Patterns of reproductive effort in the brown alga Ascophyllum nodosum

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Observation of spatial and temporal variation in the distribution and abundance of organisms is often the starting point from which questions and hypotheses about ecological processes arise. This study was designed to investigate spatial variability in abundance of macrorecruits and adults of the brown alga Ascophy11um nodosum using hierarchical sampling programs. Five spatial scales ranging from 10-' to 106 m \vere used, where the largest scale was represented by the distance between 2 areas, Tjarno on the Swedish west coast and the Isle of Man in the Irish Sea. Temporal variation was investigated separately over 3 spat~al scales as comparisons among the years from 1992 to 1995. Significant variation in abundance of 1.5 yr old juveniles was found on 2 spatial scales, 0.1 to 1.5 m and 2 to 30 m. A large variation among replicates suggested substantial variation on a smaller scale (10.15 m). There was no significant variation in the abundance of juveniles among years as suggested by earlier studies. The abundance of the adult population varied between areas but not on smaller spatial scales. There was a significant variation in the abundance of the adult population among years. The potential egg production in female individuals was also investigated as a means of relating the abundance of juveniles to fertility estimates. The number of eggs per conceptacle and the number of conceptacles per receptacle did not vary significantly among indiv~duals and the mean number of eggs per receptacle was estimated to be 7 X 10"he potential egg production was estimated to be 2.5 X log eggs a value much higher than previously reported for fucoids. Given the mean value of 40 juveniles m-', the transition probability from egg to juvenile was estimated to be 2 X 10-'

Section: Discussionmentioning

confidence: 49%

Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

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Temporal and multiple scale spatial variation in juvenile and adult abundance of the brown alga Ascophyllum nodosum

Åberg¹,

Pavia²

1997

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“…The existence of such a trade-off has been reported for Sargassum and other fucoid algae (e.g. McCourt 1985, Ang 1992, Åberg 1996, Gillespie & Critchley 2001). Although we did not measure reproductive allocation as such (see e.g.…”

Section: Possible Trade-off Between Growth and Reproductionmentioning

confidence: 73%

Seasonal dynamics of Sargassum ilicifolium (Phaeophyta) on a shallow reef flat in the southern Red Sea (Eritrea)

Ateweberhan¹,

Bruggemann²,

Breeman³

2005

The seasonality of Sargassum ilicifolium was studied in the southern Red Sea by monitoring thallus density, thallus size and the initiation, growth, reproduction and survivorship of primary laterals. Thallus density showed slight but significant seasonal variation; it was highest at the end of the hot season and lowest at the end of the cold season. Mean thallus and lateral lengths peaked in the second half of the cold season. Initiation of new laterals was highest in the first half of the cold season. High lateral densities suppressed new lateral initiation. In the first month after initiation, laterals grew out to the same length as those formed earlier in the year. Thus, elongation rates of young laterals were highest during the period of maximum canopy height. In older laterals, growth rates decreased with length, due to increased tissue loss. Growth rates were independent of reproductive status. Reproduction occurred in the second half of the cold season and was independent of lateral size, but laterals had to be at least 1 to 2 mo old before reproducing. Highest loss rates of laterals occurred at the end of the growth season. Survivorship was independent of lateral size or reproductive status. Loss rates were lowest in the hot season. We conclude that there is no direct trade-off between reproduction and growth/survival of the laterals, and that the dynamics of S. ilicifolium are directly related to the seasonal extremes in environmental conditions. Morphogenetic responses at the level of individual laterals also contribute to the overall phenological pattern.

“…We also wished to investigate the recruitment and growth of Ascophyllum following its removal. This very successful canopy alga has an extensive distribution throughout the North Atlantic, but despite a high investment in reproduction (Josselyn & Mathieson 1978, Aberg 1996 and a high level of successful fertilisation (Baardseth 1970) recruitment of new individuals into mature stands can be surprisingly low (e.g. David 1943).…”

Section: Introductionmentioning

confidence: 99%

Direct and indirect effects of a macroalgal canopy and limpet grazing in structuring a sheltered inter-tidal community

Jenkins¹,

Hawkins²,

Norton³

1999

136

152

The dominant components of the mid-shore community of 4 sheltered, rocky shores in the south of the Isle of Man, UK, were surveyed. A 2-way factorial experiment to investigate the community structuring roles of Ascophyllum nodosum (hereafter AscophyUum) canopies and Patella vulgata grazing was undertaken at 1 site and monitored over a period of 6 yr. Removal of the canopy had a marked impact on the understorey community, with both direct and indirect effects. In contrast, the effect of limpet removal was limited, owing to the restriction of this grazer to small patches of bare substrate within a turf of red algae. The Ascophyllum canopy directly facilitated the presence of the red algal turf in the mid-shore; canopy removal resulted in bleachmg and death of turf species with a consequent loss of entrapped silt. This degradation of the turf resulted in an increase in the area grazed by limpets and a subsequent increase in limpet recruitment, proportional to the increased area of bare substratum. Thus, the AscophyUwn canopy indirectly limits the population of P. vulgata by facilitating the growth of a red algal turf. Eighteen months after Ascophyllum removal, a mixed canopy of Fucus vesiculosus and Fucus serratus developed. This acted in a similar manner to the original canopy, providlng shade for turf species, which resulted in restoration of the balance between algal turf and limpet grazing. Despite this, the red algal turf had not fully recovered 5 yr after it was originally bleached, illustrating the long-term effects of Ascophyllum canopy loss on this community. Removal of the canopy also resulted in high levels of Ascophyllum recruitment, but the slow growth rate of these juvenile plants meant that nearly 6 yr after canopy removal, an Ascophyllum canopy had still not developed. Nonetheless, we predict that Ascophyllum will eventually outcompete the established Fucus spp. canopy. Detailed exammation of the distribution of Ascophyllum juveniles suggests that the low density of juveniles in the natural population is due to a lack of substratum free from both limpets and space-occupying turf, rather than a direct effect of the canopy.