Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis

The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s^-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.     

Geography and Recovery under the U.S. Endangered Species Act

Abstract: The U.S. Endangered Species Act (ESA) defines an endangered species as one “at risk of extinction throughout all or a significant portion of its range.” The prevailing interpretation of this phrase, which focuses exclusively on the overall viability of listed species without regard to their geographic distribution, has led to development of listing and recovery criteria with fundamental conceptual, legal, and practical shortcomings. The ESA's concept of endangerment is broader than the biological concept of extinction risk in that the “esthetic, ecological, educational, historical, recreational, and scientific” values provided by species are not necessarily furthered by a species mere existence, but rather by a species presence across much of its former range. The concept of “significant portion of range” thus implies an additional geographic component to recovery that may enhance viability, but also offers independent benefits that Congress intended the act to achieve. Although the ESA differs from other major endangered‐species protection laws because it acknowledges the distinct contribution of geography to recovery, it resembles the “representation, resiliency, and redundancy” conservation‐planning framework commonly referenced in recovery plans. To address representation, listing and recovery standards should consider not only what proportion of its former range a species inhabits, but the types of habitats a species occupies and the ecological role it plays there. Recovery planning for formerly widely distributed species (e.g., the gray wolf [Canis lupus]) exemplifies how the geographic component implicit in the ESA's definition of endangerment should be considered in determining recovery goals through identification of ecologically significant types or niche variation within the extent of listed species, subspecies, or “distinct population segments.” By linking listing and recovery standards to niche and ecosystem concepts, the concept of ecologically significant type offers a scientific framework that promotes more coherent dialogue concerning the societal decisions surrounding recovery of endangered species.     

Die Ektoplasmahülle von Heterostegina depressa (Foraminifera:Nummulitidae)

The structure of the rigid ectoplasm sheath was studied in living individuals of the large foraminifer Heterostegina depressa d'Orbigny 1826 (Nummulitidae). H. depressa is able to form pseudopods, which emerge from the marginal cord within a few minutes. Normally, however, the living test is entirely covered by a rigid hyalin elastic sheath, which is fixed to the substrate by terminally branched processes. In older individuals, the sheath is often incomplete and restricted to the marginal cord only. Probably, the sheath is secreted by the ectoplasm which fills the canal system of the chamber walls and the marginal cord, or it consists of transformed ectoplasm; we call it “Ektoplasmahülle”, and the processes radiating to all sides, “Ruhepseudopodien”. H. depressa is able to move while inside the elastic sheath by means of pseudopods which penetrate the sheath and attach themselves to the substrate out-side. In the same manner, H. depressa leaves a complete sheath by disrupting it through the tractive powers of the pseudopods. The procedure of breaking the sheath is described. Locomotion when leaving the sheath is performed in a zigzag manner (alternating action of several pseudopods). The sheath counteracts transportation by water movement and protects chamber formation (which takes place inside the sheath). Due to its symbiotic unicellular algae, H. depressa does not need to collect food particles; hence locomotion seems unneccssary. The formation of a rigid ectoplasm sheath may be connected with H. depressa's sessile mode of life.     

Die Bedeckungsreaktion von Seeigeln. Neue Versuche und Deutungen

The conditions under which covering (“decorating”, “masking”) takes place have been studied in the sea urchins Paracentrotus lividus, Psammechinus miliaris and 2 other species. Covering occurs equally in darkness or light. It requires suitable objects and locomotion or searching activity of the tube feet. The covering reaction which may follow chemical, mechanical or optical stimuli may be purely the result of an increase in locomotory or general activity. Initial selection of different covering objects depends on the tube feet reflexes; size, form and weight of the object are important. Whether an object is accepted or not, depends on its surface and structure, the amount of water movement and the general activity level of the sea urchin. Transparency and colour of an object do not appear to be important. It is suggested that the covering process can be explained in terms of local tube feet and spine reflexes. The loading-up of objects may be understood as “relative walking”: the same reflexes which move the urchin on stable ground, draw loose particles towards the animal and then upwards.     

Experimental analysis of byssus thread production by Mytilus edulis and Modiolus modiolus in sediments

Laboratory experiments have been conducted on byssus thread production by two species of mussel, Mytilus edulis L. and Modiolus modiolus (L.), representing the epibyssate and endobyssate species of the Mytilidae, respectively. Mussels were placed in seven particle sizes of sediment ranging from 50 m to 16 mm for 12 d. The number of byssus threads per mussel, length of threads, number of threads per particle and size of pads were then recorded. Modiolus modiolus (endobyssate) produced more threads than Mytilus edulis (epibyssate). M. edulis produced most threads in the size range 2 to 16 mm and Modiolus modiolus in the size range 500 to 1000 m. M. modiolus produced longer threads than Mytilus edulis. Both species produced longer threads in particle sizes finer than 2 mm. M. edulis produced smaller pads than Modiolus modiolus. Both species produced larger pads in sediments coarser than 1 000 m. Results were also analysed in terms of attachment units (a thread attached to one or more particles, or a particle to which more than one thread is attached). The thread:particle ratio of the attachment units ranged from ca. 1:10 in the finest sediments to ca. 10:1 in the coarsest sediments. Mytilus edulis attached more threads to single particles (72% of attachment units) than Modiolus modiolus (37% of attachment units). M. modiolus had a wider spread of ratios in the finer particle sizes than Mytilus edulis. The significance of our results are discussed in relation to the ecology and palaeoecology of epibyssate and endobysste species.     

Teil VI: Die Ökobilanz der Universität Osnabrück

Within the development of the “Osnabrück Environmental Management Model for Universities,” an environmental audit for the university has been carried out for the first time. It was implemented by way of a Life Cycle Assessment (LCA) based on ISO 14 040. Following this, an LCA includes the four steps:goal and scope definition, inventory analysis, impact assessment andinterpretation. The impact assessment phase of the LCA was carried out following the ”UBA-Method” of the German Federal Environmental Agency (UBA) which is based on the method of impact categories described in ISO 14 040 and implemented in the software Umberto^®. The most significant results are that the University contributes “considerably” towards both categories, “Depletion of fossil energy resources” and “Climate change”. The main causes of this are electricity and heat consumption as well as traffic. In order to improve its environmental situation, the university has been recommended to reduce its CO₂ emissions, its consumption of fossil energy resources and its methane emissions.     

On the functional morphology of Hiatella solida (Hiatellidae: Bivalvia)

Hiatella solida (Sowerby, 1834) is the only species of the genus Hiatella represented in Southern Brazilian waters. It occurs on the coast of São Paulo and Rio Grande do Sul. The bivalves were found nestling or attached by byssus threads to specimens of the sea squirt Polyandrocarpa zorritensis or between the tubes of the polychaete Phragmatopoma lapidosa in the intertidal zone. The structure, adaptation and functional morphology were studied in detail, including the functioning of the stomach. H. solida were found with mature ova in August.     

Feinstruktur des Riechepithels von Chimaera monstrosa (Holocephali)

The epithelia of the olfactory folds of Chimaera monstrosa L. were studied by electron microscope. The greater part of each fold — including the secondary ones — is covered by sensory epithelium, whereas mere ciliary epithelium occurs on the tips of the folds. The olfactory epithelium is composed of ciliary cells, receptor cells, a few supporting cells, and basal cells. Mucous cells are restricted to the ciliary epithelium. As the apical region of the ciliary cells contains numerous vacuoles, including probably mucous substances, they may serve as producers of the superficial olfactory mucous layer. The ciliary basal bodies have two types of rootlets, the structure of which is described. Two morphologically different olfactory receptor cells could be identified: (1) receptors with a single, rod-shaped, free appendage (length 1.5 to 2 μm, diameter 0.1 to 0.5 μm), containing neurotubules, fibril bundles, and vesicles; (2) receptors whose dendrite bears few microvilli (length 2 to 3 μm, diameter 0.06 to 0.08 μm) projecting from a small vesicula olfactoria. Ciliary receptors are absent. The olfactory epithelium also contains sparsely distributed “brush” cells and a very few “giant” cells. Each “brush” cell bears a cluster of up to 250 microvilli (length 5 to 6 μm, diameter 0.1 μm) with 1 or more central tubulus and fibrils, the latter running into the cell body. The apical region of a brush cell contains densely packed mitochondria, which may indicate high metabolic activity; the function of this cell is unknown. The “giant” cell extends from the basal lamella to the epithelial surface. The ultrastructure of this cell does not reveal its special function.     

Induction of anti-predator responses in the green-lipped mussel Perna viridis under hypoxia

Hypoxia due to the over enrichment of waters by nutrients is becoming a global problem. In mussels, enhanced byssus thread production is an important adaptation to the presence of crustacean predators and to energetic hydrodynamic regimes. Thread production is an energy-consuming process, so this study used the green mussel Perna viridis (L.) to examine the response to predator exposure combined with hypoxia. Hypoxia is common in sheltered bays in Hong Kong, and the mussels were collected in one such bay, Lok Wo Sha (latitude/longitude: 22o18′ N/114o10′ E) in January, 2009. The predator used in the experiments was the swimming crab Thalamita danae. Oxygen concentrations used in the 48-h experiments ranged from hypoxic to normoxic (1.5 ± 0.3 mg l⁻¹, 3.0 ± 0.3 mg l⁻¹ and 6.0 ± 0.3 mg l⁻¹). Fewer byssus threads which were also shorter and thinner were produced at reduced oxygen levels, no matter if the predator was present or not; the frequency the mussels shed stalks was also lower. Mussels exposed to the predator, however, have enhanced byssus thread production at all oxygen levels when compared with the control. This has highlighted the significance of anti-predator responses for the survival of individuals even under a stressful environment in which energy supply is limited by aerobic metabolism. Interactive effects between oxygen level and predator exposure were observed for the byssus thread production (frequency of shed stalks, mean byssus thread length, cumulative byssus thread volume), with values obtained at 1.5 and 3.0 mg O₂ l⁻¹ being statistically indistinguishable for the control group without predator but not for the predator group. The lack of differences in the byssus thread production at lower oxygen levels in the absence of predator may indicate the minimum amount of byssus that is required for settlement on a substrate.     

Observations on the function of the glands of the foot of the pediveliger of Ostrea edulis during settlement

The use during settlement of secretions of the 9 different types of gland in the foot of the pediveliger of Ostrea edulis L. was examined experimentally. During settlement, there is a progressive decrease in the crawling speed of the larva and a strengthening of its bond with the substratum. Both changes are related to (a) a change from ciliary to muscular pedal locomotion; (b) the increasing acidity and viscosity of the mucoid secretions used; (c) the secretion of a byssus thread by the glands of the byssus duet; (d) changes in the form and composition of this byssus. At the termination of settlement, the entire contents of 2 types of gland are discharged. Their secretions give rise to the cement which permanently fixes the larva to the substratum. The 9 types of gland are utilised sequentially in a manner closely related to the 6 phases recognised in settlement behaviour.     

Ultrastructure of the byssal apparatus of Mytilus galloprovincialis. I. Associated fungal hyphae

Electron-microscope observations on ultrathin sections of Mytilus galloprovincialis byssus have revealed the existence of fungal hyphae. The ultrastructural features of these hyphae identify them as ascomycetes. A saprophytic nature is suggested for this fungus, and its probable role in the degradation of the byssus is discussed.     

Multivariate analysis of the mud crab Scylla serrata (Brachyura: Portunidae) from four locations in Southeast Asia

The large, edible mud crab Scylla serrata (Forskål) exhibits different phenotypes which are recognised by the fishermen of Southeast Asia and are given local names such as “white”, “green”, “red” or “black” crabs on the basis of their colouration. A preliminary study using multivariate techniques was undertaken in order to examine the degree of dissimilarity between the different morphs of commercially fished stocks of S. serrata. Twenty-two morphometric and 20 meristic characters were measured on male crabs from four locations in three countries in Southeast Asia, including Surat Thani in Thailand where “black” and “white” morphs exist sympatrically. Canonical variate analysis (CVA) on the morphometric data discriminated three groups with no chain-linking. Surat Thani “white” crabs and those from south Vietnam were phenotypically similar and formed one distinct group; a second group contained crabs from Ranong (Thailand) and Sarawak which were phenotypically “black”; the third group contained “black” crabs from Surat Thani. CVA on meristic data confirmed two groupings, but implied that the Surat Thani “black” morph may only be a variant of the Surat Thani/Vietnam “white” form, rather than a third species. These findings are discussed in relation to the ecology, fishery management and aquaculture potenial of S. serrata.     

Ökologie von Asterocheres lilljeborgi,eines auf Henricia sanguinolenta parasitisch lebenden Copepoden

Living specimens of Asterocheres lilljeborgi (Boeck, 1859) (Copepoda: Cyclopoida) were observed on the sea star Henricia sanguinolenta from the Gullmarfjord, Sweden. Copepodid stages as well as males and females live ectoparasitically on the sea star. They maintain a motile way of life and do not posses special adaptations of body form and extremity structure to the echinoderm host. A. lilljeborgi digests the skin of H. sanguinolenta extra-intestinally and sucks up the food by means of the siphon-shaped mouth. The intestine has caeca, which become increasingly branched during the development from copepodid stages to male or to female. The number of eggs is low, 7 to 9 in each egg sack. During copulation, the ventral sides of the genital segments of both male and female approach each other closely, thus facilitating transfer of spermatophores. All larger H. sanguinolenta of the Gullmarfjord are infested by A. lilljeborgi. Comparison between Scottomyzon gibberum and A. lilljeborgi shows that the female of S. gibberum has become more modified in structure and behaviour than the A. lilljeborgi female. In order to characterize the degree of parasitic life of the two species (both Cyclopoida siphonostoma) the term “parasitic” (not “semiparasitic” or “associated”) is suggested, because the nauplius larvae only are free living.     

Long-term trend in substratum occupation by a clonal, carbonate bryozoan in a temperate rocky reef in times of thermal anomalies

Studies over time provide opportunities to detect variations in the spatial and temporal patterns of clonal organisms and measure changes on their population dynamics related to extreme events. We assessed population dynamics for a bryozoan species dominating a subtidal rocky reef at Tino Island, in the eastern Ligurian Sea (NW Mediterranean). Using 9 years of annual photosurveys (1997–2005), rapid decline in Pentapora fascialis colony cover was shown at 11 and 22 m depths following the anomalous warming events in 1999 and 2003. An 86 % reduction in live colony portion was found after the 1999 warming event (2.3 °C higher than normal), with larger colonies being most affected. Effects from the 2003 event were delayed, and gradual cover decline occurred during the following 2 years. At the “Shallow” photostations, none of the larger colonies (>1,000 cm²) survived after the first cover decline. Availability of new substrate after the 1999 disturbance resulted in enhanced recovery through new colony production. At the “Deep” photostations, the population structure did not change over the duration of the monitoring period showing the same monomodal structure and same dominant size class (50–500 cm²). In the 4 years following the first cover decline, the deeper population regained colony cover to levels similar to pre-disturbance level, showing a good resilience. This 9-year monitoring analysis provided the temporal resolution needed to detect changes occurring in the P. fascialis population and will contribute to the assessment of long-term changes on benthic populations suffering during recent decades from dramatic increases in extreme events.     

Cementation vs mobility: development of a cemented byssus and flexible mobility in Anomia chinensis

The mobility of Anomia chinensis Philippi was studied in relation to its byssal development stage. This species shows high mobility even after it begins cementation in its post-larval stage. Juveniles develop a calcified byssus in the post-larval stage and cement to substrata. However, juveniles up to about 10 mm in shell length can relocate by repeating a sequence of formation of the calcified byssus, abandonment of it, locomotion by crawling, reattachment, and recementation. Juvenile anomiids up to 25 mm in shell length also can move, without breaking their byssal attachments, by shifting the center of byssal calcification dorsally. Even an adult can change its orientation by forming a twisted byssus. These possible methods of movement are closely related to five stages of byssal development. Anomiids can use this mobility to seek a preferable position for attachment after initial cementation, or to adjust their orientation, and thus promote higher survivorship. Received: 18 August 1997 / Accepted: 19 July 1998     

Rüstungsaltlasten

Risk assessment of contaminated sites from abandoned ammunition plants follows a multi-stage procedure with its own specific requirements for the toxicological assessment of chemical contaminants. Thus, the 22 explosives and related compounds (STVs) were classified according to carcinogenicity, genotoxicity and evaluation numbers for their toxicological potential (ENs). These characteristics permit a specific toxicological assessment and ranking at the stage of “historical reconnaissance”, independent of an evaluation of the contaminant concentrations. With a view to “orientative site evaluation” for the assessment of explosives and related compounds in groundwater and drinking water, toxicologically related guide values based on the ENs of toxicological potential as well as TDI-based guide values for STVs in soil were derived as based on toxicologically safe body doses and lifelong exposure (TDI=Tolerable Daily Intake). For regulatory purposes, substance related precautionary values are defined for probable carcinogens and contaminants with essential lacks in the toxicological data base.     

Influence des conditions hivernales sur les productions phyto- et zooplanctoniques en Méditerranée Nord-Occidentale. II. Biomasse et production phytoplanctonique

Hydrological observations, and measurements of nutrient chemistry, plankton biomass, and production were carried out during the Médiprod I cruise of the R.V. “Jean-Charcot”. The March cruise was characterized by almost winter conditions, exhibiting strong vertical mixing of water masses in the offshore region and nutrient transport up to the photic zone. According to the working hypothesis, the strong vertically mixed area (e.g. Station 15) and the surrounding oligotrophic area are separated by an intermediate zone, where both nutrients and stability have produced phytoplankton-bloom conditions. During the April cruise, highest biomass and production rates were encountered everywhere in the offshore region, and especially in the previously mixed area of central divergence. Production was as high as 2 gC·m^-2 day^-1, and the standing crop of chlorophyll was 3 mg·m^-3; such values are rather important for the so called “poor” Mediterranean Sea. Salinity-phosphate and chlorophyll-phosphate diagrams are presented. Biomass and production rates are in agreement with the potential fertility based on the nutrient content of the waters. The disappearance of 1 μatg P·PO₄ by photosynthetic uptake corresponds to 7.7 mg chlorophyll a, which represents the autotrophic biomass remaining after grazing by the simultaneous zooplankton bloom. Biomass and production features are analyzed in regard to interaction of both nutrient availability and the stability of water masses. Stability conditions can be created either by intrusion of local mixing in a stratified oligotrophic area (“winter bloom”), or by thermal stratification of the upper layer (“spring bloom”). In the latter case, the highest biomasses are present in the zone where the nutrients were previously introduced by mixing. The oligotrophic situation remained constant during the two crunises in the surrounding coastal area, which is characterized by low-salinity water and, therefore, absence of vertical nutrient transport into the photic zone. Chlorophyll pigment concentration and photosynthetic rates in the “Cote d'Azur” region are similar to those in the “Provence” region; this situation may result more from upwelling of nutrient-rich intermediate water than from the mixing process which predominates in the latter region.     

Influence des conditions hivernales sur les productions phyto- et zooplanctoniques en Méditerranée nord-occidentale. I. Structures hydrologiques et distribution des sels nutritifs

During two periods (1 to 15 March and 3 to 17 April, 1969), the R.V. “Jean Charcot” accomplished hydrological, chemical, and biological observations in the northern portion of the Western Mediterranean Sea. The main aim was to study the influence of the intensive vertical mixing of water masses on primary and secondary productions during winter. Earlier work in this area had revealed, in the offshore region, relatively large biomasses and high production rates during spring; considering the low potential fertility of Mediterranean waters, this finding may be explained by the effective vertical transport of nutrients upwards to the photic zone. The present paper discusses the hydrological features and the distribution of nutrients (phosphates and nitrates), in these areas, where, in winter, formation of deep water occurs. Observations were made down to 1,000 m on a grid of stations centred at 42°N; 5° E (“région provençale”) and another series of stations in the region “Corse-Côte d'Azur”. These two areas are characterized by cyclonic gyres, in which each centre shows a sector of high surface density (σ _t > 29.00). The surface mixed layer encountered is not deeper than 100 m; however, the Medoc Group (1970) has described formation of a homogeneous layer down to more than 1000 m. Many well-mixed water columns (maximum temperature and salinity at any depth do not exceed 13°C and 38.45‰, respectively) remain and occupy the western portion of the high surface density area; everywhere, the Mediterranean 3-layer system (superficial, intermediate and deep waters), more or less affected by mixing, remains well developed in the coastal region, and especially in the region of Côte d'Azur and Corsica. At some places, relatively high surface temperature (>13°C) associated with high salinity shows that the intermediate water fraction reaches the surface not only by direct vertical mixing, but also by any other dynamic lifting process, which constitutes another way of nutrient transport to the photic layer. The highest surface nutrient (0.3μ atg/l P?PO₄; 5 μ atg/l N?NO₃) and the lowest surface oxygen content (saturation <90%) are encountered in the mixed area; they are the best indicators of recently upwelled water. The surface layer around the cyclonic area is characterized by the low nutrient content of water of Atlantic origin. The lower salinity (<38%) of this water does not allow deep vertical mixing. During 3 to 17 April, 1969, the survey carried out on the same grid and sections reveals heating effects on all surface waters; the resulting stability in the most superficial layer accomodates the general spring bloom of phytoplankton. Nutrient consumption by photosynthesis in the upper 100 m layer of the surveyed area south of Marseilles was calculated to be: 129.1×10⁶ g-at P?PO₄ per 16,000 km² per month, converted on the atomic basis of P:C=1:106 represents almost 75% of the carbon production obtained by ¹⁴C-uptake measurements.     

Material investment and prey capture potential of reduced spider webs

Summary The webs of Miagrammopes animotus have a simple structure and variable form. However, both the length of their lines and the total surface area of their capture threads are closely associated with spider size. These spiders' ability to deposit both linear and looped cribellar capture threads along a web's diverging capture lines plays an important role in establishing these relationships. Looped capture threads have the greater surface area and are more prominent in the webs of older spiders where they increase a web's surface area and enhance its ability to retain prey. The predicted performance of these webs is supported by comparisons of the stickiness of their threads and a survey of the prey their owners capture. Cribellar thread stickiness increases with spider size, and larger spiders capture prey that have greater masses.