Effects Of Limpets Research Articles

Grazing by two species of limpets on artificial reefs in the northwest Mediterranean.

The extensive presence of artificial reefs in marine coastal habitats demands a better understanding of the extent to which these structures can be considered surrogates of natural rocky shores for populations of plants and animals. The primary aim of this study was to test the hypothesis that removing limpets from the midlittoral of artificial breakwaters in the northwest Mediterranean led to changes in assemblages similar to those observed on rocky shores in the same area. Orthogonal combinations of the presence/absence of two species of limpets, P. aspera and P rustica, were produced using manual removals from June 1997 to February 1998. To test the hypothesis that the effects of limpets were variable at spatial scales comparable to those investigated on rocky shores, we repeated the experiment at two locations tens of kilometres apart, and on two reefs within each location a few kilometres apart. The results revealed strong and relatively consistent negative effects of limpets on filamentous algae, whereas interactions with other members of assemblages were complex and variable. Several taxa (Cyanophyta, encrusting and articulated coralline algae, Ralfsia and Rissoella) were abundant at one location but nearly absent at the other. This large-scale variability in patterns of distribution generated inconsistencies in the effects of limpets between locations. Within locations, several effects of P. aspera and P. rustica were observed, ranging from independent effects on some organisms, to additive or interactive effects on others. Apparently, the removal of filamentous algae by limpets resulted in positive indirect effects on Ralfsia and Rissoella. Collectively, these effects were comparable to those described for rocky shores in the northwest Mediterranean. The processes accounting for large-scale variation in grazing, however, appeared different between the natural and the artificial habitat.

The interplay of physical and biological factors in maintaining mid-shore and low-shore assemblages on rocky coasts in the north-west Mediterranean

This study examined the interactive effects of grazing by limpets and inclination of the substratum in maintaining differences between mid-shore and low-shore assemblages of algae in the northwest Mediterranean, at different scales of space and through time. Alternative models leading to different predictions about these effects were proposed and tested. Limpets were excluded by fences from areas of the substratum at mid levels on the shore. The response of algal assemblages to this manipulation was compared with control and enclosure plots at the same level, and with unmanipulated plots in the low shore where limpets are less abundant. The effects of limpets were examined at several replicated sites (0.1-4 km apart) for each slope of the substratum (nearly horizontal vs vertical), at different locations (hundreds of kilometres apart) and at different times. Individual taxa responded differently to limpet exclusion. The percentage cover of the coarsely branched and filamentous algae increased significantly in exclosure plots, in some loser reaching values found on the low shore. These patterns, however, varied greatly from shore to shore and significant effects were found both on horizontal and vertical substrata. Multivariate analyses indicated that grazing by limpets accounted for about 20% of the differences between mid-shore and low-shore assemblages. This effect was independent of substratum inclination and was consistent in space and time, suggesting that physical conditions were not as stressful for macroalgae on vertical substrata as initially supposed. Variable recruitment of algae is proposed as a possible explanation for the lack of consistency in the effects of limpets at the scale of the shore. The results of this study emphasize the need for multiple-scale analyses of the interactive effects of physical and biological factors to understand the organization of natural assemblages.

Effects of limpets on competition and diversity in a community of marine sessile invertebrates

Abstract The effect of disturbance on species diversity was explored in a benthic marine fouling community of sessile macroinvertebrates. Mediterranean intertidal limpets Patella coerulea L. (Gastropoda, Prosobranchia) served as an experimental disturbance agent, when transplanted to subtidally immersed panels on which a fouling community developed for seven months. The panels were then removed and the invertebrate populations censused and compared with those on panels with no limpets. The movement of the limpets on the experimental panels constituted the disturbance: while foraging for algae the limpets bulldozed and removed young animal recruits. It was found that the limpets (a) allowed individuals of different species to persist in relative proximity to each other; and (b) promoted species diversity by increasing evenness through reduction of dominance.

Analysis of spatial and temporal variability in interactions among algae, limpets and mussels in low-shore habitats on the west coast of Italy

Spatial and temporal variation in interactions between algae, limpets (Patella spp.) and mussels (Mytilus galloprovincialis) were examined in low-shore habitats south of Livorno, on the west coast of Italy (western Mediterranean), from August 1993 to February 1995. Experiments were set up to: (1) contrast the response of the length of fronds and coverage of the brown alga Cystoseira compressa to the removal of algal turfs and mussels in habitats dominated by these organisms; (2) test whether any effect of mussels on C. compressa was consistent in space (at scales ranging from 1 to 1000 m) and as a function of the presence of limpets; (3) test for the temporal consistency in any effect of limpets on the development of macroalgae in habitat dominated by mussels and (4 ) test for spatlal consistency in the temporal patterns of algal recovery in this hab~tat. Removal of the algal turfs had no effect on the length of fronds of C. compressa; no effect was observed on its coverage but this result was probably confounded by artifacts. In contrast, mussels had both positive and negatlve effects on C. compressa. The mean length of fronds of this alga was significantly reduced by the removal of mussels. this effect being particularly evident after a period of severe storms occurring soon after the initiation of the experiment. A possible mechanism to explain this could involve the stabilisation of the basal fronds of the plants, because mussels were often packed around them. Conversely, the coverage of C. compressa increased significantly after the removal of the mussels, this effect probably resulting from the lnhlbition of recruitment of the alga. The effects of mussels were consistent in space and almost independent of the presence of limpets. In contrast, the herbivores influenced the temporal changes in abundance of the coarsely-branched algae and articulated corallines, but not those of the filamentous and foliose algae or of C. compressa. Finally, no space-time interactions were found in the analyses of variance, indicating that the course of succession was consistent among areas distributed along a stretch of shore about 1.5 km in length. The results of this study suggest that the assemblage of species dominated by mussels on the rocky coasts south of Livorno was not a highly interactive system. Most of the biological processes investigated were consistent in space and/or in time.

Molluscan grazing and macroalgal zonation on a rocky intertidal platform at Perth, Western Australia

AbstractIntertidal limestone platforms off Perth show a characteristic pattern of algal zonation, with dense macroalgal beds nearshore bounded by a ‘barren zone’ along the seaward edge. Abalone (Haliotis roei) and several species of limpets and chitons are abundant in the barren zone, which is generally devoid of non‐coralline macroalgae. The relative importance of abalone versus limpets and chitons in limiting macroalgal abundance in the barren zone was evaluated by manipulating the presence of each group in a factorial experiment. Percentage algal cover was measured photographically in 0.25m2plots at 1–2 month intervals for 9 months. Mean algal cover (mainly the foliose green alga,Ulva rigida) was highest in plots where all grazers were excluded (77–99%), intermediate where only limpets and chitons were excluded (37–85%), and lowest where only abalone were excluded (4–30%) or where no grazers were excluded (2–19%). The effect of limpets and chitons accounted for 55–89% of the variance in total algal cover, whereas the effect of abalone generally accounted for <10% of the variance. Similar results were obtained in terms of the biomass ofUlva rigidaat the end of the experiment.Haliotis roeiare relatively large and sedentary herbivores, feeding mainly on drift algae. Their effect on algal abundance was mediated both through pre‐emption of space, which might otherwise be colonized by algae, and by grazing around their home scar. Limpets and chitons are smaller than abalone, but were much more abundant. Intensive grazing of the reef surface by limpets and chitons precluded the establishment of non‐coralline macroalgae, even where abalone were absent.

Effect of limpets on the fouling of ships in the Mediterranean

Limpets reduce the cover of algae and barnacles on intertidal rocks, but do not inhabit ship-fouling communities. Patella caerulea (L.) from Israeli Mediterranean shores were successfully transplanted onto 20x20 cm initially non-fouled steel panels in 1983–1984, hung vertically in a commercial port at depths of 1 and 5.5 m. The limpets (15 individuals of ca 20 to 25 cm in length on each panel) controlled the fouling organisms that settled on the panels throughout a month of lowest settlement (December) and throughout a month of highest settlement (August). After 7 d of immersion the limpets restricted the total cover of fouling organisms from 2.4 and 4.8% to 0.6 and 0.2% (at 1 and 5.5 m depths, respectively), and brought down the barnacle density from 1.2 and 2.6 to 0.3 and 0.4 individuals per cm2 (at 1 and 5.5 m depth, respectively). After 26 d the equivalent figures were a cover of 72 and 92% reduced to 14 and 9% and a density of 2.9 and 1.1 reduced to 0.3 and 0.2 individuals per cm2. The limpets presumably achieved this by preventing the attachment of propagules and by removing already settled organisms through their movements during grazing excursions.

Experimental analyses of the structure and dynamics of mid-shore rocky intertidal communities in New South Wales.

At mid-shore levels on rocky shores in New South Wales, grazing gastropods are the dominant species in sheltered areas. Where wave-exposure is great, barnacles occupy most of the space. At intermediate levels of waveexposure, there are mixtures of grazing gastropods and barnacles, and the patterns of occupancy of space, and structure of the community change from time to time. The major species found in these areas are the coronuloid barnacle Tesseropora rosea, the patellid limpet Cellana tramoserica, the smaller acmaeid limpet, Patelloida latistrigata, which is mostly confined amongst barnacles, and the predatory whelk Morula marginalba. The roles of each of these species in determining the structure and persistence of intertidal communities were investigated by experimental manipulations of the densities of each of these organisms. In most experiments, a range of densities of limpets and barnacles was used, rather than the simple removal of all of one species.Recruitment of Cellana was negatively associated with increasing density of adult limpets, and with increasing density of barnacles. Growth and survival of juvenile Cellana were decreased by increasing densities of barnacles, probably because barnacles occupied space, preventing limpets from grazing. Morula had no effect on recruitment or survival of juvenile Cellana. Recruitment of juvenile Patelloida was not affected by different densities of barnacles, but survival to adult sizes was poor in areas where whelks are active. In areas where whelks were removed, Patelloida showed increased survivorship with increased cover of barnacles, probably because Patelloida amongst barnacles found refuge from the superior competitive effects of Cellana.The settlement and subsequent survival of Tesseropora were affected in complex ways by the activities of Cellana. At great densities, Cellana can have deleterious effects on newly-settled barnacles, probably by crushing them whilst grazing. In some areas, and at some densities, however, limpets can have beneficial effects on the recruitment and/or survival of Tesseropora. The limpets graze the juvenile stages of growth of foliose macroalgae, preventing them from growing up to pre-empt the rock-surface (thus preventing settlement of barnacles) or to smother alreadysettled barnacles. The effect of limpets on the recruitment and survival of barnacles in any area is a function of the densities of limpets and barnacles, and the height on the shore and local weather (the latter factors influence the rates of growth of algae).Increased cover of the rock-surface by adult barnacles caused reductions in the densities of Cellana. Limpets migrated away from areas of great cover of barnacles, and, if confined in such areas, starved and lost weight. The dispersion, as well as the density of the barnacles was important in determining the effects of barnacle cover. Where barnacles occupied half the space, but were scattered, leaving only small patches of bare rock, they had the same deleterious effects on Cellana as in areas where they were spread evenly to occupy most of the rock-surface. Thus, barnacles could invade areas dominated by limpets provided they recruited in sufficient numbers. They did not have to saturate an area to displace the Cellana.In these communities, all of the species can be considered to have important roles in the establishment and maintenance of community structure. We conclude that interpretations of the roles of individual species must be based on direct, experimental investigation. In this system, there was no indication that many of the species were functionally insignificant.The present experiments also revealed that the interactions among even a few species are very varied and complex; proper investigation requires considerable replication and repeated experimentation in different places and years.Finally, although the present studies allow reliable interpretations of observed patterns of occupancy and dominance on natural shores, the experiments did not provide a predictive framework to anticipate the future events in any area. This is because of great variability in the timing and intensity of recruitment of planktonic propagules of all the components in the system, and in the density and activity of predatory whelks in different areas. These results suggest that tightly co-evolved community relationships are not likely to be important, even if they appear to exist, in communities where most of the species have widely dispersed pelagic offspring and interact in diverse and complex ways at different densities.