Marine Water Environments Research Articles

A Sound Approach to Soft Sediment Resolution

The last few years has seen a surge in research activities directed towards investigating properties and dynamics of young marine, limnic and fluvial sediments. It is by now a well established fact that the sequence of sediments ranging from concentrated benthic suspension over fluid mud to un-consolidated material summarized as liquid sediments (LS), act as carriers for a wide range of pollutants discharged or migrated into waterways. Knowledge of the transport and fate of LS allows determining the transport and fate of adsorbed constituents (e.g., heavy metals, pesticides, PCBs, PAHs). To assess the environmental impact of LS, efforts have to be made to better understand the processes in relation to hydrodynamics and the chemical and physical properties of the layers. Since physical laws limit the resolution and detection power of conventional seismo-acoustic systems in respect of LS, alternative measurement, data analysis and processing approaches have to be found. Adapted acoustic procedures initially developed for shallow water marine environments to extreme shallow water regimes using matched field inversion techniques can reveal geoacoustic parameters including density, compressional wave speed and attenuation as a function of depth and time. The paper outlines the effects of sediment mobility upon the environment followed by a short overview of techniques commonly used to investigate sediments and other freshwater/marine events. The problems faced and limitations of existing systems are briefly outlined. Results obtained with recently developed and refined geoacoustic inversion methods are presented highlighting their potential for long-term study of physical properties and dynamics of LS.

WHITE SPOT SYNDROME VIRUS IN FROZEN SHRIMP SOLD AT MASSACHUSETTS SUPERMARKETS

One of the most damaging viral diseases affecting the shrimp aquaculture industry is white spot disease (WSD) caused by white spot virus (WSSV), which causes high morbidity and mortality rates in penaeid shrimp and other crustaceans. The rapid spread of WSSV within wild and cultured stocks of shrimp may be caused by unregulated processing, disposal of infected imported shrimp, or the use of contaminated broodstock. The risk of introducing this virus to cultured and wild shrimp and other native species of crustaceans in the United States warrants investigation. The aim of this study is to determine the prevalence of WSSV in frozen commodity shrimp sold at four stores in the Boston area belonging to different supermarket chains. Samples from two size classes were collected in two different batches a month apart. Polymerase chain reaction was used to amplify a portion of the WSSV genome using a commercial PCR kit (ShrimpCare, DiagXotics). WSSV positive samples were visualized by electrophoresis and amplified product of selected samples was sequenced. Results showed a range of 0% to 38.7% for WSSV prevalence rate in the test populations, with an overall prevalence of 4.7%. Significant (P < 0.001) differences in WSSV prevalence were observed between shrimp from the two batches purchased a month apart, the two size classes, and the four test stores. Country of origin seemed to dominate the results. Sequence analysis confirmed the presence of WSSV genome in PCR-positive samples. Results provide preliminary evidence that an appreciable proportion of the shrimp sold in Massachusetts' supermarkets are carrying WSSV, and this constitutes a substantial risk of importation of this virus into the local environment. Further investigation is necessary to determine the risk of release of this virus into native fresh and marine water environments in Massachusetts and throughout the United States.

Degradation in Cemented Marine Clay Subjected to Cyclic Compressive Loading

The influence of cyclic loading on the strength and deformation behavior of cemented marine clay has been studied. This marine clay is of recent Pleistocene origin and deposited in a shallow water marine environment. Open pits were dug in sheeted enclosures and from these pits, undisturbed samples were taken for strength testing. A series of standard triaxial shear tests and stress controlled one-way cyclic load tests were conducted at consolidation stress ranges below and above the preconsolidation pressure. For the stress levels below the preconsolidation pressure, the cyclic loading has brought about the collapse of the cementation bond through an increase in strains, and at higher pressure ranges, the soil behaves like typical soft clay. This experiment studied the rate of development of strain and pore water pressure and shows that rate is a function of number of cycles, applied stress, and stress history. In addition, soil degradation during cyclic loading is studied in terms of Degradation Index. Attempt has been made to predict stain, pore water pressure, and degradation index through an empirical model.

Observations of the Sediment-Water Interface: Marine and Fresh Water Environments

The sediment at the interface immediately beneath the water column is distinct from deeper-lying sediments in its properties and, at least quantitatively, in the processes driving diagenesis. Progress in understanding the sediment-water interface can be based on consideration of fundamentals of biogeochemical particle / fluid interactions and on application of certain biological techniques especially suited to this challenging portion of the sediment column. This article reports results achieved by combining theoretical fundamentals and specialized experimental techniques in the study of the interface from selected depositional environments. For fine-grained and sandy deposits from fresh-water to coastal marine environments, the interface is characterized by exaggerated microrelief, great porosity, and significant biological alteration. Additional application of this research approach is poised to further our understanding of engineering, and acoustic and xenochemical responses of sedimentary materials, with special emphasis on the influence of the bio-organic phase of the interface upon its fabric and physical properties.

Sturgeons (Chondrostei: Acipenseridae) and their metazoan parasites: patterns and processes in historical biogeography

Abstract Aim The historical biogeography of host‐parasite associations is examined in a geologically old group of fishes, the sturgeons (Osteichthyes: Acipenseridae), and their parasite assemblage. Evidence from phylogenetics and biogeographical studies of several parasite groups is used to formulate and evaluate hypotheses about the coevolutionary history of this host‐parasite association and, ultimately, the origin of sturgeons. Location The geographical areas discussed in this study are the temperate regions of North America and Eurasia, including the North Atlantic, North Pacific, Mediterranean and Ponto‐Caspian basins and their drainages. Methods Relationships of parasites in several clades (Truttaedacnitis, Diclybothriidae, Deropristiidae, Spinitectus and Acrobothriidae) are analysed or re‐analysed using cladistics. These results are combined with hypotheses of relationships of sturgeons and their biogeography. We largely follow an ‘empirical synthetic pattern approach' (Grande &amp; Bemis, 1998) where the search is primarily for broadly congruent patterns, keeping interpretations close to the data and to known or postulated Earth history (palaeogeography). The evidence from the cladistic analyses is first interpreted within the context of vicariance events, but dispersalist scenarios are also discussed where warranted. We also use the concept of Croizat's ‘biogeographical tracks' to characterize broadly congruent distributional patterns. Results Phylogenetic hypotheses and biogeography of parasites indicate three major biogeographical tracks, of which a Holarctic track involving northern and north‐eastern Asian regions and North America is predominant (in Crepidostomum auriculatum, Polypodium hydriforme, Truttaedacnitis, Capillospirura, Diclybothriidae, Amphilina), with evidence for a recurring basal trans‐Pacific track (in Truttaedacnitis, Diclybothriidae). Trans‐Atlantic tracks appear to be either independent of (in Deropristidae) or secondarily derived from (in Bothrimonus and Truttaedacnitis sphaerocephala) a Holarctic track. Evidence from parasites supports the hypothesis of sister relationships between Acipenser medirostris and A. mikadoi, and between A. fulvescens and A. brevirostrum. Main conclusions This host–parasite association was historically structured by colonization and subsequent coevolution. Dispersal and vicariance of acipenserids resulted in small but widespread, highly distinct, monophyletic parasite lineages. Species of such parasite clades remain associated with major and often discrete continental and oceanic formations, and occasionally with related sturgeon species. Biogeographical tracks implicate the Cretaceous and early Tertiary Asian–American peninsula (Beringian region) as a historically important region in the origin and early geodispersion of the parasite fauna. This is consistent with hypotheses of the northern north‐eastern Asian region, or the more inclusive Asian–American peninsula, as a key area in the early diversification of sturgeons and the acquisition of their parasite fauna. The parasite fauna supports the hypothesis of a former continuous distribution of Nearctic and eastern Palaearctic (Siberian) sturgeons that was subsequently fragmented by geological and climatic events, resulting in major displacement of ancestral sturgeon populations in North America. The parasites also reflect a historical connection with marine and brackish water environments that pre‐dates the diversification of sturgeons, indicating that ancestral acipenserids were diadromous.

Foraminiferal response to Holocene environmental changes of a tidal estuary in Victoria, southeastern Australia

The Holocene strata in the Anderson Inlet area in Victoria can be stratigraphically divided into four units, Unit I, Unit II, Unit III, and Unit IV. Unit I and Unit IV lack fossils and were deposited in non-marine, probably fluvial environments. Unit II and Unit III contain abundant foraminifera with molluscs, ostracods and bryozoans. Foraminiferal analysis suggests that Unit III was formed in a partially sheltered marine environment, while the high plankton content and relatively high diversity of benthic species in Unit II indicate that this unit was deposited in an open bay at water depths possibly less than 5 m. The foraminiferal data are integrated with radiocarbon dates to arrive at the following Holocene palaeoenvironmental history in this area: (1) low alluvial plain stage (10,000–7000 yr B.P.); (2) open bay environment stage (7000–5500 yr B.P.); (3) partially sheltered marine environment stage (5500–4500 yr B.P.); (4) alluvial plain and coastal lagoon environment stage (since about 4500 yr B.P.). The foraminiferal fauna show a clear response to these palaeoenvironmental changes. Globigerina bulloides can be used as an indicator for cold water marine environments. The high concentration of this species in these middle Holocene sediments shows a strong cold water influence on the coastal environments which reduced the effect of regional warm currents during this period. The Holocene palaeoenvironmental changes in the area were controlled by the Holocene sea-level fluctuations associated with the deglaciation history during this period. Similar integrated studies of shallow to marginal marine strata in southern Africa, America and New Zealand will lead to a better understanding of Holocene relative sea-level change and the interplay between Holocene cold and warm water regimes in the Southern Hemisphere.

A molecular view of archaeal diversity in marine and terrestrial hot water environments

Molecular phylogenetic survey of naturally occurring archaeal diversities in hot water environments was carried out by using the PCR-mediated small subunit rRNA gene (SSU rDNA) sequencing. Mixed population DNA was directly extracted from the effluent hot water or sediment of a shallow marine hydrothermal vent at Tachibana Bay, or the acidic hot water of hot spring pools at Mt. Unzen, in Nagasaki Prefecture, Japan. Based on the partial rDNA sequences amplified with an Archaea-specific primer set, the archaeal populations of hot water environments consisted of phylogenetically and physiologically diverse group of microorganisms. The archaeal populations were varied in each sample and subject to its environmental conditions. In addition, the large number of archaeal rDNA sequences recovered from hot water environments revealed the distant relationship not only to the rDNA sequences of the cultivated thermophilic archaea, but also to the sequences of unidentified archaeal rDNA clones found in other hot water environments. The findings extend our view of archaeal diversity in hot water environments and phylogenetic organization of these organisms.

A molecular view of archaeal diversity in marine and terrestrial hot water environments

Molecular phylogenetic survey of naturally occurring archaeal diversities in hot water environments was carried out by using the PCR-mediated small subunit rRNA gene (SSU rDNA) sequencing. Mixed population DNA was directly extracted from the effluent hot water or sediment of a shallow marine hydrothermal vent at Tachibana Bay, or the acidic hot water of hot spring pools at Mt. Unzen, in Nagasaki Prefecture, Japan. Based on the partial rDNA sequences amplified with an Archaea-specific primer set, the archaeal populations of hot water environments consisted of phylogenetically and physiologically diverse group of microorganisms. The archaeal populations were varied in each sample and subject to its environmental conditions. In addition, the large number of archaeal rDNA sequences recovered from hot water environments revealed the distant relationship not only to the rDNA sequences of the cultivated thermophilic archaea, but also to the sequences of unidentified archaeal rDNA clones found in other hot water environments. The findings extend our view of archaeal diversity in hot water environments and phylogenetic organization of these organisms.

A review of Wanganui Basin, New Zealand: global reference section for shallow marine, Plio–Pleistocene (2.5–0 Ma) cyclostratigraphy

Wanganui Basin, New Zealand, contains one of the most complete late Neogene marine stratigraphic records in the world. The ca. 2 km thick basin-fill for the last ca. 2.5 Ma comprises 47 superposed cyclothems which correspond to successive 5th (100 ka) and 6th (41 ka) order glacio-eustatic, sea-level fluctuations on the palaeo-New Zealand shelf since oxygen isotope stage 100. Stages 100 to 5 are represented by marine cyclothems, whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences. Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12–2. The presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for Wanganui Basin which correlates closely with the global oxygen isotope scale. In all except two cases (cycles 12 and 36), individual unconformity-bound cyclothems (sequences) represent a single glacial/interglacial couplet of Milankovitch frequency. Lithologic and faunal variation within the cyclothems corresponds closely to that predicted by the sequence stratigraphic model. Each cyclothem generally contains a transgressive systems tract, a mid-cycle condensed shellbed, a highstand systems tract, and often a regressive systems tract. Six common cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines, viz. the Hawera, Maxwell, Turakina, Seafield, Castlecliff, and Rangitikei motifs. A seventh type, the Nukumaru motif, includes coquina limestone and represents deposition in shoreface and very shallow water marine environments.

Marine ostracods in the Lower Carboniferous fluviatile Fell Sandstone Group: evidence for base level change and marine flooding of the central graben, Northumberland Basin

SUMMARY Seven species of ostracod have been identified from the coarser, more silty laminae within a thin shaly siltstone interval within the Lower Carboniferous Fell Sandstone Group in the eastern part of the Northumberland Basin, all of which indicate a quiet, nearshore, shallow water marine environment. This is the first documented occurrence of marine ostracods from the Fell Sandstone which has always been regarded as entirely of non-marine origin, with any marine influences confined to the westernmost part of the basin. The shaly siltstone was proved in the Alnwick Borehole drilled through the upper section of the Fell Sandstone in an otherwise sandstone-dominated succession. The presence of marine influenced conditions more than 60 km inland from the coeval shoreline reflects contemporaneous intrabasinal tectonics and the location of the Alnwick Borehole at the northeastern end of the central graben within the Northumberland Basin. Marginal fault activity, contemporaneous with Fell Sandstone deposition, caused gentle tilting of the graben floor, thus allowing marine conditions to penetrate farther inland than previously known. The ostracod-bearing marine shaly siltstone, which lies above and below braided river sandstones, provides a key sequence stratigraphic surface across this part of the basin. The base of the unit is a transgressive surface with the shale itself equivalent to a maximum flooding to truncated shale prone early high stand. The immediately overlying erosion surface records low stand incision, facies tract dislocation and the development of a possible sequence boundary, with the overlying stacked, cross-bedded, coarse pebbly braided channel sandbodies referred to the lower and middle parts of a transgressive systems tract that spans the boundary between the Fell Sandstone and succeeding, more marine influenced Scremerston Coal Group. The lower, finer-grained, fluvial succession beneath the transgressive surface is tentatively assigned to part of an incompletely exposed transgressive systems tract.

Two billion year old isotopically heavy carbon: evidence from the Labrador Trough, Canada

Forty-eight samples of bulk carbonates were studied from the Dunphy, Portage, Alder, Uvé, Denault, and Abner formations and the undivided Pistolet subgroup in the Labrador Trough, Quebec, Canada. The carbonate units occur as a number of thick beds (up to 300 m) within 100–600 m thick formations. They are interbedded with siliciclastic sediments and are composed of crystalline, sparry, micritic allochemical and stromatolitic dolostones. The carbonate rocks are recrystallized and metamorphosed (up to amphibolite grade). They are chemically dolostones, and include chemical or biochemical laminated and massive dolostones, dolorudites, dolarenites, and dololitites, which were deposited in shallow-water (Dunphy, Denault, and Abner formations) to relatively deep water (Uvé Formation) marine environments. Reef facies are present in the Denault and Abner formations. The Dunphy, Portage, Alder, and Uvé formations, deposited between 2.17 and 2.14 Ga, yield isotopically heavy values of δ13C(PDB) ranging from + 5.3 to + 15.4‰, whereas δ18O(SMOW) values range from + 16.2 to + 25.4‰, which is rather normal for Precambrian sedimentary carbonates. The average values of δ13C show a decreasing trend upwards in the stratigraphy from 14.8 ± 0.5‰ (Dunphy Formation), to 9.5 ± 0.7‰ (Alder Formation), to 8.0 ± 1.7‰ (Uvé Formation). Average δ18O values exhibit a similar tendency, 23.6 ± 1.1, 22.6 ± 1.1, and 20.0 ± 1.9‰, respectively. The Alder and Uvé formations display clustering in a δ13C histogram, while the Dunphy Formation plots as a separate offset. The Abner and Denault formations, deposited at about 1.88 Ga, show an average δ13C of 2.1 ± 0.6 and 1.3 ± 1.4‰, and an average δ18O of 21.4 ± 1.9 and 22.6 ± 2.0‰, respectively. δ13C for these two formations is similar to that of Recent marine carbonates. The isotopically heavy carbonates (13Ccarb) of the Dunphy, Portage, Alder, and Uvé formations and those of the undivided Pistolet subgroup were accumulated during approximately 30 Ma over a vast area of at least 20 000 km2. The 13Ccarb enrichment occurs in connection with diverse depositional environments, not controlled by any detectable local factors (e.g., facies, diagenetic or metamorphic alteration) and therefore considered to be part of the world-wide development of high δ13Ccarb documented at around 2.2 ± 0.1 Ga. The Canadian Shield is the fourth continent, in addition to Africa, northern Europe, and Australia, to show extensive development of isotopically heavy carbonate formations of this age.

Origen epiclástico de estratificaciones cruzadas afectando a materiales volcanoclásticos jurásicos en la Sierra de Javalambre (Teruel)

Tu 11w Sierra dc Javalambrc a prc-middle Bajocian volcaniclastie outcrop (Camarena-’?> showing cross-bedding is analysed; sedimentological mid paleontological dala suggest that this struetuTe was formed by piling dunes up n a shallow water marine environment. Epiclastie processes have reworked the primary volcanielastic material. On flie basis of petrological and sedimentological data, which are deseribed in detail, abase surge origin forIhese volcaiuclastic deposits is challenged. Caedoreos de Geologia Iberica, ~nim.22, 121-137. Scalejo dc i~ ob i caciones, 1 Jiive.rsidad complutense. Madrid, 1997. 122 R. M. Martinez Gonzalez, J. 1? Valenzuela Rios, M. Lago,1 Bastida yR. Vaquer

BRECEM: A RAPID HARDENING CEMENT BASED ON HIGH ALUMINA CEMENT.

The Building Research Establishment (BRE) has developed a blended cement based on high alumina cement (HAC) with ground granulated blastfurnace slag. This cement has been given the trademark 'BRECEM' and the properties of concrete made from the new cement are being studied at BRE in collaboration with the industry. In this paper, the chemical and thermal stability of BRECEM and HAC mortars and concretes is compared as a necessary preliminary to determining engineering properties in due course. Concrete durability studies are at an early stage and, as such, the uses for this cement are still under development. The addition of slag alters the course of hydration reactions in HAC. A chemical compound, gehlenite hydrate (stratlingite), not seen in plain HAC in significant amounts, forms readily and becomes the major hydrate constituent in due course, and is thought to provide a more stable phase assemblage. Studies to determine the chemical and physical properties of BRECEM in mortars and concrete over a range of temperatures and storage conditions have been set up at BRE. BRECEM mortars show excellent sulphate resistance. HAC and BRECEM concrete durability specimens have performed very well following storage for a year in aggressive sulphate, marine and soft water environments. Longer term tests will be carried out at two, five and 10 years. BRECEM concretes have shown a greater tolerance to high water-to-cement ratio mix designs in forming stable assemblages with reduced temperature rises and enhanced durability, and there are cost savings compared with HAC concretes. A number of potential, practical applications have been advocated.

Toxicity of acrylamide derivatives to embryos of the rotifer Adineta vaga.

The invertebrate rotifer, introduced into toxicological research more than 40 years ago (Marriott et al. 1948; Allee and Rosenthal 1949), has since been used both as a model organism to investigate the biochemical and physiological actions of toxins (Lindner and Goldman 1964; Kleinow 1986) and as a test organism in bioassays to monitor pollution in marine and fresh water environments (Snell and Persoone 1989; Fern~indez-Casalderrey et al. 1991). The selection of rotifers as the experimental animals has several justifications. First, being multicellular animals, they offer a better choice over bacteria and protozoans. Second, they are easy to collect, culture and inexpensive to maintain. Third, several species are all parthenogenetic females. This enables one to prepare clones of genetically identical individuals, all descendants of one female. Consequently, the genetic factor is largely eliminated from the interpretation of the experimental results. Fourth, since the lifespan of most species is short (5 to 40 d), the chronic effects of toxins on lifespan and reproduction can be evaluated relatively quickly.

Paleontologia y ambientes del Triásico Medio en el sector noroccidental de la Cordillera Ibérica (provs. de Soria y Guadalajara, España)

The Triassic of the NW Iberian Ranges consists of two carbonatic formations equivalent to the Upper Carbonatic Formation of the Muschelkalk Facies and pass laterally into siliciciastic deposits to the NW. Fossillocalities have been found in both formations. Taphonomic and sedimentologic studies allow for the interpretation as autochthonous associations of the infaunal Bivalves of shallow water marine environments with siliciciastic input. Three faunal associations have been distinguished: 1. Costatoria-Lyriomyophoria association, found in the lower carbonatic formation and the equivalent siliciciastic formation; 2. «Teruel Fauna» association, found in the upper carbonatic formation; 3. Lingula-Pseudocorbula association, found near the top of the upper carbonatic Formation. The «Teruel Fauna» is well represented in the Iberian Ranges, and always occur in the «Royuela Marls and Limestones» Formation, and our fossil localities are its most Northwestern record in the Iberian Ranges up to now, thus extending the presence of the endemic «Sephardic Faunas» during the Ladinian.

Monitoring of persistent, lipophilic pollutants in water and sediment by solvent-filled dialysis membranes

Dialysis membranes filled with solvents can be used to monitor persistent, lipophilic pollutants in marine and fresh water environments, to predict levels of bioavailable compounds in organisms, and to study bioaccumulation mechanisms. The membranes are filled with n-hexane and exposed for 1 to several weeks in the water or in the sediment. The solvent impregnates the membrane, makes it unsuitable for periphyton growth, and prevents bacterial degradation. The membranes can also be used in environments too polluted for biological indicators to survive. The use of membranes with a molecular weight cutoff of 1000 Da prevents substances of higher molecular weight from diffusing through their walls, thereby simplifying the cleanup procedure. Internal standards in the solvent can be quantified to ensure that the membrane functions properly during the exposure. Uptake and depuration of organochlorine residues by the membranes seem to be governed by equilibrium partitioning.

A new source of 4-methyl sterols and 5α(H)-stanols in sediments: prymnesiophyte microalgae of the genus Pavlova

Lipid analyses of four species of marine unicellular prymnesiophyte algae of the genus Pavlova have shown that each contains significant amounts of 4α-methyl sterols, the major one being the C 30 sterol 4α-methyl-24-ethyl-5α-cholest-22E-en-3gb-ol. This sterol has a similar structure to dinosterol, which occurs in dinoflagellates, except that the side-chain contains a 24-ethyl group rather than 23,24-dimethyl substitution. Other 4-methyl sterols include 4α,24-dimethyl-5α-cholest-22E-en-3β-ol, 4α,24-dimethyl-5α-cholestan-3β-ol and 4α-methyl-24-ethyl-5α-cholestan-3β-ol. The major 4-dimethyl sterol in each of the species is 24-ethylcholesta-5,22E-dien-3β-ol. Two species also contain significant amounts of the 5α(H)-stanol 24-ethyl-5α-cholest-22E-en-3β-ol. Unusual hydroxylated compounds found in each species were tentatively identified as dihydroxylated 4-methylsteranes. Species of Pavlova are common in marine and brackish water environments and so might be important sources of 4-methyl and 4-desmethyl stenols and stanols in some sediments.

ZONATION OF DEEP WATER BENTHIC ALGAE IN THE GULF OF MAINE1

ABSTRACT Algal community structure is described for a deep‐water rock pinnacle in the Gulf of Maine. Three depth zones of algal dominance were apparent consisting of 1) leathery macrophytes (to 40 m), 2) foliose red algae (to 50 m) and 3) crustose algae (fleshy crusts to 55 m and coralline crusts to 63 m). Microscopic filamentous and erect calcareous algae were also present but inconspicuous. Upright macroscopic filamentous and thin sheet‐like forms were not observed on the pinnacle. Sea anemones (Metridium senile) dominated some vertical faces and abrupt prominences in the shallowest regions of the pinnacle (to 24 m) and locally appeared to set the upper vertical limits of kelp and possibly foliose reds. Laminaria sp. formed an open park‐like canopy from 24 to 30 m whereas Agarum cribrosum, the deepest kelp, grew as isolated individuals to 40 m. Peyssonnelia sp. and Leptophytum laeve were the deepest occurring fleshy (to 55 m) and calcareous crusts (to 63 m), respectively. The occurrence of these algae at record depths for the Gulf of Maine and for cold water marine environments may be the result of an absence of large herbivores and the high productivity potential of the benthos in these relatively clear waters. By compiling data on depth distribution patterns world‐wide, it is evident that the three zone structure of algal morphologies observed in the Gulf of Maine is a global phenomenon.

Selected examples of Scholte wave propagation in deep and shallow water

The Naval Ocean Research and Development Activity recently completed a series of three experiments to measure very low‐frequency (VLF) seismo‐acoustic propagation in both shallow and deep water marine environments. A vertical hydrophone array and ocean bottom instruments were deployed in all three experiments. The ocean bottom instruments contained both hydrophone and three‐component geophone sensors. In the single shallow water experiment, measurements were also made with buried three‐component geophones. We compare the VLF propagation characteristics in deep and shallow water seen with ocean bottom and water column sensors. The importance of Scholte wave propagation in accounting for both signal and ambient noise energy at near bottom receivers is shown for selected frequencies using both measured and modeled results. Necessary environmental conditions for Scholte wave excitation are also examined.

POTENTIAL SOURCES OF AEROMONAS HYDROPHILA

ABSTRACTAeromonas species are associated with marine and fresh water environments, including natural mineral springs, chlorinated and unchlorinated domestic supplies, and polluted water sheds. Most studies attribute water supplied as the principal source for A. hydrophila. Recently, Aeromonas has been recognized as a potential cause of food‐associated gastroenteritis outbreaks. Its actual involvement in large foodborne outbreaks is presently unknown. Aeromonas can be readily isolated from a variety of food sources such as seafoods, meats, dairy products, and poultry. Another potential source is asymptomatic and immuno‐compromised individuals, particularly, food‐handling workers.