Barnacle Recruitment Research Articles

Current reversals as determinants of intertidal recruitment on the central Oregon coast

AbstractDudas, S. E., Grantham, B. A., Kirincich, A. R., Menge, B. A., Lubchenco, J., and Barth, J. A. 2009. Current reversals as determinants of intertidal recruitment on the central Oregon coast. – ICES Journal of Marine Science, 66: 396–407. The influence of current reversals on intertidal invertebrate recruitment was investigated using two seasons of nearshore physical and intertidal biological observations along the central Oregon coast, an intermittent upwelling system. In 1998, upwelling periods were punctuated by infrequent wind reversals and widespread increases in nearshore temperature, whereas 1999 was characterized by frequent, shorter wind reversals. In 1998, barnacle recruitment was best at the site experiencing more frequent reversals of the predominantly equatorward currents, higher poleward velocities, and coincident temperature increases. In 1999, barnacle recruitment peaked at the site with greater poleward current velocities, and maximum mussel recruitment at the site with consistent deep (10 m) onshore currents. Barnacle recruitment generally increased with onshore surface currents and temperature; mussel recruitment showed variable, weaker correlations. The data indicate that substantial decreases or complete reversals of upwelling-driven alongshore currents may be important for barnacle recruitment, but topographically driven differences in the response of currents to wind changes may generate local recruitment differences. This suggests that even relatively straight coastlines may have enhanced recruitment zones attributable to the variable local oceanography. Further, the interannual differences observed in current reversals and recruitment patterns highlight the potential importance of upwelling variation for onshore communities.

PROPAGATION OF SCALE-DEPENDENT EFFECTS FROM RECRUITS TO ADULTS IN BARNACLES AND SEAWEEDS.

The interplay between local and large spatial scale processes in open systems is often dependent upon ecological context and species specific factors such as longevity, dispersal capability, or vulnerability to predation. When disturbance clears patches in open systems, the successful reestablishment of adult colonizers and the trajectory of succession may depend upon both the scale of the disturbance event and scale of life history characteristics. Here we examine the links between the size of a disturbance event and long term patterns of variation in recruitment, density, and percent cover in a relatively short-lived but long-range disperser, the acorn barnacle Semibalanus balanoides, and a relatively long lived and short range disperser, the fucoid alga Fucus vesiculosus. Further, a model of linked scale-dependent processes is developed and we explore how long term patterns of scale-dependent recruitment are related to successful establishment of adults. Recruitment, densities, and cover were monitored for five years for both species in a single experiment using clearings of different sizes spread over two north-facing and two south-facing bays on Swan's Island, Maine, USA. Barnacle recruitment was particularly variable in small clearings and was lower overall at more interior sites within bays. While local-scale factors also strongly influenced patterns of variation in fucoid recruitment, fucoids dominate surface cover in large clearings and in south-facing bays. Recruitment was a poor predictor of density, whereas density itself was a good predictor of percent cover for both species. These results indicate that scale dependencies, location-specific factors, and life history traits contribute to patterns of community development on rocky shores and may ultimately determine whether an open patch converges to or diverges from its initial community state.

SPATIAL ENVIRONMENTAL CORRELATES OF INTERTIDAL RECRUITMENT: A TEST USING BARNACLES IN NORTHERN CHILE

Nearshore circulation processes and local geomorphological patterns are thought to be important correlates of spatial variation in larval recruitment of benthic organisms. However, few studies have attempted to quantitatively separate their relative influences upon recruitment dynamics. Here we use 12 study sites spanning 250 km of the northern Chile upwelling ecosystem and the intertidal barnacles Jehlius cirratus and Notochthamalus scabrosus to examine the extent to which spatial variation in larval recruitment is related to environmental variability and how these relationships depend on spatial autocorrelation. We find that upwelling intensity and wind velocity are negatively related to larval recruitment while surface slicks showed a positive correlation. However, the pure effect of each environmental variable was lower than its combined effects. Taking spatial autocorrelation into account, we find that the spatially structured variation of upwelling dynamics, distance to upwelling fronts, wind velocity, and slick occurrence explained most of the variation in barnacle recruitment. Spatial variation in recruitment rates of barnacles showed a characteristic length scale of 60–70 km, similar to the scale estimated for the spatially structured variables (upwelling, wind velocity, and surface slicks). We find that conditions for the occurrence of surface slicks (as surrogates of internal waves activity) seem to operate across several sites, suggesting a meso‐ instead local‐scale influence over spatial variation in barnacle recruitment. Our results suggest that spatial variation in barnacle recruitment is modulated by the combined influence of several spatially structured nearshore processes operating at scales of 60–70 km and that spatial autocorrelation must be taken into account in the study of the recruitment–environment relationship. However, the influence of local and small‐scale factors on recruitment dynamics of benthic invertebrates should be interpreted cautiously.

INTERHEMISPHERIC COMPARISON OF RECRUITMENT TO INTERTIDAL COMMUNITIES: PATTERN PERSISTENCE AND SCALES OF VARIATION

Recruitment variation can be a major source of fluctuation in populations and communities, making it difficult to generalize results. Determining the scales of variation and whether spatial patterns in the supply of individuals are persistent over time can provide insight into spatial generality and the application of conservation and metacommunity models. We examined these issues using eight-year-long data sets of monthly recruitment of intertidal mussels (Mytilus spp., Perumytilus purpuratus, Semimytilus algosus, Brachidontes granulata) and barnacles (Balanus glandula, Chthamalus dalli, Jehlius cirratus, Notochthamalus scabrosus) at sites spanning > 900 km along the coasts of Oregon-northern California (OR-NCA, 45.47-39.43 degrees N) and central Chile (CC, 29.5-34.65 degrees S). We evaluated four general "null" hypotheses: that despite different phylogenies and great spatial separation of these taxa, their similar life history strategies and environmental settings lead to similar patterns of recruitment (1) between hemispheres, (2) in time, (3) in space, and (4) at larger and smaller spatial scales. Hypothesis 1 was rejected: along the OR-NCA coast, rates of recruitment were between two and three orders of magnitude higher, and patterns of seasonality were generally stronger and more coherent across space and time than along CC. Surprisingly, however, further analysis revealed regularities in both time and space for all species, supporting hypotheses 2 and 3. Temporal decorrelation scales were 1-3 months, and characteristic spatial scales of recruitment were approximately 250 km. Contrary to hypothesis 4, for the ecologically dominant species in both hemispheres, recruitment was remarkably persistent at larger mesoscales (kilometers) but was highly stochastic at smaller microscales (meters). Across species, increased recruitment variation at large scales was positively associated with increased persistence. Our results have several implications. Although the two regions span distinct latitudinal ranges, potential forcing processes behind these patterns include similar large-scale climates and topographically locked hydrographic features, such as upwelling. Further, spatial persistence of the recruitment patterns of most species at the mesoscale supports the view that marine protected areas can be powerful conservation and management tools. Finally, persistent and yet contrasting spatial patterns of recruitment among competing species suggest that recent metacommunity models might provide useful representations of the mechanisms involved in species coexistence.

Oceanographic gradients and patterns in invertebrate assemblages on offshore oil platforms

Abstract Page, H. M., Culver, C. S., Dugan, J. E., and Mardian, B. 2008. Oceanographic gradients and patterns in invertebrate assemblages on offshore oil platforms. – ICES Journal of Marine Science, 65: 851–861. We explored variability in the composition and cover of subtidal macroinvertebrate assemblages, and the recruitment and growth rates of selected invertebrate species, on seven offshore oil and gas platforms arrayed across a gradient in oceanographic conditions in the Santa Barbara Channel, CA, USA. The major macroinvertebrate taxa (sea anemones, mussels, barnacles, tubiculous amphipods, hydroids, and sponges) were common to all platforms. However, discriminant function analysis (DFA) revealed that the assemblages of two platforms (Gilda and Gail) clearly differed from the other platforms, a pattern attributable, in part, to the presence of conspicuous exotic species (the anemone, Diadumene sp., and encrusting bryozoan, Watersipora subtorquata) on these platforms. If these exotic species were excluded from the analysis, platforms in proximity to each other generally tended to have invertebrate assemblages more similar to each other than to platforms located farther away. Spatial variation in barnacle recruitment onto ceramic plates and mussel growth rate reflected prevailing oceanographic gradients. The existence of along-channel patterns in the composition of platform invertebrate assemblages, and in invertebrate recruitment and growth associated with oceanographic gradients, suggests that assemblages attached to platforms or other artificial structures may be useful barometers of short and perhaps longer term change in ocean climate.

Barnacle recruitment on ice-scoured shores in eastern Canada

Previous observations in the St Lawrence Estuary (eastern Canada) suggested that larvae of intertidal barnacles (Semibalanus balanoides) would settle almost exclusively inside crevices on shores that are scoured by sea ice every winter. It was suggested that the strong ice scour in winter on that coast (which removes organisms outside of crevices) would select for such a larval behaviour. We tested the generality of this pattern by sampling other ice-scoured shores within the Gulf of St Lawrence system. In particular, we surveyed a shore in Nova Scotia where exposed habitats (subjected to strong ice scour in winter) are interspersed with sheltered habitats (which suffer milder ice scour). Such a topographical complexity might allow for the coastal larval pool to contain a proportion of larvae that have no particular settlement preference for crevices, as selective pressures for such a behaviour would be minimal in ice-sheltered habitats. Consistently with this notion, barnacle recruits (which appear after the winter ice melts) occurred abundantly both inside and outside of crevices across the shore in the spring seasons of 2005 and 2006. Average recruit density on rocky surfaces ranged between 337 and 588 recruits dm−2, depending on the habitat. It is therefore possible that barnacle recruitment patterns on ice-scoured shores may be affected indirectly by the structural complexity of the coast.

Nutrient enrichment affects recruitment of oysters and barnacles in a mangrove forest

We tested the hypothesis that nutrient enrichment affects recruitment of the oyster Sac- costrea glomerata and the barnacle Hexaminius popeiana, which are dominant occupiers of space on tree trunks in temperate mangrove forests in New South Wales, Australia. We measured recruitment on artificial settlement plates at high and low intertidal levels under ambient conditions and where we manipulated nutrient levels by adding fertiliser to the water column for 2 mo. To determine whether nutrients influenced temporal patterns of settlement and early mortality of larvae, we quan- tified recruitment for 2 sampling intervals: on plates that were replaced 4 times at 2 wk intervals and on those left in the field for the entire 2 mo. For both intervals, recruitment of oysters was 3 to 4 times and significantly higher under elevated than ambient nutrient conditions. Recruitment of barnacles was also significantly higher under elevated nutrient conditions, but only on plates sampled at 2 wk intervals. On plates left out for 2 mo, the effect of nutrients on recruitment was variable, but recruits were generally higher in number under ambient conditions, suggesting that nutrients might enhance postsettlement mortality. Nutrient enrichment clearly affected recruitment of oysters and barnacles, possibly by mimicking natural settlement cues of conspecific individuals. Considering the central role of recruitment to the population dynamics of marine benthic invertebrates, nutrient enrichment has the potential to alter species assemblages in estuarine and marine habitats.

Grazing effects of the periwinkle Echinolittorina peruviana at a central Peruvian high rocky intertidal

Echinolittorina peruviana is the most common gastropod in the high intertidal zone of Peru, representing more than 80% of the individuals present at that zone. Experimental removal of snails was used to evaluate their effects on (a) abundance of epilithic biofilm, (b) barnacle recruitment, and (c) abundance of macroalgae under “normal” conditions of the El Nino Southern Oscillation (ENSO). Experiments were carried out from October 2005 to April 2007 at two intertidal levels of a semi-protected rocky shore of central Peru. Results demonstrated that E. peruviana is able to control biofilm abundance and barnacle recruitment at both heights investigated, with marked effects in the lower zone. Erect macroalgae (Ulva spp. and Gelidium spp.) were less affected by grazing; but negative effects were observed on macroalgal crusts. Season and physical stress seem to play a more important role in the abundance of macroalgae in the high intertidal. Our results are similar to those reported elsewhere for high shore littorinids and represent baseline data to understand how the role of intertidal consumers will vary under the cold (La Nina) and warm (El Nino) phases of ENSO on these shores.

Effect of predation by the invasive crab Hemigrapsus sanguineus on recruiting barnacles Semibalanus balanoides in western Long Island Sound, USA

Since its introduction fewer than 20 yr ago, the spread of the Asian shore crab Hemigrapsus sanguineus along the east coast of the US has been remarkable. By many accounts it is now the numerically dominant brachyuran in rocky intertidal sites in Long Island Sound. Evidence from several laboratory studies has suggested that H. sanguineus could have significant consequences for barnacle abundance and distribution. In this study we used field caging experiments to determine the effect of this invader on recruitment (sampled at weekly intervals) of the indigenous barnacle Semibalanus balanoides. We found that although H. sanguineus readily consumed settling cypris larvae and early post-settlement juveniles, crab predation did not have a negative impact on barnacle recruitment when predator density was low (15 crabs 0.25 m–2). We also found a measurable decrease in barnacle density at medium (45 crabs 0.25 m–2) and high (90 crabs 0.25 m–2) predator densities after the larval settlement period had ended, but this effect was short-lived. Based on available estimates of Asian shore crab abundance in Long Island Sound, we conclude that crab predation will not have a significant impact on the recruitment success of S. balanoides populations.

MECHANISMS GENERATING MODIFICATION OF BENTHOS FOLLOWING TIDAL FLAT INVASION BY A SPARTINA HYBRID

Many coastal habitats are being substantially altered by introduced plants. In San Francisco Bay, California, USA, a hybrid form of the eastern cordgrass Spartina alterniflora is rapidly invading open mudflats in southern and central sections of the Bay, altering habitat, reducing macrofaunal densities, and shifting species composition. The invasion has resulted in significant losses of surface-feeding amphipods, bivalves, and cirratulid polychaetes, while subsurface feeding groups such as tubificid oligochaetes and capitellid polychaetes have been unaffected. In the present paper, we document the causes and mechanisms underlying the changes observed. Through a series of in situ manipulative experiments we examined the influence of hybrid Spartina canopy on a range of physical, chemical, and biological properties. The hybrid Spartina canopy exerted a strong influence on the hydrodynamic regime, triggering a series of physical, chemical, and biological changes in the benthic system. Relative to tidal flats, water velocity was reduced in hybrid patches, promoting deposition of fine-grained, organic-rich particles. The resulting changes in the sediment environment included increased porewater sulfide concentrations and anoxia, which led to poor survivorship of surface feeders such as bivalves, amphipods, and polychaetes. These are key taxa that support higher trophic levels including migratory shorebirds that feed on tidal flats. Altered flow in the Spartina canopy further contributed to changes in barnacle recruitment and resuspension of adult benthic invertebrates. Increased crab-induced predation pressure associated with Spartina invasion also contributed to changes in benthic invertebrate communities. Our results suggest that multiple physical, chemical, biotic, and trophic impacts of the Spartina invasion have resulted in substantial changes in benthic communities that are likely to have important effects on the entire ecosystem.

Intertidal community structure and oceanographic patterns around Santa Cruz Island, CA, USA

Recent studies suggest that nearshore oceanographic conditions can have important effects on the structure of benthic communities. On Santa Cruz Island (SCI), CA, USA there is a persistent difference in mean annual sea surface temperature (SST) around the island due to its location at the confluence of opposing cold and warm ocean current systems. Over the course of a 4-year study (1997–2001) seawater nutrient and chl-a concentrations, algal tissue C:N ratios, recruitment and growth of filter-feeders (barnacles and mussels), and intertidal community structure were measured at six intertidal sites around the island. There were strong associations between remotely sensed SST and patterns of community structure. Macrophyte abundance was highest at sites with persistently low SST, while recruitment, abundance, and growth of filter-feeding invertebrates were strongly, positively correlated with SST. The cold-water sites were associated with higher nutrient concentrations and lower algal C:N ratios, particularly in the winter months. Values of chl-a were generally low and variable among sites, and were not correlated with the predominant SST gradient. Recruitment of barnacles and mussels was positively correlated with adult abundance across all sites. While detailed experimental studies are needed to further evaluate the mechanisms underlying community dynamics, these results indicate that the confluence of cold- and warm-water masses around SCI may determine the contrasting patterns of intertidal community structure.

Recruitment of intertidal invertebrates and oceanographic variability at Santa Cruz Island, California

To examine geographical variation in oceanographic forcing on larval delivery, we studied spatial and temporal variability in larval recruitment of mussels and barnacles in a key oceanographic region around Santa Cruz Island, California. Larval recruitment patterns differed among sites located on the eastern and western shores of the island associated with differences in oceanographic regimes. Western sites had low but variable sea surface temperatures, whereas eastern sites were warmer (1-1.5°C higher) and less variable. Larval arrival was extremely low at western sites relative to eastern sites. Mussels and barnacles differed in the duration and seasonality of larval recruitment. Mussel recruitment occurred over a long period between winter and summer, whereas barnacle recruitment occurred in pulses in spring-summer. Mussel recruitment was not correlated with sea surface temperature anomalies, whereas barnacle recruitment was significantly and positively correlated with temperature anomalies, with time lags ranging from 0 to 3 months across all sites. Oceanographic and larval recruitment patterns suggest that western sites are dominated by an energetic flux of cold, recently upwelled water depleted of larvae, whereas eastern sites receive high numbers of larvae associated with the influx of warmer surface water, likely originating outside the Santa Barbara Channel.

Recruitment of the barnacle Balanus amphitrite in a tropical estuary: implications of environmental perturbation, reproduction and larval ecology

Phytoplankton blooms are known to influence barnacle recruitment and in boreal regions spring blooms work as an important trigger. Close to the west coast of the sub-continent of India, blooms tend to be triggered by breaks in the monsoon and the recurrence of the monsoon after a short break can stress the new recruits. The recruitment of Balanus amphitrite, an acorn barnacle, at Dona Paula Bay at the mouth of Zuari estuary, Goa, India was studied. Observations included variations in recruitment, larval abundance, development and reproduction. Adult conditioning and inter-brood variations were important factors in the larval ecology of this organism. The results indicate that the impulsive release of larvae during breaks between monsoons could be a short-sighted luxury for Balanus amphitrite in these waters. Temporal variations or recruitment failure in such environments can be attributed to inappropriate cue synchronization.

Do effects of ultraviolet radiation on microbial films have indirect effects on larval attachment of the barnacle Balanus amphitrite?

We have examined the indirect effects of UV-A and UV-B on cypris attachment of the barnacle Balanus amphitrite Darwin through their effects on microbial films. Specifically, we tested the hypothesis that both UV-A and UV-B radiation can indirectly affect the larval attachment of barnacles by altering the microbial film bioactivity. Microbial films were developed from mid-intertidal region (∼1 m above Mean Low Water Level) for 6 days and subjected to ambient levels of ultraviolet radiation. Response of cyprids to untreated and UV-treated microbial films was investigated using double-dish still water choice bioassay. Results showed that both UV-A and UV-B caused a decrease in the percentage of respiring bacterial cells in microbial films and this effect increased with UV energy. With the same UV energy, UV-B caused a greater decrease in respiring bacterial cells than UV-A. However, despite strong UV radiation, the bioactivities of microbial films (i.e., stimulation of cypris attachment) remain unchanged. Results of this study suggest that increased UV radiation, which might occur due to ozone depletion, may not significantly affect the barnacle recruitment by means of affecting the inductive larval attachment cues of microbial films.

Temporal and spatial variability in the recruitment of barnacles and the local dominance of Elminius modestus Darwin in SW Ireland

Deployment of processed natural substrata is a common method of investigating early settlement and recruitment processes, but has been under-utilised as a multi-depth method for barnacle study and analysis. Replicate, machined-slate panels (15 cm×15 cm×1 cm) were placed at 0 m (lower portion of the intertidal with ≈2 h emersion per tidal cycle), 6 m and 12 m at two sites of differing flow rate in Lough Hyne, SW Ireland. These panels were replaced serially every 30–60 days for a period of 3 years (2000–2003) to give monthly recruitment rates. Panels were also submersed for 60–120 days (Whirlpool Cliff, two locations) to show seasonal patterns and 370–400 days (Labhra Cliff) to show annual recruitment and survival patterns. The number, percentage cover and identity of all cirripede recruits were recorded. The greatest source of variability was with depth: between the intertidal (with many recruits) and the subtidal zones (few recruits). In general, intertidal recruitment was dominated by the introduced barnacle Elminius modestus Darwin. The high degree of water retention in Lough Hyne, combined with the high reproductive potential of E. modestus, has led to it becoming a self-perpetuating and locally dominant population. Balanus crenatus and Verruca stroemia dominated the longer immersed panels, highlighting the importance of post-recruitment processes to the survival of E. modestus recruits in the subtidal. Although E. modestus were found on subtidal monthly and seasonal panels, none were present on the subtidal annual panels. Temporally, month, season and time of placement were all found to be significant in explaining recruit number variability. Spatially, depth explained most variability of recruit numbers (6 m spatial separation), whilst site (≈200 m spatial separation) only ever being significant in combination with other factors, as was location (≈50 m spatial separation). The work highlights the importance of examining both temporal and spatial scales when investigating recruitment and post-recruitment processes of marine invertebrates, including introduced species.

Meso-scale spatial variation in settlement and recruitment of intertidal barnacles along the coast of central Chile

Spatial and temporal variation in recruitment can be the leading determinant of popu- lation fluctuations in species with pelagic larval stages. Characterizing and identifying the causes of such variation is, therefore, necessary to understand population dynamics, and to develop conserva- tion and management strategies. We examined spatial patterns in settlement and recruitment of the intertidal barnacles Jehlius cirratus, Notochthamalus scabrosus and Notobalanus flosculus, and their relationships with environmental variables operating at meso- (sea surface temperature, SST) and small (local topography) scales. Settlement and recruitment were studied over 6 mo at biweekly intervals at 16 sites along 120 km of coastline in central Chile. All species showed similar temporal patterns, with a peak in settlement and recruitment during austral spring. We decomposed the spa- tial patterns into their corresponding meso-scale trend (from a few to 10s of kilometers) and into their small-scale (site) residual variation. Recruitment of chthamaloid species was highly and positively correlated at meso- and small-scales, and the among-site rankings showed consistency of the spatial structure throughout the recruitment season. SST explained a significant fraction of the variance in recruitment of the chthamaloids at the meso-scale, and spatial analysis showed coincident decorrela- tion scales of about 35 km for SST and recruitment. In contrast, recruitment of balanoid species did not show a clear spatial structure, was not associated with meso-scale variation in SST, and local topography seemed to play a significant role in their settlement. Topographically modified upwelling dynamics over scales of 10s of kilometers is the most plausible factor shaping meso-scale variation in recruitment of chthamaloid barnacles, whereas settlement and recruitment of balanoid species seem more strongly influenced by processes acting at local scales. The spatial scale and structure of recruitment provide guidelines for the placement and spacing of protected areas in the region.

Manipulating larval supply in the field: a controlled study of marine invasibility

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 298:9-19 (2005) - doi:10.3354/meps298009 Manipulating larval supply in the field: a controlled study of marine invasibility Graeme F. Clark*, Emma L. Johnston School of Biological, Earth and Environmental Science, University of New South Wales, Sydney, New South Wales 2052, Australia *Email: g.clark@unsw.edu.au ABSTRACT: In order to gather experimental data to test theories of invasion biology, ecologists have recently adopted a rigorous experimental approach in which community traits and propagule supply are manipulated independently. However, these studies have been limited to terrestrial systems and their generality is not well understood. We conducted a manipulative field experiment to test the relationship between common human disturbances and invasibility in hard-substrate marine epifaunal communities. A larval dosing technique was developed to allow marine experimental units to be dosed with a controlled supply of propagules under field conditions. Six month old assemblages were exposed to 3 fully crossed factors of (1) physical disturbance, (2) chemical disturbance, and (3) timing of larval dose relative to the disturbances. Physical disturbance was shown to increase the invasion success of the introduced species, Bugula neritina, up to 30 d following the disturbance. This was mainly through an increase of recruitment onto primary space, however physical impacts with an antifoulant surface also led to increased recruitment on secondary space. After 15 d, B. neritina recruits on primary space were found to be larger than recruits on secondary space, suggesting an elevated threat of invasion through primary recruitment. Natural recruitment of barnacles, ascidians, and sedentary polychaetes was also increased by physical disturbance, although these effects were weaker and varied between taxa and sampling times. This study supports the theory that disturbance facilitates invasions in marine epifaunal communities, and contributes a new technique of manipulating propagule supply in the marine environment. KEY WORDS: Invasion biology · Disturbance · Propagule supply · Recruitment · Marine ecology · Ecotoxicology · Fouling communities · Bugula neritina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 298. Online publication date: August 15, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Vertical structure and predator refuge mediate oyster reef development and community dynamics

In addition to their economic value, oysters supply a number of critical ecosystem services such as controlling eutrophication, recycling nutrients, and providing habitat for many invertebrates and fishes. Thus, the maintenance and restoration of oyster reefs is vital for properly functioning estuarine ecosystems. We hypothesized that spatially heterogeneous and refuge-rich reefs are superior habitats for oysters and associated invertebrates and fishes. If this is shown to be the case, then vertical structure and refuge should be included in the design of newly constructed oyster reefs and conserved in existing reefs. To test our hypothesis, models were built as concrete blocks into which shells were placed horizontally, vertically, and widely spaced, and vertically and closely spaced. Respectively, the units represent horizontal orientation with no refuge (HNR), vertical orientation with no refuge (VNR), and vertical orientation with refuge (VWR). Flume studies of velocity distributions over each model type showed distinctive differences that may contribute to differential settlement on the models in the absence of predators or sediment. A subsequent settlement study in the same flume showed significantly higher settlement densities to horizontal shells than to vertical shells regardless of refuge (HNR>VNR=VWR). This result indicates the primary importance of settlement surface orientation (horizontal vs. vertical) over predation refuge when predators are absent. In contrast, two field recruitment studies indicated that the importance of orientation relative to predation refuge might depend on sedimentation rates. When sedimentation was low, the number of oysters and barnacles (live, dead, and total) was significantly higher on no-refuge models than on refuge models (HNR=VNR>VWR). However, percent mortality was lower on the refuge models than on the no refuge models (HNR=VNR>VWR). This leads to a conclusion that although fewer oysters may settle on refuge shells, those that do have a higher rate of survival. In a year when sedimentation was high, recruitment and survival of oysters, barnacles, and bryozoans was higher on vertical models regardless of refuge. In aggregate, our results indicate that both vertical orientation and predation refuge are critical to the early development of the oyster reef community and should be included in restoration designs.

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui Southward and Chthamalus stellatus (Poli) (Crustacea: Cirripedia) over an European scale

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui and Chthamalus stellatus was examined over an European scale. The study was carried out using standardised protocols at a series of locations. The five locations chosen (SW Ireland, NW Spain, SW Portugal and NW and NE Italy) span a large part of the range of these species in Europe. The spatial scales were location (hundreds of kilometres) and shore (thousands of metres). Estimates of total cumulative recruitment (cyprids and metamorphs) summed over the year (April 1997 to March 1998) showed substantial variation between locations which was dependent on the species. Recruitment was highest in SW Portugal for C. montagui and in SW Ireland and NW Spain for C. stellatus. Overall recruitment of C. montagui was higher than that of C. stellatus at all locations except SW Ireland, where recruitment of the two species was not significantly different. There were significant differences among shores in each location. The recruitment period of both species varied with location, with recruitment beginning earlier further south. In general, recruitment of C. montagui and C. stellatus was recorded in 8 months in NW Spain and NE Italy, while only in 7 months in SW Ireland. Recruitment of C. montagui occurred in 10 months in SW Portugal, but no recruits of C. stellatus were found. In all locations there was at least one distinct peak of recruitment. In SW Ireland both species showed only one peak of recruitment, a month after initiation. At the more southerly Atlantic locations, as well as in the Mediterranean, two unequal peaks of recruitment were generally seen. During recruit census, the number of cyprids, in comparison to metamorphs, found at any location was very low. In SW Ireland and NW Spain cyprids of both species were found, while in SW Portugal and in the Mediterranean, only cyprids of C. montagui were found.

Dominance of blue mussels versus consumer-mediated enhancement of benthic diversity

In the shallow subtidal of Kiel Fjord (western Baltic Sea), the blue mussel Mytilus edulis is the dominant competitor for space. Vertically suspended settlement substrata in the upper 6 m of the water column almost invariably become dominated by M. edulis within a few summer months. However, not all naturally available hard substrata bear mussel monocultures. In three in situ experiments we investigated the dominance of mussels and the influence of local consumers on establishment and dynamics of a benthic community: (a) the natural course of succession in the absence of benthic consumers was followed on vertically suspended settlement substrata, (b) settling plates were exposed to natural recruitment being either accessible or inaccessible to all benthic consumers, and (c) the three major local consumer species, viz. the shore crab Carcinus maenas, the starfish Asterias rubens and the periwinkle Littorina littorea, were enclosed separately in cages containing a settling panel to assess species-specific consumer effects on recruitment. The results illustrate that in this region of the Baltic Sea mussels do have the potential to dominate ungrazed substrata within a few weeks and that top-down effects (predation and grazing) may control community structure. While some species - mussels in particular - were suppressed by consumption, others seemed to benefit from the presence of consumers. Thus, barnacles and algae thrived when consumers were present. Blue mussels being the locally dominant competitor, the beneficial effects of consumers on barnacles and algae were presumably indirect ones through consumer-caused release from asymmetrical competition. The isolated effects of C. maenas, A. rubens and L. littorea, on recruitment differed in quality (positive vs. negative), quantity (strength of effect) and specificity. Barnacle recruitment was significantly reduced in the presence of both starfish and shore crabs. Diatom recruitment was significantly reduced by snails and shore crabs. Scyphozoan recruitment was significantly reduced by crabs only, but was significantly increased by snails. The influence of the shore crabs was most remarkable: recruitment by any potential coloniser species was impeded to a point where in the presence of single individuals of C. maenas the plates stayed perfectly clean macroscopically.