scholarly journals High recruitment of the introduced bryozoan Membranipora membranacea is associated with kelp bed defoliation in Nova Scotia, Canada

2008 ◽  
Vol 369 ◽  
pp. 139-151 ◽  
Author(s):  
M Saunders ◽  
A Metaxas
Keyword(s):  
Nova Scotia ◽  
Membranipora Membranacea ◽  
Kelp Bed ◽  
High Recruitment

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

1981 ◽  
Vol 38 (11) ◽  
pp. 1339-1349 ◽  
Author(s):  
W. G. Wharton ◽  
K. H. Mann
Keyword(s):  
Population Structure ◽  
Nova Scotia ◽  
Sea Urchins ◽  
Atlantic Coast ◽  
Homarus Americanus ◽  
Strongylocentrotus Droebachiensis ◽  
American Lobster ◽  
History Of ◽  
Kelp Bed ◽  
The Relationship

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

Some Estimates of Population Density and Feeding Habits of the Rock Crab, Cancer irroratus, in a Kelp Bed in Nova Scotia

1982 ◽  
Vol 39 (4) ◽  
pp. 636-639 ◽  
Author(s):  
N. C. Drummond-Davis ◽  
K. H. Mann ◽  
R. A. Pottle
Keyword(s):  
Nova Scotia ◽  
Population Density ◽  
Sea Urchins ◽  
Feeding Habits ◽  
Atlantic Coast ◽  
Carapace Width ◽  
Hermit Crabs ◽  
Cancer Irroratus ◽  
Kelp Bed ◽  
Rock Crab

The population density of rock crabs (Cancer irroratus) in a kelp bed on the Atlantic coast of Nova Scotia was examined by mark–recapture techniques and found to be about one crab (> 45-mm carapace width) per 2 square metres. Prey taken by the crabs included hermit crabs (Pagurus), mussels (Mytilus), sea urchins (Strongylocentrotus), and various small crustaceans and polychaetes. It was concluded that the crab population would exert a strong predation pressure on these invertebrates.Key words: Cancer irroratus, rock crabs, predation, population density, kelp

Destructive grazing, epiphytism, and disease: the dynamics of sea urchin - kelp interactions in Nova Scotia

1999 ◽  
Vol 56 (12) ◽  
pp. 2300-2314 ◽  
Author(s):  
Robert E Scheibling ◽  
Allan W Hennigar ◽  
Toby Balch
Keyword(s):  
Nova Scotia ◽  
Sea Urchin ◽  
Canopy Cover ◽  
Strongylocentrotus Droebachiensis ◽  
Exposed Site ◽  
Membranipora Membranacea ◽  
Kelp Beds ◽  
Sheltered Site ◽  
Kelp Canopy ◽  
Over Time

We measured the rate of advance of urchin (Strongylocentrotus droebachiensis) feeding aggregations (fronts) as they destructively grazed kelp beds (Laminaria longicruris) at both a wave-exposed site and a sheltered site in Nova Scotia over 3.5 years. The grazing fronts were composed of high densities of large adults (up to 98 and 70 per 0.25 m2 at the exposed and sheltered sites, respectively). Urchins in the recently formed barrens, or in adjacent kelp beds, occurred at much lower densities and consisted mainly of juveniles. The fronts moved onshore into shallower water at each site, but their rate of advance varied markedly between sites and over time at each site, ranging from 0 to 4 m·month-1. The rate of advance of a front was related to the biomass of urchins; fronts did not advance below a threshold biomass of ~2 kg·m-2. Infestations of kelp by an epiphytic bryozoan (Membranipora membranacea) caused marked reductions in kelp canopy cover and biomass during winter, but the canopy regenerated through recruitment of juvenile sporophytes in spring. A localized outbreak of disease decimated S. droebachiensis at the exposed site in 1993, which enabled kelp to recolonize the barrens. Surviving urchins gradually reaggregated and resumed destructive grazing after ~1.5 years. A recurrence of disease in 1995 eliminated urchins at both sites and terminated the transition from kelp beds to barrens on a coastal scale. Our findings have important implications for the management of the urchin fishery, which targets grazing fronts for harvesting.

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