Selective settlement of the barnacle Semibalanus balanoides (L.) facilitates its growth and reproduction on mussel beds in the Wadden Sea

On the unstable sedimentary tidal flats of the Wadden Sea, a suitable attachment substrate for sessile organisms is generally lacking. Epibenthic mussel beds (Mytilus edulis L.) provide the only and strongly limited settlement sites available for the barnacle, Semibalanus balanoides (L.). Field investigations showed that barnacles were non-randomly distributed within a mussel bed. They preferentially occurred near the siphonal apertures of living mussels but rarely grew on dead mussels or shell fragments. Field experiments revealed that this was due to selective settlement of barnacle cyprid larvae. Growth of barnacles was significantly higher upon living mussels than on empty mussel shells. Moreover, a higher reproductive output was obtained by individuals on living mussels which produced twice as many nauplii larvae than barnacles attached to empty shells. This study shows that selective settlement of S. balanoides cyprid larvae on living mussels is adaptive with respect to individual fitness. Received in revised form: 15 January 2001 Electronic Publication     

Effects of environmental stress on intertidal mussels and their sea star predators

Consumer stress models of ecological theory predict that predators are more susceptible to stress than their prey. Intertidal mussels, Mytilus californianus, span a vertical stress gradient from the low zone (lower stress) to the high zone (higher thermal and desiccation stress), while their sea star predators, Pisaster ochraceus, range from the low zone only into the lower edge of the mussel zone. In summer 2003, we tested the responses of sea stars and mussels to environmental stress in an experiment conducted on the Oregon coast. Mussels were transplanted from the middle of the mussel bed to cages in the low and high edges of the mussel bed. Sea star predators were added to half of the mussel cages. Mussels and sea stars were sampled between June and August for indicators of sublethal stress. Mussel growth was measured, and tissues were collected for heat shock protein (Hsp70) analyses and histological analyses of reproduction. Sea stars were weighed, and tissues were sampled for Hsp70 analyses. Mussels in high-edge cages had higher levels of total Hsp70 and exhibited spawning activity earlier in the summer than mussels in the low-edge cages. Sea stars suffered high mortality in the high edge, and low-edge sea stars lost weight but showed no differences in Hsp70 production. These results suggest that stress in the intertidal zone affected the mobile predator more than its sessile prey, which is consistent with predictions of consumer stress models. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hard rock versus soft bottom: the fauna associated with intertidal mussel beds on hard bottoms along the coast of Chile,and considerations on the functional role of mussel beds

The fauna associated with hard bottom mussel beds along the exposed Pacific coast of Chile was examined. The abundance of adult (>10 mm body length) purple mussels Perumytilus purpuratus varied between 32 and 75 individuals per 50 cm², and their biomass between 4.8 and 8.6 g AFDW per 50 cm² at eight sampling sites between Arica (18°S) and Chiloé (42°S). At all sampling sites, the associated fauna was dominated by suspension-feeding organisms (cirripeds, spionid and sabellid polychaetes, a small bivalve) followed by grazing peracarids and gastropods. Predators and scavengers also reached high abundances while deposit- and detritus-feeding organisms were of minor importance. The majority of organisms associated with these hard bottom mussel beds feed on resources obtained from the water column or growing on the mussels rather than on materials deposited by the mussels. This is in contrast to the fauna associated with mussel beds on soft bottoms, which comprises many species feeding on material accumulated by mussels (faeces and pseudofaeces) and deposited within the mussel bed. Many of the organisms dwelling between mussels both on hard bottoms and on soft bottoms have direct development, but organisms with pelagic development also occur abundantly within mussel beds. We propose that species with direct development are disproportionately favoured by the structurally complex habitat with diverse interstitial spaces between the mussels, which provides ample shelter for small organisms. We conclude that mussels on hard-bottoms primarily provide substratum for associated fauna while mussels on soft bottoms provide both substratum and food resources. Electronic Publication     

Depth distribution of the native freshwater mussel (Echyridella menziesii) in warm monomictic lakes: Towards a general model for mussels in lakes

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The site of settlement indicates commensalism between bluemussel and its epibiont

Summary The site of settlement of barnacles (Balanus improvisus) attached on shells of bluemussels (Mytilus edulis) was mapped from a sample of mussels collected in the Baltic Sea. Most barnacles had settled near the siphonal apertures of the mussel. An experiment was made to measure the disadvantages and advantages that living in close association brings to barnacles and mussels. The barnacles on shells of living mussels were shown to grow significantly faster than those on empty mussel shells. Presence of barnacles had no effects on growth of mussels. The two-species association under study was demonstrated to be a case of commensalism.     

Muskrat predation on a diverse unionid mussel community: impacts of prey species composition,size and shape

1. The muskrat, Ondatra zibethicus, is a predator known to affect species composition, population size and age structure of freshwater unionid mussel communities. Muskrats leave large piles of dead shells (middens) on the edges of rivers, lakes and streams. We compared the species composition and size structure of shells collected from muskrat middens to the nearby live unionid community in the lower Licking River (Kentucky, USA). 2. Like previous studies, our results suggest that muskrats are both size‐selective and species‐specific predators; however, our results indicate that mussel shape is also an important factor. 3. We generated a shape metric (‘cubocity’) sensitive to the overall shape of the mussel. Species with relatively lower cubocity values (around 0.85) are plate‐like or spike‐like, while mussels with more cuboidal shells have higher cubocity values (near 1.0). 4. Our results suggest muskrats prefer cuboidal mussels and generally avoid spike‐shaped mussels. The endangered fanshell, Cyprogenia stegaria, was the most favoured prey; the fanshell’s relative size and shape appear to make it particularly vulnerable to muskrats. 5. We believe the predictive capabilities of this shape metric will be of benefit to those who monitor and manage threatened mussel populations.     

Zebra mussels decrease burrowing ability and growth of a native snail, <Emphasis Type="Italic">Campeloma decisum</Emphasis>

Invasive species can drive native organisms to extinction by limiting movement and accessibility to essential resources. The purpose of this study was to determine if zebra mussels (Dreissena polymorpha) affect the burrowing ability and growth rate of a native snail, Campeloma decisum. Snails with and without zebra mussels were collected from Douglas Lake, MI, and burrowing depths were studied in both the laboratory and Douglas Lake. Growth rates were calculated as the amount of shell growth from 2004 to 2005. Both the tendency of snails to burrow and the depth to which they burrowed into the substrate were significantly decreased by the presence of zebra mussels on snail shells in both laboratory and lake experiments. There was no difference in the percentage of snails that exhibited growth as a function of zebra mussel presence. However, for those snails that grew, there was a 50% higher growth rate for snails without zebra mussels compared to snails with zebra mussels. These negative effects of zebra mussels on growth and burrowing ability will likely lead to decreases in snail population densities in the future. Handling editor: S. Wellekens     

Mussel culture in a changing environment: the effects of a coastal engineering project on mussel culture (Mytilus edulis L.) in the Oosterschelde estuary (SW Netherlands)

To evaluate the effects of a large scale coastal engineering project on the mussel (Mytilus edulis) bottom culture in the Oosterschelde estuary (S.W. Netherlands), mussel growth and production in the period 1980–1990 are studied in relation to food supply and the hydrodynamic conditions. Due to the construction of a storm-surge barrier and two additional dams, the risk that mussels are swept away by high current velocities decreased, resulting in an increase of the area in the Oosterschelde potentially suitable for mussel culture and in food availability now being more important as a limiting factor. For the Oosterschelde, a clear relation between mussel growth, stock sizes, and phytoplankton dynamics has been demonstrated. The meat yield of mussels landed in autumn — which is an index for growth rate — seems to be determined by the phytoplankton production in the preceding summer. In years with dense bivalve stocks, phytoplankton production and meat yields are relatively low. It is concluded that an increase of the mussel biomass cultured can result in a reduction of the primary production and, consequently, in a deterioration of the growing conditions for suspension-feeders in the estuary. This conclusion is supported by model calculations. An expansion of mussel culture in the new Oosterschelde is therefore dissuaded. Apart from primary production and stock sizes, food supply for mussels on culture lots appeared to be controlled by the horizontal advection of phytoplankton between and within the tidal channels. An observed decline in mussel landings from certain areas is attributed to the reduced mixing energy of the estuary in relation to the present distribution of the lots over the estuary. Production figures from the experimental lots, established in 1988 in the newly available areas, demonstrate that the yield of mussels can be enhanced by relaying culture lots towards the areas where the phytoplankton is produced. It is expected that by redistributing the culture lots, without expanding the biomass cultured, the carrying capacity of the Oosterschelde for mussel culture can be maintained.     

Mytilus galloprovincialis (Mollusca: Bivalvia) in a warm-temperate South African estuarine embayment

The distribution, population structure, condition and gonad indices, and the attachment strengths of the invasive Mediterranean mussel Mytilus galloprovincialis are described from the Knysna Estuary, South Africa. Mussels were found in the rocky intertidal at the mouth of the estuary and on all man-made hard substrata as far as 12?km from the mouth in 2013. However, mussel beds were found only in the lower reach of the estuary, where mussel densities were as high as 120 per 0.01?m². When compared to mussels from the embayment regions of the estuary, those at the estuary mouth, where wave action was high, were generally smaller, had significantly lower condition and gonad indices, and greater attachment strength. This suggests that mussels within the sheltered regions of the estuary invest more energy in growth and reproduction, and that this is one reason for their success as an invasive species in the Knysna estuarine embayment.     

Does the recruitment of a non‐native mussel in native eelgrass habitat explain their disjunct adult distributions?

We studied variability in the abundance of small individuals of an invasive mussel (Musculista senhousia) across the depth distribution of a native marine angiosperm, eelgrass (Zostera marina). Adult mussels and eelgrass have a disjunct local distribution, each limiting the other in complex ways. To assess whether eelgrass also influenced the distribution of juvenile mussels, we sampled inside and outside eelgrass beds in one site in Mission Bay and two in San Diego Bay, California, USA. We sampled mussels in size classes 0.26–0.50 mm, 0.51–1.00 mm, 1.10–2.00 mm and > 2.00 mm from September 1997 to April 1999. We also monitored gonad development in larger mussels and in situ growth of mussels ≤ 2 mm tagged with the chemical marker calcein. Spatial and temporal variations in mussel abundances were high but seasonal patterns were roughly similar at San Diego Bay sites; very few mussels were found in Mission Bay. Mussels with full gonads were found year‐round in San Diego Bay, as were mussels in the smallest size class (with a large peak in fall and a smaller secondary one in spring), suggesting that many of the smallest mussels represent recruitment. The observation that most, although not all, tagged mussels increased in size provides further support for recruitment. Some of the highest numbers of mussels in the smallest size class were found inside eelgrass beds, indicating that eelgrass does not restrict and may actually enhance the distribution of very small mussels. The disjunct distribution of adult mussels and eelgrass thus is apparently established primarily postrecruitment. M. senhousia is capable of year‐round reproduction, recruitment and growth, and thus is poised to preempt space from eelgrass following any disturbance that results in eelgrass declines, such as habitat fragmentation, eutrophication, or disease.     

The endangered thick-shelled river mussel (<Emphasis Type="Italic">Unio crassus</Emphasis>): a new host species for the European bitterling (<Emphasis Type="Italic">Rhodeus amarus</Emphasis>)

Large freshwater mussels (Unionoida) are declining throughout the world. The European bitterling Rhodeus amarus (Bloch, 1782) female spawns its eggs inside the unionids’ shells, where fertilisation and further embryonic development take place; thus its reproduction depends fully on the presence of large freshwater mussels. Unio crassus, previously regarded as one of the most numerous unionids in Europe, is now listed in the IUCN Red Data List as being globally endangered. Despite its previous prevalence, it was never reported as a host for the bitterling. A large population of U. crassus was studied in small river at the ?wi?tokrzyskie Mts (Poland), where also electrofishing was conducted. In each bitterling territory located on the study plots, we found individuals of U. crassus, with the bitterling eggs or larvae developing on mussel’s gills. That proves that this species can be also used by the bitterling for reproduction. We suggest that this relationship has not been reported to date due to the mussels’ rarity and ongoing decline. However, it is also possible that the endangered mussel is a novel host for the bitterling, which is expanding its range throughout Europe.     

The influence of two differently sized dams on mussel assemblages and growth

Dams have been shown to impact freshwater mussels. We examined how mussels respond to differently sized dams (18 vs. 4 m) on the St. Croix River and its tributary, the Sunrise River. We hypothesized that: mussel density and growth rate would be greater downstream of the smaller dam due to the relatively greater food subsidies and temperature effects of the reservoir above it; and the effects of the small dam would moderate downstream as the localized impacts of the dam were reduced. We quantitatively sampled mussels upstream and downstream of the dams. For a common species, Actinonaias ligamentina, we ascertained growth rates by measuring successive growth rings. The highest mussel richness and diversity were upstream and downstream of the large dam. Higher mussel density was found immediately below the small dam but declined downstream. A. ligamentina downstream of the small dam grew faster and were larger than individuals in other reaches. Food availability and temperature appeared to influence mussel density and growth rate for A. ligamentina downstream of the small dam. This study provides information that may help managers decide whether to remove small dams or to maintain them because of the unique mussel habitats below these structures.     

Habitat structure is more important than nutrient supply in modifying mussel bed assemblage in an upwelling area of the Peruvian coast

Upwelling intensity modifies coastal primary production and influences individual traits of habitat-forming species. Along the Peruvian coast, beds of the mytilid Perumytilus purpuratus provide structurally complex habitats that harbour many organisms. We predict that in the nutrient-rich system of Central Peru, the modification of structural complexity would have stronger effects on the Perumytilus community than nutrient addition. We experimentally examined the effects of nutrient addition on the Perumytilus-dominated assemblage and we evaluated the potential effect of varying shell size on the Perumytilus-dominated assemblage. Nutrient addition to the mussel bed with slow-release fertilizers caused no changes in the total macro- and microalgal biomass and did not affect abundances or composition of the assemblage. To explore the effect of structural complexity on the Perumytilus assemblage, we manipulated mussel size with experimental bags containing small and large individuals. Predators, grazers and mobile organisms were more abundant among smaller mussels, with smaller gap volume, whereas the barnacle Jehlius cirratus was more abundant on larger mussels. In conclusion, point-source nutrient addition to the mussel bed did not enhance primary production. However, the modification of structural characteristics related to mussel size induced changes in the faunal assemblage. Thus, it seems that in this nutrient-rich system, nutrient enhancement would not significantly affect Perumytilus and its assemblage, whereas structural habitat seems to play an important role in shaping this community.     

Turbidity-mediated interactions between invasive filter-feeding mussels and native bioturbating mayflies

1. Invasive dreissenid mussels are known to cause large ecosystem changes because of their high filter‐feeding capacity, while native bioturbators may interfere with the mussels filter feeding. In this experiment, we investigated indirect environmental interactions between invasive filter‐feeding dreissenid mussels (zebra and quagga mussels) and native recolonizing bioturbating hexagenid mayflies (Hexagenia) at two mussel densities and two Hexagenia densities in a 2‐month long laboratory experiment. 2. Mean turbidity increased with increasing density of Hexagenia and decreased with increasing density of mussels. Turbidity showed the fastest decline at the highest mussel density, and no decline or a lower rate of decline at the low mussel density, dependent on Hexagenia density. 3. Mussel growth decreased with increasing Hexagenia density at low but not at high mussel density. Moreover, growth of mussels decreased as a function of increased mean turbidity at low mussel density but not at high mussel density. Filtering activity at the highest mussel density increased after introduction of food at the lower two densities of Hexagenia, but was constantly high at the highest Hexagenia density. 4. There was no difference in emergence of Hexagenia among the treatments, but mortality of Hexagenia was higher in the presence of mussels than in their absence. 5. Our results indicate that interactions between dreissenids and hexagenids are mediated through the sediment, and depend on density of both dreissenids and hexagenids. As the natural densities of these animals vary considerably within lakes, their growth and survival because of indirect environmental interactions is expected to vary spatially.     

Parasitic mite and trematode abundance are associated with reduced reproductive output and physiological condition of freshwater mussels

Although historically understudied, parasites may play an important role in freshwater invertebrate population ecology and evolution. We quantified abundance of parasitic mites and trematodes in the freshwater mussel Pyganodon grandis, in a southeastern Alabama stream (USA), to assess parasite impact on adult mussel physiological condition and reproductive output. We used stepwise multiple regression analyses to assess the effects of mussel size and parasites on reproduction and condition. Multiple regression analysis found no multivariate models that predicted reproductive output or physiological condition. However, univariate models revealed that increased parasite densities predict reduced mussel reproductive output and physiological condition. These findings suggest that parasites may have important negative consequences for freshwater mussels. We hypothesize that elevated parasite loads may reduce mussel fitness in impounded or nutrient-enriched streams with high densities of intermediate hosts (chironomid midges).     

The Effects of Food Concentration and Quality on the Feeding Rates of Three Size Classes of the Greenshell<Superscript>TM</Superscript> Mussel, <Emphasis Type="Italic">Perna canaliculus</Emphasis>

In order to calibrate carrying capacity models, investigations were conducted into the effects of food concentration and food quality on the feeding rates of small (25–50 mm), medium (60–85 mm) and large (90–115 mm) Greenshell mussels (Perna canaliculus). Experimental diets varying from 3.3 to 6.0 μg l⁻¹ chlorophyll a concentration and 12–25% organic content were fed to mussels housed in individual flow through chambers. Not surprisingly, this study found that the main factor affecting feeding rates is mussel size. Small mussels were observed to maintain a constant filtration rate of approximately 20 mg h⁻¹ irrespective of food concentration or quality, whereas mussels of greater than 60 mm length had more variable filtration rates between 30 and 80 mg h⁻¹. The filtration rates of these large mussels were also observed to increase positively with organic content, and showed no sign of levelling out, even at the highest organic content tested (25%). Highest rejection rates (50–70 mg h⁻¹) were observed when the organic content of the available seston was low, suggesting that P. canaliculus are able to selectively reject organic material, thereby organically enriching their diet. It appears that the organic content of the seston is the primary determinant of the net efficiency with which food is selected from the available seston by the mussel. The present study shows that P. canaliculus of all sizes are capable of adapting their feeding behaviour to compensate for changes in the food supply, which may occur over relatively short time periods, in the culture environment.     

Effects of Adult Dreissena polymorpha on Settling Juveniles and Associated Macroinvertebrates

The impact of Dreissena polymorpha settlement on recruitment of juvenile mussels and density of other macroinvertebrates was studied in field experiments using blank concrete blocks and tiles (control), blocks and tiles with attached empty zebra mussel shells, and blocks and tiles with attached living mussels. On blocks, dominant invertebrate taxa showed colonization patterns coinciding with increased habitat complexity owing to zebra mussel settlement or the biodeposition of faeces and pseudofaeces. Adult and especially juvenile zebra mussels preferred blocks with empty shells to blank blocks and blocks with living mussels; this might possibly be caused by a chemical cue that induces gregarious settlement. Lower recruitment on blocks with attached living mussels compared to blocks with only shells could be the consequence of ingestion of larvae by adult mussels and of competition for food. On tiles, the sediments deposited and the organic content of the sediment were investigated. Sedimentation was significantly higher on shell‐only and live‐mussel tiles compared to blank tiles. Organic matter differed significantly between blank and live‐mussel tiles.     

Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22-mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer-based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.     

A mineralogical record of ocean change: Decadal and centennial patterns in the California mussel

Ocean acidification, a product of increasing atmospheric carbon dioxide, may already have affected calcified organisms in the coastal zone, such as bivalves and other shellfish. Understanding species’ responses to climate change requires the context of long‐term dynamics. This can be particularly difficult given the longevity of many important species in contrast with the relatively rapid onset of environmental changes. Here, we present a unique archival dataset of mussel shells from a locale with recent environmental monitoring and historical climate reconstructions. We compare shell structure and composition in modern mussels, mussels from the 1970s, and mussel shells dating back to 1000–2420 years BP. Shell mineralogy has changed dramatically over the past 15 years, despite evidence for consistent mineral structure in the California mussel, Mytilus californianus, over the prior 2500 years. We present evidence for increased disorder in the calcium carbonate shells of mussels and greater variability between individuals. These changes in the last decade contrast markedly from a background of consistent shell mineralogy for centuries. Our results use an archival record of natural specimens to provide centennial‐scale context for altered minerology and variability in shell features as a response to acidification stress and illustrate the utility of long‐term studies and archival records in global change ecology. Increased variability between individuals is an emerging pattern in climate change responses, which may equally expose the vulnerability of organisms and the potential of populations for resilience.     

Average annual growth and condition of mussels as a function of food source

Prior to 1986, before completion of a storm surge barrier, the average annual condition of mussels at culture plots in the Eastern Scheldt was better in the western part near the North Sea, than in the central part of the estuary. No such difference was observed in 1986 and 1987.To predict the effects of the barrier on mussel culture, the condition of the mussels, which is an index of growth rate, is analysed and correlated with food sources for the period 1981–84. In the western and central part of the Eastern Scheldt, mussel condition correlates strongly with average annual primary production, but not with chlorophyll-a concentrations. This suggests a direct link between primary production and the growth of mussels.In the western part of the estuary, the relation between condition and primary production has a less steep slope than in the central part. Import of food from the North Sea is suggested to act as an additional food source in the west of the Eastern Scheldt; hence the better condition values of the mussels, also in years with relatively low primary production.The storm surge barrier reduces the water exchange with the North Sea. Reduced import of food and consequently lower mussel condition are expected in the western part of the estuary. Preliminary data from 1987 confirm this prediction.