Species In Marine Environment Research Articles

Counting at low concentrations: the statistical challenges of verifying ballast water discharge standards

Discharge from the ballast tanks of ships is one of the primary vectors of nonindigenous species in marine environments. To mitigate this environmental and economic threat, international, national, and state entities are establishing regulations to limit the concentration of living organisms that may be discharged from the ballast tanks of ships. The proposed discharge standards have ranged from zero detectable organisms to < 10 organisms/ m3. If standard sampling methods are used, verifying whether ballast discharge complies with these stringent standards will be challenging due to the inherent stochasticity of sampling. Furthermore, at low concentrations, very large volumes of water must be sampled to find enough organisms to accurately estimate concentration. Despite these challenges, adequate sampling protocols comprise a critical aspect of establishing standards because they help define the actual risk level associated with a standard. A standard that appears very stringent may be effectively lax if it is paired with an inadequate sampling protocol. We describe some of the statistical issues associated with sampling at low concentrations to help regulators understand the uncertainties of sampling as well as to inform the development of sampling protocols that ensure discharge standards are adequately implemented.

Dietary carotenoids regulate astaxanthin content of copepods and modulate their susceptibility to UV light and copper toxicity.

High irradiation and the presence of xenobiotics favor the formation of reactive oxygen species in marine environments. Organisms have developed antioxidant defenses, including the accumulation of carotenoids that must be obtained from the diet. Astaxanthin is the main carotenoid in marine crustaceans where, among other functions, it scavenges free radicals thus protecting cell compounds against oxidation. Four diets with different carotenoid composition were used to culture the meiobenthic copepod Amphiascoides atopus to assess how its astaxanthin content modulates the response to prooxidant stressors. A. atopus had the highest astaxanthin content when the carotenoid was supplied as astaxanthin esters (i.e., Haematococcus meal). Exposure to short wavelength UV light elicited a 77% to 92% decrease of the astaxanthin content of the copepod depending on the culture diet. The LC50 values of A. atopus exposed to copper were directly related to the initial astaxanthin content. The accumulation of carotenoids may ascribe competitive advantages to certain species in areas subjected to pollution events by attenuating the detrimental effects of metals on survival, and possibly development and fecundity. Conversely, the loss of certain dietary items rich in carotenoids may be responsible for the amplification of the effects of metal exposure in consumers.

Phytophthora gemini sp. nov., a new species isolated from the halophilic plant Zostera marina in the Netherlands

Eight strains belonging to the Oomycete genus Phytophthora were isolated from Zostera marina (seagrass) in The Netherlands over the past 25 y. Based on morphology, isozymes, temperature–growth relationships and ITS sequences, these strains were found to belong to two different Phytophthora species. Five strains, four of them isolated from rotting seeds and one isolated from decaying plants, could not be assigned to a known species and hence belong to a new species for which we propose the name Phytophthora gemini sp. nov. Three strains were isolated from decaying plants and were identified as Phytophthora inundata, thereby expanding the known habitat range of this species from fresh to brackish-saline areas. The possible role of both Phytophthora species in the decline of Z. marina in The Netherlands and the evolutionary significance of the presence of Phytophthora species in marine environments are discussed.

Bacteriophages drive strain diversification in a marine Flavobacterium: implications for phage resistance and physiological properties

Genetic, structural and physiological differences between strains of the marine bacterium Cellulophaga baltica MM#3 (Flavobacteriaceae) developing in response to the activity of two virulent bacteriophages, Phi S(M) and Phi S(T), was investigated during 3 weeks incubation in chemostat cultures. A distinct strain succession towards increased phage resistance and a diversification of the metabolic properties was observed. During the incubation the bacterial population diversified from a single strain, which was sensitive to 24 tested Cellulophaga phages, into a multistrain and multiresistant population, where the dominant strains had lost susceptibility to up to 22 of the tested phages. By the end of the experiment the cultures reached a quasi steady state dominated by Phi S(T)-resistant and Phi S(M) + Phi S(T)-resistant strains coexisting with small populations of phage-sensitive strains sustaining both phages at densities of > 10(6) plaque forming units (pfu) ml(-1). Loss of susceptibility to phage infection was associated with a reduction in the strains' ability to metabolize various carbon sources as demonstrated by BIOLOG assays. This suggested a cost of resistance in terms of reduced physiological capacity. However, there was no direct correlation between the degree of resistance and the loss of metabolic properties, suggesting either the occurrence of compensatory mutations in successful strains or that the cost of resistance in some strains was associated with properties not resolved by the BIOLOG assay. The study represents the first direct demonstration of phage-driven generation of functional diversity within a marine bacterial host population with significant implications for both phage susceptibility and physiological properties. We propose, therefore, that phage-mediated selection for resistant strains contributes significantly to the extensive microdiversity observed within specific bacterial species in marine environments.

Internal borders for managing invasive marine species

Summary This study discusses theoretical and practical issues around the definition of internal borders for the management of marine pests, drawing on principles from freshwater and terrestrial pest management. Internal borders are defined as post‐border intervention points around which vector management and related activities, such as pest surveillance and incursion response, can be undertaken. Internal borders can be identified in marine systems based on knowledge of natural barriers to the dispersal or establishment of pests, including planktonic life stages. We highlight opportunities to define internal borders at broad spatial scales according to oceanographic features or environmental conditions. At smaller spatial scales, habitat barriers based on relatively permanent features (e.g. substratum) could be defined for target organisms (or suites of similar organisms), especially those having both restricted habitat requirements and a limited planktonic duration. Where internal borders are identified, risk‐based approaches can be used to determine vector management priorities, incorporating knowledge of the connectivity and strength of interactions between hubs of vector activity. However, greater biosecurity and biodiversity benefits may arise from approaches that combine risk‐based measures for target pests, with generic measures (e.g. vessel hull anti‐fouling) that are applied equally across all human‐mediated invasion pathways. Case studies of high‐profile marine pests in New Zealand illustrate situations where the benefits of internal border management have been realized. The challenge now is to identify how practical it is to widely apply internal borders in a marine biosecurity context, and to identify new internal borders around which management can practically be undertaken. Synthesis and applications. Effective control of pest species in marine environments is possible even when they become relatively widespread and established. The definition of internal borders provides an approach to marine biosecurity that assists in elucidating opportunities and priorities for management. Although marine systems are regarded as relatively open, the principles and approaches necessary for the successful management of marine pests are conceptually the same as those applied in freshwater systems and on land.

Development of a sensitive and controlled real-time RT-PCR assay for viral haemorrhagic septicaemia virus (VHSV) in marine salmonid aquaculture

A survey was undertaken to determine the potential distribution of viral haemorrhagic septicaemia virus (VHSV) in marine cage-based salmonid farms in Scotland. A rapid, accurate and sensitive quantitative real-time RT-PCR (qRT-PCR) assay was developed, targeting a conserved region of the nucleoprotein (N) gene of the virus. The qRT-PCR assay was shown to be more sensitive than the conventional VHSV RT-PCR. A validation protocol included several different virus isolates as the target and confirmed that the assay could detect all European VHSV genotypes (I, II and III). Both endogenous and exogenous controls were designed to control for integrity of template and distinguish between true VHSV positives and contamination with the positive control material. In total, the universal European VHSV qRT-PCR assay with exogenous positive control was applied to screen 2040 individual Atlantic salmon Salmo salar and 150 individual rainbow trout Oncorhynchus mykiss. No evidence of the presence of VHSV in association with either salmonid species in Scottish marine farms was detected. However, both marine Atlantic salmon and rainbow trout are still considered possible carriers of VHSV, which remains a potential threat to freshwater farming. Therefore, a continued surveillance of these species in marine environment is recommended.

Experiments on the survival of six brackish macro-invertebrates from the Baltic Sea after dredged spoil coverage and its implications for the field

Physical disturbance by disposal of dredged materials in estuarine and coastal waters may result in burial of benthic fauna. Survival rates depend on a variety of factors including the type and amount of disposed materials and the lifestyle of the organisms. Laboratory burial experiments using six common macrobenthic invertebrates from a brackish habitat of the western Baltic Sea were performed to test the organisms' escape reaction to dredged material disposal. Experimental lab-results were then extrapolated to a field situation with corresponding bottom topography and covering layer thicknesses at experimental field disposal study sites. Resulted survival rates were then verified by comparison with results of an earlier field study at the same disposal sites. Our experimental design in the lab included the disposal of two types of dredged material (i.e. ‘till’ and ‘sand/till mixture’) and two covering layer depths (i.e. 10–20 cm and 14–40 cm). All three bivalves Arctica islandica (Linnaeus), Macoma balthica (Linnaeus), Mya arenaria (Linnaeus) and the polychaete Nephtys hombergii (Savigny) successfully burrowed to the surface of a 32–41 cm deposited sediment layer of till or sand/till mixture and restored contact with the overlying water. These high escape potentials could partly be explained by the heterogeneous texture of the till and sand/till mixture with ‘voids’. The polychaete Bylgides ( Harmothoe) sarsi (Malmgren) successfully burrowed through a 16 cm covering layer whereas the polychaete Lagis koreni (Malmgren) showed almost no escaping reaction. No general differences in escape behaviour after burial were detected between our test species from the brackish habitat and those reported in the literature for the same species in marine environments. However, a size-dependence in mobility of motile polychaetes and M. arenaria was apparent within our study. In comparison to a thick coverage, thin covering layers (i.e. 15–16 cm and 20 cm) increased the chance of the organisms ( N. hombergii and M. arenaria) to reach the sediment surface after burial. This was not observed for the other test species. While crawling upward to the new sediment surfaces burrowing velocities of up to 8 cm d − 1 were observed for the bivalves and up to 20 cm d − 1 for N. hombergii. Between 17 and 79% of the test organisms showed burrowing activity after experimental burial. The survival rate (defined as the ability to regained contact with the sediment surface) ranged from 0 to 33%, depending on species and on burial depth. The organisms reached the sediment surface by burrowing (polychaetes and bivalves) and/or by extending their siphons to the new sediment surface (bivalves). The extrapolation of laboratory survival rates to the two disposal sites was obtained based on the in situ thicknesses of the dredged spoil layers measured by multi-beam echo sounder. This resulted in total average survival rate estimates for the test species of 45 and 43% for the two disposal sites. The results obtained during the laboratory tests and the following extrapolation to the field were verified by the range of results from a previous field study, using grab sampling shortly before and after a disposal event in June 2001. The effect of dredged material disposal on the tested Baltic Sea benthic macrofauna was assessed by extrapolating the verified laboratory results to the field.

A dual‐labeling method for the simultaneous measurement of dissolved inorganic carbon and phosphate uptake by marine planktonic species

The measurement of primary production is the foundation for aquatic biogeochemistry research. The biogeochemical cycles of phosphate (P) and other biolimiting elements are tightly linked to marine primary production. We have optimized an existing method of carbon (C) and P dual isotope labeling to study the simultaneous C and P uptake by plankton species in marine environments. The two main objectives of this study were (1) to test the preservation properties of the labeled samples and the calculation methods used in separating the signals of the different radionuclides, and (2) to adapt the method to marine environments. The procedure was successfully implemented in contrasting locations within the southeast Pacific (between 146.36°W and 72.49°W). The uptake rates determined using this method ranged from 14 to 900 nM h−1 for dissolved inorganic C and from 0.03 to 4.5 nM h−1 for dissolved inorganic P in surface water. The detection limit found in ultraoligotrophic surface water was 3.33 nM h−1 and 0.01 nM h−1 for C and P, respectively. C and P assimilation fluxes in low‐ and high‐productivity open‐ocean systems may be studied using this sensitive method. We outline a protocol for marine environments that is appropriate for use under oceanographic cruise conditions. Results from the application of this method will lead to a better understanding of the interplay between carbon and phosphate biogeochemical cycles in the upper ocean.

Detection of two diatoms using sandwich hybridization integrated with nuclease protection assay (NPA-SH)

Nuclease protection assay (NPA) probes were designed to target the rRNA of Chaetoceros curvisetus and Skeletonema costatum, and quantitative sandwich hybridization integrated with nuclease protection assay (NPA-SH) was developed to detect C. curvisetus and S. costatum in culture and field samples in Jiaozhou Bay, China. The specificity and validity of the NPA-SH technique were tested with cultured pure strains, mixed strains and field samples, and by comparison with that of microscopy observation. The linear detection range for C. curvisetus was 4.2 × 104 to 1.2 × 106 cells with a detection limit of 42 cells ml−1. The linear range for S. costatum was 6.0 × 104 to 1.0 × 106 cells with a detection limit of 60 cells ml−1. The NPA-SH in this study provides a convenient tool for rapid assessment of HAB species in marine environments.

Production and flux of carbohydrate species in the Gulf of Mexico

Carbohydrates are an important organic compound class in seawater and play an active role in the biogeochemical cycling of organic carbon and trace elements in the ocean, but are poorly characterized. To better understand the sources and role of carbohydrate species in marine environments, the concentrations and fluxes of particulate carbohydrates (CHO), total acid polysaccharides (APS), uronic acids (URA), phytoplankton composition and bacterial production were measured in the Gulf of Mexico in 2000 and 2001. A strong positive correlation between APS concentration and cyanobacteria abundance was found in 2000. In 2001, prymnesiophyte abundance correlated well with both concentrations of APS and URA. Bacterial production data, measured simultaneously in 2001, showed significant positive relationships with particulate organic carbon (POC), CHO, APS and URA concentrations, respectively. The average fluxes out of the euphotic zone of CHO, APS and URA in 2000 were 8.1, 1.3, and 0.7 mg C m−2 d−1, respectively. In 2001, the average fluxes of CHO, APS and URA were about 3 times higher than those in 2000, which was a time of lower nutrient concentrations, indicating that the fluxes of carbohydrate species are related to the nutrient status and phytoplankton composition. The results suggest that APS in the upper water column can be produced by cyanobacteria, prymnesiophytes, and heterotrophic bacteria. Most importantly, our data indicate that APS and CHO compounds are more resistant to biological degradation than other organic compounds, suggesting that the role of CHO compounds in carbon cycling in the ocean is more complex than previously thought.

Kinetics and mechanism of the reaction between atomic chlorine and dimethyl selenide; comparison with the reaction between atomic chlorine and dimethyl sulfide

Dimethyl selenide is the most abundant gaseous selenium species in marine environments. In this work, the value of the rate coefficient for the gas-phase reaction between dimethyl selenide and Cl atoms has been determined for the first time. The value of the second-order rate coefficient obtained was (5.0 ± 1.4) × 10−10 cm3 molecule−1 s−1. The very fast nature of the reaction means that, when estimating the lifetime of dimethyl selenide in the atmosphere, loss due to reaction with Cl atoms should be considered along with loss due to reaction with O3 and with OH and NO3 radicals. Analysis of the available kinetic data suggests that at 760 Torr the dominant reaction pathway for the reaction of Cl atoms with dimethyl selenide will be the addition of Cl to the Se atom forming an adduct of the type CH3Se(Cl)CH3. Theoretical calculations, at the B3LYP/6-311++G(2df,p)//B3LYP/6-311++G(d,p) level of theory, show that at 298 K the value of ΔrH for the formation of the adduct is −111.4 kJ mol−1. This value may be compared to −97.0 kJ mol−1, the value calculated for ΔrH for the formation of the analogous sulfur adduct, CH3S(Cl)CH3, following the reaction between Cl atoms and dimethyl sulfide. Variational RRKM theory was used to predict the thermal decomposition rates of the two adducts back to starting materials. The estimated rate constant for the decomposition of the selenium adduct to the reactants is 5 × 10−5 s−1, compared to 0.02 s−1 in the case of the sulfur adduct. However, our calculations suggest that the CH3Se(Cl)CH3 adduct, which is initially formed highly excited, will not be stabilised under atmospheric conditions, but rather will decompose to yield CH3SeCl and CH3, a process that is calculated to be exothermic with respect to the initial reactants by 5.8 kJ mol−1. The formation of CH3SCl and CH3 from the sulfur adduct, on the other hand, is endothermic by 20.8 kJ mol−1 with respect to the initial reactants, and is thus not expected to occur.

Reproductive isolation and genetic differentiation of a scleractinian coral Mycedium elephantotus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 201:179-187 (2000) - doi:10.3354/meps201179 Reproductive isolation and genetic differentiation of a scleractinian coral Mycedium elephantotus C.-F. Dai1,*, T.-Y. Fan1,2, J.-K. Yu1 1Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC 2National Museum of Marine Biology and Aquarium, 2 Houwan Road, Checheng, Pingtung 944, Taiwan, ROC *Corresponding author. E-mail: corallab@ccms.ntu.edu.tw ABSTRACT: Sexual reproduction and genetic variation of the scleractinian coral Mycedium elephantotus at Maoao (MO), Yenliao Bay, northern Taiwan, and at Tiaoshi (TS), Nanwan Bay, southern Taiwan, were studied from 1990 to 1996. M. elephantotus is a hermaphroditic broadcast spawner with an annual reproductive cycle. Gametogenesis of the MO population began in January, and spawning occurred in July-August. In the TS populations, there were 2 reproductive groups with different timing of gametogenesis and spawning. Gametogenesis of the first group started in November, and spawning occurred in April or May, while gametogenesis of the second group started in March and spawning occurred in August or September. The temporal reproductive isolation of the 2 groups was possibly the byproduct of adaptation. Allozyme electrophoresis was applied to study the genetic variations among regional coral populations and the 2 reproductive groups. Significant genetic variations were detected among the MO and TS populations and between the 2 reproductive groups at TS, but no fixed differences were found. The MO population demonstrated larger genetic distances with TS populations (Nei¹s unbiased D = 0.229 and 0.165, for the first and second reproductive groups respectively) reflecting the effect of isolation by distance. Significant genetic variation and moderate genetic distance (D = 0.045) between the 2 reproductive groups at TS indicate the effect of genetic differentiation due to reproductive isolation in sympatric populations. The lack of morphological differences and the moderate genetic distance between the 2 reproductive groups suggest recent diversification within the taxon. The presence of 2 reproductive groups of M. elephantotus in Nanwan Bay may represent the initial stage of sympatric speciation in marine environment or a secondary contact of allopatric populations. KEY WORDS: Reproductive isolation · Genetic variation · Scleractinian coral Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 201. Online publication date: August 09, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

GENETIC DIVERGENCE, REPRODUCTIVE ISOLATION, AND MARINE SPECIATION

In marine species, high dispersal is often associated with only mild genetic differentiation over large spatial scales. Despite this generalization, there are numerous reasons for the accumulation of genetic differences between large, semi-isolated marine populations. A suite of well-known evolutionary mechanisms can operate within and between populations to result in genetic divergence, and these mechanisms may well be augmented by newly discovered genetic processes. This variety of mechanisms for genetic divergence is paralleled by great diversity in the types of reproductive isolation shown by recently diverged marine species. Differences in spawning time, mate recognition, environmental tolerance, and gamete compatibility have all been implicated in marine speeiation events. There is substantial evidence for rapid evolution of reproductive isolation in strictly allopatrie populations (e,g. across the Isthmus of Panama). Evidence for the action of selection in increasing reproductive isolation in sympatric populations is fragmentary. Although a great deal of information is available on population genetics, reproductive isolation, and cryptic or sibling species in marine environments, the influence of particular genetic changes on reproductive isolation is poorly understood for marine (or terrestrial) taxa. For a few systems, like the co-evolution of gamete recognition proteins, changes in a small number of genes may give rise to reproductive isolation. Such studies show how a focus on the physiology, ecology, or sensory biology of reproductive isolation can help uncover the

Extraction of mercury(II) from chloride solutions by ethyl acetate

Studies on the extraction of mercury(II) halides are of considerable interest and importance in the field of pollution control and also of speciation in marine environment. Little [1, 3] is known about mercury(II) extraction from chloride media. The authors have, therefore, taken up a detailed investigation using the radio tracer technique on the extraction of Hg(II) from chloride media into ethyl acetate in order to establish the nature of the extracted species.