The filtration rate of Mytilus edulis as a function of acute change in temperature was measured by means of the clearance method in a group of mussels seasonally acclimated to 18 degree C. This was ...done by stepwise changes in temperature in order to both determine the temperature-tolerance interval within which the mussels were fully open, and to ensure that the acute effects were reversible. The filtration rate (F, ml min super(-1) ind. super(-1)) as a function of temperature (T, degree C) could be expressed by a regression line with the equation: F = 3.27T + 38.2 in the temperature-tolerance interval between 8.3 and 20 degree C. A reduction in temperature to below 8.3 degree C initiated valve closure, and at 6.1 degree C all mussels were completely closed. The same group of mussels was then acclimated to 11 degree C over a period of 5 d before the measurements were repeated, and the filtration rate as a function of temperature was subsequently found to be: F = 3.27T + 38.1 in the temperature- tolerance interval which had extended down to 4.1 degree C. Next, a group of mussels seasonally acclimated to about 15 degree C was split up into 3 subgroups which were exposed to 10.2, 15.6 and 20.3 degree C over the following 23 d. During the acclimation period, the filtration rate of fully open mussels was measured every 3 to 4 d in the 3 groups. Because none of the slopes of the 3 regression lines appreciably differed from 0, it is concluded that the acute effect of a change in temperature is not modified in M. edulis over a 3 wk acclimation period; i.e., there is no evidence for temperature compensation.
Clearance rates of the hydromedusaeSarsia tubulosa, Rathkea octopunctataandBougainvillea superciliarisand the scyphomedusaAurelia auritawere measured in the laboratory. Gut contents analyses ofA. ...auritawere also collectedin situand subsequently used for estimation of clearance rate. The clearance rate ofA. auritavaried widely with prey organisms. Large crustacean prey with low escape capabilities (Artemia salinanauplii and cirripede larvae) were cleared at high rates, whereas copepodites were cleared at lower rates, and clearance rates of small bivalve larvae and copepod nauplii were comparatively low. These data were used to assess the impact of jellyfish predation upon zooplankton and fish larvae in Limfjorden, Denmark. Repeated sampling of zooplankton, fish larvae and medusae was undertaken during the first half of 2003. Nine taxa of hydromedusae and 4 taxa of scyphomedusae were identified. Abundance estimates were combined with estimated clearance rates of individual medusae to calculate potential jellyfish-induced mortality on prey in Limfjorden. Copepoda was used as a model prey group to estimate the collective predation impact by all medusae. Medusa species with unknown clearance potential were given assumed clearance rate values, but the collective predation potential by these species was evaluated to be small. Hydromedusae dominated numerically and had their highest potential clearance impact in spring, but overall jellyfish clearance potential on copepods was low during this period. From MayA. auritawas the most abundant jellyfish and the potential jellyfish predation impact became totally dominated by this scyphomedusa. Clearance potential was locally high on some prey, and predation byA. auritaprobably controlled the abundance of cirripede larvae and fish larvae in Limfjorden. For these prey groups, half-life expectancy was less than 1 d at several locations.
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This review deals with the measurement of filtration rates in suspension feeding bivalves. Currently used methods are described, and some reliable filtration rate data obtained under optimal ...laboratory conditions are presented. The different methods have often caused troubles, and a number of problems and shortcomings are brought to light. The conflicting data on filtration rates seem partly to be due to the incorrect use of methods, and partly to be caused by differences in experimental conditions.
The relationship between body dry weight (W) and shell length (L) of blue mussels, Mytilus edulis, can be expressed by the condition index (CI = W/L ³) which varies from population to population and ...during the year. Here, we examine the influence of CI on the relationships between maximum filtration rate (F, l h⁻¹), W (g), and L (mm) as described by the equations: F W = aW ᵇ and F L = cL ᵈ , respectively. This is done by using available and new experimental laboratory data on M. edulis obtained by members of the same research team using different methods and controlled diets of cultivated algal cells. For all data, it was found that F W = 6.773W ⁰.⁶⁷⁸ and F L = 0.00135L ².⁰⁸⁸ which are very similar to equations for mussels with ‘medium condition’ (CI = 4–6 mg cm⁻³): F W = 6.567W ⁰.⁶⁸¹ and F L = 0.00150L ².⁰⁵¹, with b- and d-values within a few percent of the theoretically expected of 2/3 and 2, respectively. Further, based on the present data, we propose a correction factor expressed by the empirical relation F W /F L = 0.3562CI²/³ which implies that F W tends to underestimate the actual filtration rate (F L ) when CI < 4.70 and to overestimate the filtration rate when CI > 4.70.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The population density and individual size of the common jellyfish Aurelia aurita were studied during 2014 and 2015 in two Danish fjord systems, Kertinge Nor and Mariager Fjord in order to obtain a ...better understanding of the driving forces for somatic degrowth (shrinkage) of medusa during late summer and autumn. In both fjord systems the numerous medusae were characterized by their small body size and by a distinct phase of degrowth. The population predation impact of A. aurita, with estimated zooplankton half-lives of only about 1 to 3 d, indicated that shortage of prey controls the maximum umbrella size of only 60 (Kertinge Nor) to 100 mm (Mariager Fjord) and the subsequent degrowth. When jellyfish were brought into the laboratory in early spring and the late degrowth period and continuously fed with zooplankton (Artemia salina), equivalent to 5.8 mu g C l-1, this resulted in initial growth rates of 11.3 and 24.4 % d-1 in two series of experiments with 56.9 and 5.5 mm umbrella diameter, respectively, and considerably longer survival than of jellyfish in their natural environment. The degrowth rates in Kertinge Nor (-1.2 % d-1) and Mariager Fjord (-1.5 and -0.7 % d-1 in 2014 and 2015, respectively) were slightly lower than observed in laboratory starvation experiments (-3.2 and -4.2 % d-1), indicating that the starvation of jellyfish in nature was less pronounced, i.e. some prey organisms may have been available although the short estimated half-lives of zooplankton suggested a pronounced predation impact exerted by the jellyfish.
The effect of salinity on the filtration rate of blue mussels, Mytilus edulis, from the brackish Great Belt (Denmark) and the low-saline Central Baltic Sea, respectively, was studied. First, we ...measured the effect of long-term (weeks) constant ambient salinities between 5 and 30 psu on the filtration rate of M. edulis collected in the Great Belt where the mean salinity is 17 psu. At salinities between 10 and 30 psu, the filtration rates did not vary much, but at 5 psu the filtration rates were significantly lower. Next, we studied dwarfed M. edulis (<25 mm shell length) from Central Baltic Sea (Askö, Sweden) where the mean salinity is 6.5 psu. The maximum filtration rate (F, ml min⁻¹ ind.⁻¹) as a function of shell length (L, mm) and dry weight of soft parts (W, mg) were found to be: F = 0.003L ².⁷¹ and F = 0.478W ⁰.⁹², respectively, and these results indicate that the filtration rates of dwarfed Baltic Sea mussels are comparable to filtration rates of Great Belt mussels of similar size exposed to salinities >10 psu. When Baltic Sea mussels acclimatized to 20 psu in the laboratory were exposed to 6.5 psu this caused a drastic reduction in the filtration rate, but after about 2 days the previous high filtration rate was regained at 6.5 psu, and further, a similar pattern was observed when the 6.5 psu exposed mussels were finally re-exposed to 20 psu. The observed lack of Great Belt mussels to completely adjust to 5 psu, in contrast to the ease of Baltic Sea mussels to adjust back and forth between 6.5 and 20 psu, is remarkable and may perhaps be explained by different genotypes of Great Belt and Baltic Sea mussels.
A comparative study of feeding rates and structures was made with the 2 ciliary filter-feeding polychaetesDitrupa arietinaandEuchone papillosafrom the Mediterranean Sea (Gulf of Lions, France) and ...the Gullmarsfjord (Sweden), respectively. The feeding rate (clearance) was measured as the volume of water cleared of 6 μm diameter flagellate cells (Rhodomonassp.) per unit time. Most experiments were conducted at algal concentrations equivalent to about 0.4 to 3.8 μg chlorophyllal–1. The clearance rates of ‘standard’ 1.5 mg dry wtE. papillosaand ‘standard’ 3.0 mg dry wtD. arietinashowed that the maximum weight-specific clearance rate was 114.7 ml h–1mg–1forE. papillosaand about 7 times lower, 15.7 ml h–1mg–1, forD. arietina. A relative large tentacle crown inE. papillosa, resulting in the higher specific clearance rate, may be the evolutionary result of ‘minimal scaling’ and adaptation to extremely low food concentrations. When the algal concentration was increased from 2000 to 10 000 cells ml–1a 50% decrease in the clearance rate was observed inD. arietina, presumably because the gut capacity was exceeded. A more pronounced tendency to become satiated was found forE. papillosa. No tendency to reduce the filter-feeding activity at even very low algal concentrations was noticed in the 2 polychaetes, and the filtering activity of both worms seems to be a basically continuous process. Video-microscope observations ofE. papillosashowed that suspended algal cells approaching the pinnules suddenly accelerate and move through an arc of over 180° to be delivered on the frontal side of the pinnule. The transfer takes place at a maximum distance (radius) of about 25 μm from the pinnule. Scanning micrographs show the compound lateral cilia to be 20 to 25 μm long in bothD. arietinaandE. papillosaand to consist of 1 row of 4 cilia. The feeding current is generated by these compound cilia, which, during their power stroke, catch up with the particles.
Properties of the pump and filter system were studied in the occasionally suspension-feeding polychaete Nereis diversicolor. Feeding behaviour was observed on worms in glass tubes immersed in ...seawater. When algal cells were added to the surrounding water the worm made a funnel-shaped net-bag through which water was pumped by means of vigorously undulating movements of the body. Particles suspended in the inhalant water were retained by the net and later swallowed by the worm. The times spent on net-spinning, water-pumping through the complete net bag, and net-eating were: 97 ± 35, 191 ± 58, and 16 ± 4 s, respectively. Stereotyped suspension-feeding behaviour was continuously recorded for 10 h by means of a computer-aided monitoring system. The volume of water cleared of algal cells (Rhodomonas baltica, diameter = 6.3 μm) per unit time (clearance) was measured in worms of different size. Clearance (C, μl s−1) as a function of body dry wt (W, mg) was: C = 3.52 + 2.46W (17 °C). The clearance of 6.3 μm algal cells was 86 % of directly measured pumping rate, while the clearance rates of 7.5 and 13.1 μm particles were identical with the directly measured pumping rate, thus indicating 100 % retention efficiency of particles >7.5 μm. For smaller particles the retention efficiency rapidly decreased to about 30 % for 3 μm particles. In order to characterize the Nereis pump the relation between imposed hydrostatic back pressure and pumping rate was measured in a number of worms. In several cases the pumping rate was not influenced by the imposed back pressure up to 3 mm H2O; but at higher back pressures the pumping rate was reduced simultaneously with a reduction in the undulation frequency. The maximum pressure head was around 8 mm H2O. It was found that N. diversicolor pumps about 40 l of water per ml oxygen consumed, and the worm thus fulfills conditions for subsisting exclusively as a suspension feeder. The population pumping rate at the collecting site (2400 ind. m−2) was estimated to 9.8 m3 d−1 or 10 times the whole water column daily. This indicates that N. diversicolor is a hitherto undervalued key organism in the control of phytoplankton production in shallow brackish water areas.
The common jellyfish
Aurelia
spp. often appears in large numbers in coastal regions around the world, having a considerable predation impact on zooplankton. To better understand and quantify this ...phenomenon, several laboratory and field studies have determined growth rates by recording umbrella diameter and/or dry weight versus time. However, there appears to be no model describing such data. Here, we use a bioenergetic model for growth of
Aurelia
spp. dry mass (
W
) based on ingested food minus respiration, leading to the weight-specific growth rate μ (1/
W
) d
W
/d
t
=
a
W
b
, where the constant
a
depends on prey concentration and the exponent is
b
= -0.2. The model is tested against
Aurelia
spp. data in several examples, some of which represent well-fed conditions that show fair agreement with the model (
b
= -0.2 to -0.4), while others depart increasingly from the model (
b
< -0.4) with increasing
W
, likely due to suboptimal and fluctuating prey concentrations. Based on the model and available data, it is suggested that for a given size
W
, the specific growth rate increases linearly with prey concentration up to about 5 to 6
Artemia
sp. l
-1
, where a maximal growth rate (μ
max
) is reached which is not exceeded for higher prey concentrations.
A number of studies have shown that temperature-dependent viscosity of the ambient water controls or strongly affects bio-mechanical activity such as beat frequency of water-pumping cilia in mussels ...and ascidians, swimming velocity of sperm cells, ciliates and small (micro- and meso-scale) aquatic organisms using cilia or small appendages for propulsion. Here we summarize results from the literature and from own studies on bio-mechanical activities in response to changing temperature or manipulated viscosity at constant temperature, both having the same change in kinematic viscosity. The survey is used to assess to what extent the response is purely physical/mechanical or biological. We argue that a power-law dependence of bio-mechanical activity (
a) on kinematic viscosity (
ν), i.e.
a
∝
ν
−
m
, should be applied to available data. Based on a general close matching of the response data to power-law regressions for viscosity manipulation (by means of an additive) and/or temperature we suggest that viscosity and not biological mechanisms often control the response. This knowledge enhances our basic understanding of the effect of temperature not only on the swimming and feeding behaviour of small aquatic organisms, but also on larger ciliary suspension-feeding bivalves and ascidians.
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