Margaret's Bay Research Articles

Recruitment and growth of the sea urchin Strongylocentrotus droebachiensis (Muller) following mass mortalities off Nova Scotia, Canada

Recruitment of Strongylocentrotus droebachiensis (Muller) was monitored for four successive years following a mass mortality of this species on a subtidal boulder bottom in St. Margaret's Bay, Nova Scotia. Recently recruited juveniles (1–2 mm diameter) were observed in the fall (September–November) between (1982) and (1984), but not in (1985). Juveniles grew to 6–8 mm diameter at 1-yr post-settlement and 19 mm diameter ((1983) cohort) at 2-yr post-settlement. Individuals > 18 mm diameter had macroscopic gonads in the spring of their third year and spawning probably occurred at 2.75-yr post-settlement. The growth rate of juveniles (3–6 mm initial diameter) maintained in cages with coralline-covered rocks was similar to that of the natural population. Growth and gonad index increased significantly when kelp ( Laminaria longicruris (Pylaie)) was added to cages, suggesting that juveniles were food limited in St. Margaret's Bay. Despite an abundance of kelp and other fleshy algae, they remained cryptic under rocks and were not observed grazing on attached plants. The effects of temperature and food supply on juvenile growth and survival were examined in laboratory experiments using factorial designs. Recently-metamorphosed juveniles (from laboratory cultures), maintained at three temperature regimes (5°C, ambient, 16 °C) and two feeding regimes (no added food, coralline algae added), had similar growth rates (over 9 mth) among treatment combinations. However, growth was asymptotic at 16 °C and ambient temperatures, suggesting food limitation. Survival of these juveniles was higher in treatments with coralline algae, but survival was not affected by temperature. Field-collected juveniles (3–6 mm diameter), maintained at three temperature regimes (5°C, ambient, 16 °C) and three feeding regimes (no added food, coralline algae added, and kelp and coralline algae added), grew only in treatments with kelp added as food. In these treatments, growth rates increased with temperature. However, the growth curve at variable ambient temperature regimes was linear, suggesting seasonal acclimation. Survival of the field-collected juveniles was highest in treatments at 5 °C and/or with added kelp.

Spatial pattern of soft-bottom Polychaeta off Nova Scotia, Canada

Patchiness of polychaetes at the micro-scale (i.e. proportional to the sphere of influence of an organism) and macro-scale was investigated in the Northwest Atlantic in 1977 and 1981. Seven box-core samples (each 2 500 cm2) from three sites off Nova Scotia, Canada were completely subsampled as 25 contiguous 100cm2 cores and analysed for their polychaete faunas. Dispersion chi-square and autocorrelation analyses were performed on the complete data set. The inshore fauna (St. Margaret's Bay) was strongly clumped with patchiness at several scales: 50cm. Polychaetes in samples from off-shore stations were much less aggregated, and discordantly dispersed to varying degrees. The results conform with the present understanding of infaunal spatial patterns and reject the hypothesis that a depth gradient in patchiness exists in addition to the well documented density and biomass gradients.

Paragyptis margaretae, new genus and species of Hesionidae (Annelida: Polychaeta) from St. Margaret's Bay, Nova Scotia

Paragyptis margaretae n.g., n.sp. is described from St. Margaret's Bay, Nova Scotia. It is the only genus of the family Hesionidae with eight pairs of tentacular cirri, two antennae, and strongly biramous parapodia. Its relationship to other members of the family is discussed.

The Channel Navigation Information Service

Since its inception in 1972 progress of the Channel Navigation Information Service (CNIS) has twice been described in the Journal. The tenth anniversary of the first broadcast bulletin of information occurred on 31 July 1982, and it is perhaps appropriate to review and bring up to date the major milestones in the history of the Service and to review the safety of navigation in the Dover Strait.It will be recalled that, following the multiple collision off the Varne in 1971 and bearing in mind previous major disasters – Torrey Canyon, Pacific Glory, etc. – the Department of Trade concluded that a voluntary Traffic Separation Scheme (TSS), without surveillance and without a coordinating information service, was inadequate for the dense and complex maritime traffic problems of the Dover Strait. Thus was born the Dover Strait Information Service, now CNIS, under the aegis of HM Coastguard, and located on the upper floor of an old Port War Signal Station at Leathercote Point, St Margaret's Bay. The Decca Marine Radar Company installed a simple harbour radar and its associated display towards the end of 1971 and Coastguard evolved the essential elements of what remains to this day a half-hourly bulletin, broadcast on vhf/rt Channel 10. In low visibility intermediate broadcasts are given, based on actual visibilities reported from sea.In August 1973 the French authorities installed a similar system at Cap Gris Nez and a very close co-ordination, vital from the mariner's point of view, developed.

Genetic Differentiation in the Face of Gene Flow: A Study of Mussel Populations from a Single Nova Scotian Embayment

There are significant genetic differences among populations of the blue mussel, Mytilus edulis, from six localities in St. Margaret's Bay, N.S., Canada, despite the presence of gene flow. The populations are differentiated into two groups, those at the head of the bay where ambient conditions fluctuate widely during the year, and those at the mouth of the bay where conditions (particularly salinity) fluctuate to a lesser degree. Three isoenzyme loci, i.e. leucine aminopeptidase 1, peptidase 2, and phosphoglucose mutase, show a clear shift in the predominant frequencies, from slow migrating alleles at the mouth of the bay to faster migrating alleles at the head of the bay. This shift is a microgeographic parallel of the pattern we observed in 1980 on a macrogeographic scale. A genetic comparison of these populations with those studied previously shows that allele "populations" cluster according to their environment and not according to geographical proximity. We conclude that differences in allele frequencies among localities index heterogeneity among environmental conditions, and that the sensitivity to environmental selective forces varies from locus to locus.

Ecotypic differentiation of Laminaria longicruris in relation to seawater nitrate concentration

Genetic differentiation of Laminaria longicruris populations has been demonstrated in nitrate-poor (St. Margaret's Bay) and nitrate-rich (Bay of Fundy) regions of Nova Scotia, Canada. At 9°C half-saturation constants for growth (Ks) were smaller (1.1 μM NO 3 - ) for St. Margaret's Bay plants than for plants from the Bay of Fundy (2.3 μM NO 3 - ). Maximum specific growth rate (μmax) and maximum uptake rate (Vmax) were higher for St. Margaret's Bay than for Fundy plants. However half-saturation constants for nitrate uptake (Km) were similar for plants from the two populations. The capacity to accumulate nitrate in an internal tissue pool was larger in St. Margaret's Bay plants than in Fundy plants. The differences among the populations are thought to be adaptive responses to the local nitrate environments.

Deposition of atmospheric acid from local and distant sources at a rural site in Nova Scotia

An analysis of local surface wind direction during the sampling of individual precipitation events at St. Margaret's Bay, a rural site in Nova Scotia, suggests that, during a one-year sampling period, approximately 50% of the wet deposition of hydrogen and sulphate ion was due to SO 2 emissions in Halifax, a city of 260,000 located 25 km to the east. Similar analyses at other sampling sites in Nova Scotia support this finding. However, the effect of Halifax appeared to be small at distances greater than 100km. The data also support a removal coefficient in rain of 2 × 10 −4 s −1 for sulphur emissions from Halifax. The estimated deposition of 2.9gSO 4 −2y −1 and 33 meqH + m −2y −1 coming in 1979 from directions other than Halifax are consistent with regional background values attributed to distant source regions. Back trajectory analyses on 850 mb charts indicated that about 65% of the deposition from distant source regions came from the eastern United States south of the Great Lakes, 31% from the Lower Great Lakes-St. Lawrence Valley region, and 4% from the regions of Canada outside the preceding area. The dry deposition of aerosol sulphate was only 0,035gSm −2y −1, or only 1% of the total estimated deposition; wet deposition was estimated to be the dominant mechanism. The relative contributions of each source region to wet and dry deposition appeared to depend upon a complicated interplay of source strength, distance to the receptor and meteorological factors such as frequency of transport flow and precipitation amount. It is very likely that strategies for the reduction of acid precipitation in Atlantic Canada must include not only a reduction of emissions in distant source regions, but, equally importantly, a reduction within the region itself.

Relationship Between Destructive Grazing by the Sea Urchin, Strongylocentrotus droebachiensis, and the Abundance of American Lobster, Homarus americanus, on the Atlantic Coast of Nova Scotia

Relationships between percentage cover of macroalgae, population structure of sea urchins (Strongylocentrotus droebachiensis), and the history of the lobster fishery were examined at nine sites distributed along the Atlantic coast of Nova Scotia from Guysborough County in the northeast to Pubnico in the southwest. At Pubnico there was dense algal cover and a small number of urchins living in crevices, and at Cape Sable there was an area of transition, but at all other sites there were urchin-dominated barren grounds. When the population structure of the urchins was compared with that previously observed in St. Margaret's Bay before, during, and after destruction of beds of kelp (Laminaria spp. and Agarum) by overgrazing, it was concluded that kelp bed destruction occurred on the coast north of Halifax prior to 1970, and on the coast south of Halifax after 1970. From the records of American lobster (Homarus americanus) catches it was concluded that a critical decline in catches at each site occurred a few years after kelp bed destruction. Information from various sources is synthesized into a coherent theory of the relationship between lobsters, other predators, sea urchins, and kelp.Key words: lobsters, Homarus americanus; sea urchins, Strongylocentrotus droebachiensis; destructive grazing, kelp, Laminaria, Agarum

Methods for estimating secondary production in marine Amphipoda

For the 1971 year-class of Pontoporeia femorata from St. Margaret's Bay, N.S., secondary production was 11.06–13.61 g wet weight/m2 and annual turnover ratio was 3.64–4.78 as measured by three methods. These included cohort summation of losses, integrated production from the Allen curve, and size frequency, or modified Hynes methods. Sampling bias against early life history stages of amphipods collected with sieve meshes [Formula: see text] can be corrected by back calculation from population data thus enabling cohort-based estimates of secondary production to be made.Key words: secondary production, annual turnover ratio, Pontoporeia femorata, Crustacea, Amphipoda

Stability of sea urchin dominated barren grounds following destructive grazing of kelp in St. Margaret's Bay, Eastern Canada

Kelp regeneration was observed for the first time in St. Margaret's Bay, Nova Scotia, Canada in an area known to have been devoid of macroalgae for several years. The regeneration was destroyed by sea urchins within 10 months. Experimentally induced kelp regeneration met a similar fate under normal grazing pressure. At the lowest sea urchin biomass and density encountered re-establishment of mature kelp stands seems highly unlikely. The sea urchin population required to suppress kelp regeneration is fed by benthic microalgae. Diatoms and other pioneer algal community species were found in the guts of sea urchins. The mean standing crop of benthic microalgae was found to be, 2.2 g C m-2 and production estimated as ca 15 g C m-2yr-1 at 8m depth. Most of the primary production of St. Margaret's Bay has been lost with the disappearing kelp populations.

Stability of sea urchin dominated barren grounds following destructive grazing of kelp in St. Margaret's Bay, eastern Canada : Chapman, A.R.O., 1981. Mar. Biol., 62(4):307–311

Stability of sea urchin dominated barren grounds following destructive grazing of kelp in St. Margaret's Bay, eastern Canada : Chapman, A.R.O., 1981. Mar. Biol., 62(4):307–311

Distribution of Fatty Acids in Lipids of the Common Atlantic Sea Urchin Strongylocentrotus droebachiensis

Lipid classes and fatty acid details of sea urchins Strongylocentrotus droebachiensis harvested in subtidal water near Halifax, and in deep water in St. Margaret's Bay, were compared. All samples contained an eicosenoic acid with 5,6-ethylenic unsaturation and two non-methylene-interrupted eicosadienoic acids (NMID) with the one 5,6 bond and a second in either the 11,12 or 13,14 positions. Structures were identified by combinations of ozonolysis, partial hydrazine reduction and argentation-TLC and by mass spectra of pyrrolidine derivatives. No 3,11-eicosadienoic acid was observed and elongation of C20 materials with few ethylenic bonds to C22 homologues was confined to 11–20:1 and to the minor 5,13–20:2 NMID and did not include either the relatively important 5–20:1. monoene or the 5,11–20:2 NMID. Individual animals showed considerable variation in total lipid and lipid classes, but the consistent distribution of the fatty acids with 5,6 unsaturation, irrespective of the nutritional status of the animal, suggests a basic role in membrane function.Key words: Strongylocentrotus droebachiensis, sea urchin lipids, sea urchin fatty acids, non-methylene-interrupted fatty acids, eicosadienoic fatty acids

Mode of Life and Feeding in Maldanid Polychaetes from St. Margaret's Bay, Nova Scotia

The habits and behavior of Axiothelia catenata, Praxillella gracilis, and Nicomache lumbricalis (Polychaeta: Maldanidae) are described. Each feeds from a different level in the sediment thereby reducing competition for food and space. All three maldanids are generally unselective in the material they ingest and from which they construct tubes. Thus within certain limits the particle size of the sediment is thought not to be a critical factor in determining their distribution and abundance. Axiothella catenata does not produce fecal pellets but particles are still aggregated in the gut and a large proportion of bacteria attached to sediment particles though the gut undigested. Axiothella catenata egests material in proportion to its size; a specimen of 4-mm internal tube diameter egests 1.10 ± 0.15 mL/d. Key words: benthos, detritus feeders, Annelida, Polychaeta, Maldanidae

Studies on the Sediment of St. Margaret's Bay, Nova Scotia

A detailed examination of the sediment in a small area of St. Margaret's Bay revealed it to be composed of two main types of particles, mineral particles and particles of organic debris. Debris was also adsorbed onto the mineral particles. Particles generally had relatively low numbers of bacteria associated with them indicating that most of the organic carbon in the sediment is refractory. Variation in size distribution of the component particles with depth in the sediment was found to be minimal, but a slight decrease in the proportion of debris particles was seen. Variation in size distribution along a transect was also limited, but where the mineral particles became coarser the size range of the debris particles remained constant. The relative amount of debris particles along the transect varied little but values for total organic carbon (by weight) changed dramatically. Key words: sediment, particle composition, size distribution, organic carbon

Environmental controls of methane production in Holocene basins in eastern Canada

Rapid rates of sedimentation from 54 to 134 cm/1000 yr are typical of the Holocene basins in St. Margaret's Bay and the Grand Manan Basin, Nova Scotia. The water column is well oxygenated but, because of the rapid rate of sedimentation, anoxic conditions developed and enhanced the preservation of organic matter and its fermentative degradation; also the concentrations of sulfide increased and soluble sulfates were rapidly depleted. A direct result of this has been the production of methane in amounts exceeding 22,000 ppm. In contrast, nearby cores with rates of sedimentation of less than 20 cm/1000 yr have only 30–40 ppm methane. High rates of sedimentation and the ensuing anaerobic conditions appear to be the principal factors for the genesis and preservation of methane. The δ 13C values and the n-alkane distribution show that there is more terrestrial organic matter in the Grand Manan Basin than in St. Margaret's Bay. This could account for the high concentrations of methane in the Grand Manan cores despite the low concentrations of organic carbon.

Destruction of kelp-beds by sea-urchins: A cyclical phenomenon or irreversible degradation?

A stable kelp bed ecosystem in St. Margaret's Bay, Nova Scotia (Canada), had as its main producersLaminaria longicruris andL. digita. Most algal production was exported as detritus, but there was a moderate population of herbivores, mainly the sea urchinsStrongylocentrotus droebachiensis. These were eaten by crabs,Cancer irroratus and by lobsters,Homarus americanus. Lobsters also preyed on crabs. Beginning in 1968, sea urchins became locally abundant and overgrazed the kelp beds, converting large areas to urchindominated barren grounds. Almost all kelp beds in St. Margaret's Bay (140 km2) have now been destroyed. During the same period, lobster biomass decreased, and the hypothesis was put forward that reduction in lobster predation led to increased urchin abundance and kelp bed destruction. Evidence is presented for the hypothesis that urchin-dominated barren grounds are a new, stable configuration of the ecosystem, and that a long-term decrease in primary and secondary productivity of these coastal waters can be expected.

Nitrogen Fixation (Acetylene Reduction) Associated with Sea Urchins (Strongylocentrotus droebachiensis) Feeding on Seaweeds and Eelgrass

Sea urchins feeding in different macrophyte zones in St. Margaret's Bay, Nova Scotia, in November and December 1975 were examined for nitrogenase activity using the acetylene reduction technique. For sea urchins feeding on Laminaria digitata and L. longicruris, the average rate of acetylene reduction was equivalent to N2 fixation of 55 μg N2 per sea urchin per day assuming a 3:1 molar ratio of C2H2 reduction to N2 fixation. Lower nitrogenase activities were observed for sea urchins feeding on Agarum cribrosum and Zostera marina, and no nitrogenase activity was observed for sea urchins taken from bare rock substrate on which kelp had been absent for 4 yr. Samples of separated digestive tracts but not the degutted bodies of sea urchins exhibited nitrogenase activity, suggesting that the digestive tract is the site of nitrogen fixation in whole sea urchins.

DDT residues in benthic invertebrates and demersal fish in St. Margaret's Bay, Nova Scotia

DDT residues in benthic invertebrates and demersal fish in St. Margaret's Bay, Nova Scotia

Kelp, methane, and an impenetrable reflector in a temperate bay

St. Margaret's Bay is one of the bays of the Atlantic coast of Nova Scotia, which owes its present form to flooding as sea level rose following deglaciation. It has a central, rather flat, deep basin, separated from the shelf by a sill. Two metres or so below the central basin floor lies a prominent acoustic reflector, not due to lithological changes within the sediment. We suggest that this is caused by gas, in part at least methane. Methane content increases with depth in sediment cores, and could be present in gaseous form (not just dissolved). There is a concomitant decrease in organic carbon with depth, and it appears that a part of this carbon is responsible for the generation of methane under reducing conditions below 2 m or so. The source of the organic carbon could be kelp, produced in abundance in the Bay, which has a very high primary productivity.

Changes in sea urchin populations after the destruction of kelp beds

In St. Margaret's Bay, Nova Scotia, Canada, there are large areas in which sea urchins (Strongylocentrotus droebachiensis) have eliminated beds of kelp (Laminaria spp.). Sites were identified where destruction of kelp beds had taken place 1, 2, 3, 3.5 and 4 years ago. With increase of time since kelp disappearance, the sea urchins showed decreased growth rate, reduced gonad size, but an increase in numbers resulting from high recruitment rates in the first two years after kelp bed destruction. These sea urchin populations, by their browsing, effectively prevent the regeneration of kelp. There is, as yet, no evidence of the sea urchin populations being starved out to allow the kelp to return.