Reproduction, recruitment and mortality in two species of Laminaria in southwest Nova Scotia

Chapman, A. R. O.

doi:10.1016/0022-0981(84)90072-8

Cited by 143 publications

(112 citation statements)

References 8 publications

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“…The survivorship data presented here are very similar to those recently reported by Chapman (1984) for L. longicruris and L. digitata, but note that although his site was geographically very close to mine, it was considerably deeper than my harvest plots at 10-12 m below MSL (Figure 1). Chapman observed an increasing mortality risk with increasing plant length for L. longicruris, which I did not, possibly because I did not consider plants < 50 cm total length whereas he did.…”

Section: Discussionsupporting

confidence: 88%

Recovery following experimental harvesting ofLaminaria longicruris andL. digitata in southwestern Nova Scotia

Smith

1985

Helgolander Meeresunters

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Laminaria population variables and understory community composition were monitored just prior to, and for two summers following, a September 1980 experimental total harvest of L. longicruris De la Pylaie and L. digitata (L.) Lamouroux within two plots in Lobster Bay, Nova Scotia. Both plots, distinguished mainly by depth, were characterized by high Laminaria standing crop and no recent history of extensive sea urchin grazing. Within the shallower plot (2-3 m below MSL), recovery could not be assessed thoroughly due to ice damage, but within the deeper plot (3--4m below MSL), L. longicruris regrew cropped biomass and attained maximum observed abundance within one year. Both Laminaria species required two years to mature to pre-harvest population characteristics. Survivorship of 0-1 year old and mature populations of both species was generally low (0--67 % per year); however, the higher maximum life expectancy of L. digitata (> 4 years vs 2 years) can result in that species persisting to the disadvantage of L. longicruris. Analysis of understory community composition for both harvested plots and their adjacent controls weakly distinguished the harvested plots one summer after harvesting from all others. It is doubtful the distinction is attributable to harvesting and in neither site was there evidence of a critical change in the understory community. Management implications for the commercial harvest of the brown alga Laminaria are discussed.

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Section: Discussionsupporting

confidence: 88%

Recovery following experimental harvesting ofLaminaria longicruris andL. digitata in southwestern Nova Scotia

Smith

1985

Helgolander Meeresunters

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“…Chapman (1984) estimated probabilities of 10 .01 x 10 -9 and 8 .9 x 10 -9 for Laminaria digitata Pyl . and L. longicruris Pyl ., respectively, in eastern Canada, and Ang (1991) showed that the probability for Fucus distichus L .…”

Section: Discussionmentioning

confidence: 94%

Fecundity, spore recruitment and size in Gelidium sesquipedale (Gelidiales, Rhodophyta)

Santos

Duarte

1996

Hydrobiologia

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Gelidium sesquipedale fecundity was quantified by counting tetrasporangial sori and cystocarps per meter squared and by estimating the number of spores contained inside them . These were obtained by regression on a size metric of reproductive structures . Tetrasporangial sori length and cystocarp thickness were the best estimators of spore number. To assess spore recruitment, 12 pottery tiles were fixed to the bottom, and the appearance of small fronds was monitored.No clear seasonal pattern of reproduction was found . Tetraspore production peaked in March 1990 with 10.4 x 10 6 spores m -2 , whereas the carpospore peak was lower, 4 .9 x 10 5 spores m -2 in July 1989 . Recruitment followed tetraspore peaks . The probability of a G. sesquipedale tetraspore making the transition to a recruit was 4 .7 x 10 -5 . Frond length was significantly related to tetrasporangial sori number, while cystocarp number was only related to frond branching order. Minimum size for reproduction was 6 .9 cm for gametophytes and 5 .4 cm for tetrasporophytes; very rarely were cystocarpic fronds smaller than 9 cm, while tetrasporic fronds were often longer than 15 cm . Cystocarpic fronds were significantly shorter and had more branches than tetrasporic fronds .

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“…We assume that the recruitment we are measuring represents the sum of survival, on all available substrata, of all stages subsequent to the 'spore rain' (Chapman 1984), Including the newly settled spores, the microscopic gametophytes and the young sporophytes. Demographic and recruitment studies indicate that mortality is highest among microscopic stages, followed by young sporophytes (e.g.…”

Section: Discussionmentioning

confidence: 99%

Holdfasts of adult kelp Ecklonia maxima provide refuges from grazing for recruitment of juvenile kelps

Anderson¹,

Carrick²,

Levitt³

et al. 1997

Mar. Ecol. Prog. Ser.

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The distribution of young sporophytes (up to 0.25 m stipe length) of the kelp Ecklonia maxima, on various substrata, at depths of 2.5 to 5.0 m, was studied at 8 sites on the southwest coast of South Africa. The most common substratum available was rock (bare or covered with encrusting coralline algae), followed by kelp holdfasts, and the ascld~an Pyura stolonlfera at some sites. A disproportionately high rat10 (relative to the available substrata) of young sporophytes grew on the holdfasts of mature kelps at most sites, but particularly where hlgh densities of benthic Invertebrate grazers were present (mainly the urchin Parechinus angulosus, also abalone Haliotis mjdae, limpets Patella spp. and gastropods Turbo spp. and Oxystele spp.). Jacobs' index of electivity was used an indicator of 'preference for' (interpreted as indicating survival on) the substratum type. This showed a statistically significant 'negative select~on' of rock as a substratum at sites where grazers were numerous The ratios of young sporophytes on holdfasts/young sporophytes on rock were directly proport~onal to grazer d e n s~t~e s when sites were compared (r = -0.90, p = 0.0021, supporting the hypothesis that mature holdfasts are an important refuge for recruitment of E. maxlma sporophytes. There was a n inverse relationship between percentage cover of understorey algae and grazer densities (r = 0.92. p = 0.001). In general, sites east of Cape Point (west coast/south coast transition zone) have far more grazers and reduced understorey algal biomasses compared to west coast sites. There thus appear to be fundamental differences In some of the major ecological processes in kelp beds In these 2 areas. w~t h important implications for commercial kelp harvesting.

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Reproduction, recruitment and mortality in two species of Laminaria in southwest Nova Scotia

Cited by 143 publications

References 8 publications

Recovery following experimental harvesting ofLaminaria longicruris andL. digitata in southwestern Nova Scotia

Recovery following experimental harvesting ofLaminaria longicruris andL. digitata in southwestern Nova Scotia

Fecundity, spore recruitment and size in Gelidium sesquipedale (Gelidiales, Rhodophyta)

Holdfasts of adult kelp Ecklonia maxima provide refuges from grazing for recruitment of juvenile kelps

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