Growth and age class distribution of Pterygophora California (Phaeophyta)

Pterygophora californica Ruprecht, Eisenja arborea Areschoug and Laminana setchellii Silva are 3 common kelps (Laminariales, Phaeophyta) found in the shallow subtidal of open coastal British Columbia, Canada. Earlier laboratory studies showed that P. californica stipes had a cr~tical flaw length (CFL, the length of a flaw which, if exceeded, results in structural failure) of 0.2 mm. In this paper w e report on studies to determine whether this CFL is valid in situ, whether all 3 species of kelp respond similarly to stipe damage and whether tissue that regrows in the site of a wound increases the mechanical strength of the stipe. We tested the effect of razor cuts less than the CFL and also razor cuts and cuts imposed by a triangular file that exceeded the CFL. Results were not as predicted. Neither razor cuts nor file cuts greater than the CFL significantly decreased the survivorship for P californica over control thalli. L. setchellii had a significantly lower survivorship when cut by a triangular file but not when cut by a razor Tissue regrowth does not significantly increase mean strength of the stipe. We hypothesize that the low survivorship of L. setchellii a s a result of stipe damage is one factor responsible for preventing successful establishment of adults of this species in sites where sea urchins a r e common. In contrast, the comparatively h~g h e r survivorship of P. calilornica adult plants subjected to similar damage may b e one factor enabling this species to survive in such sites.

Section: --------------------------supporting

confidence: 76%

Section: --------------------------mentioning

confidence: 88%

Wounding, healing and survivorship in three kelp species

DeWreede¹,

Ewanchuk²,

Shaughnessy³

1992

“…Growth rates, generally expressed as size changes, have been studied for many seaweed species (Chapman & Craigie 1977, De Wreede 1984, Kain 1987, Ang 1991, as has survivorship, usually reported as cohort depletion curves (e.g. Chapman 1984, Dayton et al 1984, Schiel 1985, Dean et al 1989.…”

Section: Introductionmentioning

confidence: 99%

Frond dynamics of the commercial seaweed Gelidium sesquipedale: effects of size and of frond history

Santos¹

1994

Ge'dium sesquipedale (Clem.) Born. et Thur. is commercially exploited along the northeast Atlantic for the production of agar. Its frond dynamics were studied by tagging individual fronds in a typlcal, dense, monospecific G. sesquipedale stand located in a commercial bed off Cape Espichel, Portugal. Storms and commercial harvesting play a key role in the regulation of the species population dynamics. Frond mortality was relatively constant throughout the year, but peaked in August-September during harvest season. High probabilities of frond breakage and low frond mortality during late fall and winter (periods coincident with severe storms) suggest that under natural disturbances, G. sesquipedale fronds break rather than detach. Frond elongation rate shows a distinct seasonal pattern: high during spring and summer and low In winter. The relat~onships among G. sesquipedalevital rates and both size and frond history (i.e. effects of frond length on mortality, growth and breakage, and effects of frond length, growth, breakage and presence of epiphytes on the next month's growth, breakage and mortality) were analysed using log-linear methods. Shorter fronds (S 10.1 cm) were less susceptible to breakage and had higher growth probability than longer fronds, while longer fronds showed higher elongation rates, particularly during the periods of faster growth (late spring and summer). During storms (late fall and winter), longer fronds had a greater chance of being detached than smaller ones. By contrast, during spring and early summer, frond mortality was greater for shorter fronds. There were no clear indications that G. sesquipedale recent biological history influenced its fate. Results indicate the potential for yield-overharvesting of the Cape Espichel G. sesquipedale bed, because the harvest season starts before peak summer production. Particularly when the previous winter and fall were stormy, as was the case during this study, could better yields be obtained by delaying the harvest season.

“…hdarlne herbivores are thought to have their greatest impact upon juvenile forms of kelp, and other algae, by creating 'herbivory bottlenecks' during which sporelings are highly susceptible to being grazed to mortality (Lubchenco 1983, DeWreede 1984, Harris et al 1984, Dean et al 1989. Three mechanisms may increase the probability that juvenile kelps survive through herbivory bottlenecks: (1) production of compounds which deter feeding (Lubchenco & Gaines 1981, Steinberg 1985, Duffy & Hay 1990), (2) spatial refuges or noncoexistence escapes in which herbivores are not encountered (Lubchenco & Gaines 1981, Menge & Lubchenco 1981, Pfister & Hay 1988, Farrell 1991, and (3) size-related escapes wherein the relative amount of tissue lost to herbivores by mature (large) kelps is unlikely to affect the survival of those individuals (Lubchenco & Gaines 1981, Harris et al 1984, Duffy & Hay 1990).…”

Section: Introductionmentioning

confidence: 99%

Mechanisms underlying the effect of the chiton Katharina tunicata on the kelp Hedophyllum sessile:size escapes and indirect effects

Markel¹,

DeWreede²

1998

ABSTRACT:We monitored the population size-structure and demography of the intertidal kelp Hedophyllum sessile (C. Agardh) Setchell in areas of manipulated chiton Katharina tunicata (Wood) density to examine size-related 'escapes' and other mechanisms which may underlie the effects of this herbivore on H. sessile. This research was done on the west coast of Vancouver Island, British Columbia, Canada. We find that K. tunicata is associated with decreased juvenile H. sessile ( < l cm holdfast diameter) survivorshlp. While young adults of H sessile (1-4 cm holdfast diameter) were found to survive significantly longer than juveniles between areas of low, control and high chiton density, adult (>4 cm h.oldfa.st diameter) survivorship did not dlffer among the dens~ty treatments. We argue that the mechanism underlying the effect of K. tun~cata on young adult H. sessjle survivorship IS an indirect interaction wherein h.o!dfast irrtegrity i< degraded, rozulting in an increased silsrpptihility to wave-induced mortality. These find~ngs provide a quantification of the mechanism of macrophyte size-escapes, may explain the geographically variable effects of K. tunicata and hold implications for studies which aim to assess the effects of wave exposure on macrophyte survivorship.