Use of the intertidal zone by fish in Nova Scotia

Synopsis In Nova Scotia the annual harvest of the intertidal seaweed Ascophyllum nodosum exceeds 20 000 tons. This study investigated the possible impact of removal of the seaweed on intertidal abundance of fishes and their gut contents. At sites near Lower Argyle, Nova Scotia, absolute abundance of fish in small areas with Ascophyllum removed and intact was determined with pop-up seines. Gut contents were investigated from fish collected with the seines and with trammel nets. Number and weight of fish were not significantly different between cleared and intact areas and averaged 4.6 individuals and 160 g per 400 m² during June to October. Cunner and sculpins had more food in their guts when leaving than when entering the intertidal, but only cunner had more food in their stomachs when leaving intact areas than when leaving cleared areas. Most fish captured in the intertidal were small (< 15 cm) and of no commercial value, and the numbers of commercial species were too low to be of much value. Numbers of fish in the intertidal was significantly lower than in the shallow subtidal. This study provided no evidence for adverse effects of the removal of patches of Ascophyllum on fishes.     

Trends in abundance of rocky intertidal seaweeds and filter feeders across gradients of elevation,wave exposure,and ice scour in eastern Canada

On NW Atlantic rocky shores, the main basal organisms in intertidal communities are seaweeds (Ascophyllum nodosum, Fucus spp. and Chondrus crispus) and filter feeders (barnacles, Semibalanus balanoides, and mussels, Mytilus spp.). Their ecology has been extensively studied in New England (United States), but knowledge gaps exist for northern shores, which are subjected to stronger environmental stress. Therefore, we studied the above organisms on Canadian shores. We quantified the summer abundance of these seaweeds and filter feeders across full vertical (intertidal elevation) and horizontal (wave exposure and winter ice scour) environmental gradients on the Gulf of St. Lawrence and open Atlantic coasts of Nova Scotia. At the regional scale along the open Atlantic coast, seaweeds showed similar abundances in Nova Scotia than values reported for New England. However, both filter feeders were considerably less abundant in Nova Scotia. At the local scale in Nova Scotia, intense winter ice scour (which only occurs on the Gulf of St. Lawrence coast) was associated with a very low abundance of all species except barnacles. Spatial trends in Nova Scotia were similar to patterns known for certain species elsewhere, such as A. nodosum being almost restricted to sheltered habitats, regardless of elevation, and C. crispus being almost restricted to low elevations, regardless of exposure. Other trends were, however, characteristic of Nova Scotia, such as C. crispus being frequent at low elevations in exposed habitats, unlike in New England, where mussels often predominate there because of competitive advantages. In Nova Scotia, mussels were always restricted to cracks and crevices, unlike in New England, where they form extensive intertidal beds on exposed shores. The direct effects of increased environmental stress and indirect effects through altered interspecific interactions might explain the regional differences in local species distribution, which will require experimental validation. Handling editor: K. Martens     

Biomass and height of Ascophyllum nodosum after two decades of continuous commercial harvesting in eastern Canada

With the increasing demand for seaweed resources worldwide, management must ensure that the harvest of wild seaweed stocks is sustainable. We evaluate the impact of over 25 years of commercial harvesting of Ascophyllum nodosum in eastern Canada by comparing the biomass and height of the seaweed in the late 1990s to the late 2010s over a broad spatial scale spanning the provinces of Nova Scotia and New Brunswick. There has been no significant decrease in the biomass of A. nodosum in either province, and biomass has increased in some regions of New Brunswick during that period. The average height of A. nodosum has decreased by 7.8 cm in Nova Scotia while it increased by 13.8 cm in New Brunswick. Biomass of A. nodosum in unharvested sectors was 7% higher than that in harvested sectors while height of A. nodosum in unharvested sectors in New Brunswick is similar to the values observed in harvested sectors. Over the same period, water temperature has increased in both provinces and, in recent years, has at times exceeded the optimal growing temperature for A. nodosum within bays in Nova Scotia. We conclude that the current management and harvest of A. nodosum in eastern Canada are sustainable and maintain the biomass and height of A. nodosum beds but that control sites are necessary to offer adequate comparisons as environmental conditions are changing.

     

Changes in the population structure of Ascophyllum nodosum (L.) Le Jolis due to mechanical harvesting

The use of a Norwegian suction cutter to harvest populations of the brown alga Ascophyllum nodosum (L.) Le Jolis in southwestern Nova Scotia started in 1985. The impact of this type of mechanical harvest on the algal population structure was evaluated. Changes in the length and density of individual plants (clumps) within 0.25 m^–2 quadrats, as well as the length of individual shoots within clumps were monitored before and after an experimental harvest. The mechanical harvest cut mainly the longer plants, thus changed the initial bimodal size structure of the population to unimodal. There was a 20 to 36% plant mortality, reducing the plant density from 92.6 to 73.6 individuals m^–2. Pre-harvest size distribution of the tagged shoots was skewed to the right and became more normal after the harvest. Tagged shoots in the harvested quadrats suffered a 42% mortality as compared to 11% of those in the control quadrats. An understanding of the impact of the mechanical harvesting on the harvested population is essential in the design of a management strategy. Sources of variation in the impact of mechanical harvest include the tide level at time of harvest, length of time the machine operated in one site, skill of the machine operator, and sharpness of the machine cutting blades.     

The effects of seaweed harvesting on fishes: a critique

Synopsis Black & Miller (1991) concluded that there was no large impact of an experimental harvest of rockweed,Ascophyllum nodosum, on fishes. A critique of their study demonstrates that this conclusion cannot be substantiated by their data because of sampling biases, errors in experimental design and low statistical power. Further, evidence is presented which supports the hypothesis that rockweed may provide an important nursery habitat for juvenile fishes.     

Research note: Field evaluation of epiphyte recruitment (Vertebrata lanosa,Rhodophyta) in different microsite types on host fronds (Ascophyllum nodosum,Phaeophyceae)

The seaweed Ascophyllum nodosum (Phaeophyceae, Fucales) often forms extensive beds in wave‐sheltered, rocky intertidal habitats on northern Atlantic shores. Since this alga is an ecosystem engineer that influences benthic biodiversity, it is important to understand the factors that regulate its performance. Epiphytism is known to affect the performance of macroalgal hosts. In this study, we investigated the effects of surface irregularities on A. nodosum fronds (wounds, branch axils, and lateral pits resulting from receptacle shedding) on the recruitment rate of its obligate epiphyte Vertebrata lanosa (=Polysiphonia lanosa, Rhodophyta, Ceramiales). For this purpose, we performed a field experiment in Nova Scotia, Canada. In June–July 2007, we created wounds on the surface of host fronds that mimicked the wounds that result from invertebrate grazing. At that time, we also mapped the position of epiphyte‐free lateral pits and branch axils on host fronds. In October 2007, after the reproductive season for V. lanosa, the percentage of microsites colonized by this epiphyte was statistically similar for wounds and lateral pits, but significantly lower for branch axils, although by a small difference (mean recruitment rates ranged between 37 and 50%). Since V. lanosa is known not to colonize smooth frond surfaces, our study suggests that the degree of epiphyte load on A. nodosum beds should largely be affected by the overall amount of surface irregularities, with little influence of the relative availability of each microsite type.     

ROLE OF SURFACE WOUNDS AND BROWN ALGAL EPIPHYTES IN THE COLONIZATION OF ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FRONDS BY VERTEBRATA LANOSA (RHODOPHYTA)1

Ascophyllum nodosum (L.) Le Jol. forms extensive beds in wave‐sheltered, rocky intertidal habitats on the northwestern Atlantic coast. This fucoid seaweed is host to an obligate red algal epiphyte, Vertebrata lanosa (L.) T. A. Chr. [=Polysiphonia lanosa (L.) Tandy], and two facultative brown algal epiphytes, Elachista fucicola (Velley) Aresch. and Pylaiella littoralis (L.) Kjellm. Although V. lanosa can occur throughout most of the length of host fronds, it largely predominates in midfrond segments. The two brown algal epiphytes are restricted to distal segments. Through field experiments conducted in Nova Scotia, Canada, we tested the hypothesis that surface wounds are required for the colonization of distal segments of host fronds by V. lanosa. Distal tissues normally have a smooth surface because of their young age (A. nodosum fronds grow apically). By creating small wounds that mimicked grazing wounds distributed elsewhere on host fronds, we demonstrated that V. lanosa can colonize distal frond segments during the growth and reproductive season (summer and autumn). Approximately half of the artificial wounds were colonized by V. lanosa during this time. The experimental exclusion of both brown algal epiphytes from distal frond segments did not affect colonization by V. lanosa. Thus, we conclude that the absence of surface irregularities on distal segments of host fronds, specifically small wounds, is the main factor explaining the absence of V. lanosa there. We propose that further experimental work clarifying epiphyte distribution in host beds will enhance our ability to understand the functional role of epiphytes in intertidal ecosystems.     

PHYSIOLOGICAL AND POPULATION ECOLOGY OF INTERTIDAL AND SUBTIDAL ASCOPHYLLUM NODOSUM (PHAEOPHYTA)1

Morphological, demographic and physiological characteristics of Rhode Island intertidal and subtidal populations of Ascophyllum nodosum (L.) Le Jolis were compared in order to examine factors influencing vertical distribution. The two populations had distinctive morphologies: subtidal plants were narrower (more terete) and highly branched compared with intertidal plants. The subtidal population showed signs of necrosis and breakage, which was reflected in significantly shorter mean plant size. High survivorship and low recruitment of both population resulted in relatively constant densities, averaging 91 and 50 plants per m² in the intertidal and subtidal habitats, respectively. Intertidal plants had higher mean annual growth rates (25 cm.yr^?1) than subtidal plants (2 cm.yr^?1). In general, intertidal plants had higher photosynthetic capacity and nutrient (NO₃^?) uptake rates than the subtidal population but maintained lower light-harvesting pigment and tissue nitrogen concentrations. Although Ascophyllum nodosum is capable of survival and growth in subtidal as well as intertidal areas, results of this study suggest that different selective pressures affect persistence in each habitat. The scarcity of plants in the subtidal environment may be due to the lack of a critical balance between algal production, allocation of photosynthate, and the negative effects of grazers or competitors.     

Spatial distribution and quantification of Fucus species and Ascophyllum nodosum beds in intertidal zones using spot imagery

Low tide SPOT images were selected from two French coast areas characterized by important Fucaceae populations (Pleubian-Bréhat site in Northern Brittany and Ré Island on the Atlantic coast).A specific data transformation yielding the theoretical algal cover was used. This index takes the radiometric properties of the intertidal zone and of the Fucaceae into account. Satellite data cover was validated by comparing it with selected field samples.Other field data indicate that a linear relation exists between cover and biomass. This relationship is quite independent of cover patchiness. However, it can vary according to species, season and location. Hence it was possible to estimate Fucus sp and Ascophyllum nodosum harvestable biomass using appropriate segments of the intertidal zone.     

Comparison of the structure of populations of Ascophyllum nodosum (Fucales,Phaeophyta) at sites with different harvesting histories

Changes in the structure of the Ascophyllum nodosum population at Pubnico, southwest Nova Scotia, Canada, at an experimental site subjected to mechanical harvest and at two control sites never subjected to mechanical harvest were monitored from 1991 to 1994. A bimodal population structure measured in terms of plant length was characteristic of all these sites before the experiment. The population structure of the experimental site became unimodal immediately after experimental harvest by machine and remained unimodal for the subsequent two years. However, a bimodal population structure began to appear in the third year. A bimodal population structure remained evident at the control site with bedrock as the substratum but was less evident at the other control site where the substratum is made up of boulders and cobbles. Movement of loose rocks with rockweeds still attached may have contributed to the less distinct modal structure of this control site. Other sites with different harvesting histories monitored in the summer of 1992 showed some interesting patterns. A unimodal population structure was evident in Argyle Sound and Pubnico Point South and at Charlesville, which had been harvested one and two years before, respectively. A bimodal population structure was more evident at Frenchman's Point, which had been harvested three years prior. The rate of change from a unimodal to a bimodal population structure may depend on the intensity of harvest. Extensive canopy removal in intensively harvested areas may be conducive to an influx of recruits and to regeneration from the holdfast. Hence, plant length modal structure may be a useful measure of the relative state of recovery of a harvested population.     

Changes in the Brown Seaweed Ascophyllum Nodosum (L.) Le Jol. Plant Morphology and Biomass Produced by Cutter Rake Harvests in Southern New Brunswick, Canada

Shoots and clumps of shoots of the commercial brown seaweed Ascophyllum nodosum (“rockweed”) add to the benthic complexity of the intertidal environment, providing an important habitat for invertebrates and vertebrates. To protect the structure of this habitat, management plans for the rockweed harvest of southern New Brunswick include restrictions on gear type and exploitation rates limited to 17% of the harvestable biomass. However, owing to physical and environmental factors, the harvest is not homogeneous, creating patches of exploitation ranging from 15 to 50%.A direct relationship existed between clump vulnerability, weight and length in a controlled harvest at 50% exploitation within 8 m by 8 m plots. At this exploitation rate, the gear rarely impacted clumps below 50 g or 60 cm in length. Clumps larger than 300 g and 130 cm were reduced by up to 55% of their length and 78% of their biomass. The overall impacts of the harvest on intertidal habitat is however of short duration as biomass recovers after a year of the experimental harvest. The rapid recovery is mostly due to a stimulation of growth and branching of the suppressed shoots of the clumps. Some harvested plots showed biomass even higher than initial levels, suggesting an increase in productivity at least during the first year after the harvest.     

Management and production of the brown algae Ascophyllum nodosum in the Canadian maritimes

Commercial exploitation of Ascophyllum nodosum (rockweed) along the coast of Nova Scotia began in the late 1950s when it was used as a raw material for manufacturing alginate and “kelp” meal. Today, this resource is used as a biostimulant extract for crops and animal feed supplements and is the main economic resource of the seaweed industry in the Maritime Provinces and Canada. The management of rockweed, by dividing the resource into many sectors, permitted the assessment of yield per unit area of bed. In Nova Scotia, mechanical harvesting of A. nodosum operated on a pulse of 2- to 3-year schedule providing yields of 21.9 to 47.7?wet?t ha^?1 averaging 35.3?±?7.6?wet?t ha^?1. Acadian Seaplants Limited (ASL) has become the dominant player in the region since 1995 with more than 75% of the total biomass under its leases and more than 90% of the total landing of rockweed in the last 13?years. Sustained harvests at ASL leases and under an annual harvest schedule using hand cutting methods have averaged 17.4?±?2.6?t ha^?1. Exploitation rates above 35% of the harvestable crop lead to a pulse harvest strategy and the need to move infrastructure year after year. In New Brunswick, a new approach to management began in 1995 with a regulated 17% exploitation rate. Thus, the yield in that province is 14.3?wet?t ha^?1. The current summer standing crop for this region has been calculated at 352,723?wet?t, covering an area of 4,960?ha, with an average biomass of 71.3?t ha^?1. The harvest in the region reached peak landings in 2010 with just over 40,100?t. The consistent yield per hectare of A. nodosum beds is proof of good management practices and an ecologically sustainable harvest in the Canadian Maritimes.     

Characterization of microsatellite loci in the marine seaweed Ascophyllum nodosum (Phaeophyceae; Fucales)

Ascophyllum nodosum L. dominates rocky intertidal shores throughout the temperate North Atlantic. Six microsatellite loci were developed for A. nodosum using enriched libraries. The number of alleles ranged from 9 to 24 and heterozygosities from 0.2213 to 0.7785. Ascophyllum is monotypic. There was no cross‐reactivity observed with Fucus serratus, F. vesiculosus or F. evanescens.     

COLONIZATION AND GROWTH OF ASCOPHYLLUM NODOSUM (PHAEOPHYTA) IN MAINE1

Colonization and growth of Ascophyllum nodosum (L.) Le Jol. were investigated in two Maine estuaries from 1972 to 1978. Following denudation of intertidal rock, substrata were initially colonized by Fucus vesiculosus L.; eventually, Ascophyllum supplanted Fucus, and became dominant in terms of percentage cover. Ascophyllum settled first and most densely in the low intertidal zone, but its fastest growth occurred in the mid-intertidal zone. Some, but not all, Ascophyllum germlings produced a vesicle within one year of colonization. The mean annual growth of A. nodosum was variable among sites, zones and years.     

A MODEL FOR GAMETE RELEASE IN ASCOPHYLLUM NODOSUM (PHAEOPHYTA)1

The question of what controls gamete release in Ascophyllum nodosum (L.) Le Jolis was studied at six sites along the central coast of Maine. Percent release was assessed weekly along randomly marked transect lines in the mid-intertidal zone. Six independent variables–water temperature at high tide, air temperature at low tide, nitrogen (ammonia, nitrite, and nitrate), and salinity–were measured concurrently. Stepwise multiple regression analysis on the percentage of plants having released gametes revealed that water temperature at high tide accounted for most of the among-site variation (R²= 0.77) in the timing of release. The addition of Julian day increased the R² to 0.82; no other variables were significant. Probit analysis, based on water temperature at high tide, generated an environmentally realistic model for predicting gamete release. The model predicts the onset, midpoint, and termination of gamete release at 6, 10, and 15°C, respectively, and the midpoint at a cumulative water temperature of 358°C. This model has value for developmental studies and, potentially, for reseeding A. nodosum populations. Probits may be useful for characterizing phenological events in other fucoids and algal species.     

A NEW RECORD AND ERADICATION OF THE NORTHERN ATLANTIC ALGA ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FROM SAN FRANCISCO BAY,CALIFORNIA, USA1

A new record of the Northern Atlantic fucoid Ascophyllum nodosum (L.) Le Jolis (Knotted wrack) was discovered on a shoreline in San Francisco Bay, California during a survey of intertidal habitats in 2001–2002. The alga showed no signs of deterioration 2.5 months after its initial detection. The healthy condition, presence of receptacles with developing oogonia, potential for asexual reproduction, and ability to withstand environmental conditions, both inside the Bay and on the outer Pacific coast, prompted a multiagency eradication effort. Given the relatively small area of shoreline inhabited by the alga, in combination with its absence in 125 other surveyed locations, we decided that manual removal of the seaweed would be the most environmentally sensitive yet effective eradication approach. No A. nodosum has been detected at the site since December 2002, and the species is thought to have been locally eradicated. The site continues to be monitored to assess the success of the eradication efforts.     

Extracts of the Brown Seaweed <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> Induce Gibberellic Acid (GA<Subscript>3</Subscript>)-independent Amylase Activity in Barley

Extracts of the brown seaweed Ascophyllum nodosum have been used as a biostimulant to promote growth and productivity in a number of agricultural production systems. Although the extracts have been shown to improve seedling emergence and vigor in a variety of plants, including barley, the mechanism(s) of this growth-promoting effect is(are) largely unknown. In our study, A. nodosum extract induced amylase activity in barley seed-halves; a significant difference in amylase activity was observed in seeds without an embryo. The addition of activated charcoal to the treatment media negated the bioactivity of the extracts suggesting the organic nature of bioactive compounds in A. nodosum extracts. The extracts induced amylase activity in a gibberellic acid (GA)-deficient barley mutant (grd2). LC-MS-MS analysis failed to detect the presence of GA₃ in the extracts. ABA supplementation of the medium caused a significant reduction of amylase activity in GA-treated seeds compared with those treated with the A. nodosum extract. Taken together, our results suggest that the organic components of A. nodosum extract induce amylase activity independent of GA₃ and might act in concert with GA-dependent amylase production leading to enhanced germination and seedling vigor in barley. Being derived from a renewable resource, the bioactive compounds from A. nodosum could be used to improve crop productivity in sustainable agricultural systems.     

GROWTH,YIELD AND MORPHOLOGY OF ASCOPHYLLUM NODOSUM (PHAEOPHYTA) UNDER CONTINUOUS AND INTERMITTENT SEAWATER SPRAY CULTURE REGIMENS1

Growth and yield of the brown alga Ascophyllum nodosum (Le Jolis) were measured under various regimens of seawater spray culture. One-hour periods of desiccation throughout the day and night and cessation of spray throughout the night did not affect growth relative to that in continuous spray. Desiccation for four hours during the day resulted in death. Changes in morphology from the normal intertidal growth form to that resulting from spray culture are described.     

Larval and juvenile fishes occurring with flood tides on an intertidal mudflat in the Tama River estuary, central Japan

Intertidal movements of fish larvae and juveniles on a mudflat in the Tama River estuary, central Japan, were investigated by comparing the abundance and sizes of fishes caught in the intertidal zone during flood tides with those in the subtidal zone during low tides. A total of 28465 individuals, belonging to 9 families and 20 species, were collected by small purse seine. Among the abundant species, planktonic larvae and juveniles of gobiids and Konosirus punctatus were more abundant in the intertidal zone at flood tide than the subtidal zone at low tide. Similar occurrence patterns were found in juvenile Plecoglossus altivelis altivelis and Lateolabrax japonicus, having fully developed swimming abilities. In contrast to these species, much higher abundances of epibenthic juveniles of 2 gobiids (Acanthogobius flavimanus and Gymnogobius macrognathos) were found in the subtidal zone at low tide, although they also utilized the intertidal zone at flood tide.     

Changes in composition of rockweed (Ascophyllum nodosum) beds due to possible recent increase in sea temperature in Eastern Canada

Ascophyllum nodosum (rockweed) is the main economic resource of the seaweed industry in the Atlantic Provinces of Canada. The annual harvest steadily increased since 1995, reaching a historic peak of 37,000 tonnes in 2007. Due to a high demand for fertilizers and animal feed supplements derived from rockweed, this trend seems likely to continue. The current management plan for the sustainable harvest of the A. nodosum resource is considered conservative. The resource has been managed with a precautionary approach since 1995 to protect the integrity of the habitat. Acadian Seaplants Limited (ASL) has been granted approximately 90% of the government-issued licenses to harvest A. nodosum resources in the Maritimes. The Canadian approach is based on an annual harvest from a given bed and not strip-and-return after several years. Since 1995, ASL has proactively undertaken extensive annual surveys and research on biomass productivity of this renewable resource to establish acceptable annual exploitation rates. Historically, the rockweed beds of southwestern Nova Scotia (NS) have been almost 99% pure A. nodosum, with a minor component of Fucus vesiculosus. However, since 2004, a steady increase in F. vesiculosus, with a peak of 4.6% of the total biomass in 2008, was recorded. This coincided with one of the mildest winters on record for the Maritimes. This increase in temperature seemed to be also responsible for an unusual recruitment of the blue mussel Mytilus edulis in rockweed beds in some areas of southern New Brunswick (NB) in 2006, causing the detachment of up to 30% of the seaweed biomass in some harvesting sectors. Another phenomenon observed in southwestern NS during 2003 and 2004 was extensive ice damage on rockweed beds produced by an early melting of the ice, with losses of up to 90% of the rockweed biomass in some areas.