The annual gametogenic cycle of the sea anemone Metridium senile from the Gulf of Maine

A year-long study was conducted to quantify the reproductive cycle of the clonal sea anemone, Metridium senile, an important member of the benthic community in the Gulf of Maine (GOM). M.senile is an abundant sessile invertebrate that forms identifiable clonal aggregations that are maintained by pedal laceration but individuals can also reproduce sexually. Specimens were collected monthly from a shallow (< 10 m) subtidal site and the reproductive cycle of male and female anemones was described on a seasonal basis using histological preparation of the gonads and light microscopy. Gametogenesis was determined for both sexes and showed that females undergo spawning during the seasonal transition from summer to fall, while males have mature sperm within testicular cysts in the winter, spring, and summer. Environmental data recorded at the study site shows that the spawning period occurs during a period of peak water temperature (August-September), and rapid gametogenesis occurs during periods of high food availability (April). The low percentage of reproductively mature anemones and the dominance of asexual reproduction in this population are believed to be the result of the high flow regime at this site.     

Ultrastructure of the photosynthetic ciliate Mesodinium rubrum

New cellular structures, bifurcated oral tentacles, were observed in many specimens of the photosynthetic ciliate Mesodinium rubrum from the northern Baltic Sea. Cross-sections of tentacles revealed rings (cylinders) of 14 microtubules with spokes. The number of microtubules per ring decreased from 14 to 12 or 11 inside the cell but no true kinetosomes were detected. These "micro-rings" were often associated with extrusomes and the tentacle tips consisted of extrusomes. A nucleus of a symbiotic alga was present, surrounded by algal cytoplasm containing plastids and delimited from the ciliate cytoplasm by two membranes. Each plastid was bounded by four membranes and was associated with one nucleomorph, suggesting a symbiotic origin as a cryptophyte. The unique symbiotic organization and the organelles of 14 microtubules make Mesodinium rubrum an organism of unusual evolutionary interest.     

The seasonal abundance of the phototrophic ciliate Mesodinium rubrum in Southampton Water, England

The abundance of the marine phototrophic planktonic ciliateMesodinium rubrum was monitored throughout an annual cycle attwo stations in the Southampton Water estuary. Seasonal changesin the concentration of nitrate, ammonia and phosphate weremonitored both at the inner estuary station (NW Netley) andouter estuary station (Calshot). Nutrient levels in the winterwere similar at both stations, and were diminished during sequentialdiatom blooms dominated initially by Sketetonema costatum andthen by Rhizosolenia dclicatula. Nitrate was reduced to a seasonalminimum in the outer estuary following these spring diatom blooms,but in the inner estuary was sustained >500 µg I^–1until the onset of the M.rubrum bloom. During the developmentof a visible red tide of M.rubrum in June/July at NW Netley,nutrient concentrations were considerably reduced. Cell numbersof M.rubrum varied between 2 and 3 cells ml^– during winterto >400 cells ml^–1 during the bloom at NW Netley, whereasat Calshot cell abundance did not increase above 25 cells ml^–1at any time of the year. At NW Netley, dense accumulations ofthe ciliate occurred over restricted depth intervals duringthe bloom and possible factors influencing the observed verticaldistribution of cells are considered. ¹Present address: Biology Department, Faculty of Science, AddisAbaba University, PO Box 1176, Addis Ababa, Ethiopia     

Motile behaviour of the bloom-forming ciliate Mesodinium rubrum

Mesodinium rubrum (Lohman) (=Myrionecta rubra Jankowsky) swims backwards in jumps of short duration interspersed by longer periods of rest. Cells attain a velocity of up to 1.2 cm s^-1 during jumps and this is probably a speed record for ciliates. The ciliate carries long cirri that serve as mechanoreceptors and for orientating the cell at the initiation of jumps, while the ciliary rows on the posterior part of the cell are responsible for propulsion. The cirri are sensitive to shear so that they can orientate themselves against the current in a siphon flow (such as generated by filter-feeding copepods). Mesodinium cells do not reorientate their body axis during sinking, but they reorientate their direction during the initiation of jumps so that they always tend to move upwards. Because the cells sink between jumps they can regulate their vertical position by modulation of the frequency of jumps. The cells' tendency to drift vertically up or down is light dependent. The jumps are so rapid that these phototrophic organisms can enhance their uptake of dissolved mineral nutrients beyond the limitation of molecular diffusion.     

Discrete, subsurface layers of the autotrophic ciliate Mesodinium rubrum off Brazil

Highly constrained, subsurface layers of Mesodinium rubrum (Lohmann)were observed and sampled on the continental shelf off the northerncoast of São Paulo State, Brazil in calm, sunny weather.The layers of this autotrophic ciliate occurred as visible lenticularbillows of red water lying 1.5—2 m below the sea surface.Upper and lower limits of the discolored layers, as seen bydivers, were defined by sharp visual discontinuities. Maximumvertical thickness of the layers was     

The genus phymatolithon in the Gulf of Maine

Summary New information on anatomy, cytology and the development of reproductive structures is presented to show that Phymatolithon is a genus distinct from both Clathromorphum and the branching members of Lithothamnium. Also, a new species of Phymatolithon, Ph. rugulosum, is described. The reproductive cycles and geographic and bathymetric distributions of Ph. laevigatum and Ph. rugulosum in the Gulf of Maine are presented and discussed. There is strong indication that the geographic distribution of crustose corallines in the region is controlled primarily by maximum summer temperatures. The depth distributions are apparently controlled primarily by decrease of light with depth, though temperatures and substrate are also factors.Now at Colorado School of Mines, Golden, Colorado, U.S.A. The necessary field work for this study was made possible through the generous support of: The American Petroleum Institute, The Geological Society of America, the ONR (through the Department of Geology and Geophysics, Massachusetts Institute of Technology) and the Woods Hole Oceanographie Institution (Contr. No. 1500).     

The annual cycle of planktonic ciliates in nearshore waters at Signy Island, Antarctica

The abundance and biomass of marine planktonic ciliates in BorgeBay, Signy Island, were determined at monthly intervals betweenApril 1990 and June 1991. At least 24 different ciliate taxawere recorded from samples preserved in Lugol's iodine, includingthe tintinnids Codonellopsis balechi, Cymalocylis convallaria,Laackmaniella naviculaefera and Salpingella sp., and the aloricatetaxa Didinium sp. and Mesodinium rubrum. Ciliate abundance andbiomass exhibited a clear seasonal cycle with high values duringthe austral summer and low values in the austral winter. Abundanceranged from 0.3 10³l^–1 in September to 2.3 10³l^–1in January, while biomass ranged from 0.5 µg C l^–1in October to 12.6 µg C l^–1 in December. Small ciliatesdominated abundance throughout the year, and biomass duringwinter. Larger ciliates contributed most to biomass during summer.Aloricate ciliates were common throughout the year, while tintinnidscontributed substantially to abundance and biomass only duringsummer. Salpingella sp. was the commonest tintinnid, but C.convallariacontributed most to tintinnid biomass. The seasonal patternof ciliate abundance and biomass matched that of chlorophylla concentration and bacterial biomass, suggesting tight trophiccoupling between ciliates and other components of the pelagicmicrobial community. ¹Present address: Scott Polar Research Institute, Universityof Cambridge, Lensfield Road, Cambridge CB2 1ER, UK     

Planktonic microbes in the Gulf of Maine area

In the Gulf of Maine area (GoMA), as elsewhere in the ocean, the organisms of greatest numerical abundance are microbes. Viruses in GoMA are largely cyanophages and bacteriophages, including podoviruses which lack tails. There is also evidence of Mimivirus and Chlorovirus in the metagenome. Bacteria in GoMA comprise the dominant SAR11 phylotype cluster, and other abundant phylotypes such as SAR86-like cluster, SAR116-like cluster, Roseobacter, Rhodospirillaceae, Acidomicrobidae, Flavobacteriales, Cytophaga, and unclassified Alphaproteobacteria and Gammaproteobacteria clusters. Bacterial epibionts of the dinoflagellate Alexandrium fundyense include Rhodobacteraceae, Flavobacteriaceae, Cytophaga spp., Sulfitobacter spp., Sphingomonas spp., and unclassified Bacteroidetes. Phototrophic prokaryotes in GoMA include cyanobacteria that contain chlorophyll (mainly Synechococcus), aerobic anoxygenic phototrophs that contain bacteriochlorophyll, and bacteria that contain proteorhodopsin. Eukaryotic microalgae in GoMA include Bacillariophyceae, Dinophyceae, Prymnesiophyceae, Prasinophyceae, Trebouxiophyceae, Cryptophyceae, Dictyochophyceae, Chrysophyceae, Eustigmatophyceae, Pelagophyceae, Synurophyceae, and Xanthophyceae. There are no records of Bolidophyceae, Aurearenophyceae, Raphidophyceae, and Synchromophyceae in GoMA. In total, there are records for 665 names and 229 genera of microalgae. Heterotrophic eukaryotic protists in GoMA include Dinophyceae, Alveolata, Apicomplexa, amoeboid organisms, Labrynthulida, and heterotrophic marine stramenopiles (MAST). Ciliates include Strombidium, Lohmaniella, Tontonia, Strobilidium, Strombidinopsis and the mixotrophs Laboea strobila and Myrionecta rubrum (ex Mesodinium rubra). An inventory of selected microbial groups in each of 14 physiographic regions in GoMA is made by combining information on the depth-dependent variation of cell density and the depth-dependent variation of water volume. Across the entire GoMA, an estimate for the minimum abundance of cell-based microbes is 1.7×10(25) organisms. By one account, this number of microbes implies a richness of 10(5) to 10(6) taxa in the entire water volume of GoMA. Morphological diversity in microplankton is well-described but the true extent of taxonomic diversity, especially in the femtoplankton, picoplankton and nanoplankton--whether autotrophic, heterotrophic, or mixotrophic, is unknown.     

The genus Pseudolithophyllum (Corallinaceae) in the Gulf of Maine

Summary This is the third of a series of papers covering the anatomy, morphology, systematics and ecology of the crustose corallines of the Gulf of Maine. Pseudolithophyllum orbiculatum, the only species of this genus in the region, is treated in this paper.Part of a study undertaken while working on a Ph. D. program at the University of Michigan. The necessary field work was made possible by the generous support of: the American Petroleum Institute (Grant-in-aid No. 85), the Geological Society of America (Penrose Grant No. 912-62), the Office of Naval Research (Nonr 1841-74), through the Department of Geology and Geophysics, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution.     

The genus Clathromorphum (Corallinaceae) in the Gulf of Maine

Summary This paper is the second of a series covering the crustose corallines of the Gulf of Maine. Information on anatomy, cytology and the development of the reproductive structures is presented to show that Clathromorphum is a genus distinct from both Phymatolithon and the branching members of Lithothamnium. Also, for the two species of this genus present in the region, reproductive cycles and geographic and bathymetric distributions are presented and discussed.Part of a study undertaken while working on a Ph. D. program at the University of Michigan. The necessary field work was made possible by the generous support of: the American Petroleum Institute (Grant-in-aid No. 85), the Geological Society of America (Penrose Grant No. 912-62), the Office of Naval Research (Nonr 1841 (74), through the Department of Geology and Geophysics, Massachusetts Institute of Technology) and the Woods Hole Oceanographic Institution.     

Vagile macrofauna and the hydrographic environment of the Saco River Estuary and adjacent waters of the Gulf of Maine

We studied the vagile epibenthic and nektonic macrofauna and hydrographic environments of the Saco River estuary and adjacent waters, including Biddeford Pool lagoon and Saco Bay (Gulf of Maine), over a 3-year period (1979–82). Twice as many species of vagile macrofauna were found in Saco Bay as in the estuarine environments, and none were found at the head of the estuary below the dam. Field distributions of various species and life stages agreed with their locomotor responses in the laboratory to physicochemical gradients, supporting the view that habitat correlations are at least in part determined by active habitat preference and/oor avoidance behavior of vagile species. We also examined the stomach contents of specimens of two common fish species to determine their local feeding habits. Yearling Pollachius virens fed primarily on Ammodytes americanus, while yearling Pseudopleuronectes americanus stomachs contained primarily small, whole Echinarachnius parma.     

Notes on a Mesodinium rubrum red tide in San Francisco Bay (California, USA)

Discrete red patches of water were observed in South San FranciscoBay (USA) on 30 April 1993, and examination of live samplesshowed that this red tide was caused by surface accumulationsof the pigmented ciliate Mesodinium rubrum. Vertical profilesshowed strong salinity and temperature stratification in theupper 5 m, peak chlorophyll fluorescence in the upper meter,and differences in the small-scale density structure and fluorescencedistribution among red patches. Events preceding this Mesodiniumred tide included: (i) heavy precipitation and run-off, allowingfor strong salinity stratification; (ii) a spring diatom bloomwhere the chlorophyll a concentration reached 50 mg m^–3;(ii) depletions of dissolved inorganic N and Si in the photiczone; and (iv) several days of rapid warming and stabilizationof the upper surface layer. These conditions may be generalprerequisites for M.rubrum blooms in temperate estuaries. ¹Present address: Station Marine d'Endoume, Centre d'Oceanologiede Marseille, rue Batterie des Lions, 13007 Marseille, France     

Formation of blooms by the symbiotic ciliate Mesodinium rubrum: the significance of nitrogen uptake

Mesodinium rubrum, a holotrichous ciliate that harbors endosymbioticchloroplasts, was responsible for patches of red water in thecoastal upweUing ecosystem at 15°S, Peru during March—May1977. Stations within red patches showed elevated concentrationsof paniculate nitrogen, chlorophyll a and dissolved organicnitrogen (DON), and lower concentrations of nitrate comparedwith areas where there were no ciliate blooms. These naturallyoccurring populations of M.rubrum took up nitrate, ammoniumand DON. Light was required for nitrate uptake and to a lesserextent for ammonium uptake. Dark uptake of ammonium occurredin all experiments. There was no effect of light on DON uptake.Possession of endosymbiotic chloroplasts enables this protozoanto use upwelled nitrate efficiently for development of largeblooms and concentrate into patches in the face of relativelystrong advective regimes.     

The vertical distribution of Radiolaria in the waters surrounding Japan

Geographic and vertical distribution patterns of living Radiolaria are closely related to the characters of the water column. We studied living Radiolaria in samples collected at closely spaced depth intervals in the waters surrounding Japan in order to understand their vertical distribution and its controlling factors. Such information is needed to reconstruct past vertical water mass structure. The Japanese Islands are surrounded by the marginal Japan Sea and the North Pacific Ocean, and from approximately 46° N to 26° N. They thus extend across a large latitudinal range and are exposed to a similarly wide range of environmental conditions, inducing the warm Kuroshio, Tsushima, and Tsugaru Currents and the cold Oyashio Current.We performed plankton tows (mesh size 63 mm) from late May to early June 2002 at eight sites, sampling the upper 200 m of the water column, at seven depth intervals.We recognized five radiolarian assemblages: the Upper Surface Assemblage (0–40 m), the Lower Surface Assemblage (40–80 m), the Surface Assemblage (0–80 m), the Subsurface Assemblage (80–200 m), and the Lower Surface–Subsurface Assemblage (40–200 m) groups. Pseudodictyophimus gracilipes and Tetrapyle octacantha (juvenile) show “tropical submergence”, i.e. they live at the surface in high latitudes and at greater depth in low latitudes. Four taxa live at specific temperature and salinity: Acrosphaera spinosa, Larcopyle butschlii, Challengeron diodon, and Stichocorys seriata. Four taxa are associated with characteristic temperatures: Neosemantis distephanus, Arachnocorys umbellifura, Antarctissa sp. 1, and Saccospyris conithorax.     

Use of Herring Bait to Farm Lobsters in the Gulf of Maine

Background

Ecologists, fisheries scientists, and coastal managers have all called for an ecosystem approach to fisheries management, yet many species such as the American lobster (Homarus americanus) are still largely managed individually. One hypothesis that has yet to be tested suggests that human augmentation of lobster diets via the use of Atlantic herring (Clupea harengus) as bait may contribute to recent increases in lobster landings. Currently 70% of Atlantic herring landings in the Gulf of Maine are used as bait to catch lobsters in traps throughout coastal New England.

Methodology/Principal Findings

We examined the effects of this herring bait on the diet composition and growth rate of lobsters at heavily baited vs. seasonally closed (i.e., bait free) sites in coastal Maine. Our results suggest that human use of herring bait may be subsidizing juvenile lobster diets, thereby enhancing lobster growth and the overall economic value and yield of one of the most valuable fisheries in the U.S.

Conclusions/Significance

Our study illustrates that shifting to an ecosystem approach to fisheries management should require consideration of cross-fishery interactions.     

The Seasonal Relationship Between Meroplankton and Megabenthos on Georges Bank,Gulf of Maine,Northwest Atlantic

A broad based environmental study of Georges Bank included samples of zooplankton and dredge samples of megabenthos for four seasons. The purpose of this account is to examine the seasonal relationship between meroplankton and megabenthos. Mean densities of meroplankton were relatively high at shallow near shore stations and the central Bank and low at deeper stations. Densities were highest in the summer and lowest in the winter for major taxa. For megabenthos the number of species, relative abundance and relative biomass was also highest in the summer and lowest in the winter. Dominant megabenthos provided year round occupants and seasonal pulses. Year round occupants and seasonal peaks of some megabenthos facilitate year round foraging by demersal finfish enhancing the general production of the Bank. It was concluded that Georges Bank megabenthos was part of a broad ranging continental shelf, sand bottom fauna extending at least from Gaspe Bay to the offing of Chesapeake Bay.     

Marine Foraging Birds As Bioindicators of Mercury in the Gulf of Maine

From existing databases, we compiled and evaluated 604 total mercury (Hg) levels in the eggs and blood of 17 species of marine foraging birds from 35 Gulf of Maine islands to provide baseline data and to determine the best tissue, age class, and species for future biomonitoring. While mean Hg levels in most species did not exceed adverse effects thresholds, levels in some individual eggs did; for all species arithmetic mean egg Hg levels ranged from 0.04 to 0.62 (μg/g, wet weight). Piscivorous birds had higher Hg levels than invertivores. Leach’s storm-petrel (Oceanodroma leucorhoa), razorbill (Alca torda), and black guillemot (Cepphus grylle) adult blood and egg Hg levels were higher than other species. Our results indicate that adult blood is preferable to chick blood for detecting long-term temporal trends because adult levels are higher and not confounded by metabolic effects. However, since we found that eggs and adult blood are comparable indicators of methylmercury bioavailability, we determined that eggs are the preferred tissue for long-term Hg monitoring because the relative ease in collecting eggs ensures consistent and robust datasets. We suggest specific sampling methods, and based on our results demonstrate that common eider (Somateria mollissima), Leach’s storm-petrel, double-crested cormorant, and black guillemot are the most effective bioindicators of Hg of the Gulf of Maine.