Fucoid Canopy Research Articles

Thermal moderation of the intertidal zone by seaweed canopies in winter

Canopy-forming seaweeds are important foundation species or ecosystem engineers in intertidal habitats. By limiting a variety of abiotic stresses during low tides, algal canopies improve the performance of many understory organisms. The reduction of heat stress through substrate shading and moisture retention has received considerable attention in marine biology. However, the thermal influence of canopies during winter has not been empirically evaluated. Using intertidal fucoid canopies (Ascophyllum nodosum) from Atlantic Canada, we did a field experiment contrasting canopy-covered and no-canopy areas to test the hypothesis that canopies limit low temperatures during winter low tides. During 35 days between January and March, mid-intertidal temperature was often negative near the time of the lowest daily tides, on average more than 1 °C lower on bare substrate than under full canopy cover. The difference between both canopy treatments was higher around spring tides than around neap tides. Temperature on bare substrate was once even up to 10 °C lower than under a full canopy. Previous studies have shown that single occurrences of lethal negative temperatures and frequent occurrences of sublethal temperatures kill intertidal organisms every winter. Thus, our study suggests that, in addition to their bioprotective role during summer, canopy-forming seaweeds might also play a relevant facilitative role during winter.

Community-level facilitation by macroalgal foundation species peaks at an intermediate level of environmental stress

This paper examines how community-level facilitation by macroalgal foundation species changes with environmental stress. In rocky intertidal habitats, abiotic stress (mainly due to desiccation and thermal extremes during low tides) increases sharply with elevation because of tide dynamics. A previous study done on the Atlantic coast of Nova Scotia (Canada) showed that, at low elevations, where conditions are benign because low tides are brief, fucoid algal canopies (Ascophyllum nodosum and Fucus spp.) do not affect the structure of benthic communities. However, at middle and high elevations, where low tides last longer, fucoid canopies limit abiotic extremes near the substrate and, in that way, increase the richness of benthic communities. Richness was measured as the number of benthic algal (except fucoids) and invertebrate species found in replicate quadrats. Using the published data from that study, the present study compares the intensity of facilitation and its importance (relative to all other sources of variation in richness) between middle and high elevations, which represent intermediate and high stress, respectively. Facilitation intensity was calculated as the percent increase in benthic richness between quadrats with low canopy cover and quadrats with high canopy cover, while the importance of facilitation was calculated as the percentage of observed variation in richness that was explained by canopy cover. Data for a total of 688 quadrats surveyed along 350 km of coastline were used. The analyses revealed that both the intensity and importance of facilitation were greater at middle elevations than at high elevations. As canopies were previously found not to affect benthic communities at low elevations, this study indicates that the facilitation-stress relationship viewed at the community level is unimodal for this marine system. Such a trend was already found for some terrestrial systems involving canopy-forming plants as foundation species. Thus, this unimodal pattern may be ubiquitous in nature and, as further studies refine it, might help to predict community-level facilitation depending on environmental stress.

Regional consistency of intertidal elevation as a mediator of seaweed canopy effects on benthic species richness, diversity, and composition

Through a regional-scale study, we tested the hypothesis that seaweed canopies affect benthic species richness, diversity, and composition differently depending on intertidal ele- vation. The theory behind that prediction recognizes that macroalgal canopies (composed mainly of Ascophyllum nodosum and secondarily of Fucus spp. on the studied shores) limit temperature and desiccation stresses in understory habitats during low tides at high and intermediate eleva- tions but have little influence at low elevations because of prolonged submergences due to tide dynamics. We measured the abundance of all benthic algae and invertebrates in 1033 quadrats covering the natural range of fucoid canopy cover at high, middle, and low elevations in wave- sheltered rocky intertidal sites spanning 350 km of coast in Atlantic Canada. Univariate and mul- tivariate analyses indicated that benthic species richness, diversity, and composition differed sig- nificantly between low-cover (0�40%) and high-cover (60�100%) canopy treatments at high and middle elevations but not at low elevations. At high and middle elevations, high canopy cover increased benthic richness and diversity by allowing several species to occur and enhancing the abundance of most species, compared with low canopy cover. At low elevations, species generally occurred in both canopy treatments and showed a similar abundance between them. These results reveal the ecological generality of the dependency of canopy effects on elevation, which we pre- viously found through a manipulative experiment done at one location. Overall, we conclude that environmental stress mediates seaweed canopy effects on the structure of intertidal communities.

Bioengineer effects on understory species richness, diversity, and composition change along an environmental stress gradient: Experimental and mensurative evidence

Canopy-forming bioengineer species are commonly assumed to increase local species richness and diversity. We tested this notion by investigating the effects of fucoid seaweed canopies on understory communities along rocky intertidal elevation gradients in Atlantic Canada. Such gradients exhibit increasing thermal extremes and variation from low to high elevations, and are broadly used in stress gradient studies. A manipulative experiment created canopy and no-canopy treatments at the low, middle, and high intertidal zones, eliminating all species (except fucoid canopies) from replicate quadrats. After recolonization, overall richness and diversity (considering all primary producers and consumers) were higher under canopies than uncovered by canopies at the high and middle zones, but no effects occurred at the low zone. Similarly, species composition was affected by canopies at the high and middle zones, but not at the low zone. A mensurative study that surveyed the full range of canopy cover (0–100%) using nearly five times more quadrats from pristine areas yielded the same results: richness and diversity increased with canopy cover at the high and middle zones (approaching stabilization toward high cover values), but no effects occurred at the low zone. Lack of canopy effects at low elevations is related to mild habitat conditions, which canopies are unable to modify, while positive effects at higher elevations relate to the capacity of canopies to ameliorate harsh conditions. This is the first time that a combined experimental and mensurative approach shows that the same bioengineer species affect overall species richness, diversity, and composition differently along a stress gradient. Overall, protecting canopy-forming bioengineers to preserve local biodiversity should be most effective in stressful environments.

Gametophyte life-history dominance of Chondrus crispus (Gigartinaceae, Rhodophyta) along the Atlantic coast of Nova Scotia, Canada

adeceased December 2010 Similar to other species of Gigartinaceae Chondrus crispus has an alternation of perennial, isomorphic gametophytic and sporophytic generations. As these two generations co-exist independently within populations and obtain their resources in a similar manner, intraspecific competition is expected. In populations within the southern Gulf of St. Law rence, fronds of both generations of C. crispus occur in similar numbers. This equivalency can be related to substratum instability, where the population is dynamic with a high turn-over rate of genets. These observations support a stochastic hypothesis to account for distribution of gametophytes and sporophytes in this area. Along the Atlantic coast of Nova Scotia, where the substratum is stable, gametophytes are overwhelmingly predominant. Gametophytic predominance is greatest in the lower littoral zone where C. crispus is abundant and space is limited. Under the fucoid canopy where “free-space” exists, the gametophyte to sporophyte ratio is lower. Gametophytic and sporophytic fronds are distributed equally among different size-classes and size-distribution is not considered a competitive factor. Previous studies have shown that sporophytic fronds of C. crispus are more susceptible to infections by endophytic algae and other pathogens, and are more heavily grazed by herbivores than are gametophytic fronds. Thus, mechanistic factors are strongly implied in the selection of gametophytes in the Atlantic population.

Characteristics of the Ascophyllum nodosum stands and their associated diversity along the coast of Brittany, France

The present study aimed at estimating the characteristics of the Ascophyllum nodosum stands along the coast of Brittany, France. Although both an ecologically and economically important macroalga on sheltered rocky shores of the North Atlantic, no study has simultaneously dealt with the variability of the densities, lengths and biomasses of A. nodosum together with a description of its associated algal and animal diversity. There were significant differences in mean lengths and variations in the length–population structures between sites. However, the biomasses and densities showed no significant differences. The biomasses are amongst the highest ones estimated over the entire species distribution. The algal and animal assemblages were typical of A. nodosum zones, but only the identity composition of the algal communities seemed to reflect site differences in environmental forces. The biomasses measured in the present study should help improve future macroalgae biomass and metabolism estimates on regional or global scales. Finally, the data will provide a reference state for future studies on the responses of fucoid canopies to environmental changes.

Regional scale differences in the determinism of grazing effects in the rocky intertidal

Patellid limpets are dominant grazers on intertidal rocky shores of NW Europe with a key role in structuring the eulittoral community. Localised loss of limpets and the subsequent reduc- tion in grazing pressure is known to result in important changes in community structure, through the development of canopy-forming macroalgae, and an associated increase in species diversity and community complexity. The level of determinism in the community level response to localised loss of patellid limpets was assessed at spatial scales from 100s of kilometres to 10s of metres and temporal scales from weeks to months at mid-tide level of exposed rocky shores. Limpets were removed and excluded from experimental plots to simulate localised limpet loss and appropriate controls estab- lished. Experimental plots were established in replicate patches at 2 shores at each of 2 regional locations, separated by approximately 500 km: the Isle of Man and SW England. Removals were con- ducted on 2 dates within each of 2 seasons (summer and winter) and the community level response monitored for a period of 12 mo. There was a clear effect of limpet loss at all spatial and temporal scales, with rapid development of green ephemeral algae followed by a fucoid canopy. However, the degree of determinism in the development of canopy-forming algae differed markedly between the 2 locations. At the northerly location, the Isle of Man, fucoid algae developed quickly and dominated all areas of limpet exclusion; there was little variability between plots. In contrast, in SW England, the abundance of fucoid algae was significantly lower and much more variable. Such geographic changes in the development of macroalgae in the absence of the dominant grazer are discussed in relation to rocky shore community dynamics and the latitudinal change in balance between grazers and algae over the wave exposure gradient.

Barnacle larval supply to sheltered rocky shores: a limiting factor?

In northwest Europe, sheltered rocky shores are dominated by fucoid canopy algae and barnacles are rare, although the latter are extremely abundant on exposed shores. The supply of the intertidal barnacle Semibalanus balanoides (L.) to sheltered, fucoid dominated rocky shores was investigated to determine the importance of larval supply in limiting the abundance of adults in shelter. Larval supply was measured at two spatial scales, at the scale of shore (100s of metres), by comparing larval concentrations at exposed and sheltered sites, and at a smaller spatial scale (m), by examining the role of fucoid canopies in limiting supply to the substratum. Replicate plankton trawls were carried out above the intertidal zone at high water at two sheltered sites and nearby exposed headlands. The concentration of S. balanoides cyprid larvae was significantly higher at the sheltered sites on two out of three sampling occasions with up to 14 times greater larvae on one occasion than the nearby exposed site. The effect of the macroalgal canopy on supply to the substratum was assessed in two ways: directly, by pumping water from the substratum in areas with and without Ascophyllum nodosum (L.) Le Jolis, and indirectly by measuring cyprid settlement in a canopy-manipulation experiment. Pumped plankton samples from mid tide level showed that the A. nodosum canopy did not form a barrier to larval supply and may have had a positive effect on larval concentrations at the substratum. Cyprid settlement was assessed in the mid shore A. nodosum and low shore Fucus serratus L. zones to areas with canopy algae (but protected from the sweeping effects of macroalgal fronds) and without canopy. Settlement over three consecutive 24-h periods showed a consistent pattern; settlement was consistently lower beneath the F. serratus canopy than in cleared areas, suggesting that this algal species forms a barrier, limiting supply of cyprid larvae to the substratum.

Settlement and post-settlement interactions between Semibalanus balanoides (L.) (Crustacea: Cirripedia) and three species of fucoid canopy algae

Manipulative field experiments carried out on sheltered rocky shores investigated settlement and post-settlement interactions between Semibalanus balanoides and three species of fucoid canopy algae, Fucus spiralis L., Ascophyllum nodosum (L.) Le Jolis and Fucus serratus L. All three species had a negative effect on settlement and early recruitment of S. balanoides, densities being significantly lower on settlement tiles beneath the canopy compared to cleared areas. Investigation of the mechanism by which settlement and recruitment were inhibited showed the importance of sweeping of algal fronds at all three shore heights. In addition, we found that the F. serratus canopy inhibited settlement not only by its sweeping action but also by limiting the access of cyprids to the substratum. Detailed examination of the sweeping effect in F. serratus showed that newly settled cyprids transplanted beneath a canopy suffered extremely high mortality (between 82 and 97%) over just one high water period. Mortality was significantly reduced for individuals that had settled within a matrix of adults. Metamorphosis of cyprids to spat conferred no additional resistance to sweeping-induced mortality but resistance increased in 6 day old spat. Mortality in S. balanoides after the end of the settlement season was monitored for three months in experimental treatments and controls. Mortality rates were significantly lower under the canopy than in cleared areas in both the F. spiralis and Ascophyllum zones. The overall influence of each canopy species on the development of barnacle populations on sheltered shores is discussed.

Interaction between a fucoid canopy and limpet grazing in structuring a low shore intertidal community

The relative roles of a macroalgal canopy, Fucus serratus L., and a grazer, Patella vulgata L., in structuring a low shore community of a sheltered, rocky intertidal site were examined using a factorial experimental design. Canopy removal and grazer exclusion treatments were used to determine the effects of both factors on the understorey community. Re-establishment of the canopy was studied in relation to grazing pressure and substrate type in order to determine how this macroalga maintains its spatial and temporal dominance on the low shore. In addition, the size of canopy clearances were varied to determine the effect of gap size on community structure. Removal of the F. serratus canopy alone resulted in little change to the understorey community. Few understorey species were adversely affected by exposure to increased light levels and the grazing pressure of limpets was sufficient to prevent large scale recruitment of algae. Removal of limpets alone resulted in little change except for a greatly enhanced recruitment of F. serratus juveniles, indicating that grazing pressure rather than the canopy was inhibiting recruitment of the canopy species. Large changes in community structure only occurred following removal of both the canopy and grazers together since either the canopy or limpet grazing alone was sufficient to prevent large scale recruitment of algae. Limpet grazing did not prevent the re-establishment of a F. serratus canopy, although recovery was delayed in comparison to plots where limpets were removed. The size of gaps in the canopy had no discernible effect on the species composition or rate of succession in experimental treatments.

Rocky shore distribution patterns along the Somerset coast

Along the coast of Somerset, the numbers of animal and plant species progressively decline from west to east. Changes in zonation patterns thus reflect a decrease in species richness as well as the direct influences of increasing tidal range and turbidity. The patterns are also complicated by the differing rock types: quartzite to the west, limestone to the northeast with softer marls and shales inbetween. The overall appearance of some shores has changed in recent years as a result of fucoid responses to hot summers and cold winters. This has greatly influenced community structure. In contrast to the Quoddy Region (Bay of Fundy), Ascophyllum nodosum is confined to sheltered sites whilst Nucella lapillus (together with several other gastropods) becomes increasingly restricted to lower levels – especially where a fucoid canopy is present.

Rocky shore distribution patterns along the Somerset coast

Along the coast of Somerset, the numbers of animal and plant species progressively decline from west to east. Changes in zonation patterns thus reflect a decrease in species richness as well as the direct influences of increasing tidal range and turbidity. The patterns are also complicated by the differing rock types: quartzite to the west, limestone to the northeast with softer marls and shales inbetween. The overall appearance of some shores has changed in recent years as a result of fucoid responses to hot summers and cold winters. This has greatly influenced community structure. In contrast to the Quoddy Region (Bay of Fundy), Ascophyllum nodosum is confined to sheltered sites whilst Nucella lapillus (together with several other gastropods) becomes increasingly restricted to lower levels - especially where a fucoid canopy is present.

Community succession following massive ice-scour on an exposed rocky shore: effects of Fucus canopy algae and of mussels during late succession

In April 1987, exposed rocky shores near Halifax, Nova Scotia, Canada, were severely scoured by rare sea-ice. These shores are normally dominated by a lush canopy of perennial fucoid rockweeds, with an associated understory of mussels, barnacles and crustose algae. Several observational and experimental studies have been carried out on the succession which has followed this scouring. This paper reports experimental tests of the effects of fucoid canopy algae and mussels on each other and on other species, during later succession. Previous work suggests that, in the absence of predation or disturbance, mussels Mytilus edulis (L.) would increase and outcompete Fucus vesiculosus L. as the dominant space occupant at the mid-shore level. However, during this experiment, 2–3 yr after the scour, abundance of mussels (as understory) decreased. This decrease was dependent on the presence of canopy and may be mediated by whelk carnivory. Mussels had no effect on canopy cover of Fucus vesiculosus L., and caused only a small decrease in Fucus density. Self-thinning appeared to affect Fucus density far more than mussels. Removal of canopy also affected Fucus recruitment, ephemeral algae, grazers and whelks, but did not affect crustose algae or barnacles significantly. In contrast, mussel removal was not found to affect any of these species, except to decrease whelk abundance. These results suggest that the interactions may be more variable than previous work implies. Although much of the Northwest Atlantic rocky seashore is dominated by rockweeds, and rockweeds are thought to be competitively inferior to mussels, we believe this study is the first to directly examine the effects of mussels on rockweeds.

Interactions of Patella and macroalgae with settling Semibalanus balanoides (L.)

Biological interactions affecting densities of settling and newly-settled Semibalanus balanoides (L.) have been investigated by manipulative field experiments on the Isle of Man. The effects of sweeping by fucoid clumps of different species and Patella browsing have been compared on moderately-exposed shores. Patella allowed barnacle settlement by preventing growth of competing green algae, but reduced post-settlement densities. Small clumps of Fucus spiralis L., F. vesiculosus L, and F. serratus L. all reduced settlement considerably more so than limpets. F. serratus had the greatest sweeping effect. Interactions between macroalgae and Semibalanus balanoides have been investigated at all levels on sheltered shores and low down on more exposed shores. In the Fucus spiralis and F. vesiculosus zones, post-settlement numbers were higher than in adjacent areas where the canopy was removed. Barnacles did not settle readily in the Ascophyllum zone in either experimental or control areas. Settlement occurred in the upper part of the Fucus serratus zone in experimental areas where the canopy was removed but not in control areas. No settlement occurred in either treatment or control areas lower in the F. serratus zone. At all levels on the shore fucoid canopies seemed to reduce cyprid settlement, but the effect was greatest amongst F. serratus where there was total prevention. High on the shore the effect of enhanced post-settlement survival under the canopy outweighs reduction of cyprid settlement thus there are greater numbers in the controls. Competition with red algal turfs was shown to set the lower limit of the barnacle zone on a vertical pier face.

Intertidal macroalgae and macroinvertebrates: Seasonal and spatial abundance patterns along an estuarine gradient

Quantitative sampling of the dominant intertidal epibiota was conducted seasonally along an estuarine gradient within the Great Bay Estuary System, New Hampshire, U.S.A. The abundance and zonation of the dominant macroorganisms varied with distance into the estuary. Replacement of marine by estuarine species occurred, and overall abundance and species richness decreased along the estuarine gradient. Zonation patterns within the inner estuary were primarily allied with substrata. Maximum abundance of invertebrates occurred in the mid-intertidal zone where a dense fucoid canopy provided habitat heterogeneity. Densities of epibiotic organisms decreased toward low water, especially in the inner estuary where hard substratum was limiting. Settlement blocks, introduced into the low intertidal zone, were dominated by barnacles and fucoid algae; after 16 months, the species composition on the settlement blocks resembled the adjacent community. Semibalanus balanoides settled in the spring, while Fucus vesiculosus var. spiralis exhibited low but constant settlement. Despite the physical rigors of the estuarine environment, only Semibalanus balanoides, Ilyanassa obsoleta and Spartina alterniflora showed significant seasonal changes in density. Thus, there are predictable and persistent epibiotic species assemblages within the intertidal zone of the Great Bay Estuary System.

Changes in a rocky shore community: An evaluation of monitoring

The basic aim of this study was to record the changes in the communities on a moderately exposed rocky shore by a programme of repeated non-destructive sampling (‘monitoring’) and to determine the causes of these changes. Possible causative factors were investigated by the combined approach of analysing detailed sea-temperature and meteorological data for the period of the study and establishing manipulative field experiments. Fixed quadrats (2 m by 1 m) at three levels were visited at 6–8 weekly intervals for 30 months and the abundance and spatial pattern of major species assessed. In the ‘High’ quadrat the balance between Fucus spiralis and F. vesiculosus changed, and an outburst of ephemeral algae occurred following a decline in overall canopy cover. In the ‘Mid’ quadrat F. vesiculosus decreased considerably from its initial cover and virtually disappeared by the end of the study. In the ‘Low’ quadrat F. vesiculosus increased from being absent to comprising 20% of the canopy, whilst Semmibalanus (= Balanus) balanoides and ‘understorey’ algae decreased in cover. Actinia equina, Nucella lapillus and Patella vulgata showed marked changes in number at all levels where they occurred. Only certain of these changes could be attributed to the physical environment—most were biologically controlled. For example, manipulative experiments showed that the blooms of ephemeral algae and the decline of Patella in the high-shore quadrat, and the decline of Actinia in the mid-shore quadrat, were due to decreases in the fucoid canopy. These canopy changes were, in turn, the result of biological cycles which are characteristic of these communities. However, even with the support of manipulative experiments, it was not possible to account for (or predict) all of the observed natural changes. The extent of these fluctuations poses a serious obstacle to the recognition of any but very gross pollution-induced effects. The conclusion must be that the monitoring of rocky shores as a means of detecting and measuring pollution is likely to be an unproductive investment of time and resources.

Organization of the New England Rocky Intertidal Community: Role of Predation, Competition, and Environmental Heterogeneity

Organization of the New England Rocky Intertidal Community: Role of Predation, Competition, and Environmental Heterogeneity