Josef Daniel Ackerman

Reduced mixing in a marine macrophyte canopy

We report the effects of a marine plant canopy on flow in the coastal environment. In addition to reducing the magnitude of the ambient flow, a Zostera marina canopy was observed to undulate under unidirectional flow. Spectral analyses of the velocity fluctuations in the canopy revealed a fundamental frequency of approximately 0.125-0.156 Hz. These fluctuations were not caused by ambient flow conditions but rather by the hydroelasticity of the plants («monami»). Flow within the canopy can be, therefore, considered a function of plant movement rather than ambient conditions. Calculations incorporating these observations and the resistance of the canopy indicate that eddy viscosity is between 10 −5 and 10 −4 m 2 s −1 . Mixing within Z. marina canopies is reduced and more like the deep ocean than the coastal environment (...)

Abiotic pollen and pollination: ecological, functional, and evolutionary perspectives.

The transport and capture of pollen in ~20% of all angiosperm families occurs in air and water. In other words, pollination is abiotic and occurs via the fluid media, not an animal vector. Whereas some early concepts considered abiotic pollination to be largely a stochastic phenomenon, there is sufficient evidence to indicate that wind pollination (i.e. anemophily) and water pollination (i.e. hydrophily) have deterministic features and are sophisticated fluid dynamic solutions to the problem of pollen release, dispersal, and capture.An abiotic pollination syndrome is defined in which there is spatial or temporal separation of carpellate and staminate flowers, which are drab, a reduction in perianth parts, stigmas and anthers are exposed to the fluid, and typically unclumped pollen may be produced in large amounts. Separate pollination syndromes are defined for anemophilous (i.e. wind-pollinated), ephydrophilous (i.e. surface-pollinated), and hydrophilous (i.e. submarine-pollinated) plants. Distinctions are based on habitat and physical conditions for pollination, pollen size, shape, and ultrastructure, morphology and ultrastructure of stigmas, and outcrossing rates. For example, anemophilous pollen are spherical and small, ephydrophilous pollen are spherical or reniform and large, while hydrophilous pollen are filiform (i.e. filamentous) or functionally filiform. The pollination mechanisms and mechanics associated with these syndromes reveals a strong evolutionary relationship between plant morphology and fluid dynamics.

Fluid dynamics in seagrass ecology - from molecules to ecosystems

Fluid dynamics is the study of the movement of fluids. Among other things, it addresses velocity, acceleration, and the forces exerted by or upon fluids in motion (Daugherty et al.. 1985; White. 1999: Kundu and Cohen, 2002). Fluid dynamics affects every aspect of the existence of seagrasses from the smallest to the largest scale: from the nutrients they obtain to the sediment they colonize; from the pollination of their flowers to the import/export of organic matter to adjacent systems; from the light that reaches their leaves to the organisms that live in the seagrass habitats. Therefore, fluid dynamics is of major importance in seagrass biology, ecology, and ecophysiology. Unfortunately, fluid dynamics is often overlooked in seagrass systems (Koch, 2001). This chapter provides a general background in fluid dynamics and then addresses increasingly larger scales of fluid dynamic processes relevant to seagrass ecology and physiology: molecules (μm), leaves and shoots (mm to cm), seagrass canopies (m), sea- grass landscapes (100—1.000 m), and seagrasses as part of the biosphere (>1.000 m). Although gases are also fluids, this chapter is restricted to water (i.e. compressed fluids), how it flows through seagrasses, the forces it exerts on the plants, and the implications that this has for seagrass systems. Seagrasses are not only affected by water in motion, they also affect the currents, waves and turbulence of the water masses surrounding them. This capacity to alter their own environment is referred to as “ecosystem engineering” (Jones et al.. 1994, 1997; Thomas et al., 2000). Readers are also encouraged to consult a recent review by Okubo et al. (2002) for a discussion on flow in terrestrial and aquatic vegetation including freshwater plants, seagrasses, and kelp.

Sensitivity of the glochidia (larvae) of freshwater mussels to copper : Assessing the effect of water hardness and dissolved organic carbon on the sensitivity of endangered species

The assessment of the potential impact of waterborne contaminants on imperilled freshwater mussels is needed. Acute copper toxicity was assessed in a standardized soft water (hardness 40-48 mg CaCO(3)equivalents L(-1)) using the larvae (glochidia) from three common and six (Canadian) endangered mussel species. The resulting 24h EC50s ranged from 7 to 36 microg Cu L(-1), with the EC50s of two endangered species <10 microg Cu L(-1). Acute copper sensitivity was also determined in Ptychobranchus fasciolaris, a species that employs conglutinates (packets of glochidia) in its reproductive strategy. Conglutinates were found to provide significant protection from acute copper exposure as the EC50 of the encased glochidia was more than four-fold higher than freed glochidia (72.6 microg Cu L(-1) vs. 16.3 microg Cu L(-1)). The glochidia from two endangered species, Epioblasma triquetra and Lampsilis fasciola, were used to examine the influence of water hardness and dissolved organic carbon (DOC) on copper sensitivity. Exposures in moderately-hard water (165 mg CaCO(3) L(-1)) demonstrated that an increase in water hardness resulted in a significant reduction in copper sensitivity. For example, in L. fasciola the 24 h EC50s were 17.6 (14.2-22.6) microg Cu L(-1) and 50.4 (43.5-60.0) microg Cu L(-1) in soft water and moderately-hard water, respectively. The addition of DOC (as Aldrich Humic Acid) also resulted in a significant decrease in Cu sensitivity, such that a 10-fold increase in the EC50 of E. triquetra was observed when the reconstituted soft water was augmented with 1.6 mg DOC L(-1). To determine if current water quality regulations for copper would protect all glochidia, the USEPAs Biotic Ligand Model (BLM) was used to derive water quality criteria for these exposures. While BLM-derived criteria for the soft water exposures indicate that protection would be marginal for the sensitive endangered species, the criteria derived for the DOC exposures suggest that the natural complexity of most natural waters in Southern Ontario (Canada) will provide glochidia with protection from acute copper exposure.

Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms

SummaryThe peculiar filiform pollen morphology and ability to pollinate in an aquatic medium have evolved convergently in the marine angiosperms or ‘seagrasses’. A comparison of these systems with freshwater ones, reveals that reproductive strategy alone does not provide sufficient information to understand this convergence. Several models have, however, been proposed to explain the function and evolution of seagrass pollen morphologies. The first is a mathematical model, random search theory, which requires pollen to travel both ‘randomly’ and perpendicularly to its path. It is elegant conceptually, but does not hold up to physical and empirical scrutiny. Conversely, a biophysical model, which requires pollen to obey the fluid dynamic principles of boundary-layer flow, may be complicated conceptually, but it is consistent with mathematics and nature. The correct modelling of pollination mechanisms in seagrasses provides an understanding of contemporary adaptations as well as the processes that selected them.

Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). II. Pollen transport in flow fields and capture by stigmas.

Flow chamber observations of the filamentous pollen of Zostera marina L. (Potamogetonales) revealed that pollen rotated and moved toward inflorescences where they were captured by stigmas. The mechanics of this abiotic pollination process were examined and found to be related to the flow environment around emergent flowers. The translational movement of pollen was imparted by the advection of the fluid (e.g., pollen kinetic energy, K, ranged from 0.8 x 10-14 to 2.4 x 10-14 J, and the average K of the fluid was _ 0.7 x 10-14 J), while the rotational motion was imparted by the fluid shear stress (tau) within the velocity gradient (e.g., pollen shear stress, sigmat = omegamu where omega is the rotational velocity and mu is the dynamic viscosity, ranged from 3.4 x 10-4 to 26 x 10-4 Pa, and the average fluid shear stress was tau _ 10 x 10-4 Pa; Ackerman, 1997, American Journal of Botany 84: 1099-1109). These results indicate that there is a greater potential for pollination by filamentous pollen relative to spherical pollen. Functionally, while spherical pollen needs to be directly upstream from stigmas to be captured, filamentous pollen need only be in the vicinity of inflorescences and flowers to be captured by stigmas. Thus, in addition to direct interception on stigmas, filamentous pollen can be captured while they rotate past flowers or when they are redirected through the velocity gradient towards flowers. Filamentous pollen is an adaptation to submarine pollination in seagrasses.

Host fish quality may explain the status of endangered Epioblasma torulosa rangiana and Lampsilis fasciola (Bivalvia∶Unionidae) in Canada

Abstract Freshwater unionid mussels are among the most endangered groups of organisms in the world. They develop indirectly via a host, usually a fish, and this dependence appears to limit the reproduction and distribution of freshwater mussels. Epioblasma torulosa rangiana and Lampsilis fasciola are 2 endangered species in Canada. Epioblasma t. rangiana has a low abundance and limited distribution, whereas L. fasciola has a higher abundance and less-constrained distribution. Three known host species were examined for each mussel species. Results were that: 1) E. t. rangiana glochidia had significantly higher metamorphosis rates (i.e., proportion of attached glochidia that successfully metamorphosed to the juvenile mussel stage) on Etheostoma exile (mean ± SE: 44 ± 9%) and Cottus bairdi (42 ± 6%) than on Etheostoma nigrum (10 ± 3%) and 2) L. fasciola glochidia had significantly higher metamorphosis rates on Micropterus dolomieu (82 ± 2%) and Micropterus salmoides (63 ± 8%) than on C. bairdi (37 ± 7%). Variation in the co-occurrence of mussels and their primary vs marginal host species (i.e., high vs low infestation and metamorphosis rates, respectively) appears to explain the distributions and abundances of these 2 endangered mussels in Canada. An understanding of the quality of different host fishes of endangered mussel species is needed to facilitate effective conservation strategies.

Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. The influence of floral morphology on fluid flow.

An understanding of the process of submarine pollination should provide insight into the evolutionary and reproductive ecology of the marine angiosperms (seagrasses). The flow around the reproductive organs of the seagrass Zostera marina L. (Potamogetonales) was, therefore, examined in a flow chamber. The phenological emergence of flowers during (1) pollen capture and (2) pollen release, and by fruit during (3) seed release, led to a reduction in flow rate toward the inflorescence. This change in flow due to floral emergence was associated with a 50% increase in the fluid shear stress [tau = (2.2 _ 0.3) x 10-3 Pa for an immature flower vs. tau = (3.1 _ 0.5) x 10-3 Pa for a receptive flower]. The Reynolds number (Re) and fluid shear stress around inflorescences and infructescences were comparable, indicating a dynamic similarity in the processes of pollen capture and fruit dehiscence [Re = 47 _ 5, tau = (1.6 _ 0.3) x 10-3 Pa for inflorescences; Re = 38 _ 5, tau = (1.3 _ 0.1) x 10-3 Pa for infructescences]. These results indicate that the emergence of reproductive organs leads to changes in fluid shear stress, which will affect the release, transport, and capture of particles including pollen. Theoretical considerations of these observations using aerosol-filtration theory suggest that pollen capture in Z. marina occurs through direct interception of pollen by stigmas.

Lake Brienz Project: An interdisciplinary catchment-to-lake study

Keywords: dams and reservoirs ; downstream effects ; fish decline ; hydropower ; oligotrophic and turbid lakes ; Lake Brienz Reference EPFL-ARTICLE-186906doi:10.1007/s00027-007-0016-0View record in Web of Science Record created on 2013-06-10, modified on 2016-08-09

Genetic and environmental implications of reintroducing laboratory-raised unionid mussels to the wild

The reintroduction of endangered species is a potentially useful conservation strategy, which in the case of freshwater unionid mussels, must be preceded by the successful laboratory rearing of juvenile mussels on their host fishes. However, an understanding of the genetic and environmental implications of reintroductions of artificially propagated mussels is required. Unfortunately, there is a dearth of information on these issues with respect to freshwater mussels. In general, regarding the genetic effects of reintroductions, small founder populations may lead to low heterozygosity (reduced genetic variability) in the reintroduced populations, which can make them more susceptible to extinction. Captive breeding programs may also alter the genetic composition of species through artificial selection, whether intentional or unintentional. Captive breeding may also affect an individual’s interactions with conspecifics or predators by altering behaviour. Genetic problems in reintroduced populations also have...