Pre- and post-barrage scenarios of the relative productivity of benthic and pelagic subsystems of the Bristol Channel and Severn Estuary

The relative importance of benthic and pelagic production within the ecosystem energy cycle, varies considerably for different regions of the Bristol Channel and Severn Estuary. In regions of high turbidity, pelagic primary production is negligible whereas, in the clearer waters of the Outer Channel, the much higher pelagic production contributes to both benthic and pelagic secondary production, The construction of a tidal power scheme would most probably reduce turbidity, so increasing the overall productivity of the enclosed estuary. A range of scenarios, and their implications, are discussed.     

Intertidal zonation of animals and plants on rocky shores in the Bristol Channel and Severn Estuary–the northern shores

The vertical distribution of common species of macroalgae and fauna on rocky shores extending through the length of the estuary is described. In the west, the shores are fully marine and exposed to Atlantic waves. In an eastward direction, greater shelter and an increasing tidal range occur along a gradient of salinity and turbidity. The flora and fauna change along this gradient. No single biological feature signals a transition from the Bristol Channel to the Severn Estuary but four arbitrary regions are recognized: a 'marine' section eastwards to Swansea, a 'transitional' section between Swansea and Cardiff, an 'estuarine' section up to Newnham, and the tidal river Severn.     

Effect of Algal Exudates on Substratum Selection by Motile Telotrochs of the Marine Peritrich Ciliate Vorticella marina

SYNOPSIS. Several species of marine peritrichs are found as epiphytes on small strands of filamentous green and red algae affixed to the substratum of marine intertidal rock pools. In pools located along the coast of Narragansett Bay, the motile vorticellid telotrochs appear to show a substratum selection for specific algae. Exudation products by marine algae have distinct differences; some Phaeophyta have particularly high values for dissolved organic matter (DOM), and for phenolic compounds. Algal exudates appear to influence population growth of vorticellids. The mean survival percentage of vorticellid populations increased with exposure to exudates from Cladophora gracilis, Polysiphonia harveyi and Polysiphonia lanosa ; and decreased with exposure to those of Ascophyllum nodosum, Fucus spiralis and Scytosiphon lomentaria. Telotroch settlement of Vorticella marina was enhanced by exudates of Cladophora gracilis, Polysiphonia harveyi and Polysiphonia lanosa , but was reduced by exudates of Ascophyllum nodosum , and was prevented by exudates of Fucus spiralis and Scytosiphon lomentaria .
Algal exudates were obtained by allowing photosynthetic activity of the experimental algae for 6 hr. The exudates were filtered and the concentration of DOM, total phenols and carbohydrates determined. The filtered seawater containing the exudate was placed in a box-type plastic dish on which the vorticellids had colonized. Survival percentages and the percentage of population due to telotroch settlement were calculated. This investigation indicates that algal exudates may exert a significant influence on the selection of substrata by vorticellid telotrochs and suggests that the ecologic stability of a given rock pool may be considerably lessened by a high level of Phaeophtya and the consequent reduction of Aufwuchs species.     

Description of Proales litoralis sp. nov. (Rotifers, Monogononta: Proalidae) from the marine littoral

Proales litoralis sp. nov. (Rotifers, Monogononta: Proalidae) collected from littoral algae and psammon of the Channel (France) and the Eastern Scheldt (the Netherlands) is described. The affiliation of the new species is discussed.     

Intertidal ecology and potential power impacts, Bay of Fundy, Canada

A large-scale tidal power project in the upper reaches of the Bay of Fundy would cause major changes in the tidal elevations of the headpond which would have a pronounced effect on intertidal ecology. The new mean low water level would be, on average, slightly above the present mean sea level whilst the new mean high water level would drop about 0.7 m. This would result in a much compressed intertidal zone. Mud and sand flats, below the present mean sea level, would be converted to sub-tidal habitat, whilst the high saltmarsh, flooded at present only on the highest spring tides, would become colonized by terrestrial vegetation. There would be major shifts in the relative importance of primary production by saltmarshes, intertidal microalgae and phytopiankton, but overall, it is likely that production would increase. Changes in both primary food sources and habitat area would affect the abundance of intertidal invertebrate organisms and the fish and migratory shorebirds that feed upon them.     

Growth, reproduction and mortality in marine littoral Collembola at different salinities

ABSTRACT. 1. A comparative study was performed on growth, reproduction and mortality of three species of marine littoral Collembola: the grassland species, Isotoma viridis (Bourlet), the littoral Hypogastrura viatica (Tullberg) and the intertidal Anurida maritima (Guérin), at different salinities.
2. I. viridis and H. viatica both occur in salt marshes that are only inundated by seawater at very high tides. The first species lives in the higher less saline area and the second in the lower area, where during summer brackish and even hypersaline conditions may occur. The intertidal A.maritima is mainly found at salinities similar to the local seawater.
3. I.viridis and H.viatica both show maximal growth and reproduction and a very low mortality at low salinities, but the latter species is better adapted to higher salinities. A difference between A.maritima and the other two species is that A.maritima is unable to survive freshwater conditions; rather it has an ecological optimum at salinities similar to seawater.
4. A salt-marsh population of I.viridis showed a better survival and a slightly better growth at saline conditions than an inland population of this species.
5. We suggest that H.viatica , living in a very unstable environment, can be considered as a typical r-strategist, while A.maritima , living in a predictable habitat, is more a K-strategist.     

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.     

Fish Reliance on Littoral–Benthic Resources and the Distribution of Primary Production in Lakes

Pelagic, littoral, and terrestrial resources can all play a role in supporting consumers in lakes. The role of benthic algal-derived food web pathways in lakes is perhaps the least understood because limnologists have historically focused on pelagic (open-water) production and processes. We compiled carbon stable isotope data from 546 fish populations (75 lakes), and used a two end-member mixing model to calculate littoral–benthic reliance for each fish species in each lake. Fish littoral–benthic reliance values were averaged by lake to assess overall fish species benthic reliance for each lake. Lake-specific mean littoral reliance (BR_L; fish species not weighted according to production or biomass) averaged 57% and was independent of lake morphological and limnological attributes. For these same lakes, water column nutrients, light, and morphometry data were used to estimate whole-lake benthic algal and phytoplankton primary production. On average, benthic algae comprised 36% of whole-lake primary production (BP_f = 0.36). BP_f and BR_L were weakly correlated: BR_L tends to be high even in large/deep lakes in which benthic algae is a minor contributor to whole-lake primary production. The high littoral–benthic contribution to individual fish species appears to reflect the high concentration of fish species diversity in the littoral zone. Our work cannot be extrapolated to whole-lake fish production. However, the result is consistent with other work indicating that most fish species inhabit the littoral zone, whereas relatively few exclusively inhabit the pelagic. Our results suggest that it takes less primary production to support a single fish species in the littoral zone than is required to support a species in the pelagic.     

Genotypic stability and physiological tolerance in the dog-whelk (Nucella lapillus)

Populations of dog-whelks living on fully marine shores are in genotypic equilibrium: variation is produced during zygote formation in proportion to the exposure of the shore to wave action, and this variation is eliminated during life. However, populations collected on the Somerset coast where the salinity of the Bristol Channel begins to be reduced by land-water from the River Severn show no such regular pattern. Out of 15 samples (a total of 4711 individuals) 13 showed signs of temporary extinction or of disruptions of growth apparently caused by periodic food shortages. It is concluded that dog-whelks from the Bristol Channel live in a colonizing situation in which they are struggling to survive rather than extending their range by increasing their physiological tolerance.     

The Response of Experimental Rocky Shore Communities to Nutrient Additions

The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by established littoral communities dominated by fucoids. The response to nutrient enrichment was followed for almost 2 1/2 years. Fast-growing opportunistic algae (periphyton and ephemeral green algae) grew significantly faster in response to nutrient enrichment, but the growth of red filamentous algae and large perennial brown algae was unaffected. However, these changes were not followed by comparable changes in the biomass and composition of the macroalgae. The biomass of opportunistic algae was stimulated only marginally by the nutrient enrichment, and perennial brown algae (fucoids) remained dominant in the mesocosm regardless of nutrient treatment level. Established rocky shore communities thus seem able to resist the effects of heavy nutrient loading. We found that the combined effects of the heavy competition for space and light imposed by canopy-forming algae, preferential grazing on opportunistic algae by herbivores, and physical disturbance, succeeded by a marked export of detached opportunistic algae, prevented the fast-growing algae from becoming dominant. However, recruitment studies showed that the opportunistic algae would become dominant when free space was available under conditions of high nutrient loading and low grazing pressure. These results show that established communities of perennial algae and associated fauna in rocky shore environments can prevent or delay the accumulation of bloom-forming opportunistic algae and that the replacement of long-lived macroalgae by opportunistic species at high nutrient loading may be a slow process. Nutrient enrichment may not, in itself, be enough to stimulate structural changes in rocky shore communities.     

Tidal activity rhythms and depth distribution of rocky shore fish in an altered intertidal environment

In this note we report on changes of activity level of littoral fish and their use of different microhabitats in an altered intertidal environment, where intertidal fish are never emersed and turbulence is confined to high tides. Despite these atypical conditions, the structure of the assemblage is basically the same found in a typical rocky-shore situation. Two intertidal fish known to possess internal tidal rhythms, Lipophrys pholis and Coryphoblennius galerita, retain those rhythms in these altered conditions, and the associated social changes in L. pholis are also retained. These observations support the studies of Gibson (1971), who showed that changes in hydrostatic pressure were of prime importance in keeping the tidal rhythm entrained. The subtidal Parablennius pilicornis, on the contrary, is more active during low tide than at high tide. The hypothesis that some subtidal species are excluded from the intertidal by a turbulence-avoiding mechanism is discussed.     

胶州湾潮间带生态学的研究——Ⅱ.沧口潮间带

本文是胶州湾潮间带生态学研究的第二部分。主要研究沧口潮间带的生物群落结构和优势种的数量变动等问题。 该潮间带可分为三个带。(1)高潮带:有两个群落,即圆球鼓窗蟹群落和中国绿螂-双齿围蚕群羝;(2)中潮带:确三个群落,即蓝蛤-日本大眼蟹群落,蛤仔-蓝蛤群落和蛤仔-(?)氏肌蛤群落;(3)低潮带:以蛤仔-滩栖蛇尾群落为主。 本文还对潮间带生物群落合成种类的多样性进行了分析。     

Phylogeography and cryptic introduction of the ragworm Hediste diversicolor (Annelida,Nereididae) in the Northwest Atlantic

Many benthic marine invertebrates show striking range disjunctions across broad spatial scales. Without direct evidence for endemism or introduction, these species remain cryptogenic. The common ragworm Hediste diversicolor plays a pivotal role in sedimentary littoral ecosystems of the North Atlantic as an abundant prey item and ecosystem engineer, but exhibits a restricted dispersal capacity that may limit connectivity at both evolutionary and ecological time scales. In Europe, H. diversicolor is subdivided into cryptic taxa and genetic lineages whose distributions have been modified by recent invasions. Its origin in the northwest Atlantic has not been adequately addressed. To trace the age and origin of North American ragworm populations, we analyzed mtDNA sequence data (COI) from the Gulf of Maine and Bay of Fundy (n=73 individuals) and compared our findings with published data from the northeast Atlantic. Our results together with previous data indicate that two species of the H. diversicolor complex have independently colonized the northwest Atlantic at least three different times, resulting in two distinct conspecific assemblages in the Bay of Fundy and Gulf of Maine (respectively) that are different from the species found in the Gulf of St. Lawrence. North American populations had significantly lower genetic diversity compared with populations in the northeast Atlantic, and based on patterns of shared identity, populations in the Bay of Fundy originated from the Baltic Sea and North Sea. Populations from the Gulf of Maine were phylogenetically distinct and most likely originated from unsampled European populations. Analyses of the North American populations revealed patterns of post‐colonization gene flow among populations within the Gulf of Maine and Bay of Fundy. However, we failed to detect shared haplotypes between the two regions, and this pattern of complete isolation corroborates a strong phylogeographic break observed in other species.     

Regional climatic warming drives long-term community changes of British marine fish

Climatic change has been implicated as the cause of abundance fluctuations in marine fish populations worldwide, but the effects on whole communities are poorly understood. We examined the effects of regional climatic change on two fish assemblages using independent datasets from inshore marine (English Channel, 1913-2002) and estuarine environments (Bristol Channel, 1981-2001). Our results show that climatic change has had dramatic effects on community composition. Each assemblage contained a subset of dominant species whose abundances were strongly linked to annual mean sea-surface temperature. Species' latitudinal ranges were not good predictors of species-level responses, however, and the same species did not show congruent trends between sites. This suggests that within a region, populations of the same species may respond differently to climatic change, possibly owing to additional local environmental determinants, interspecific ecological interactions and dispersal capacity. This will make species-level responses difficult to predict within geographically differentiated communities.     

Antioxidant response to natural organic matter (NOM) exposure in three Baikalean amphipod species from contrasting habitats

The aim of the present work is to comparatively evaluate the oxidative stress response on exposure to natural organic matter (NOM) in three amphipod (Crustacea, Amphipoda) species from different taxonomic groups and different habitats of Lake Baikal. Endemic species from Lake Baikal were used: the shallow-water dwelling Gmelinoides fasciatus (Dyb.), Pallasea cancelloides (Gerstf.), and the deep-layer inhabitant Ommatogammarus flavus (Dyb.). Three key enzymes, catalase (CAT), peroxidase (POD), and glutathione S-transferase (GST), were studied. The applied NOM from Lake Schwarzer (Germany) directly impacts the two littoral species which quickly respond. The response is characterized by a significant decrease of POD and an increase of CAT activities. GST activity remains stable or decreased slightly. In contrast to the littoral amphipods, the deep-layer inhabitant O. flavus showed no significant reaction to NOM exposure, probably due to decreased adaptive ability of this species. The stable environment of the Baikalean deep zones obviously does not provide triggers for the development of flexible antioxidant or general defense systems.     

Benthic macrofauna and sediments in the Severn Estuary

In the Severn Estuary and Bristol Channel, a multivariate analysis indicated eight groupings of macrobenthic fauna, each associated with a different physical habitat. Samples were faunistically impoverished, especially in sublittoral areas, but greater species richness was associated with reefs of Sabellaria alveolata , which extended well into the estuary.     

Production and Distribution of the Microphytobenthos in the Sediment of Lake Mikolajskie

Chlorophyll-α concentration, algal biomass and photosynthetic activity decrease with increasing sediment depth. Chlorophyll-α and biomass minima were found at the sediment surface on several occasions. This may be due to the removal of algae by wave action or vertical migrations of the algae in the sediment. By comparing stations with different degrees of exposure it was shown that wave action affects the size of the benthic populations. The epipsammic microphytobenthos is an important primary producer in the littoral zone of Lake Mikolajskie.     

The influence of spawning and nursery grounds on the distribution of sole Solea solea (L.) in the Irish Sea, Bristol Channel and adjacent areas

In the coastal waters of west England and Wales, sole, Solea solea (L.), are found in greatest abundance in the north-east Irish Sea and the Bristol Channel. Data from research and charter vessel surveys in these areas showed differences in the spatial distribution of age-groups between the two regions. Juvenile sole (0-group, 1-group and 2-group) were found almost exclusively in the shallow (<20 m deep) parts of the north-east Irish Sea and adults (3-group and older) were also found in the same area and in deeper water. In contrast, while juvenile sole in the Bristol Channel were abundant in and around Carmarthen Bay, Swansea Bay and the Severn estuary, they also occurred frequently in deeper areas of the Bristol Channel down to depths of 40 m. Adult sole in the Bristol Channel were also relatively more abundant at depths >40 m than adults in the Irish Sea. The movements of sole which produce these patterns of distribution in the two areas are also shown by the recaptures of sole tagged in the respective nursery areas. The differences in the distribution of sole in the two areas may be related to the depths of their spawning grounds and the distances that maturing fish must travel to reach them.

In the north-east Irish Sea, sole spawning grounds are generally in waters of <40 m depth and within an extensive area of relatively shallow and gently shelving sediments close to the coastal nursery grounds. The bottom topography of the Bristol Channel is more steeply shelving and the spawning grounds of sole are at a depth of 40–75 m off Trevose Head, ≈100 km from the main nursery areas. The hydrographic conditions in the two areas are described, and it is concluded that one of the more important requirements of a successful spawning ground is the presence of suitable hydrographic conditions to transport eggs and larvae to nursery areas.     

Recovery of photosynthesis after exposure of intertidal algae to osmotic and temperature stresses: comparative studies of species with differing distributional limits

Summary This study examines possible relationships between stress tolerance by marine algae and distributions of these species. The ability to recover photosynthetic activity following dehydration or temperature treatments was the assay used to evaluate stress tolerance, and Porphyra perforata, Rhodoglossum affine, Gelidium coulteri, and Smithora naiadum differed in thresholds of tolerance, even though plants were collected from low tidal sites.Limits of dehydration tolerance were well correlated with limits of tidal distribution for these species. Additionally, other high tidal species tolerated severe dehydration while subtidal and low tidal species were sensitive to dehydration. High tidal individuals of P. perforata were also more tolerant of dehydration than were low tidal thalli of P. perforata.Limits of high or low temperature tolerance were not well correlated with tidal elevation for any groups of algae studied. However, cold-tolerant species had more northerly extensions, and warm-tolerant species had more southerly distributions. Thus, differential tolerance to temperature extremes may be an important influence for latitudinal ranges of species.By comparing the experimentally determined thresholds of stress with distributions of species, we test the role of stress in influencing photosynthesis and ultimately distributions of marine algae.     

Grazing effects in macroalgal communities depend on timing of patch colonization

Rocky macroalgal assemblages are typically composed of patches differing in age and species composition and grazing is generally a very important modifier of such assemblages. We hypothesized that patch colonization time determines its algal community and that grazing effects depend on the colonization time and vary with depth. We created patches by placing empty substrates at two sublittoral depths over five consecutive months, manipulated grazer entry and determined the algal species composition in each patch in the next growing season. Distinct algal colonization periods resulted in different algal assemblages. Although algal communities in our study area consist mainly of opportunistic species, thus being highly dynamic, the resulting macroalgal assemblages differed in species richness, diversity, composition, and total biomass even a year after first colonization. Substrates close to the water-surface supported a higher species richness and diversity than those in the deeper littoral. The community characteristics, total density, total biomass and species richness were only slightly, if at all affected by grazing. However, individual algal species or taxa showed varying and even contrasting responses to grazing, often differently between depths and depending on colonization time. In the deeper littoral, but not close to the water surface, grazing increased the density of filamentous brown algae while reducing the green alga Cladophora glomerata. In these taxa, grazing effects were strongest in patches colonized during the early growing season. Grazing at the colonization stage had lasting consequences for the density of several individual species.