Bivalve Filter Feeding: Variability and Limits of the Aquaculture Biofilter
Total Page：16
File Type：pdf, Size：1020Kb
Chapter 4 Bivalve fi lter feeding: variability and limits of the aquaculture biofi lter Peter J. Cranford , J. Evan Ward , and Sandra E. Shumway Introduction acquisition, which is regulated by feeding activity (Hawkins et al. 1999 ). Predictions of A fundamental knowledge of bivalve feeding bivalve growth and the maximum aquaculture behavior is a minimum requirement for under- yield that can be produced within an area (pro- standing how aquaculture interacts with the duction carrying capacity) often involve eco- surrounding ecosystem. The potential environ- physiological modeling, which includes mental effects and ecological services of bivalve equations describing how feeding processes culture (Chapters 1 and 9 in this book) are (particle capture, selection, and ingestion) are related, in large part, to how the cultured pop- related to population dynamics and environ- ulation interacts with the ecosystem by means mental changes. Uncertainty or inaccuracy in of suspension feeding. A close interplay feeding parameter estimates strongly infl uence between water fi ltration activity, primary pro- model predictions of bivalve growth and car- duction, seston availability, and hydrodynam- rying capacity (Dowd 1997 ). ics defi nes the magnitude of many of the Suspension feeding always results in some ecological services provided by bivalves, as local food depletion. The ecological costs of well as the sustainable level of aquaculture for seston depletion by bivalve aquaculture are a given area. Shellfi sh growth is limited pri- of concern only when the depletion zone is marily by a species ’ capacity for nutrient persistent and of an ecologically signifi cant Shellfi sh Aquaculture and the Environment, First Edition. Edited by Sandra E. Shumway. © 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc. 81 82 Shellfi sh Aquaculture and the Environment magnitude and spatial scale. Accurate informa- ence of predictive relationships for the clear- tion on how fast resident bivalve stocks can ance rate of key aquaculture species that can fi lter a body of water is required to assess the be used to help understand both positive and ecological carrying capacity of a region, which negative interactions between bivalve aquacul- is the level of aquaculture that can be supported ture activities and the environment. Our goal in the growing environment without leading to was to synthesize knowledge on specifi c aspects signifi cant changes to ecological processes, of bivalve feeding behavior relevant to the species, populations, or communities (Gibbs aquaculture issues outlined above. Several pre- 2007 ). Beyond the need to understand the viously published reviews have addressed potential direct effects of biofi ltration, indirect divergent hypotheses on physiological regula- effects on ecosystem processes and structure tion of feeding activities and autonomous may result from the by - products of suspension behavior (J ø rgenson 1996 ; Bayne 1998 ; feeding, including ammonia excretion and the Riisg å rd 2001b ). Such considerations are not egestion of particulate organic materials (feces the focus of this review, but it is not possible and pseudofeces) on marine particle transport, to address our task without contributing to energy fl ow, and nutrient cycling. this long - standing theoretical debate. Bivalve feeding activity has been studied across a wide range of laboratory and natural conditions and there is a vast literature, par- Constraints on m aximum ticularly on clearance rate, which is the volume f eeding a ctivity of water cleared of particles of a certain size in a period of time. Despite this large research Suspension - feeding lamellibranchiate bivalves effort, there remains uncertainty in the mea- rely on ciliated structures to capture and trans- surement of clearance rate, which affects our port suspended particulate matter for selection confi dence in predictions of individual to and ingestion. The particle capture organ is the community - level feeding rates (Doering and ctenidium (Ward et al. 1998 ), which also Oviatt 1986 ; Cranford and Hill 1999 ; Riisg å rd serves as the respiratory organ (gill). The asyn- 2001a, 2001b, 2004 Cranford 2001 ; Widdows chronous beating of lateral cilia on gill fi la- 2001 ; Bayne 2004 ; Petersen et al. 2004 ). A ments serves as a pump that creates a water fundamental understanding of the feeding current which fl ows into the inhalant siphon behavior of individual bivalves provides the or aperture, through the spaces between the foundation for estimating population clear- gill fi laments (or ostia) and then out of the ance rate, which is critical to understanding exhalent siphon or aperture. Particles sus- the ecological role of bivalves and environ- pended in the feeding current are captured on mental interactions with shellfi sh culture, the gill. An in - depth review of food capture, including the capacity of dense bivalve assem- transport, and processing mechanisms in blages to control the phytoplankton at the bivalve molluscs is provided by Ward and coastal ecosystem scale (Chapter 5 in this Shumway (2004) . book). Feeding rate measurements must refl ect The ciliary activity of the gill delivers a fl ow the actual responses of specifi c species and cul- that can be measured as a pumping ( = ventila- tured populations to the multiple physical, tion) rate ( P ; L h − 1 ) by various means such as chemical, and biological factors that can infl u- the constant - level apparatus developed by ence feeding behavior in the natural environ- Galtsoff (1926) , the delivery of exhaled seawa- ment. In this review, we summarize the ter into a constant fl ow of fresh water available literature pertaining to feeding (Davenport and Woolmington 1982 ), the laser behavior with a focus on ascertaining the pres- apparatus developed by Famme et al. (1986) , Bivalve fi lter feeding 83 the use of micro- fl ow meters (Meyhö fer 1985 ; clearance rate and fi ltration rate interchange- Jones et al. 1992 ), and by the application of ably, but the latter term is more often used to particle image velocimetry (Frank et al. 2008 ). defi ne the mass of particles cleared per unit Pumping rate scales with the size of the gill, time (e.g., mg h − 1 ). Clearance and pumping which is somewhat proportional to the square rates are equal if all particles in the inhalant of shell length ( L 2 ). Tissue dry weight ( W ) is current are removed from suspension. Small proportional to L 3 so pumping rate can, at particles ( < 2 - μ m diameter) in natural waters least in theory, be expected to scale with W 2/3 are not effectively retained by most species, ( = W 0.67 ). This translates into a large increase but these particles can account for a high pro- in pumping rate for a small increase in body portion of the total suspended particulate size ( L or W ). These relationships are described matter. Clearance rate, therefore, is measured by the allometric equations for a particle size range that is retained by the species with 100% effi ciency ( > 4 - to 7 - μ m PaW==bband PaL , (4.1) diameter, depending on the presence of eu - or pro - laterofrontal cilia, respectively; reviewed where a and b are fi tted parameters. The allo- by Riisg å rd 2001a ). While pumping rate can metric exponent ( b ) describes how fast the rate be measured directly by a number of methods, increases relative to body size. Jones et al. clearance rate is most often determined using (1992) reported that maximum pumping rate indirect methods that involve measuring for Mytilus edulis scaled with L 2.1 (Fig. 4.1 ) changes in particle abundance or concentra- and W 0.70 , and showed that that these allome- tion due to suspension - feeding activity of the tric coeffi cients were not signifi cantly different bivalves. from the predicted values. Under laboratory conditions, optimal food Clearance rate (C ; L h − 1 ) is the more gener- concentrations have been identifi ed that stimu- ally used measure of water processing than late the full exploitation of water pumping and pumping rate, although the two measures are particle clearance capacity in many species of closely related. Some studies use the terms bivalves (e.g., 1000 – 6000 Rhodomonas sp. cells mL − 1 for Mytilus edulis ; Kittner and Riisg å rd 2005 ). Riisg å rd et al. (2003) reported 3.5 2.09 that under these conditions, the valves of Pmax = 0.0002 (L ) 2.19 Cardium edule , Mytilus edulis , and Mya are- ) 3.0 Pmean = 0.0004 (L ) –1 naria are fully open within an hour after a 2.5 starvation period of at least 24 h, and maximum 2.0 clearance rate (C max ) is thereafter maintained. 1.5 The results of Cmax measurements on 13 bivalve species of different sizes from eight studies 1.0 have been summarized by Riisg å rd (2001a, Pumping Rate (L h 0.5 2001b) . Reanalysis of the parameters of the 0.0 allometric relationships reported in these eight 10 20 30 40 50 60 70 80 studies provide the following average ( ± stan- Length (mm) dard deviation [SD ]) relationships for dry Figure 4.1 Allometric relationship between pumping rate tissue weight ( W ) and shell length ( L ): ( P ) of the mussel Mytilus edulis and shell length ( L ). Multiple individual measurements for each mussel are shown, −±10=± ..72009 ᭛ CWmax ()..Lh 654 241 (4.2) including the maximum ( P max ; ). Regression lines and equations are shown for average P (P mean ; broken line) and −±11=±..60045 Pmax (solid line) values. (Redrawn from Jones et al. 1992 .) CLmax ().Lh 0 0036 0 . 10 (4.3) 84 Shellfi sh Aquaculture and the Environment As noted above, clearance rate is theoretically the external pressure fi eld caused by fl ow expected to scale with body geometry ( L2 and velocity (Wildish and Kristmanson 1997 ). W 0.67 ), and the above equations generally Back - pressure on the ciliary pump results confi rm the assumed constraints of body size in reduced pumping effi ciency and valve on maximum feeding activity.