Natural Beds Research Articles

Ostreid herpesvirus type 1 genomic diversity in wild populations of Pacific oyster Crassostrea gigas from Italian coasts

Ostreid herpesvirus 1 (OsHV-1) is a significant pathogen affecting the young Pacific oyster Crassostrea gigas, worldwide. A new variant, OsHV-1 μVar, has been associated with recurrent mortality events in Europe since 2008. Epidemiological data collection is key for global risk assessment; however little is known about health status and genotypes present in European wild oyster beds. Most studies to date have involved only cultivated individuals during mortality events, and reported low genotype diversity. With this study, conducted along the Italian coasts, we investigated for the first time the presence of OsHV-1 in European natural oyster beds. Analysis of three genomic regions revealed the presence of at least nine different genotypes, including two variants close to the OsHV-1 reference, known since the early 1990s but with no European record reported since 2010, and highlights relevant genotype diversity in natural environment. Phylogenetic analysis distinguished two distinct clusters and geographical distribution of genotypes, with the exception of a variant very closely related to the μVar, which appeared the single genotype present in all the Adriatic sites. Interestingly, these wild symptom free populations could represent, in Europe, an accessible alternative to the import of OsHV-1-resistant oyster strains from the East Pacific, the native area of C. gigas, avoiding the high-risk of non-native marine species and new pathogen introductions.

Historical context of commercial exploitation of seaweeds in Brazil

Harvested by coastal populations for centuries, seaweeds have played an important role in the economy of a number of countries. In Brazil, they occur along the coastline, but are more diversified and abundant from the northeast to a portion of the southeast coast. Historically, the seaweed industry in Brazil is based on seaweed harvesting of natural beds. This practice continues to this day in a number of coastal communities in Northeastern Brazil. Since the 1960s, species of the genera Gracilaria and Hypnea have been collected in the intertidal zone for extraction of agar and carrageenan. Maximum production was achieved in 1973–1974, a period in which the country exported around 2000 t annually (dry weight) to Japan. Later (1977–1979), there was a sharp drop and annual exports fell to 250 t (dry weight). In 1981, Brazil exported only 150 t of dried seaweed for agar extraction. Between 1990 and 2000, overexploitation, decline in a number of agarophyte populations, poor quality, low price, and lack of a socioeconomic policy led to the almost total disappearance of this industry in Northeastern Brazil. Seaweed harvesting on natural beds is currently in decline, and the population that depended on this resource had to migrate or convert to other economic activities, such as fishing, aquaculture, and underwater tourism. However, the promising results obtained in pilot projects (Gracilaria and Kappaphycus) show that Brazil has significant potential as a seaweed biomass producer.

An Agar-Based Method for Plating Marine Protozoan Parasites of the Genus Perkinsus

The genus Perkinsus includes protozoan parasites of mollusks responsible for losses in the aquaculture industry and hampering the recovery of natural shellfish beds worldwide, and they are a key taxon for understanding intracellular parasitism adaptations. The ability to propagate the parasite in liquid media, in the absence of the host, has been crucial for improving understanding of its biology; however, alternative techniques to grow the parasite are needed to explore other basic aspects of the Perkinsus spp. biology. We optimized a DME: Ham’s F12–5% FBS- containing solid agar medium for plating Perkinsus marinus. This solid medium supported trophozoite propagation both by binary fission and schizogony. Colonies were visible to the naked eye 17 days after plating. We tested the suitability of this method for several applications, including the following: 1) Subcloning P. marinus isolates: single discrete P. marinus colonies were obtained from DME: Ham’s F12–5% FBS– 0.75% agar plates, which could be further propagated in liquid medium; 2) Subcloning engineered Perkinsus mediterraneus MOE[MOE]: GFP by streaking cultures on plates; 3) Chemical susceptibility: Infusing the DME: Ham’s F12–5% FBS– 0.75% agar plates with triclosan resulted in inhibition of the parasite propagation in a dose-dependent manner. Altogether, our plating method has the potential for becoming a key tool for investigating diverse aspects of Perkinsus spp. biology, developing new molecular tools, and for biotechnological applications.

Multidrug-resistant and epidemic clones of Escherichia coli from natural beds of Venus clam

Epidemic Escherichia coli clones have been recovered in marine sediment along the coast of Marche, an Adriatic region in central Italy. In the present study, E. coli strains from the clam Chamelea gallina, sampled from seven natural beds in the same area, were detected. Selected E. coli isolates from all sampling sites were screened for antimicrobial susceptibility, genetic diversity and correlation. The majority (60%) belonged to phylogroups A or B1, 31% to the other groups (B2, C, D, E, F), 8% to cryptic clades, and 1% were untypable. Moreover, 33.3% of isolates were resistant to at least one drug and 11% were multidrug resistant (MDR). The most common resistance was to tetracycline, ampicillin, and streptomycin. No clonality was detected, but the strains' high genetic heterogeneity pointed at multiple sources of microbiological contamination. MLST analysis found potentially pathogenic and even epidemic MDR strains in clams collected in class A (ST746 and ST46) and class B (ST393, ST58 and ST131) areas, indicating that strains of clinical origin are detectable in clams. These data highlight that eating raw or lightly cooked clams may pose a health risk if purification is not performed or is ineffective.

Development of zygote for seed production of Sargassum swartzii in India

Sargassum swartzii is economically exploited in India for alginate production. Indiscriminate harvesting of S. swartzii in natural beds leads to fast depletion. For sustainable utilization of this alga, it is inevitable to undertake its mass cultivation. Therefore, investigations were undertaken to develop a technology that can boost cultivation of this important species. An attempt was made to optimize the culture conditions for developing zygote-derived germlings for artificial seed production through vegetative parts such as vesicles and tertiary leaves. Vesicles and tertiary leaves (n = 90) were subjected to a range of irradiances (05, 25, and 45 μmol photons m−2 s−1), salinity (15, 20, 25, 30, 35, 40, 45, 50, and 55 psu), and photoperiod (8:16, 10:14, 12:12, 14:8, and 16:8-h (L/D) regimes under 30-day culture. Maximum regeneration (%) of receptacle from vesicles and tertiary leaf was observed at an irradiance of 45 μmol photons m−2 s−1, 35 psu salinity, and 12:12-h (L/D) photoperiod which appears to be the most optimal condition. Variations in receptacle regeneration through vesicles and tertiary leaves were highly significant under different irradiances, salinities, and photoperiods (p 0.05). Germlings development followed the eight nuclei, one egg pattern which is quite common in the Sargassaceae. Within a day, multicellular germlings were developed with a bunch of unicellular rhizoids from fertilized oospores through repeated cell divisions. These findings confirmed that vesicles and tertiary leaves can be used as seed stock for the development of artificial seed production in S. swartzii as they contain primordial tissue for receptacle development.

Restocking Natural Beds with Remote-Set Disease-Resistant Oysters in Connecticut: A Field Trial

ABSTRACT Oyster production in Connecticut historically has had large fluctuations due to two major factors: disease epizootics caused by a protozoan parasite multinucleate sphere X (Haplosporidium nelsoni), and long periods without successful natural sets. A field trial was performed to investigate whether the remote set of oysters can be used to restock natural beds during mortalities caused by disease epizootics and lack of recruitment due to periods without sets. Disease-resistant oysters were remote set in a hatchery and placed either in or without biodegradable nets on a natural bed. Aged, clean cultch was used as the control, and the growth, mortality, predation, fouling, and prevalence of disease were monitored for two growing seasons. The oysters grew to market size (3 inches, 76.2 mm) in 15 mo. Predation, due mainly to Atlantic oyster drills Urosalpinx cinerea, and overgrowth of oysters caused a mortality of 72% in the oyster seed during the first growing season. More abundant wild oysters set bu...

Cheating the Locals: Invasive Mussels Steal and Benefit from the Cooling Effect of Indigenous Mussels.

The indigenous South African mussel Perna perna gapes during periods of aerial exposure to maintain aerobic respiration. This behaviour has no effect on the body temperatures of isolated individuals, but when surrounded by conspecifics, beneficial cooling effects of gaping emerge. It is uncertain, however, whether the presence of the invasive mussel Mytilus galloprovincialis limits the ability of P. perna for collective thermoregulation. We investigated whether varying densities of P. perna and M. galloprovincialis influences the thermal properties of both natural and artificial mussel beds during periods of emersion. Using infrared thermography, body temperatures of P. perna within mixed artificial beds were shown to increase faster and reach higher temperatures than individuals in conspecific beds, indicating that the presence of M. galloprovincialis limits the group cooling effects of gaping. In contrast, body temperatures of M. galloprovincialis within mixed artificial mussel beds increased slower and exhibited lower temperatures than for individuals in beds comprised entirely of M. galloprovincialis. Interestingly, differences in bed temperatures and heating rates were largely dependent on the size of mussels, with beds comprised of larger individuals experiencing less thermal stress irrespective of species composition. The small-scale patterns of thermal stress detected within manipulated beds were not observed within naturally occurring mixed mussel beds. We propose that small-scale differences in topography, size-structure, mussel bed size and the presence of organisms encrusting the mussel shells mask the effects of gaping behaviour within natural mussel beds. Nevertheless, the results from our manipulative experiment indicate that the invasive species M. galloprovincialis steals thermal properties as well as resources from the indigenous mussel P. perna. This may have significant implications for predicting how the co-existence of these two species may change as global temperatures continue to rise.

Beneficial effects of carpet shell clam (Ruditapes decussatus) depuration during short periods of conditioning in shellfish hatchery: Role of the temperature and phytoplankton on reduction and diversity of vibrios

Broodstock conditioning in hatcheries is the step previous to spawning and its optimization may be a key to the success of larval cultures. Cleaning and brushing of the broodstock and the utilization of antibiotics to reduce their vibrios load are used regularly as routine prophylactic measures prior to spawning induction. The development of protocols to reduce these bacteria using cheap and harmless techniques is of utmost importance for commercial bivalve production in hatcheries. With this aim, we have evaluated initially different conditionings (A–D) during short periods (a total of four weeks): first two weeks under gradient temperature (increasing +0.3°Cday−1 from 14.5°C to 20°C), without (A) or with phytoplankton (B), and constant temperature (20°C) without (C) or with phytoplankton (D). Afterwards, all conditionings were kept at 20°C and fed for two more weeks. Furthermore, broodstock optimal feeding time was re-evaluated during a second trial series. In all conditionings, bacterial loads were determined in terms of marine heterotrophic bacteria (MHB) and presumptive vibrios (PV). Broodstock under the optimal short period of conditioning (conditioning C) obtained the best gonadal development and a significant reduction in PV load at a lower expense. A total of 61 PV were isolated from all conditionings and identified by sequencing the 16S rRNA gene. Splendidus clade was dominant in the samples coming from natural beds. Diversity of vibrios changed throughout the conditionings in the hatchery favoured by exogenous factors whose effect was mainly observed at the end of the trials: Splendidus clade was also dominant in the broodstock conditioned at gradient temperature and Mediterranei and Harveyi clades were prevalent at constant temperature. Moreover, the percentage of transformation to D-larvae was estimated and the vertical transmission of vibrios from broodstock to eggs and D-larvae was suggested. Implementation of conditioning C reduces considerably the Vibrio load of clams without using antibiotics, and thus it represents a novel, cheap, environmental friendly and harmless methodology that can be easily transferred to commercial hatchery. Statement of relevanceRoutine prophylactic measures for bivalve broodstock arriving hatchery facilities include its cleaning/brushing and the frequent use of antibiotics to reduce its bacterial load, particularly Vibrio, as step previous to spawning induction. The depuration protocol proposed reduces significantly Vibrio load without using antibiotics and represents a novel, cheap, environmental friendly and harmless methodology that can be easily transferred to commercial hatcheries.

Microplastic contamination in natural mussel beds from a Brazilian urbanized coastal region: Rapid evaluation through bioassessment

Microplastic pollution (particles <5mm) is a widespread marine threat and a trigger for biological effects, especially if ingested. The mussel Perna perna, an important food resource, was used as bioindicator to investigate the presence of microplastic pollution on Santos estuary, the most urbanized area of the coast of São Paulo State, Brazil. A simple and rapid assessment showed that 75% of sampled mussels had ingested microplastics, an issue of human and environmental concern. All sampling points had contaminated mussels and this contamination had no clear pattern of distribution along the estuary. This was the first time that microplastic bioavailability was assessed in nature for the southern hemisphere and that wild P. perna was found contaminated with this pollutant. This is an important issue that should be better assessed due to an increase in seafood consumption and culture in Brazil and worldwide.

Large Bone Vertical Augmentation Using a Three-Dimensional Printed TCP/HA Bone Graft: A Pilot Study in Dog Mandible.

Osteoflux is a three-dimensional printed calcium phosphate porous structure for oral bone augmentation. It is a mechanically stable scaffold with a well-defined interconnectivity and can be readily shaped to conform to the bone bed's morphology. An animal experiment is reported whose aim was to assess the performance and safety of the scaffold in promoting vertical growth of cortical bone in the mandible. Four three-dimensional blocks (10 mm length, 5 mm width, 5 mm height) were affixed to edentulous segments of the dog's mandible and covered by a collagen membrane. During bone bed preparation, particular attention was paid not to create defects 0.5 mm or more so that the real potential of the three-dimensional block in driving vertical bone growth can be assessed. Histomorphometric analyses were performed after 8 weeks. At 8 weeks, the three-dimensional blocks led to substantial vertical bone growth up to 4.5 mm from the bone bed. Between 0 and 1 mm in height, 44% of the surface was filled with new bone, at 1 to 3 mm it was 20% to 35%, 18% at 3 to 4, and ca. 6% beyond 4 mm. New bone was evenly distributed along in mesio-distal direction and formed a new crest contour in harmony with the natural mandibular shape. After two months of healing, the three-dimensional printed blocks conducted new bone growth above its natural bed, up to 4.5 mm in a canine mandibular model. Furthermore, the new bone was evenly distributed in height and density along the block. These results are very promising and need to be further evaluated by a complete powerful study using the same model.

Classification of US Hydropower Dams by their Modes of Operation

A key challenge to understanding ecohydrologic responses to dam regulation is the absence of a universally transferable classification framework for how dams operate. In the present paper, we develop a classification system to organize the modes of operation (MOPs) for US hydropower dams and powerplants. To determine the full diversity of MOPs, we mined federal documents, open-access data repositories, and internet sources. We then used CART classification trees to predict MOPs based on physical characteristics, regulation, and project generation. Finally, we evaluated how much variation MOPs explained in sub-daily discharge patterns for stream gages downstream of hydropower dams. After reviewing information for 721 dams and 597 power plants, we developed a two-tier hierarchical classification based on (i) the storage and control of flows to powerplants, and (ii) the presence of a diversion around the natural stream bed. This resulted in nine tier-1 MOPs representing a continuum of operations from strictly peaking, to reregulating, to run-of-river, and two tier-2 MOPs, representing diversion and integral dam-powerhouse configurations. Although MOPs differed in physical characteristics and energy production, classification trees had low accuracies (≤62%), which suggested that accurate evaluations of MOPs may require individual attention. MOPs and dam storage explained 20% of the variation in downstream subdaily flow characteristics and showed consistent alterations in subdaily flow patterns from reference streams. This standardized classification scheme is important for future research including estimating reservoir operations for large-scale hydrologic models and evaluating project economics, environmental impacts, and mitigation. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of seeding density on biomass production in mussel bottom culture

Effects of seeding density on biomass production in mussel bottom culture are investigated by detailed monitoring of culture practice in the western Wadden Sea, The Netherlands. The seeds originate from different sources. The seeds differ in size and farmers apply seeding techniques dependent on the seed size resulting in different seed densities on the culture plots. We hypothesise growth to be density dependent and that biomass production is primarily determined by survival and is therefore a function of seed density which is related to the activities of the farmers. Data was collected from 42 different culture plots over a three year period (June 2009–June 2012). During this period, 66 sub-populations were followed from seeding until harvest. Seeding at the start of the culture resulted in an instantaneous drop in biomass production, caused by large losses in mussel number. These losses were on average 42% of the mussels seeded. This seeding loss decreased with mussel size and increased with seeding density. A subsequent density dependent loss of 1.8 mussels per day was found for smaller mussels (<30mm), and a non-density dependent loss of 0.8 mussels per day for larger mussels (>30mm) during grow out. Overall loss from seeding to harvest was high, from 92% for the smallest seeds collected from spat collectors, to 54% for half-grown mussels fished from natural beds in the spring. No indication was found that growth or mussel condition was affected by culture plot scale density. Growth was dependent on mussel size and age, and this largely determined the differences in biomass production between seed sources. The density dependent seeding loss associated with seeding activities largely determined survival, and hence overall biomass production.

Prey selection, size, and breakage differences in Turbo undulatus opercula found within Pacific Gull (Larus pacificus) middens compared to Aboriginal middens and natural beach deposits, southeast Australia

Qualitative discrimination criteria are employed commonly to distinguish cultural shell middens from natural shell deposits. Quantitative discrimination criteria remain less developed beyond an assumption that natural shell beds tend to contain a wider range of shell sizes compared to cultural shell middens. This study further tests this assumption and provides the first comparative quantitative analysis of shell sizes from cultural middens, bird middens, and beach shell beds. Size distributions of opercula of the marine gastropod Turbo undulatus within two modern Pacific Gull (Larus pacificus) middens are compared with two Aboriginal middens (early and late Holocene) and two modern beach deposits from southeast Australia. Results reveal statistically significant differences between bird middens and other types of shell deposits, and that opercula size distributions are useful to distinguish Aboriginal middens from bird middens but not from beach deposits. Supplementary qualitative analysis of taphonomic alteration of opercula reveal similar opercula breakage patterns in human and bird middens, and further support previously recognised criteria to distinguished beach deposits (water rolling and bioerosion) and human middens (burning). Although Pacific Gulls are geographically restricted to southern Australia, the known capacity of gulls (Larus spp.) in other coastal contexts around the world to accumulate shell deposits indicates the broader methodological relevance of our study.

Interactions between Paramoeba perurans, the causative agent of amoebic gill disease, and the blue mussel, Mytilus edulis

Amoebic gill disease (AGD) is caused by the ectoparasite Paramoeba perurans found free-living in seawater. In recent years outbreaks of AGD have occurred in most salmon farming countries causing significant economic losses. Mussels co-cultured with salmon in integrated multi-trophic aquaculture (IMTA) systems may change pathogen dynamics on sites by acting as reservoirs or biological controls. Through the use of an 18S rRNA gene quantitative real-time PCR we tested the interactions between P. perurans and blue mussels (Mytilus edulis) under experimental conditions by means of water-borne transmission. Quantification of DNA from water samples revealed a rapid decrease in P. perurans DNA over two weeks in the presence of mussels under experimental conditions. P. perurans was detected on swabs from mussel shells up to 48h post-exposure. Additionally, no P. perurans were detected in mussels collected from natural mussel beds and fish farms. These results indicate that mussels are not a likely reservoir host for P. perurans but may in fact actively remove water-borne P. perurans. Statement of relevanceThe blue mussel does not appear to pose a biosecurity risk as a vector for the pathogen responsible for amoebic gill disease in salmon (Paramoeba perurans), instead the presence of blue mussels in experimental challenges led to a rapid removal of the parasite. The findings provide valuable information for how mussels may modulate pathogen densities on finfish-mussel farms.

2014년 추계 제주 북서부 해조장에서 해양환경과 식물플랑크톤의 일차생산력 특성

Marine environmental characteristics and primary productivity of phytoplankton were investigated in seaweed bed of northwestern coast of Jeju Island during Autumn, 2014. The trophic state based on dissolved inorganic nitrogen and phosphorus was mesotrophic. The Redfield ratio was less than 16, indicating that nitrogen was the limiting factor for the growth of phytoplankton. Dissolved organic nitrogen and phosphorus accounts for 63 and 46% of the dissolved total nitrogen and phosphorus, respectively. Light utilization efficiency () and maximum photosynthetic capacity () were highest in the Donggwi (third-year marine forest), followed by Gonae (one-year marine forest), Biyangdo (natural seaweed bed) and Geumneung (whitening area). The primary productivity of phytoplankton in the Donggwi, Gonae and Biyangdo also was higher than that in the Geumneung. Although nitrogen is the limiting factor, enriched dissolved organic nitrogen might play an important role to maintain primary productivity. In addition, phytoplankton community through photosynthesis could produce about 14% of phytoplankton carbon in one hour. These results will be able to use the important information for material cycle and ecological valuation of seaweed bed.

Importance of kelp-derived organic carbon to the scallop Chlamys farreri in an integrated multi-trophic aquaculture system

Bivalves and seaweeds are important cleaners that are widely used in integrated multi-trophic aquaculture (IMTA) systems. A beneficial relationship between seaweed and bivalve in the seaweed-based IMTA system has been confirmed, but the trophic importance of seaweed-derived particulate organic materials to the co-cultured bivalve is still unclear. We evaluated the trophic importance of the kelp Saccharina japonica to the co-cultured scallop Chlamys farreri in a typical IMTA farm in Sungo Bay (Weihai, North China). The dynamics of detritus carbon in the water were monitored during the culturing period. The proportion of kelp-derived organic matter in the diet of the co-cultured scallop was assessed via the stable carbon isotope method. Results showed that the detritus carbon in the water ranged from 75.52 to 265.19 μg/L, which was 25.6% to 73.8% of total particulate organic carbon (TPOC) during the study period. The amount of detritus carbon and its proportion in the TPOC changed throughout the culture cycle of the kelp. Stable carbon isotope analysis showed that the cultured scallop obtained 14.1% to 42.8% of its tissue carbon from the kelp, and that the percentages were closely correlated with the proportion of detritus carbon in the water (F =0.993, P= 0.003). Evaluation showed that for 17 000 tons (wet weight) of annual scallop production, the kelp contributed about 139.3 tons of carbon (535.8 tons of dry mass). This confirms that cultured kelp plays a similar trophic role in IMTA systems as it does in a natural kelp bed. It is a major contributor to the detritus pool and supplies a vital food source to filter-feeding scallops in the IMTA system, especially during winter and early spring when phytoplankton are scarce.

Extensive spread of farmed seaweeds causes a shift from native to non-native haplotypes in natural seaweed beds

Seaweed farming has been the cause of introductions of non-indigenous seaweed species and genotypes throughout the world. In Zanzibar, Tanzania, foreign genotypes of Eucheuma denticulatum were introduced for farming purposes in 1989, and in recent years a spread of non-indigenous haplotypes has been reported. The current study aimed to investigate the presence and extent of introduced and native haplotypes of E. denticulatum as well as their relative frequencies, to obtain the severity of the spread of cultivated seaweed and the current state of the native populations. The results show that all investigated sites are dominated by the introduced South-east Asian haplotypes, even where seaweed farming has never occurred. As the frequencies of East African haplotypes are remarkably low, this shows a shift from native to introduced E. denticulatum. This shift may, at least in part, be caused by earlier overharvest of natural seaweed populations, and indicates a cryptic invasion of the introduced haplotypes at the potential cost of the recovery of the native haplotype populations.

Screening of repetitive motifs inside the genome of the flat oyster (Ostrea edulis): Transposable elements and short tandem repeats

The flat oyster (Ostrea edulis) is one of the most appreciated molluscs in Europe, but its production has been greatly reduced by the parasite Bonamia ostreae. Here, new generation genomic resources were used to analyse the repetitive fraction of the oyster genome, with the aim of developing molecular markers to face this main oyster production challenge. The resulting oyster database, consists of two sets of 10,318 and 7159 unique contigs (4.8Mbp and 6.8Mbp in total length) representing the oyster's genome (WG) and haemocyte transcriptome (HT), respectively. A total of 1083 sequences were identified as TE-derived, which corresponded to 4.0% of WG and 1.1% of HT. They were clustered into 142 homology groups, most of which were assigned to the Penelope order of retrotransposons, and to the Helitron and TIR DNA-transposons. Simple repeats and rRNA pseudogenes, also made a significant contribution to the oyster's genome (0.5% and 0.3% of WG and HT, respectively).The most frequent short tandem repeats identified in WG were tetranucleotide motifs while trinucleotide motifs were in HT. Forty identified microsatellite loci, 20 from each database, were selected for technical validation. Success was much lower among WG than HT microsatellites (15% vs 55%), which could reflect higher variation in anonymous regions interfering with primer annealing. All microsatellites developed adjusted to Hardy–Weinberg proportions and represent a useful tool to support future breeding programmes and to manage genetic resources of natural flat oyster beds.

Richness, systematics, and distribution of molluscs associated with the macroalga Gigartina skottsbergii in the Strait of Magellan, Chile: A biogeographic affinity study.

Knowledge about the marine malacofauna in the Magellan Region has been gained from many scientific expeditions that were carried out during the 19th century. However, despite the information that exists about molluscs in the Magellan Region, there is a lack of studies about assemblages of molluscs co-occurring with macroalgae, especially commercially exploitable algae such as Gigartina skottsbergii, a species that currently represents the largest portion of carrageenans within the Chilean industry. The objective of this study is to inform about the richness, systematics, and distribution of the species of molluscs associated with natural beds in the Strait of Magellan. A total of 120 samples from quadrates of 0.25 m2 were obtained by SCUBA diving at two sites within the Strait of Magellan. Sampling occurred seasonally between autumn 2010 and summer 2011: 15 quadrates were collected at each site and season. A total of 852 individuals, corresponding to 42 species of molluscs belonging to Polyplacophora (9 species), Gastropoda (24), and Bivalvia (9), were identified. The species richness recorded represents a value above the average richness of those reported in studies carried out in the last 40 years in sublittoral bottoms of the Strait of Magellan. The biogeographic affinity indicates that the majority of those species (38%) present an endemic Magellanic distribution, while the rest have a wide distribution in the Magellanic-Pacific, Magellanic-Atlantic, and Magellanic-Southern Ocean. The molluscs from the Magellan Region serve as study models for biogeographic relationships that can explain long-reaching patterns and are meaningful in evaluating possible ecosystemic changes generated by natural causes or related to human activities.

Zkušenosti s měřením vodních stavů ve vodoměrných stanicích VÚV (s využitím soustavy tlakových čidel)

The paper describes the experience with measurement of water levels (particularly low ones) in natural river beds using a system of sensors recording hydrostatic pressure and air pressure.