Intertidal Assemblages Research Articles

Variation in mussel and barnacle recruitment parallels a shift in intertidal community structure in the Cook Strait region of New Zealand

Recruitment influences populations and communities of marine organisms to varying degrees and across a range of spatial scales. We hypothesised that recruitment plays a role in maintaining different intertidal invertebrate assemblages between two nearby locations in New Zealand (Wellington Harbour and the south coast), long reported to have dramatically different communities (with greater cover of sessile invertebrates in the Harbour). Sites in Wellington Harbour were hypothesised to have higher monthly recruitment rates of mussels and barnacles and greater barnacle colonisation after 1 year. Surveys were conducted to quantify community differences. In Wellington Harbour, the mid-intertidal zone was dominated by the mussel Mytilus galloprovincialis and the barnacle Chamaesipho columna and the high intertidal zone by C. columna. In contrast, on the south coast mussels were almost completely absent from both tidal heights and barnacles (predominantly Chamaesipho brunnea) were sparse. In the high zone, monthly recruitment and long term colonisation (over 1 year) of barnacles was much greater in the Harbour; in the mid-intertidal zone, mussel recruitment was up to two orders of magnitude greater in the Harbour than the south coast. Species-specific recruitment patterns differed between the locations, however and were consistent with those of adult abundance.

Patterns of spatial variation of assemblages associated with intertidal rocky shores: a global perspective.

Assemblages associated with intertidal rocky shores were examined for large scale distribution patterns with specific emphasis on identifying latitudinal trends of species richness and taxonomic distinctiveness. Seventy-two sites distributed around the globe were evaluated following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). There were no clear patterns of standardized estimators of species richness along latitudinal gradients or among Large Marine Ecosystems (LMEs); however, a strong latitudinal gradient in taxonomic composition (i.e., proportion of different taxonomic groups in a given sample) was observed. Environmental variables related to natural influences were strongly related to the distribution patterns of the assemblages on the LME scale, particularly photoperiod, sea surface temperature (SST) and rainfall. In contrast, no environmental variables directly associated with human influences (with the exception of the inorganic pollution index) were related to assemblage patterns among LMEs. Correlations of the natural assemblages with either latitudinal gradients or environmental variables were equally strong suggesting that neither neutral models nor models based solely on environmental variables sufficiently explain spatial variation of these assemblages at a global scale. Despite the data shortcomings in this study (e.g., unbalanced sample distribution), we show the importance of generating biological global databases for the use in large-scale diversity comparisons of rocky intertidal assemblages to stimulate continued sampling and analyses.

Spatial and temporal variation in relative numbers of grapsid crabs (Decapoda: Grapsidae) in northern Australian mangrove forests

Crabs belonging to the family Grapsidae are possibly one of the most important components of the fauna of mangrove forests globally, in part because of their influence in nutrient cycling by feeding on litterfall. This study investigated spatial and temporal patterns in relative numbers of 11 grapsid species in northern Australian mangrove forests. The results indicated that Perisesarma spp., Neosarmatium meinerti and an undescribed species of Episesarma were most abundant, followed by Clistocoeloma merguiensis, Ilyograpsus paludicola, Sesarmoides borneensis, Metopograpsus frontalis and Sarmatium spp. Mangrove assemblage was the most important spatial factor affecting the distribution and abundance of these species. Perisesarma sp. was most abundant in mid- and low-intertidal assemblages, whereas N. m einerti and Episesarma sp. were largely limited to high intertidal assemblages. In many cases, crab species occurrence and abundance were specific to certain assemblages, areas, aspects, and times during the two-year study period, which probably reflects the specificity of species to particular environmental conditions.

Large-Scale Spatial Distribution Patterns of Echinoderms in Nearshore Rocky Habitats

This study examined echinoderm assemblages from nearshore rocky habitats for large-scale distribution patterns with specific emphasis on identifying latitudinal trends and large regional hotspots. Echinoderms were sampled from 76 globally-distributed sites within 12 ecoregions, following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). Sample-based species richness was overall low (<1–5 species per site), with a total of 32 asteroid, 18 echinoid, 21 ophiuroid, and 15 holothuroid species. Abundance and species richness in intertidal assemblages sampled with visual methods (organisms >2 cm in 1 m2 quadrats) was highest in the Caribbean ecoregions and echinoids dominated these assemblages with an average of 5 ind m−2. In contrast, intertidal echinoderm assemblages collected from clearings of 0.0625 m2 quadrats had the highest abundance and richness in the Northeast Pacific ecoregions where asteroids and holothurians dominated with an average of 14 ind 0.0625 m−2. Distinct latitudinal trends existed for abundance and richness in intertidal assemblages with declines from peaks at high northern latitudes. No latitudinal trends were found for subtidal echinoderm assemblages with either sampling technique. Latitudinal gradients appear to be superseded by regional diversity hotspots. In these hotspots echinoderm assemblages may be driven by local and regional processes, such as overall productivity and evolutionary history. We also tested a set of 14 environmental variables (six natural and eight anthropogenic) as potential drivers of echinoderm assemblages by ecoregions. The natural variables of salinity, sea-surface temperature, chlorophyll a, and primary productivity were strongly correlated with echinoderm assemblages; the anthropogenic variables of inorganic pollution and nutrient contamination also contributed to correlations. Our results indicate that nearshore echinoderm assemblages appear to be shaped by a network of environmental and ecological processes, and by the differing responses of various echinoderm taxa, making generalizations about the patterns of nearshore rocky habitat echinoderm assemblages difficult.

Latitudinal and environmental patterns in abundance and composition of epilithic microphytobenthos

Epilithic microphytobenthos (EMPB) is of core importance in intertidal assemblages and responds to a variety of environmental variables, including season, light, temperature and exposure to waves. To help understand responses by EMPB to these variables and their interactions, EMPB was compared at 2 different latitudes in eastern Australia. In subtropical Brisbane and temperate Sydney, EMPB was sampled at 4 different heights on shores exposed to, or sheltered from, waves during the austral winters and summers of 2006 to 2008. Trends of increasing biomass with decreasing height on shore supported previous studies. In particular, the interaction between season and height was similar to results of previous studies in Australia. There were no differences in biomass of standing stock between Sydney and Brisbane. Differences in timing of sampling occasions confounded some comparisons, and some observed patterns may be due to differences in rates of recolonisation among treatments. Spectrometric assessment of the composition of pigments in EMPB differed with latitude. Spectral samples were more similar to those from assemblages of cyanobacteria than to assemblages of green algae, and this was more marked in Sydney than in Brisbane. Amounts of chlorophyll a were greater on sheltered shores than on those exposed to waves. These patterns are not easily explained, but serve to illustrate the difficulties of extrapolating patterns and processes from one area to another. Variations in pattern at different heights on the shore and in different years emphasise the need for spatially and temporally extensive data in order to make reliable predictions about EMPB. Improved capacity to make reliable predictions will help us understand how EMPB may respond to our changing climate, which is forecast to be hotter with more frequent storms. © Inter-Research 2010.

Limpets as prey: Lipophrys pholis choice for size

Patellid limpets are key species on rocky shores, structuring intertidal assemblages through their grazing. Their role as prey for fish is, however, often overlooked in studies of intertidal ecosystem functioning. The shanny Lipophrys pholis is a common predator of limpets on rocky shores in Northern Europe and, in this study, we examined the characteristics of its predation on limpets based on prey size. The limpet size range that adult L. pholis (10–12.5 cm) can eat was examined in the laboratory using Patella depressa in 0.2 cm classes, varying between 0.5 cm and 3.0 cm in maximum shell length. There was a limpet size refuge above 1.8 cm, while all smaller sizes were readily consumed by the shanny. The predator attacking behaviour was also examined and found to vary with prey size. Limpets up to 0.8 cm were crushed by the jaw-constricting force and eaten whole, whereas larger prey were prised from the substratum and the body subsequently separated from the shell. To examine whether there was a L. pholis preference for P. depressa size, a two-stage laboratory experiment was done using two size classes defined as small (0.7–0.8 cm maximum shell length) and large (1.5–1.6 cm maximum shell length). In the first stage, the predator was given each limpet size class separately. In the second stage, the fish was given a choice between the two classes. Lipophrys pholis was shown to have a preference for the large size class (1.5–1.6 cm). The average number of limpets consumed by the shanny was examined for the duration of one high-tide typical of the central region of Portugal (≈ 4 h). On average, approximately five limpets (up to an eight limpet maximum) were consumed. The present study shows that L. pholis has a feeding preference based on limpet size, which suggests that the limpet population structure and intra- and inter-specific interactions may be influenced by the shanny predation.

Canopy-forming species mediate the effects of disturbance on macroalgal assemblages on Portuguese rocky shores

Understanding the relationship between biodiversity and stability is a central issue in ecology. This is particularly needed under current scenarios of biodiversity loss due to multiple anthropogenic stressors. In this study, we experimentally examined the combined effects of the loss of key functional species (canopy-forming macroalgae) and mechanical disturbance on macroalgal intertidal assemblages at 2 sites along the rocky coast of northern Portugal. We tested the model that the canopy may buffer the effects of disturbance on associated organisms, leading to the logical hypothesis that effects of mechanical disturbance would be lower where the canopy was left intact compared to patches where it was experimentally removed. The proposed model was supported by multivariate and univariate results, as both differences in the structure of whole assemblages and in the abundance of individual taxa between disturbed and undisturbed assemblages were reduced or prevented by the presence of the canopy, independently of the examined site. Specifically, only in the absence of the canopy did disturbance determine a decrease in the abundance of the red alga Ahn- feltiopsis devoniensis and an increase in articulated coralline algae of the genus Corallina. Present findings have relevant implications for understanding and predicting the consequences of multiple factors responsible for the erosion of biodiversity occurring globally in coastal areas, as current rates of loss of canopy-forming species in urban areas may be expected to exacerbate the effects of predicted climate change, including modifications in intensity and temporal patterns of storms.

Colonization and/or mitochondrial selective sweeps across the North Atlantic intertidal assemblage revealed by multi-taxa approximate Bayesian computation

Intertidal and subtidal communities of the western and eastern coasts of the North Atlantic Ocean were greatly affected by Pleistocene glaciations, with some taxa persisting on both coasts, and others recolonizing after being extirpated on one coast during the Last Glacial Maximum. In the original spirit of comparative phylogeography, we conducted a comparative analysis using mtDNA sequence data and a hierarchical approximate Bayesian computation (ABC) approach for testing these two scenarios across 12 intertidal and subtidal coastal invertebrates spanning the North Atlantic to determine the temporal dynamics of species membership of these two ephemeral communities. Conditioning on a low gene-flow model, our results suggested that a colonization or mitochondrial selective sweep history was predominant across all taxa, with only the bivalve mollusc Mytilus edulis showing a history of trans-Atlantic persistence. Conditioning on a high gene-flow model weakened the support for this assemblage-level demographic history. The predominance of a colonization-type history also highlights concerns about analyses based on single-locus data where genetic hitchhiking may be incorrectly inferred as colonization. In conclusion, driving factors in shifting species range distributions and membership of ephemeral coastal communities could be species-specific environmental tolerances, species interactions, and/or stochastic demographic extinction. Through a re-examination of a long-standing question of North Atlantic phylogeography, we highlight the flexibility and statistical honesty of using a model-based ABC approach.

Different levels of macroalgal sampling resolution for pollution assessment

The effects of using reduced sampling resolutions to study macroalgal vegetation patterns have not been studied sufficiently. Here, we test the influence of taxonomic resolution level, removal of occasional species, aggregation of species abundances into functional groups and data transformation in the detection of a long-term recovery process by phytobenthic intertidal assemblages. Results indicate that the aggregation of species data into the genus level has very little influence. Likewise, almost any significant information is lost when occasional algae are removed. Analyses at the level of families and orders still clearly detect differences between highly degraded and reference vegetation. By contrast, analyses based on class and functional group abundances capture quite different information. The effect of transformation is similar at the different taxonomic levels. Most surrogate measures properly reflect changes in diversity. It is concluded that genus level is the most appropriate surrogate approach for detecting the recovery process.

Eocene Mollusca from the Tainohata Formation in Kôbe City, Southwest Japan

Abstract. The Tertiary Tainohata Formation of the Kobe Group has yielded 10 species of Gastropoda and 19 species of Bivalvia. The formation is of late Middle Eocene age on the basis of the dinoflagellate cyst assemblage and radiometric data. The occurrences of the genera Trinacria, Vicarya, and Sulcobuccinum strongly support an Eocene age for the Tainohata Formation. The molluscan fauna shows high endemism at the species level, whereas it is characterized by Tethyan—Indo-West Pacific genera. Two indigenous molluscan assemblages, Potamides-Cyclina and Corbicula, were discriminated. The composition of these assemblages compares with those of the Neogene intertidal assemblages in embayments. This fact indicates that “temporal parallelism” in the shallow embayment assemblages can be traced back to the late Middle Eocene age in the Japanese Islands. The following 10 new species are proposed herein: Potamides huzitai sp. nov., Cerithideopsilla hondai sp. nov., Crepidula tainohataensis sp. nov., Cantharus (s.l.)...

Composition and distribution of subtidal and intertidal crustacean assemblages in soft-bottoms of the Ria de Vigo (NW Spain)

The intertidal and subtidal soft-bottoms of the inner area of the Ria de Vigo (NW Spain) were sampled in November and December 1999, and spatial distribution of crustacean species was examined. Environmental variables from water and sediment were measured at each sampling site. Amphipods and myocopids were the numerically dominant orders (49.9 and 26.9% dominance), amphipods accounting for more than 54% of identified taxa. The highest crustacean densities occurred with 55-41 species and 5953.6-4346.4 ind. m –2 in external areas, where the diversity index reached the maximum values. Multivariate techniques revealed that distribution of crustaceans in the inlet was highly dependent on depth. Ordination analysis determined three major assemblages: Intertidal bottoms colonized by seagrasses and subjected to strong variations of salinity were dominated by the amphipod Melita palmata , harpacticoids and the isopod Idotea baltica (Group A). The amphipod Corophium cf. runcicorne and the cumacean Iphinoe tenella predominated in the muddy bottoms of central areas (Group B). These species were also present in the deep muddy bottoms of the mouth of the inlet, with high carbonate and gravel contents, and with the myocopids and the amphipod Microdeutopus cf. armatus displaying maximum dominances (Group C).

Parasite-like associations in rocky intertidal assemblages: implications for escalated gastropod defenses

Escalated prey defenses occur within multi-species assemblages but are largely evalu- ated by considering only direct interactions between predator and prey. If additional species compro- mise prey defenses, they might indirectly facilitate predation. Since the introduction of green crabs Carcinus maenas in the northwest Atlantic, many intertidal mollusks including the dogwhelk Nucella lapillus have acquired shell traits that have been interpreted as escalated defenses against this shell- crushing predator. I examined whether 'parasite-like' spionid polychaetes (Polydora sp.), which bore into and reside in dogwhelk shells but feed externally, indirectly facilitated predation by crabs. Small collections of dogwhelks from 19 sites around the Gulf of Maine (USA) revealed Polydora infestations at 16 sites. Intensive collections at 1 site showed that Polydora disproportionately infested large dog- whelks that are normally most resistant to predation. Presenting paired non-infested and fully- infested (Polydora bore holes in shell spire and siphonal canal) dogwhelks to individual crabs re- vealed that fully-infested individuals had significantly shorter times until first observed handling and shorter survival durations. In trials where single dogwhelks survived, they were always non-infested and their shell size scaled positively with crab size. These results suggest that Polydora increased both the size-specific susceptibility of dogwhelks to predation and the critical size of snails vulnera- ble to a given sized crab. Although Polydora altered this predator-prey interaction, mechanical tests showed no significant effect of Polydora on shell strength, so mechanical tests alone are not a reliable way to evaluate defensive traits. Since prey defenses can be modified by additional species, evalua- tions of changing shell defenses must consider both direct and indirect interactions.

Field-based remote sensing of intertidal epilithic chlorophyll: Techniques using specialized and conventional digital cameras

Information on the amount of chlorophyll (as an index of micro-algal abundance) on rock surfaces is essential for many reasons, including studies of grazing and its role in structuring intertidal assemblages. Many methods are destructive, error-prone and expensive. Remote sensing allows non-destructive, inexpensive and quantitative measurements to be made of chlorophyll in situ. One specialized and two inexpensive commercially-available digital cameras (Fuji IS1 and Sony DSC-V1) are evaluated for estimating amounts of chlorophyll on rock surfaces. To compare measurements from different images, they are calibrated, using reflectance standards of different brightness. To test the calibration, images of a natural rock platform were acquired under variable solar illumination and camera-exposure times. Analyses before and after calibration showed that the method was effective. A range of quantities of micro-algae was grown on sandstone disks in an aquarium over different intervals of time. Red and NIR reflectance images were obtained from the cores. For each core, the amount of chlorophyll was determined spectrophotometrically and estimated from the images using the Ratio Vegetation Index (RVI) and Normalised Difference Vegetation Index (NDVI). Each of these was linearly related to the measured chlorophyll, with r 2 ranging from 0.78 to 0.9. These techniques can be applied to the study of intertidal and freshwater benthic habitats.

Distribution, diversity, and abundance of rocky intertidal fishes in the Persian Gulf and Gulf of Oman, Iran

Distribution and abundance patterns of rocky intertidal fish assemblages in the Persian Gulf and Gulf of Oman were examined. Specimens were collected at low tide from tide pools, using chlorine as an ichthyocide. A series of collections undertaken between May and July 2006 at 6 stations yielded 1497 fishes, comprising 20 species from 8 families. Permanent tide pool residents (Gobiidae and Blenniidae) comprised 93.5% of the total fish assemblage; secondary residents comprised the remaining 6.5%. The most common fish species were Antennablennius variopunctatus (Blenniidae; 23.4%), Istigobius ornatus (Gobiidae; 19.8%), Bathygobius meggitti (Gobiidae; 18.7%) Cryptocentroides arabicus (Gobiidae; 10.5%), Istiblennius pox (Gobiidae; 7.3%), and Omobranchus fasciolatus (Blenniidae; 6.8%). The results of the present study revealed that, compared to the Gulf of Oman, diversity indices in the Persian Gulf are low. Although Qeshm Island is located in the Persian Gulf, the diversity indices are high at this station most probably due to enhanced contact with the adjacent open ocean, the Gulf of Oman. Hierarchical cluster analysis indicated that the Persian Gulf stations are more similar to each other than to the stations located in the Gulf of Oman.

Parasite communities of a fish assemblage from the intertidal rocky zone of central Chile: similarity and host specificity between temporal and resident fish

The different species of a fish assemblage can, to some extent, be similar in terms of their parasite communities, which can be associated with certain ecological host traits. This study compared the parasite community descriptors between temporal and resident fish species composing an intertidal assemblage from central Chile. Host specificity and similarity indices of parasite communities among the fish species were also considered. A total of 1097 fish representing 14 species were collected during spring and summer of 2 consecutive years. A total spectrum of 40 parasite species was found, of which copepods and trematodes were the commonest. Congeneric fish species had the highest similarities in their parasite communities. Based on a cluster analysis, using only some fish species, no group was distinguished using abundance or prevalence of parasites, because 50% of parasite species had high host specificity and only few of them were shared among fish species. Adult parasites showed high host specificity and were found mainly in resident intertidal fish, whereas the temporal fish had parasites with different degrees of specificity. Consequently, resident intertidal fish were characterized by their own parasite species, meaning that their transmissions might be restricted to the intertidal zone.

Predation: a regulating force of intertidal assemblages on the central Portuguese coast?

Predation has long been recognized as an important biological force driving community patterns in intertidal rocky shores throughout the world. Little is known, however, about the role of predation by mobile marine predators in shaping intertidal prey populations in Portuguese rocky shores. The abundance and population structure of crabs were assessed during nocturnal low-tides on two rocky shores to characterize potential predator species. To assess the effect of predation on intertidal species including limpets, barnacles and mussels, predator exclusion experiments using full cage, partial cage and no cage treatments, were set up for two months on two shores on the central Portuguese coast. Pachygrapsus marmoratus (Fabricius) and Eriphia verrucosa (Forsskål) were the most abundant crabs. Results from predator exclusion experiments suggested that predators do not exert a significant control on abundance of limpets, mussels or barnacles on the midshore during the experimental period. Despite the fact that these crabs are known to feed on the analysed prey, several factors may account for the observed absence of impact on prey abundance and these are discussed.

Effects of disturbance on marginal populations: human trampling on Ascophyllum nodosum assemblages at its southern distribution limit

The negative effects of disturbances on the long-term persistence of populations may be more severe in marginal populations, i.e. those occurring at the boundaries of geographical and eco- logical distribution ranges. Human trampling is an important source of anthropogenic disturbance for intertidal assemblages. Effects of human trampling on intertidal rocky shore assemblages dominated by Ascophyllum nodosum (L.) Le Jol. at its southern distributional limit in Europe were tested exper- imentally. Four different intensities of trampling disturbances were applied to experimental areas, over a period of 5 mo. Percentage cover of A. nodosum and associated organisms was quantified dur- ing the disturbance period and for a recovery period of 1 yr. The 2 highest trampling intensities dras- tically reduced the cover of A. nodosum. Trampling also negatively affected Fucus vesiculosus and understorey species, while indirectly allowing colonisation by ephemeral green algae. One year after the end of disturbance, A. nodosum assemblages in the highest disturbance intensity areas were still significantly different from assemblages in the control and lowest disturbance intensity areas. These results were mainly driven by a switch in the dominant canopy species, from A. nodosum to F. vesicu- losus. Results obtained in this study show that disturbance by human trampling negatively affects A. nodosum assemblages and that the effects are dependent on trampling intensity. These findings highlight the risk of local extinction imposed on these populations by anthropogenic disturbance, and the consequent need for protection measures for such sensitive populations.

Patiriella exigua: grazing by a starfish in an overgrazed intertidal system

Intertidal rocky shores in south-eastern Australia are dominated by a diverse assem- blage of grazing invertebrates that feed on micro-algal biofilms. This resource is spatially variable and frequently over-grazed, causing strong inter- and intra-specific competition among grazers. Most studies on intertidal grazing are about gastropod molluscs. We observed, however, damaged patches in intertidal biofilms that appeared to be associated with the herbivorous asterinid starfish Patiriella exigua (Lamarck). In contrast with predatory starfish, there have been few ecological studies about herbivorous starfish, even though they are often abundant. We demonstrated that these patches were caused by grazing by this starfish. We then used field-based remote-sensing methods to demonstrate that amounts of chlorophyll were reduced inside grazing marks, quantified these changes and measured their longevity. In experiments, starfish could graze up to 60% of the epilithic micro-algae beneath their everted stomach during a single feeding event lasting on average 22 min. Over 5 d, 2 caged starfish could remove nearly half of the available micro-algae from areas of 144 cm 2 . Changes to the amounts of chlorophyll in grazing marks were persistent, remaining visible on sandstone substrata for several weeks. Amounts of chlorophyll on grazed areas of substratum were significantly different from ungrazed areas up to 28 d after being grazed. Recovering areas were demonstrated to be bio-equivalent to ungrazed areas after a similar period. Thus, P. exigua can have a large effect on the temporal and spatial distribution of micro-algal food, with numerous possible consequences for intertidal assemblages. The ecological importance of herbivorous starfish may be greater than previously perceived.

Disturbance of intertidal soft sediment assemblages caused by swinging boat moorings

The impact of swinging boat moorings on intertidal benthic assemblages was investigated in a small estuary on the south coast of England. Mooring buoys fixed near low water mark on a muddy shore were attached to 5 m of galvanised steel chain and had not been let for 12 months. Core samples for macro-invertebrates and sediments were taken both within and outside the chain radius of each buoy. The assemblage structure, biomass and abundance of selected bird prey species were examined at a range of scales. The study revealed variation in the impact of mooring buoys relative to control areas at two different times of sampling. Prior to the removal of buoys, the assemblage structure within areas affected by the buoys was found to be significantly different from unaffected areas. The abundance of the amphipod Corophium volutator, an important bird prey species, was significantly less in the areas affected by the buoys. In the second sampling programme (15 months after removal of buoys), the impact of extant buoys remaining in commission was not detectable. Assemblage structure in areas from which buoys had been removed was distinct from control areas which had never had buoys. The removal of mooring buoys clearly affected the assemblage, yet convergence with control areas, indicative of recovery, was not complete after 15 months. It is suggested that the effect of swinging mooring chains scraping over the mud surface may modify sediments favouring the greater prominence of larger particles such as gravel and shell fragments. The ecological impact of swinging moorings on estuarine benthic assemblages in designated protected areas is discussed in the context of other spatial and temporal disturbances.

Influence of taxonomic resolution and morphological functional groups in multivariate analyses of macroalgal assemblages

B. Konar and K. Iken. 2009. Influence of taxonomic resolution and morphological functional groups in multivariate analyses of macroalgal assemblages. Phycologia 48:24–31. DOI: 10.2216/08-12.1This paper examines how the use of various taxonomic levels and morphological functional groups influences the interpretation of multivariate analyses when comparing macroalgal assemblages in different regions in the Northeast Pacific. We found that for intertidal assemblages, within-site variation was high at the species level and regions only became discernable from the genus level to the order level. Above order level, regions were less well distinguished. Differentiating assemblages at the genus level were similar to results from functional group analyses. This implies that various levels and morphological functional groups can be used to distinguish intertidal assemblages among regions. Intertidal strata differences could be discerned at all taxonomic levels and using functional groups. In contrast to the intertidal, only a few regions were significantly different for subtidal assemblages, independent of taxonomic resolution used. Functional grouping in subtidal assemblages yielded the same resolution as taxonomic levels. Conversely to the intertidal assemblages, strata differences in the subtidal were found at the species and genus levels and with functional groups but not at the family and higher levels. Overall, these results demonstrate differences in regional and strata comparisons in intertidal and subtidal assemblage analyses and that typically species-level analyses are not required.