Mahone Bay Research Articles

Numerical Study of Topographic Effects on Wind-Driven Coastal Upwelling on the Scotian Shelf

Wind-driven coastal upwelling can cause a sudden drop in sea surface temperatures (SSTs) of up to more than 8 °C on the inner Scotian Shelf (ScS) in the summer months. Three major coastal upwelling events on the ScS in the summer of 2012 are analyzed using in-situ SST observations and satellite remote sensing SST data. A spatial correlation analysis of satellite SST data shows an asymmetric distribution in the along-shore direction with smaller correlation coefficients in the downstream area than in the upstream area over the inner ScS during upwelling events. A regression analysis indicates that the wind impulse plays a major role in generating the SST cooling during the initial response stage of upwelling events. A nested-grid ocean circulation model (DalCoast-CSS) is used to examine the effect of irregular coastline and rugged bathymetry on the spatial and temporal variability of wind-driven upwelling over the inner ScS. The model has four submodels downscaling from the eastern Canadian Shelf to the central ScS. The model external forcing includes tides, winds, river discharges, and net heat flux at the sea surface. A comparison of model results with the satellite SST data reveals a satisfactory performance of the model in reproducing the development of coastal upwelling on the ScS. Model results demonstrate that the irregular coastline and rugged bathymetry play important roles in influencing the temporal and spatial evolution of the upwelling plume over the inner ScS. The irregular coastline (e.g., cape) is responsible for the relatively warm SSTs in two downstream inlets (i.e., St. Margarets Bay and Mahone Bay) and adjacent coastal waters. The rugged bathymetry (e.g., submerged bank) influences the spatial extent of filaments through the advection process.

The Influence of Temperature - Food Availability on the Shell Growth of Sea Scallop Placopecten magellanicus (Gmelin, 1791)

A study of the growth of the sea scallop, Placopecten magellanicus, under suspended culture conditions was carried out over a seven month period at a culture site in Graves Shoal, Mahone Bay,Nova Scotia – Canada. Scallop spat were cultivated in pearl nets at a density of 30-35 per net set at four locations corresponding to the surface (7 m) and bottom (14 m) at the outer edge and the center of the site. Shell height was measured at monthly intervals. Environmental conditions represented as temperature and food availability at the surface and bottom over the same period were also monitored. Shell Height growth rate was slightly greater at the surface than at the bottom. At the surface sites growth was greater at the outside (SUROUT) than at the center locations, but at the bottom growth was greater at the centre location (BOTIN). The only significant relationship between shell growth and temperature - food variables was chlorophyll a concentration. Key words: temperature, food availability, shell height, sea scallop

Proteomic Analysis of Eggs from Mytilus edulis Females Differing in Mitochondrial DNA Transmission Mode

Many bivalves have an unusual mechanism of mitochondrial DNA (mtDNA) inheritance called doubly uniparental inheritance (DUI) in which distinctly different genomes are inherited through the female (F genome) and male (M genome) lineages. In fertilized eggs that will develop into male embryos, the sperm mitochondria remain in an aggregation, which is believed to be delivered to the primordial germ cells and passed to the next generation through the sperm. In fertilized eggs that will develop into female embryos, the sperm mitochondria are dispersed throughout the developing embryo and make little if any contribution to the next generation. The frequency of embryos with the aggregated or dispersed mitochondrial type varies among females. Previous models of DUI have predicted that maternal nuclear factors cause molecular differences among unfertilized eggs from females producing embryos with predominantly dispersed or aggregated mitochondria. We test this hypothesis using females of each of the two types from a natural population. We have found small, yet detectable, differences of the predicted type at the proteome level. We also provide evidence that eggs of females giving the dispersed pattern have consistently lower expression for different proteasome subunits than eggs of females giving the aggregated pattern. These results, combined with those of an earlier study in which we used hatchery lines of Mytilus, and with a transcriptomic study in a clam that has the DUI system of mtDNA transmission, reinforce the hypothesis that the ubiquitin-proteasome system plays a key role in the mechanism of DUI and sex determination in bivalves. We also report that eggs of females giving the dispersed pattern have higher expression for arginine kinase and enolase, enzymes involved in energy production, whereas ferritin, which is involved in iron homeostasis, has lower expression. We discuss these results in the context of genetic models for DUI and suggest experimental methods for further understanding the role of these proteins in DUI.

First record of the invasive red alga Heterosiphonia japonica (Ceramiales, Rhodophyta) in Canada

Four specimens of the invasive red alga Heterosiphonia japonica were collected from Mahone Bay, Nova Scotia, Canada, in August 2012. The identity of these specimens was confirmed using molecular and anatomical evidence. To the best of our knowledge, this is the first report of H. japonica in Canada – an invasive red alga that has been advancing along the northeastern coast of North America since its recent

The Brown Morph of the Northern Ringneck Snake, <em>Diadophis punctatus edwardsii</em>, on Big Tancook Island, Mahone Bay, Nova Scotia

I describe a brown morph of the Northern Ringneck Snakes (Diadophis punctatus edwardsii) that occurs in a population on Big Tancook Island, Mahone Bay, Lunenburg County, Nova Scotia, Canada.

Efficiency of bait usage in the Nova Scotia lobster fishery: a first look

In studies of commercial fishing, little attention has been paid to the use of bait. We examined lobster fishery bait-to-catch ratios in St. Margaret's Bay and Mahone Bay, Nova Scotia. Data were obtained from the Fishermen and Scientists Research Society's Lobster Recruitment Project. Local ecological knowledge of the resource users from within the study area was also gathered using semi-structured interviews. The estimated amount of bait required to catch each lobster, weighing about 480 g, ranged from 185 g (November) to 1455 g (April) for average months during the 2002/3, 2003/4 and 2004/5 fishing seasons. We estimated the overall ratio of bait-to-catch to be about 1.9 units of bait per unit of catch. The eco-efficiency and food-supply implications of consuming more bait than product in a fishery are outlined.

Baroclinic dynamics of wind-driven circulation in a stratified bay: A numerical study using models of varying complexity

The baroclinic response of a stratified coastal embayment (Lunenburg Bay of Nova Scotia) to the observed wind forcing is examined using two numerical models. A linear baroclinic model based on the normal mode approach shows skill at reproducing the observed isotherm movements and sub-surface currents during a time of strong stratification in the bay. The linear model also shows that the isotherm movement in Lunenburg Bay is influenced by the wind forcing and propagation of baroclinic Kelvin waves from neighbouring Mahone Bay. The effects of nonlinearity and topography are investigated using a three-dimensional nonlinear coastal circulation model. The nonlinear model results demonstrate that the nonlinear advection terms generate a gyre circulation at the entrance of Lunenburg Bay, and the slope bottom topography at the mouth of the bay strengthens the sub-surface time-mean inflow on the southern side of the bay. A comparison of model-calculated currents in different numerical experiments clearly shows that baroclinicity plays a dominant role in the dynamics of wind-driven circulation in Lunenburg Bay.

Mapping the distribution of an invasive marine alga (Codium fragile spp. tomentosoides) in optically shallow coastal waters using the compact airborne spectrographic imager (CASI)

We collected 19 bands of ocean colour data (spanning 391–904 nm) at 1 m2 spatial resolution from Mahone Bay on the south coast of Nova Scotia during July 2001 with an airborne hyperspectral sensor (CASI). The data were classified using 16 different protocols in an effort to accurately map benthic communities over 7 km2 of seabed to 6 m water depth. The primary objective was to depict the spatial pattern of invasion of the rocky subtidal zone by an introduced macroalga: Codium fragile. The best classification results were obtained using the first three axes of a principal component analysis of all 19 spectral channels and the maximum likelihood classification of four classes of benthic community (i.e., those dominated by Codium meadow, kelp bed, Codium–kelp mix, and sand) at three depth strata using an added bathymetry channel and no correction for water-column attenuation. The overall accuracy obtained for the entire visible seabed of the bay was 83.30% (Kappa statistic = 0.82). User's and producer's accuracies of the four classes ranged from 35.00% to 97.00% and 65.00% to 100.00%, respectively, depending primarily on depth. The addition of a bathymetry channel typically increased the overall accuracy by 20.00%, and a correction for water-column attenuation had little effect at these depths. Patches of the invasive alga, kelp, and sand were clearly distinguishable at spatial scales of 1–1000 m2, but there was also patchiness at subpixel scales (i.e., <1 m2), such that Codium was frequently confused with mixed communities. We interpret this multiscale patchiness as indicative of ongoing invasion dynamics and conclude that airborne hyperspectral technology is suitable for portraying the time-dependent outcomes of these dynamics at ecologically meaningful spatial scales.

Morphological and molecular evidence for multiple invasions of Codium fragile in Atlantic Canada

Since the first collection in 1989 from Mahone Bay (Nova Scotia), the highly invasive green macroalga Codium fragile has been spreading in Atlantic Canada and has become established along the coasts of Nova Scotia, Prince Edward Island and New Brunswick. Considerable morphological variation had been found among thalli from different collection sites. This variation may be caused by the presence of different subspecies, or by phenotypic plasticity of one of the subspecies. Morphometric and molecular investigations were performed on Codium collected from seven sites in Maritime Canada and one from Maine to evaluate these hypotheses. Based on both mucron length and ISSR markers, thalli separated into three groups, suggesting multiple introductions of C. fragile into Canada. A group from the eastern shore of Nova Scotia and the coast of New Brunswick is clearly ssp. tomentosoides that likely originates from the United States. A second group, growing in Malpeque Bay in Prince Edward Island, is possibly an asexual variant of ssp. atlanticum, another invasive subspecies of C. fragile. A third group, found in Caribou Harbour only, is an intermediate in terms of both mucron length and molecular data, suggesting a hybrid of ssp. tomentosoides and ssp. atlanticum. The origin of this intermediate group remains to be established.

Depth and timing of settlement of veligers from different populations of giant scallop, Placopecten magellanicus (Gmelin), in thermally stratified mesocosms

The present study was conducted to evaluate the relative roles that water column stratification intensity and possible inter-population behaviour differences play in determining depth of larval settlement of giant scallops, Placopecten magellanicus, in relation to thermoclines. Differences in timing of settlement of larvae from various populations were also examined. Two separate experiments were conducted in a 10.5-m-deep, 3.7-m-diameter, thermally stratified tank with larvae spawned from scallops collected from several adult beds located in areas with differing oceanographic regimes (Georges Bank, Mahone Bay, Passamaquoddy Bay). Previous mesocosm experiments had shown that veligers from these various populations differ in their vertical migration patterns. In the first experiment (December 1992–February 1993), larvae from all three populations were held in separate 9.5-m-deep tubes and exposed to a 1.5 °C temperature differential established over a depth interval of 1 m. The number of settled juveniles (spat) of each population collected at the end of the experiment increased with depth and showed no peak at or above the thermocline. This depth distribution of spat was most likely driven by preferential larval settlement. In the second experiment (February–May 1994), larvae spawned from Georges Bank and Passamaquoddy Bay stocks were held in 9.0-m-deep tubes and exposed to a 5 °C temperature differential established over a depth interval of 1 m. The number of settled spat of both populations was greater above this thermal boundary and increased with decreasing depth. This depth distribution was most likely driven by preferential settlement above the thermocline followed by upward post-settlement migration. The results from the two experiments indicate that larvae from various populations show similar trends in settlement patterns in response to similar thermal stratifications. Stratification intensity, however, does affect depth of larval settlement. In the second experiment, both populations of larvae settled throughout the time interval of collector deployment (larvae 32–82 days old). These results extend the range of planktonic developmental times generally reported in the literature and may be more indicative of natural planktonic development in the field. While Georges Bank larvae settled in consistent numbers through time, Passamaquoddy Bay larvae showed peaks in settlement at certain time periods, indicating that pulses of larval settlement may occur even from an individual spawning event.

Detrital and metamorphic 40Ar/39Ar ages from muscovite and whole-rock samples, Meguma Supergroup, southern Nova Scotia

40Ar/39Ar dates from eight muscovite separates and two whole-rock samples of slate, siltstone, and sandstone provide detrital, metamorphic, and post-metamorphic overprinting ages for the low-grade metamorphic rocks of the Meguma Supergroup in the Mahone Bay region of southern Nova Scotia. Variably reset detrital muscovite ages of 600-550 Ma agree with previously obtained U-Pb dates from detrital zircon. Separates of foliation-parallel muscovite yield precise 40Ar/39Ar ages of 395-388 Ma. Petrographic and metamorphic data indicate that these are metamorphic mica growth ages. The range overlaps with the younger limit of previously reported whole-rock ages (410-380 Ma), but is more tightly constrained. An apparent inconsistency between previous 40Ar/39Ar whole-rock ages as old as 410 Ma and regional deformation that affected sedimentary rocks as young as 385 Ma has been resolved by the younger ages reported here and by recent adjustments to the early Paleozoic time scale which suggest that the Lochkovian to Emsian Torbrook Group was deposited between 419 and 394 Ma. A muscovite plateau age of 376 Ma from one sample may be related to late-stage flexural slip deformation in the Ovens gold district.

Seasonal variation in food utilization by the suspension-feeding bivalve molluscs Mytilus edulis and Placopecten magellanicus

Seston utilization by adult Mytilus edulis and Placopecten magellanicus cohorts was measured using an in situ method over a total period of 139 d during the spring, summer and fall of 1995 in Bedford Basin and Mahone Bay, Nova Scotia, Canada. Daily seston utilization measurements were combined with extensive water sampling to construct predictive empirical models of bivalve ingestion based on environmental variables. Particle concentrations were highest in May in Bedford Basin (∼5 mg l -1 ) and remained below 2 mg l -1 in Mahone Bay. Seston quality during the study varied between 30 (summer) and 90% (spring) organic content. Large seasonal changes in the rates and efficiencies of feeding and absorption were observed, but only 28 % of the variance in daily ingestion rates of both species could be explained by a wide range of potential environmental influences (temperature, seston abundance and composition and vertical particle flux). Ingestion and absorption rates of scallops and mussels were highest during the spring, when diet quantity and quality were high, and during late autumn, when quantity and quality were low. These data indicate that changes in seston utilization and related growth were not caused solely by seasonal food and temperature fluctuations, but imply physiological regulation of feeding and digestion. Both species displayed a large capacity for controlling clearance and absorption rates. Clearance rates during October and November were at least twice as high as observed at other times of the year, and absorption efficiency gradually decreased at high diet quality and increased when quality was low. Temporal variations in food utilization by both species may be explained by the combined constraints on maximizing net energy gain of relatively low food availability and the seasonally changing energy demands of reproduction. The accuracy of various bivalve clearance (filtration) rate models was assessed by comparing predicted responses with average in situ clearance rate estimates. Only those models based on natural seston rations provided adequate predictions of observed clearance behaviour. Clearance rate predictions based on algal cell rations greatly overestimated in situ clearance at all times of the year and appear to be of limited application for predicting feeding activity in nature. Current theories on the ecological role of bivalve communities in coastal regions are questionable as they commonly depend on the assumption that clearance capacity is fully exploited.

The Goldenville–Halifax transition, Mahone Bay, Nova Scotia: relative sea-level rise in the Meguma source terrane

In the Meguma Group of Nova Scotia, the transition from sand-rich turbidites of the Goldenville Formation to overlying mud-rich turbidites of the Halifax Formation shows unusually rapid vertical facies variations. The Tancook member of the Goldenville Formation is divided into four laterally continuous units. Unit 1 consists of generally thinly bedded classical turbidites interpreted as lobe facies. Unit 2 comprises mottled (bioturbated) and laminated muds. Units 3 and 4 contain packets of thick amalgamated sandstone beds, alternating with more thinly bedded muddy sections. A unique bioclastic bed occurs near the top of unit 3. In unit 4, burrowed sandstone packets traced along strike (across paleocurrent) are not significantly incised into underlying muds. Laminated slates and siltstones of the overlying Mosher's Island member (Halifax Formation) are enriched in manganese and trace metals and contain diagenetic concretions of manganoan carbonate rimmed by metamorphic garnet. The overlying Cunard member comprises dark grey to black, strongly cleaved, carbon-rich slates, interbedded with thin, pyrite-rich, graded siltstones.Changes in the transition zone can be explained by a relative sea-level rise in the Gondwanaland source area of the Meguma Group. During deposition of the Tancook member, turbidite sand supply was progressively and intermittently interrupted as sand became trapped on the shelf. In unit 1, deposition occurred in a submarine-fan system; in higher units, deposition of sandstone packets was probably controlled by transgressions and regressions in the source area. Expanded shelves, briefly colonized by a shelly fauna, led to high organic productivity and eventual anoxia. During deposition of the Mosher's Island member, manganese was concentrated in reducing waters, delivered to the sea floor close to the oxic–anoxic boundary, and trapped as carbonate during early diagenesis. Expansion of fully anoxic conditions led to deposition of black, sulphide-rich shales of the Cunard member.

The Tancook Whalers: Origins, Rediscovery, and Revival by Robert C. Post

TECHNOLOGY AND CULTURE Book Reviews 307 professionally executed by Jean-Pierre Proulx but far too short and circumscribed chronologically and geographically to be more than an introductory guide. Proulx provides chapters on prehistoric, Basque, English, Dutch, and American whaling. Matters of technology are unevenly handled chapter to chapter, as are the causes of the various fisheries’ rises and declines. Statistics are sometimes presented out of context and in unconverted sums of the period. Predictably, Proulx’s coverage of Basque whaling is best, suggesting that his forthcoming book on that subject will be noteworthy. Kenneth R. Martin Dr. Martin is a consulting historian living in Woolwich, Maine. A specialist in maritime and business history, he is the author of several works on American whaling. His latest book, written with Nathan Lipfert, is Lobstering and the Maine Coast (1985). He is currently at work with Ralph L. Snow on a history of Bath, Maine. The Tancook Whalers: Origins, Rediscovery, and Revival. By Robert C. Post. Bath: Maine Maritime Museum, 1985. Pp. xi+113; illustra­ tions, bibliography, index. $15.00 (paper). What a treat Bob Post’s boat book is! It has the charm and modesty of a study that grew simply out of pleasure yet is full of appealing information for people who may never before have felt much curiosity about maritime history. The writing is graceful, Sam Manning’s draw­ ings are wonderful, and the reader is also rewarded with informative photographs and ample technical details. But best of all, Post has incorporated these attractive qualities into a model analysis of the relations between craftsmanship and culture. The Tancook whaler was one species of several different but related types of 19th-century fishing vessels employed along the North Amer­ ican coast from Block Island, Rhode Island, to Mahone Bay in Nova Scotia. Along with all the other double-enders generically called whal­ ers, these were practical boats, built for rough work in hard conditions. However, in an evolution that reminds one of John Kouwenhoven’s idea of vernacular art, the Tancook whaler emerged in its finished form as a distinctively elegant craft—seaworthy and efficient but also sleek and fast. Those qualities made it celebrated in its own time, then a design source for pleasure yachts, and finally the inspiration for a Maine Maritime Museum 34-foot replica that would teach oldfashioned boat-building skills as well as a sense of the ways boats like this emerged from the small island communities that originally made and used them. The Tancook Islands (Big and Little) lie at the mouth of Mahone Bay, their eastern sides exposed to Atlantic weather. Neither has any natural harbors, and on their Mahone Bay sides the water is shoal, 308 Book Reviews TECHNOLOGY AND CULTURE thus denying the islanders good anchorages as well. So the settlers of these unpromising places were from the beginning pushed to develop boats with particular characteristics. They had to be shoal-draft and capable of being pulled ashore; hulls needed to be easily driven be­ cause summer morning calms meant rowing for miles out to the fish­ ing grounds; getting back home in a northwesterly gale required an ability to beat to windward; and for fast sailing the boats had to be able to carry plenty of canvas. What Post makes clear, though, is that hands, minds, and the forces of culture were the crucial ingredients shaping these long, slender, schooner-rigged centerboarders. The is­ landers’ keenness for speed, for instance, was not simply a matter of getting fish to market quickly; it had as much to do with generations of particularly skillful builders and a local tradition of boat racing, but also a certain feistiness born of the vagaries of economic life, occasional contraband trading, and a disposition to push systems— whether of mainland rules or building boats—to the limits. There are delightful nuggets of information in every chapter. We learn about an ingenious mooring system developed in the absence of usable harbors or anchorages and discover that the invention of the mackerel jig influenced boat design. We find out that in these closely knit families everyone had well-defined tasks; men planted potatoes and cabbage while women planted the...

Late Quaternary geological history of Mahone Bay, Nova Scotia

Mahone Bay is located on the Atlantic coast of Nova Scotia. It is an exhumed Carboniferous basin, overdeepened by glacial erosion, with widespread late Wisconsinan sheet and drumlin tills. Subglacial channels that cut both till and bedrock were formed when the ice sheet stagnated after marine incursion into the Bay of Fundy. Seismic reflection profiling and piston cores show up to 75 m of proglacial lake silts ponded behind a bedrock sill at the entrance to the bay. These are overlain by a thin lagoonal sequence, and then by marine sediments accumulated over the last 6000 years, reflecting the gradual Holocene transgression.