Spatial pattern of intertidal macroalgal assemblages associated with tidal levels

The zonation pattern of macroalgal assemblages was investigated from December 1995 to October 1996 on a semi-exposed, rocky intertidal shore at Chungdori (southwestern Korea) based on quantitative and qualitative estimates of species occurrences in 31 permanent quadrats. Variation in cover associated with tidal levels was described for 30 species (that could be discerned with the unaided eyes) including three green, five brown and 22 red algae. Macroalgae inhabiting intertidal zone exhibited distinct zonation patterns. The number of species increased with decreasing intertidal height and was independent of season. The community was dominated by five species (Gloiopeltis furcata, Gelidium divaricatum, Ulva pertusa, Sargassum horneri, Hizikia fusiformis). The intertidal assemblage at the study site can be divided into two groups based on the number of species and the population structure with the division occurring at the critical level of 34 cm above MLW (mean low water). Gloiopeltis furcata, Gelidium divaricatum, Sargassum thunbergii, Monostroma grevillei, and Myelophycus simplex were more abundant in the upper shore zone and rapidly declined in abundance with depth, relative to all other species. Gelidium amansii, Pachymeniopsis elliptica, Hizikia fusiformis, Gigartina intermedia, Laurencia sp., Chondrus ocellatus, Corallina spp. and Gigartina tenella became more dominant in the lower shore zone.     

Spatial analyses of intertidal assemblages on sheltered rocky shores

Abstract Understanding processes in complex assemblages depends on good understanding of spatial and temporal patterns of structure at various spatial scales. There has been little quantitative information about spatial patterns and natural temporal changes in intertidal assemblages on sheltered rocky shores in temperate Australia. Natural changes and responses to anthropogenic disturbances in these habitats cannot be accurately measured and assessed without quantitative data on patterns of natural variability in space and through time. This paper describes some suitable quantitative methods for examining spatial and temporal patterns of diversity and abundances of highshore, midshore and lowshore intertidal assemblages and the important component species for a number of shores in a bay that has not been severely altered by human disturbance. Despite a diverse flora and fauna on these shores, the midshore and lowshore assemblages on sheltered shores were characterized by a few species which were also the most important in discriminating among assemblages on a shore and, for each assemblage, among different shores. The same set of species was also important for measuring small-scale patchiness within each assemblage (i.e. between replicate sites on a shore). Therefore, these data provide a rationale for selecting species that are useful for measuring differences and changes in abundance among places and times at different scales and, hence, can be used in the more complex sampling designs necessary to detect environmental impacts. There was considerable spatial variability in all assemblages and all species (or taxa) examined at scales of metres, tens of metres and kilometres. There were no clear seasonal trends for most measures, with as much or more variability at intervals of 3 months as from year to year. Most interactions between spatial and temporal measures were at the smallest scale, with different sites on the same shore generally showing different changes from time to time. The cause(s) of this apparently idiosyncratic variability1 were not examined, but some potential causes are discussed. These data are appropriate for testing hypotheses about the applicability of these findings to other relatively undisturbed sheltered shores, about effects of different anthropogenic disturbances on sheltered intertidal assemblages and to test hypotheses about differences in intertidal assemblages on sheltered versus wave-exposed shores.     

The influence of coastal upwelling on the functional structure of rocky intertidal communities

Summary Relationships between organisms at all trophic levels are influenced by the primary productivity of the ecosystem, and factors which enhance rates of primary production may modify trophic relationships and community structure. Nutrient enrichment of intertidal and nearshore waters leads to enhanced production by intertidal algae, and it was hypothesized that where rocky shores are washed by nutrient-rich upwelled waters, the intertidal communities should show a characteristic functional structure, based on the effects of enhanced primary production. Study sites were chosen on rocky shores in southern Africa, central Chile and the Canary Islands, in areas with and without coastal upwelling, and mid-shore community structure at these sites was analysed in terms of the abundance of certain functional guilds of organisms.It was found that algal cover and the biomass of herbivorous limpets supported per unit area on rocky shores were significantly greater in regions of coastal upwelling than in regions where upwelling did not occur. Ground cover by sessile filter-feeding organisms was significantly greater on shores in non-upwelled areas. However, correspondence analysis showed no functional aspect of intertidal community structure that was characteristic of coasts washed by upwelled waters. Primary reasons for this are probably the large variations in the nature of nutrient enrichment that accompanies upwelling, and in the nutrient status of non-upwelled areas. Other factors are man's exploitation of intertidal organisms and differences in the genetic origins of the intertidal species involved.     

Littoral communities and zonation on rocky shores in the Bay of Fundy, Canada: an area of high tidal range

The Bay of Fundy, on the east coast of Canada, has a maximum tidal range slightly higher than that of the Bristol Channel and similar environmental conditions, but a more extreme climate. However, the littoral community, despite the common presence of many species, differs greatly. Fundy shores show universal domination by Ascopkyllum nodosum under all exposure conditions and its biomass is very high. Funis vesiculosus is common but its distribution is unrelated to exposure. Fucoid algae normally cover all but a few percent of the midlittoral. As a consequence of this intertidal primary primary productivity is very high and a protected sub-canopy environment very extensive. The standard littoral zones do show a typical pattern but respond only slightly to exposure. Many typical and important species show constant zonation under alt exposure conditions. Typical of this group are A. nodosum and the other fucoid algae. Although the high tidal range does reduce the effect of wave action, this factor alone does not explain the results since they are not repeated in the Bristol Channel. Differences in the suite of herbivores, particularly the absence of Patella species in Fundy, is considered to be an equally important causative factor. Also significant is the modifying effect of the heavy algal canopy itself. Clearance experiments have shown that dominance by A. nodosum is not restored within 10 years and that herbivory, especially by littorinids and limpets, does play a critical role in succession.     

Quantification of radular marks as a method for estimating grazing of intertidal gastropods on rocky shores

Wax discs have been used previously on intertidal rocky shores to record the grazing activity of gastropods. This study has evaluated this methodology for recording grazing of four common intertidal microalgal grazers on intertidal shores in New South Wales, Australia. In the laboratory, the four species examined-the patellid limpet, Cellana tramoserica (Sowerby), the trochid, Austrocochlea porcata (A. Adams), the neritid, Nerita atramentosa Reeve and the littorinid, Bembicium nanum (Lamarck)-made distinctive marks in the wax. These allowed identification of each species or combinations of species grazing over the different discs. Field experiments showed that the intensity of grazing, as indicated by the mean number of scratches per disc, was positively related to the number of gastropods in the surrounding area during low tide for C. tramoserica. The number of scratches per disc in any area was correlated with the percentage of discs scratched. The relationship for C. tramoserica was found at two scales-in sites (approximately 3x3 m) and also in plots (50x50 cm) within sites. Therefore, densities that were measured when these limpets were inactive during low tide provided good estimates of grazing activity during high tide. This is largely because these limpets do not move far between where they rest and where they feed. The amount of microalgal food in the vicinity was not correlated with density, nor with grazing intensity. No relationship between density and grazing intensity was found for N. atramentosa, although experiments were only done in the field at one spatial scale (in sites, 3x3 m). Results obtained in the laboratory and in the field show that wax discs are useful to distinguish grazing by different species of gastropods on Australian rocky shores and allow tests of hypotheses about grazing activity at different spatial scales.     

Self-similar properties of the spatial structure of intertidal macro- and microbenthic communities

Spatial distribution (SD) of White Sea intertidal soft-bottom communities was studied at scales from decimetres to dozens of kilometres on the basis of an extensive dataset (464 samples of macrofauna, 349 samples of ciliates, and 333 samples of diatoms). We used the information index of structural heterogeneity D(I) (Azovsky et al., 2000 // Mar. Biol. 136 (3): 581-590) to characterize spatial variability in the species composition of the communities at different extent (total area surveyed) and grain (finest spatial resolution). The type of distribution was determined via the relation between D(I) and parameters of the spatial scale (extent and grain). At small scale (in terms of extent), all the communities were distributed randomly (mosaic SD). At larger scales, the estimated spatial variability depended neither on extent nor grain, exclusively on their ratio, i.e., was scale-invariant. This means that at some scale the spatial patterns of communities display self-similar properties (fractal SD). Such SD was found at a rather wide range of scales scales: 10(1)-10(4) m for the macrofauna, 10(0)-10(3) m for the ciliates, and 10(-1)-10(2) m for the diatoms. At still greater scales, patchy or gradient patters were observed. Thus, the ranges of fractal distribution were proportional to the average size of the organisms (approximately 10(4)-10(7) times the body size). We suppose that such spatial pattern reflects community self-organization in a relatively homogeneous environment and may be the most efficient way to realize the highest structural diversity on the basis of pre-formed complexes of predominant species. We also suppose that fractal-like patterns may be a general feature of the spatial organization of communities.     

Composition dynamics of epilithic intertidal bacterial communities exposed to high copper levels

Copper has a dual role for organisms, both as micronutrient and toxic element. Copper mining activities have an enormous ecological impact because of the extraction process and the consequent release of copper-containing waste materials to the environment. In northern Chile, mainly in the Cha?aral coastal area, this phenomenon is clearly evident. The released waste material has caused a strong modification of the area, and copper enrichment of beaches and rocky shores has provoked a decrease in the richness and diversity of many species of macroorganisms. However, the effects that copper enrichment has on microbial (e.g. bacterial epilithic) communities associated with the rocky shore environment are poorly understood. Using a culture-independent molecular approach, field sampling and laboratory microcosm experiments, we determined the effects of copper enrichment on bacterial communities inhabiting the rocky shore environment. Field samples showed a strong effect of copper on the structure of the natural bacterial epilithic communities, and microcosm experiments demonstrated rapid changes in bacterial community when copper is added, and reversibility of this effect within 48?h after copper is removed.     

The structure and replenishment of rocky shore intertidal communities and biogeographic comparisons

Marine scientists have made many recent advances in understanding the connections between the structure of benthic communities, replenishment of populations through dispersal processes, and interactions with the nearshore water mass. In this review, some of the themes and models relating to these processes and interactions are discussed. Benthic–pelagic coupling models are in the early stages of development, but encompass oceanic processes such as upwelling and downwelling, the transport of larvae and their arrival back to shore to settle. Most current knowledge of these processes is based on a few taxa, especially barnacles and mussels. This is discussed with reference and comparison to macroalgae, which dominate much of the intertidal zone on temperate rocky shores, and have quite different life histories, transport and settlement processes. The role of key, habitat-dominating species is discussed, particularly their early life histories, with reference to the differences in community composition, nearshore dynamics and settlement processes in different countries. Finally, some suggestions are made for future work to fill gaps in understanding about rocky shore communities.     

Impacts of anthropogenic stress on rocky intertidal communities

Rocky shores provide a harsh environment for marine organisms andwe briefly discuss natural sources of variation in community structure beforeconsidering anthropogenic impacts in detail. We review impacts caused by (a) acutedisturbances: oil spills, toxic algal blooms and (b) chronic disturbances: nutrient pollution,oil, heavy metals, pesticides, antifouling paints, collecting, trampling/habitatdegradation, siltation and introduced species. Community level effects are emphasisedthroughout and illustrative examples are drawn from field-based case studies. Particularattention is given to the lessons learned from oil spills and the effect of chronicpollution by tributyltin on dogwhelks, the impacts of which ranged from the biochemical tocommunity levels of organisation. Impacts are placed in a global and historicalperspective and the potential for the recovery of shores under appropriate management isdiscussed. Finally we consider the relative merits of the multivariate and univariateapproaches to studying impacted communities and suggest priorities for future research.     

Host densities as determinants of abundance in parasite communities

Several epidemiological models predict a positive relationship between host population density and abundance of directly transmitted macroparasites. Here, we generalize these, and test the prediction by a comparative study. We used data on communities of gastrointestinal strongylid nematodes from 19 mammalian species, representing examination of 6670 individual hosts. We studied both the average abundance of all strongylid nematodes within a host species, and the two components of abundance, prevalence and intensity. The effects of host body weight, diet, fecundity and age at maturity and parasite body size were controlled for directly, and the phylogenetically independent contrast method was used to control for confounding factors more generally. Host population density and average parasite abundance were strongly positively correlated within mammalian taxa, and across all species when the effects of host body weight were controlled for. Controlling for other variables did not change this. Even when looking at single parasite species occurring in several host species, abundance was highest in the host species with the highest population density. Prevalence and intensity showed similar patterns. These patterns provide the first macroecological evidence consistent with the prediction that transmission rates depend on host population density in natural parasite communities.     

Using patterns of variability to test for multiple community states on rocky intertidal shores

Predictions based on theory of multiple stable states suggest that larger perturbations should lead to more unpredictable patterns of succession. This prediction was tested in the Gulf of Maine using data from 60 intertidal plots of varying size that were experimentally cleared of the rockweed Ascophyllum nodosum and from 14 benchmark sites from throughout the Gulf. Rockweed was removed from the experimental clearings ranging from 1 to 8 m in diameter in 1996 and data collected in 2004 were used to test effects of clearing size and location on divergence and variability in species composition. Benchmark data were collected in 2005, and the 14 sites were from a dataset on 53 sites throughout the Gulf of Maine. The selected sites were randomly chosen from all sites with > 80% canopy cover by A. nodosum and were expected to be similar to uncleared control plots from the experiment. Experimental removal of A. nodosum resulted in clearings at 12 sites within 4 bays. Abundances of gastropods, barnacles, mussels, and fucoid algae and the percentage cover of barnacles, mussels, fucoid algae, bare space, and other species were sampled. CAP and PERMDISP analyses revealed significant differences in multivariate dispersion and variability with both clearing size and location. Variability generally increased with clearing size and location effects were related to the north-south positioning of the sites. Benchmark sites were similar to the experimental control plots but as variable as the largest clearings. Results suggest that succession in larger clearings has been more unpredictable than in small clearings. The pattern of variability in the experimental clearings is consistent with the predictions of multiple stable states. However, the large amount of variation among the benchmark sites was due to mussels and was unexpected. This unexpected variability underscores the importance of sampling benchmark sites as part of experiments.     

Characterization of microbial community structure and population dynamics of tetrachloroethene-dechlorinating tidal mudflat communities

Tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants that also impact tidal flats, especially near urban and industrial areas. However, very little is known about dechlorinating microbial communities in tidal flats. Titanium pyrosequencing, 16S rRNA gene clone libraries, and dechlorinator-targeted quantitative real-time PCR (qPCR) characterized reductive dechlorinating activities and populations in tidal flat sediments collected from South Korea’s central west coast near Kangwha. In microcosms established with surface sediments, PCE dechlorination to TCE began within 10 days and 100% of the initial amount of PCE was converted to TCE after 37 days. cis-1,2-Dichloroethene (cis-DCE) was observed as dechlorination end product in microcosms containing sediments collected from deeper zones (i.e., 35–40 cm below ground surface). Pyrosequencing of bacterial 16S rRNA genes and 16S rRNA gene-targeted qPCR results revealed Desulfuromonas michiganensis-like populations predominanted in both TCE and cis-DCE producing microcosms. Other abundant groups included Desulfuromonas thiophila and Pelobacter acidigallici-like populations in the surface sediment microcosms, and Desulfovibrio dechloracetivorans and Fusibacter paucivorans-like populations in the deeper sediment microcosms. Dehalococcoides spp. populations were not detected in these sediments before and after incubation with PCE. The results suggest that tidal flats harbor novel, salt-tolerant dechlorinating populations and that titanium pyrosequencing provides more detailed insight into community structure dynamics of the dechlorinating microcosms than conventional 16S rRNA gene sequencing or fingerprinting methods.     

Assessment of a trap for measuring larval supply of intertidal barnacles on wave-swept, semi-exposed shores

Larval supply and settlement of Semibalanus balanoides (L.) on a semi-exposed wave-swept shore in E Scotland were assessed by means of a new larval trap design. Two midshore sites were utilised throughout the peak of the 2001 settlement season (May 11–June 3). Larval supply was quantified by 176 ml baffled cylinder traps filled with a 4-M killing solution of urea in seawater. Larval trap washout of urea typically ranged from 25% per day under minimal wave action to a maximum of 39% under heavy wave action during an onshore gale. The maximum capture for a single trap was 334 cyprids over one tide. Significant and consistent positional effects, both on urea retention and larval capture, were found for replicate traps separated by 9 cm. These indicated fine-scale variations in hydrodynamic flow and larval supply over the substratum which will have implications for the quantification of spatial heterogeneity of larval input to the benthos. The retention of urea and larval capture efficiency generally were not compromised by traps being serviced daily, as opposed to tidally, except perhaps for captures at very low larval densities. Larval supply measured on a tidal basis was strongly correlated between sites (r=0.975), but supply at Site C was 5× that at Site T: the reduction at Site T could not be explained by its slightly shorter immersion time and hence ‘availability’ of cyprids alone. At Site C settlement was quantified for 5×5 cm quadrats of natural substratum cleared daily. Settlement on these clearances (subject to possible grazing by limpets) was quantified only from May 20–June 3, after the peak of larval supply on May 17, and the variation in larval supply explained 65% of the variance in settlement. The larval supply/settlement relationship at Site T was quantified using grooved acrylic panels. A high correlation coefficient (0.961) was obtained for the daily supply/settlement relationship for these panels over the period May 15–June 3, which included the peak of supply. Larval supply varied up to 15-fold within a site on consecutive tides and up to 100-fold between sites on the same tide. Although further improvements to both the larval trap and the settlement panels can be made, this larval trap does appear capable of providing high-resolution data on tidal or daily larval supply over a wide range of wave conditions and larval concentrations.     

Estuarine intertidal meiofauna and nematode communities as indicator of ecosystem's recovery following mitigation measures

The Mondego estuary (Portugal) has been under environmental pressure since the early 1990s due to different anthropogenic stresses. The system has been studied following benthic communities’ features from an impacted situation until the recovery phase, focusing mostly on macrobenthos. Following the application of mitigation measures in the estuary, this study is focused on the variability of the intertidal meiobenthic and nematode communities in a system that has recovered after different anthropogenic stresses. While at the spatial level (among areas along the eutrophication gradient) no significant differences were observed regarding the structure and function of the nematode communities, at the seasonal level some differences stood out. These results broadly suggest that the system has recovered from the early situations of pressures being, to the best of our knowledge, the first attempt to investigate the variability of intertidal meiobenthic and nematode communities in the scope of a system's recovery along an estuarine gradient of eutrophication. Even if performed in a short timeline, this study provides a good baseline analysis of conditions, being important for future comparisons.     

Impact of fiddler crab foraging and tidal inundation on an intertidal sandflat: season-dependent effects in one tidal cycle

Intertidal sandflats inhabited by fiddler crabs are ideal systems in which to study the effects of physical and biological processes. This study addressed two questions: (1) Do fiddler crab feeding and tidal inundation have measurable effects on the sandflat over one tidal cycle? (2) Does the sandflat change over the course of a year? In field exclusion/inclusion experiments, fiddler crabs reduced sediment organic content by 40%, Chlorophyll a levels by 20% and meiofaunal density by 60% in one tidal cycle. Effects were most pronounced in the spring when organic content and meiofaunal densities were maximal. Effects of foraging were not erased by the tide and accumulated over time. The sandflat had highest levels of all variables in spring and minimal levels during summer and fall. Crabs graze the sandflat to minimum levels in the spring. Due to crab foraging, the flat is barren during the summer and fall, and recovers during the winter when crabs are minimally active.     

Some determinants of population variation in cortisol levels in a British urban community.

Urinary cortisol excretion rates were determined from three urine samples given over 2 days, a rest day and a working day, by 51 men and 50 women. Each subject also completed a questionnaire relating to life style factors and to perceived levels of stress, busyness and happiness on each day. In men, an association between raised cortisol and high levels of stress was found. In women, high levels of busyness were associated with low cortisol excretion rates. The subjective experiences measured accounted for around 10-20% of cortisol variation in this naturalistic setting.     

Tidal reduction and its effects on intertidal hard-substrate communities in the Oosterschelde estuary

Developments of intertidal hard-substrate communities in the Oosterschelde estuary were examined in perpendicular transects between high-water line and low-water line in the period 1982–1992. Prior to the beginning of the Oosterschelde estuary works a typology of communities was established and an overall survey of the estuary was carried out. The communities contain flora (algae) as well as fauna. Due to asphalting of dikes in 1986, much of the surface of several communities has been destroyed. The originally well developed communities with large species-richness have not returned. The small reduction in tidal amplitude due to the construction of the storm-surge barrier had a minor effect on the zonation of communities. In the upper part of the intertidal zone the boundaries of the communities moved 0.5–1.0 m downward in the transects along the dike-slopes. At an average inclination of 18° this means a vertical shift of about 15–30 cm. This reflects the reduction of the tidal amplitude: the high-water line shifted ca 22 cm downward. In a number of places sedimentation has caused a reduction in the number of smaller seaweed species in the lower eulittoral zone. At monitoring locations presence of the original communities is rather unchanged. Rare species like Pelvetia canaliculata, Actinia equina and Gelidium pusillum have been able to maintain quite successfully.