Hans Ulrik Riisgård

Hans Ulrik Riisgård
University of Southern Denmark | SDU · Department of Biology

M.Sc., Ph.D., D.Sc.

About

202
Publications
140,423
Reads
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10,668
Citations
Citations since 2017
29 Research Items
2975 Citations
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Introduction
My research deals with filter-feeding in marine invertebrates; bioenergetics (food-uptake, assimilation, respiration, energy budgets, growth, costs of growth, growth efficiency); biological filter-pumps; biomixing; fluid mechanics; population grazing impact; particle capture mechanisms; benthic-pelagic coupling; biological structure and nutrient dynamics; grazing impact of benthic filter feeders; implications of density driven currents for interaction between jellyfish and zooplankton.
Additional affiliations
January 2005 - December 2010
Education
May 1979 - May 1981
University of Copenhagen
Field of study
  • Ecophysiology of mussels

Publications

Publications (202)
Article
Full-text available
The grazing impact has been evaluated of filter-feeding animals in Odense Fjord (Denmark) that is characterized by large biomass of filter feeding polychaetes (Nereis diversicolor), clams (Mya arenaria) and cockles (Cerastoderma glaucum). The filtration rate of each population (Ftot) was related to the total water volume (Vtot) in the different are...
Article
Full-text available
The integrated function of the setal filter-basket and the pleopodal pump in the burrowing amphipod Corophium volutator was studied by video-microscopy in order to evaluate the energy costs of filter feeding. Video-microscope observations indicated that, in general, nine short, water-pumping beat cycles of the pleopods are succeeded by one slow cyc...
Article
Full-text available
Transient concentration distributions of flagellate cells (Rhodomonas sp.) previously measured by Riisgård and co-workers in laboratory experiments have been examined to develop a diffusion model for the process of phytoplankton depletion in stagnant seawater above populations of benthic filter feeders, the polychaete Nereis diversicolor and the as...
Article
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Rates of water processing and particle retention were determined in veligers and post-metamorphic juvenile M. edulis, reared in the laboratory, by measuring the rate at which particles of different sizes were cleared from suspensions. Veligers cleared 2.5 -3.5 μm particles at the highest rate, and particles smaller than 1 μm or larger than 8-9μm co...
Book
Full-text available
Filter-feeding in marine invertebrates
Article
Full-text available
According to a recently presented bioenergetic model for the weight-specific growth rate of jellyfish, Aurelia aurita, fed brine shrimp, and Artemia salina, the specific growth will remain high and constant at prey concentrations > 6 Artemia l−1. The aim of the present study was to verify this statement by conducting controlled feeding and growth e...
Article
Full-text available
Filter-feeding invertebrates are found in almost all of the animal classes that are represented in the sea, where they are the necessary links between suspended food particles (phytoplankton and free-living bacteria) and the higher trophic levels in the food chains. Their common challenge is to grow on the dilute concentrations of food particles. I...
Article
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Demosponges are modular filter-feeding organisms that are made up of aquiferous units or modules with one osculum per module. Such modules may grow to reach a maximal size. Various demosponge species show a high degree of morphological complexity, which makes it difficult to classify and scale them regarding filtration rate versus sponge size. In t...
Article
Full-text available
Sponges are one of the earliest-evolved and simplest groups of animals, but they share basic characteristics with more advanced and later-evolved filter-feeding invertebrates, such as mussels. Sponges are abundant in many coastal regions where they filter large amounts of water for food particles and thus play an important ecological role. Therefor...
Article
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...
Chapter
Full-text available
Med oprettelsen af Fjordbiologisk Laboratorium i 1990 kom Odense Universitet til Kerteminde. Det førtse meget med sig. Men i 2020 blev det lille og velfungerende fjordlaboratorium nedlagt for at give plads til nye boliger ved nordhavnen.
Article
Full-text available
Filter-feeding sponges pump large amounts of water and contribute significantly to grazing impact, matter transport and nutrient cycling in many marine benthic communities. For ecological studies it is therefore of interest to be able to estimate the pumping rate of different species from their volume size or osculum cross-sectional area by means o...
Article
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Contractile behavior is common among sponges despite their lack of nerves and muscles. As sessile filter-feeders, sponges rely on water with suspended food particles being pumped through their aquiferous system. During contractions, however, the water flow is being reduced and eventually shut down. Yet, purpose and underlying pathways of contractil...
Article
Multi-oscula sponges are organisms composed of aquiferous modules, each of which draws water through its canal system by means of pumping units (choanocytes, Cs, in choanocyte chambers, CCs) such that the filtered water leaves the module as an exhalant jet through the osculum of the module. Here we compare relations between the characteristic param...
Article
Full-text available
This study relates the lipid content of two marine filter-feeding demosponges, Halichondria panicea and H. bowerbanki to the seasonal availability of their suspended food, mainly free-living bacteria and phytoplankton at two study sites in Danish waters. The aim was to investigate if the lipid content of sponges is linked to food availability and s...
Article
Leuconoid sponges are filter-feeders with a complex system of branching inhalant and exhalant canals leading to and from the close-packed choano- cyte chambers. Each of these choanocyte chambers holds many choanocytes that act as pumping units delivering the relatively high pressure rise needed to overcome the system pressure losses in canals and c...
Article
Full-text available
Sponges are sessile filter-feeders and the basic principles for water pumping and particle retention are the same among all demosponges. Phytoplankton cells smaller than the inhalant openings (ostia) are retained and phagocytosed in the inhalant canal system before the water is sieved through the collar filter of the choanocytes, which efficiently...
Article
Sponges are modular organisms in which each aquiferous module draws water through a canal system by means of pumping units (choanocyte chambers, CC), and the filtered water leaves the module as an exhalant jet through a single opening (osculum). A constant density of CCs in sponges would imply that the filtration rate must be proportional to the sp...
Article
Full-text available
Blue mussels, Mytilus edulis, form dense beds of both commercial and ecological importance, and many attempts have been made to determine their filtration rate. The total time in which mussels actually utilise their filtration capacity in nature varies greatly, making in situ methods for filtration rate measurements relevant. Further, it is being d...
Book
Full-text available
This textbook in German for university students can be downloaded for free at bookboon.com
Article
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The common jellyfish Aurelia aurita s.l. occurs in many coastal and shelf sea environments around the world, including fjord systems such as Kerteminde Fjord/Kertinge Nor (Denmark). As observed for the majority of temperate A. aurita populations, jellyfish appear in this fjord system each spring, go through gradual declines in their initially high...
Article
In a recent paper, Specht & Fuchs (2018; Mar Ecol Prog Ser 589:129−140) claim that 2 ciliary suspension-feeding bivalves, the blue mussel Mytilus edulis and the hard clam Mercenaria mercenaria, differ in how they respond to viscosity. For M. mercenaria, the authors found no change in filtration rate or beat frequency of water-pumping cilia in respo...
Article
Growth of the blue mussel (Mytilus edulis) is closely related to the biomass of phytoplankton (expressed as concentration of chlorophyll a, Chl a), but the effect of too much food in eutrophicated areas has so far been overlooked. The hypothesis addressed in the present study suggests that high Chl a concentrations (> about 8 μg Chl a l⁻¹) result i...
Chapter
Full-text available
This chapter summarizes recent years’ studies on zoobenthic filter feeding in the sea. General principles are extracted based on experiments and mathematical modeling, mainly from own studies in shallow temperate Danish waters, in order to present primary characteristics of the sophisticated interplay between benthic filter feeders and hydrodynamic...
Article
Full-text available
The large water-pumping and particle-capturing gills of the filter-feeding blue mussel Mytilus edulis are oversized for respiratory purposes. Consequently, the oxygen uptake rate of the mussel has been suggested to be rather insensitive to decreasing oxygen concentrations in the ambient water, since the diffusion rate of oxygen from water flowing t...
Article
Full-text available
Contraction-inflation behavior, including the closure and opening of the exhalant opening (osculum), is common among sponges. This behavior may temporally affect filtration activity, making it difficult to study and understand sponge feeding biology. To examine the interplay between osculum dynamics and filtration activity, small (18 mm³) single-os...
Article
Full-text available
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...
Article
Full-text available
The F/R-ratio (litres of water filtered per ml of oxygen respired) was determined for the filter-feeding demosponge Halichondria panicea to be 15.5 l H2O (ml O2)⁻¹ which was used to evaluate the potential of the sponge to nourish solely on nano- (2–20 µm) and micro- (20–200 µm) phytoplankton cells in the sea. It was estimated that in order to balan...
Article
Full-text available
A recently developed BioEnergetic Growth (BEG) model for blue mussels (Mytilus edulis), valid for juvenile mussels, has been further developed to an ‘extended model’ and an alternative ‘ad hoc BEG model’ valid for post-metamorphic mussels, where the latter accounts for changing ambient chl a concentration. It was used to predict the growth of M. ed...
Poster
Full-text available
Poster presented on the 5th International Jellyfish Bloom Symposium 2016 in Barcelona.
Research
Full-text available
This very interesting paper reports on comprehensive field and laboratory experiments, but unfortunately a few critical comments seems appropriate. In our previous study (Riisgård et al. 1993) we estimated that the normal pump operation point for the 'standard sponge' was 0.671 mm H2O as also shown in Table 2 in the present paper. The authors state...
Chapter
Full-text available
This chapter summarizes recent years’ studies on zoobenthic filter feeding in the sea. General principles are extracted based on experiments and mathematical modeling, mainly from own studies in shallow temperate Danish waters, in order to present primary characteristics of the sophisticated interplay between benthic filter feeders and hydrodynamic...
Article
Full-text available
Life expectancy of the scyphomedusa Aurelia aurita seems closely linked to seasonal shrinkage, or somatic degrowth, which occurs synchronously with sexual reproduction in temperate regions. In the present study, the mechanisms controlling body mass losses and subsequent disappearance of medusae were examined by following seasonal dynamics in popula...
Article
Full-text available
During periods of starvation, the blue mussel Mytilus edulis reduces its valve gape and thus the filtration rate whereby the oxygen uptake becomes reduced. Considering the frequency with which M. edulis in the field experience shorter or longer periods with low phytoplankton concentrations it is of great importance to understand the bioenergetic im...
Article
Full-text available
Species composition, population densities and size of jellyfish and ctenophores were recorded during 5 cruises in the heavily eutrophicated Limfjorden in 2014. No or very few ctenophores (Pleurobrachia pileus) and jellyfish (Aurelia aurita, Cyanea lamarckii) were recorded in April and June 2014, whereas in August and September numerous small indivi...
Data
Oxygen depletion in Skive Fjord (1982-2014) Here we supplementary analyze if an apparent tendency to severe oxygen depletion in the bottom-near water in Skive Fjord during the summer months has increased after the arrival of Mnemiopsis leidyi in 2006. We hypothesize that the pronounced predation impact observed on zooplankton caused by M. leidyi re...
Chapter
Full-text available
This chapter examines filter-feeding mechanisms and hydrodynamic aspects in cladocerans, barnacles, copepods, krill, crabs, and amphipods. The feeding mechanisms often differ fundamentally among groups because filter feeding has evolved independently in many, and often filter feeding is only one of several feeding methods adopted by one species. In...
Article
Full-text available
Mussel larval densities may fluctuate considerably on both small spatial and short temporal scales. So far, only few and scattered data on the occurrence of mussel larvae have been reported from Danish waters. However, seasonal variation in density of blue mussel (Mytilus edulis) larvae as related to environmental factors (temperature, salinity, ph...
Article
Full-text available
In spite of wide use of the brine shrimp, Artemia salina(Linnaeus, 1758), as feed and model organism in evolutionary, ecological, physiological, and ecotoxicological investigations, only a few studies have attempted to quantify filtration and respiration rates in order to characterize A. salinaas a filter-feeder. Herein, we measured that the maximu...
Article
Full-text available
Mussels within the Baltic Mytilus edulis × M. trossulus hybrid zone have adapted to the low salinities in the Baltic Sea which, however, results in slow-growing dwarfed mussels. To get a better understanding of the nature of dwarfism, we studied the ability of M. trossulus to feed and grow at low salinity (7 psu) compared with its performance at re...
Article
Full-text available
Filter feeding in mussels is a secondary adaptation where the gills have become W-shaped and greatly enlarged, acting as the mussel filter–pump. Water pumping and particle capture in the blue mussel, Mytilus edulis, have been studied over many years. Here, we give a short status of the present understanding of ciliary structure and function of the...
Article
Full-text available
Limfjorden is a major Danish water system that connects the North Sea via Thyborøn Kanal in the west and to the Kattegat in the east. Limfjorden is heavily eutrophicated and certain areas suffer from oxygen depletion each summer. Bottom-dwelling fish have disappeared as the number of jellyfish and ctenophores has increased. The abundance and predat...
Article
Full-text available
Mussels from two sites within the Baltic mussel (Mytilus edulis × M. trossulus) hybrid zone were used in a comparative study on the effects of salinity-changing rates on filtration activity. The acute effect of varying salinity-changing rates was found to be similar in M. edulis from the brackish Great Belt and in M. trossulus from the low saline C...
Article
Full-text available
Abstract Between mid-December 2011 and mid-January 2012 an unusual mixture of ctenophores was observed and collected at Kerteminde harbour (Great Belt, Denmark). In addition to native zooplanktivorous species Pleurobrachia pileus (O.F. Müller, 1776) and Bolinopsis infundibulum (O.F. Müller, 1776), non-native zooplanktivorous Mnemiopsis leidyi A. Ag...
Article
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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/L3) 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...
Article
Full-text available
Average filtration and growth rates of groups of juvenile Mytilus edulis (n =2545 of 22-35 mm shell length) were measured at different concentrations of an algal cell monoculture in 9 laboratory experiments of duration 14-30 days, 4 experiments below and 5 above the limit of incipient saturation concentration (Csat ≈ 6000-7000 Rhodomonas salina cel...
Article
Full-text available
The present study is a first step towards evaluation of the potential for line-mussel production in the Great Belt region between the Kattegat and Baltic Sea, Denmark. We present experimental results for actual growth rates of juvenile/adult mussels Mytilus edulis in suspended net bags in terms of shell length and dry weight of soft parts during ex...
Article
Full-text available
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 wh...
Article
Full-text available
Experimental feeding and growth studies on filter-feeding organisms often rely on constant algal concentrations maintained over extended periods of time. Here we present a fluorometer controlled apparatus (FCA) designed for feeding experiments with suspension-feedingmussels at naturally lowchlorophyll 𝑎 concentrations above 0.5 𝜇gL−1.The principle...
Article
Full-text available
The growth rates of blue mussels Mytilus edulis on ropes in the Great Belt (Denmark) have been studied during the growth season of one year, from settling to about 30 mm shell length mussels, covering > 4 decades of body mass. Measured shell length (L, mm) and dry weight of soft parts (W, μg) for L > 10 mm followed a power-law (W = 2.15L3.40) which...
Article
Full-text available
We have investigated changes in specific contents of protein, glycogen and lipid, and fatty acids of blue mussels, Mytilus edulis, under different conditions in the field and in laboratory feeding experiments using different microalgae. Specific contents of glycogen and lipid increased in mussels relocated to net bags at a location in Kerteminde Ba...
Article
Full-text available
The effects of salinities between 10 and 30 psu on the growth of blue mussels, Mytilus edulis, were studied in laboratory feeding experiments and compared to the growth of mussels suspended in net-bags in the brackish water Great Belt, Denmark. In the laboratory, 3 series of growth experiments were conducted: in Series #1, groups of mussels were ex...
Article
Full-text available
Growth rates of blue mussels, Mytilus edulis, in suspended net-bags were measured in field experiments conducted in Limfjorden and Great Belt, Denmark, for extended periods of time (22–69 days) with up to 8 intermediate data samplings during the period. The resulting time series of growth of different overlapping size-classes of M. edulis were anal...