as a source of variation. Studies of females and males have been made on Icelandic scallop Chlamys islandica (Vahl and Sundet 1985), freshwater eastern floater mussel Pyganodon cataracta (Tankersley and Dimock 1993), Sydney rock oyster Saccostrea glomerata (Honkoop 2003), and Pacific oyster Crassostrea gigas (Soletchnik et al 1997;Tran et al 2008).…”

Field clearance of an intertidal bivalve bed: relative significance of the co-occurring blue mussel Mytilus edulis and Pacific oyster Crassostrea gigas

“…The clearance rates of undisturbed C. gigas or M. edulis were measured in the field (2009 and 2010) using the open-top chamber technique developed by Hansen et al (2011). The open-top chamber was made out of a 49 cm diameter PVC tube 80 cm high.…”

“…During deployment, the enclosed water was thoroughly mixed by an air lift supplied with compressed air from a SCUBA tank. Fluorescence, temperature and salinity of the enclosed water column were continuously monitored (4 Hz) with a CTD (SBE 19plus, SeaBird Electronics) (for further details, see Hansen et al 2011). At deployment, the water depth present in the open-top chamber was measured.…”

“…In addition, C. gigas and M. edulis both retain phytoplankton species larger than 4 to 7 μm with 100% efficiency (Møhlenberg & Riisgård 1978, Barillé et al 1993, Strohmeier et al 2012; thus, in the present study, the clearance activity of the 2 species can be compared. In the deployments, the number of individuals present, in relation to the chamber water volume, gave sufficient decreases in fluorescence within 20 to 30 min for reliable clearance rate calculations (see Hansen et al 2011). The blank clearance rate in ambient seawater was determined using the decrease in fluorescence as a function of time in 4 deployments without bivalves in the chamber.…”

“…In field studies of clearance rates, several techniques have been used (e.g. Vismann 1990, Prins et al 1996, Cranford & Hill 1999, Dolmer 2000b, Pouvreau et al 2000, Grizzle et al 2006, Saurel et al 2007, Hansen et al 2011). In the present study, we used the technique developed by Hansen et al (2011) to study the clearance rate of populations of C. gigas and M. edulis in the intertidal zone of a sheltered bivalve bed.…”