Mussel Musculista Senhousia Research Articles

Lineage distribution and barriers to gene flow among populations of the globally invasive marine mussel Musculista senhousia

Introduced species seem to rapidly adapt to non-native conditions although founder events may decrease genetic variance and impede adaptation. Cryptic introductions of an invader from different parts of its native range may allow colonization of habitat patches with compatible conditions, or admixture may restore genetic diversity lost during invasion bottlenecks. We present the first genetic study of global invasion pathways for the Asian date mussel, Musculista senhousia, comparing three putative source populations from Asia with six US estuaries and one invaded site in New Zealand and the Mediterranean Sea, totaling 117 individuals. Distribution of mitochondrial DNA and alleles of a nuclear intron revealed two genetically divergent populations in the native range. A warm-water lineage from Tokyo Bay and southwestern South Korea predominated in southern California and New Zealand, while a cold-water haplotype group sampled in northeastern Korea was more abundant at invaded sites in the northwestern US and Mediterranean Sea. The duration of high summer water temperatures accounted for substantial variance in the worldwide distribution of common haplotype groups, suggesting thermal pre-adaptation may influence invasion success for differentiated source populations. There was no gene flow across central California, but on either side of this phylogeographic barrier there was high exchange among estuaries within the northern and the southern US regional populations. Gradients in water temperature may therefore constrain post-introduction spread by limiting dispersion along a coast.

First records of the Australian dog whelk, Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849) (Mollusca: Gastropoda) from New Zealand

Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849) is a common dog whelk in subtropical and temperate regions of Australia. In April 2009, two shells of this species were found in the central Waitemata Harbour, Auckland. On the 22 June 2009, a live specimen was found at an intertidal site near Henderson Creek on the western central section of the harbour. Between August 2009 and February 2010, a further 21 living specimens in a range of sizes were found across multiple sites in the central Waitemata Harbour. This species is currently adventive and its presence in the Waitemata Harbour suggests accidental introduction from Australia and subsequent survival. If this species becomes firmly established in New Zealand, there may be significant interactions with native species such as Cominella glandiformis (Reeve, 1847), with which it may directly compete for food, and the invasive mussel Musculista senhousia (Benson in Cantor, 1842), which it is known to eat.

The apparent demise of the Asian date mussel Musculista senhousia in Western Australia: or using acts of god as an eradication tool

Musculista senhousia (Benson in Cantor, 1842) is a small thin-shelled mytilid inhabiting intertidal and shallow subtidal sediments. Prior to 2000, M. senhousia was widespread in the Swan River estuary, Perth, Western Australia. In 2000 the Perth region experienced its largest recorded summer rainfall event, with over 270 GL entering the estuary. The rainfall formed a freshwater lens over much of the river and a subsequent toxic algal bloom of the cyanobacterium Microcystis aeruginosa. M. aeruginosa produces a toxin microcystin, known to have adverse effects upon molluscs. Surveys to assess the status of M. senhousia in the estuary in 2007 failed to find any individuals. We suggest the apparent death of M. senhousia from the estuary may be attributable to a combination of high seasonal variability in the mussel’s populations, high summer rainfall reducing salinity, and a toxic algal bloom that eliminated any remaining M. senhousia individuals.

A round-the-world tour almost completed: first records of the invasive mussel Musculista senhousia in the north-east Atlantic (southern Bay of Biscay)

A round-the-world tour almost completed: first records of the invasive mussel Musculista senhousia in the north-east Atlantic (southern Bay of Biscay)

Organism responses to habitat fragmentation in two shallow-water brackish environments: the Goro Lagoon (Adriatic Sea) and the Padrongiano Delta (Tyrrhenian Sea)

Habitat fragmentation from natural or human-mediated causes is a common phenomenon in terrestrial and aquatic environments. In this study, the effects of varying the size of habitat patches on the abundance of benthic invertebrates inhabiting date mussel (Musculista senhousia) patches was studied at two different transition environments, the Goro Lagoon (Adriatic Sea) and the Padrongiano Delta (Tyrrhenian Sea). Benthic fauna responded to habitat patchiness in a complex manner that varied according to habitat type, taxon and animal body size (small: 0.5–2.0 mm; large >2 mm). Small invertebrates were mostly polychaetes, nemertea, amphipods and isopods. Large invertebrates were mostly large polychaetes, bivalves, gastropods and crabs. Invertebrate population size and diversity seemed to be maximized in landscapes that include both small and large patches of mussel beds ‘embedded’ in a continuous matrix. Musculista senhousia patches served as a critical refuge and foraging habitat for many species. Patchy and continuous areas may promote the persistence of organisms with different life histories, especially in environments like those studied where mussel patches represent the only structural refuge available.

Effects of the exotic invader Musculista senhousia on benthic communities of two Mediterranean lagoons

The impact that the alien mussel Musculista senhousia has on benthic biodiversity and community structure was investigated in two Italian transitional environments, where the species was particularly abundant: the Sacca di Goro (Adriatic Sea), and the Rio Padrongiano Deltaic area (Sardinia, Tyrrhenian Sea). Sampling campaigns were conducted by sampling mussel beds from each of two different patch size classes (small: 10.0 m2), and the surrounding bare sediments. At both study sites, mussel density varied greatly with time within and between patches. Despite the huge difference in benthic species complement at Goro and Padrongiano (33 and 115 taxa, respectively), at both sites the presence of mussel patches had a gross positive effect on the benthic community. At Goro, many trophic guilds showed a positive relationship with mussel abundance. At Padrongiano, a continuous and directional process of patches colonization (both large and small) through time seemed evident, while at Goro the process was interrupted by high-summer mortalities. At both study sites, M. senhousia played a double role: (1) as secondary substratum, enhancing the environmental structural complexity, and (2) as densely aggregated, living organisms, thus giving rise to a number of possible interactions with other invertebrates. The outcome, however, was strictly dependent by the level of anthropogenic stress, in this case water oxygen deficiency, which was different at the two study sites.

<i>Sanyuania cuneata</i> Zhao & Whatley, 1992 (Ostracoda, Cytheroidea, Cytherideidae) from Japan: morphology, distribution and environmental significance

Abstract. Sanyuania cuneata Zhao & Whatley, 1992 was reported initially from Late Pleistocene core samples from the northern part of the Yellow Sea and Recent sediments collected from supra tidal pools (17 practical salinity unit (psu)) in Xiangshangang Bay, East China Sea (Zhao & Whatley, 1992). Later, specimens were discovered, but not identified, in Lake Nakaumi, Shimane Prefecture, SW Japan (Fig. 1) (as Cytheridae gen. et. sp. indet. by Tanaka et al. (1998) and Sanyuania sp. by Seto et al. (1999)). Further examination of these Japanese specimens has clarified that they are conspecific with the Chinese specimens. This has provided an opportunity to review the distribution (Fig. 1) and potential environmental significance of Sanyuania cuneata and, for the first time, to describe its appendages (Fig. 2).Specimens figured herein were recovered from Lake Nakaumi (35°26′ 50″ N, 133°07′50″ E) at a depth of 0.3–6.0 m and salinity of 8–17 psu on 9 September 1998. The surface of the sediment was covered by the byssus of the mussel Musculista senhousia (Benson, 1842).Sanyuania cuneata is probably endemic to the East China Sea and the southwestern part of the Sea of Japan and is a potentially useful palaeoenvironmental indicator of brackish (steno-haline) environments in the area. By using the oxygen isotopic data from planktonic foraminifers and the estimated value of salinity flowing into the Japan Sea, Matsui et al. (1998) approximated that the salinity of the surface water of Japan Sea declined to about 20 psu during the Last Glacial Maximum . . .

Changes in the shelf macrobenthic community over large temporal and spatial scales in the Bohai Sea, China

Over the past 20 years, the Bohai Sea has been subjected to a considerable human impact through over-fishing and pollution. Together with the influence of the Yellow River cut-off, the ecosystem experienced a dramatic change. In order to integrate available information to detect any change in macrobenthic community structure and diversity over space and time, data collected during the 1980s and the 1990s from 3 regions of the Bohai Sea (Laizhou Bay, 16 stations, 37–38°N, 119–120.5°E; central Bohai Sea, 25 stations, 38–39°N, 119–121°E; eastern Bohai Bay, 12 stations, 38–39°N, 118.5–119°E) were reanalyzed in a comparative way by means of a variety of statistical techniques. A considerable change in community structure between the 1980s and the 1990s and over the geographical regions at both the species and family level were revealed. After 10 years, there was a considerable increase in abundance of small polychaetes, bivalves and crustaceans but decreased number of echinoderms. Once abundant in Laizhou Bay in the 1980s, a large echinoderm Echinocardium cordatum and a small mussel Musculista senhousia almost disappeared from the surveying area in the 1990s. Coupled with the increased abundance was the increased species richness in general whereas evenness was getting lower in central Bohai Sea and Bohai Bay but increased in Laizhou Bay. K-dominance plot showed the same trend as evenness J′. After 10 years, the macrobenthic diversity in the Bohai Sea as a whole was slightly reduced and a diversity ranking of central Bohai Sea > Laizhou Bay > eastern Bohai Bay over space was also suggested. Sediment granulometry and organic content were the two major agents behind the observed changes.

Effects of native predators and eelgrass habitat structure on the introduced Asian mussel Musculista senhousia (Benson in Cantor) in southern California

The ability of predators to control the abundance of non-native species has been little explored in marine systems. Native predators may be used to control non-native species or may confer invasion resistance to communities if predation rates on invaders are density-dependent. We studied the response of southern California native predators to the density of Musculista senhousia (Benson in Cantor, 1842), a small, fast growing mussel that has been introduced from Japan to several coastlines worldwide. We performed field experiments to determine if M. senhousia proportional mortality is density-dependent and if eelgrass Zostera marina L. habitat structure influenced mussel density-dependent mortality. We also evaluated the effect of seagrass habitat structure on the aggregative and functional responses of the predatory gastropod Pteropurpura festiva (Hinds, 1844) to Asian mussel density. In the summer of 2002, P. festiva aggregated in plots with high mussel density and was responsible for nearly all predation on M. senhousia. However, M. senhousia proportional mortality was inversely density-dependent at all levels of eelgrass above-ground and below-ground habitat structure. Asian mussel proportional mortality also was inversely density-dependent and was not influenced by eelgrass habitat structure in the spring of 2004 when wading birds were the chief predator of mussels. In contrast to results for mussel proportional mortality, the aggregative and functional responses of P. festiva varied with seagrass habitat structure. P. festiva density increased with Asian mussel density in plots with low simulated habitat structure, but the relationship between P. festiva density and Asian mussel density was parabolic at zero, intermediate and high levels of habitat structure. In field enclosures, P. festiva exhibited a Type I (linear) functional response to Asian mussel density at low levels of eelgrass structure, and a Type II (hyperbolic) functional response to mussel density at high levels of eelgrass structure. Our results and those of others suggest that the degree to which local benthic communities in southern California are resistant to Asian mussel invasion depends on habitat structure, mussel settlement rates, and the density and diversity of predators.

Vertical Distributions of Larvae of the Clam Ruditapes philippinarum and the Striped Horse Mussel Musculista senhousia in Eastern Ariake Bay, Southern Japan

We have examined the vertical distributions of planktonic bivalve larvae, particularly the clam Ruditapes philippinarum and the mussel Musculista senhousia which are common and abundant on tidal flats of eastern Ariake Bay, southern Japan. Submersible pumping gear was used to take samples at 2 stations every 2 hours during the spring tide over a whole tidal cycle and/or through daytime and nighttime. Water samples were pumped up from 3 to 5 depths from the surface to sea bottom. Regardless of tidal cycles, D-shaped larvae were concentrated near the surface, while umbo larvae were found at the surface to intermediate depths. On average, these larval densities were significantly higher at the station close to the shore than the offshore station, with no significant difference between daytime and nighttime and between flood and ebb tides at each station. The velocity and direction of water movement at both stations revealed remarkable difference between the surface and bottom waters. The larvae at the surface may quickly disperse and be transported elsewhere, while those in water close to the sea bottom may tend to be retained.

Foraging behaviour and mutual interference in the Mediterranean shore crab, Carcinus aestuarii, preying upon the immigrant mussel Musculista senhousia

Predator–prey dynamics between the Mediterranean shore crab Carcinus aestuarii and the immigrant mussel Musculista senhousia were examined in laboratory experiments to assess the effects of varying predator and prey densities upon predator foraging rates and prey survival. The factorial design involved three predator and three prey densities, with four trials per treatment combination. Functional responses were differentiated statistically by analysis of the exponent β of a general functional response model. Shore crabs displayed type II (decelerating rise to an upper asymptote) inversely density-dependent functional responses at low and moderate predator densities, while a non-traditional model was probably more appropriate at high predator density. No density-dependent refuge was observed for M. senhousia, whereas, at high predator density, mutual interference among crabs was evident and prey mortality was lowered. Mediterranean shore crab's combined functional and interference response, by affecting foraging rates, was important to the outcome of interactions between predators and the bivalve prey, and might play an important role in determining crab's predatory behaviour and dispersion, and prey persistence, in the field.

Native eelgrass Zostera marina controls growth and reproduction of an invasive mussel through food limitation

In southern California, native eelgrass Zostera marina L. and the invasive non-native mussel Musculista senhousia have dynamic complex interactions. Although high densities of M. sen- housia inhibit the growth of eelgrass, mussel survival and growth decline with increasing eelgrass shoot density and patch size. The correlation of these eelgrass attributes with local concentrations of chlorophyll a and water flow speeds suggested that the mussels, which feed on phytoplankton deliv- ered by water currents, might suffer food limitation inside large eelgrass beds. By supplementing phytoplankton to M. senhousia living in eelgrass, we confirmed this hypothesis: mussels grew 50% faster when food availability was enhanced. Lab and field experiments investigating the effects of food limitation on growth and reproduction of M. senhousia showed that mussels respond by reduc- ing shell growth, and subsequently fecundity. We found no evidence that mussels reallocated resources preferentially to reproduction when food was limited. Our results highlight how the effects of anthropogenic perturbations that currently threaten eelgrass populations directly could be magni- fied by interactions with a non-native species. Eelgrass habitat fragmentation and increasingly frequent phytoplankton blooms resulting from coastal development and eutrophication have well- described direct negative effects on eelgrass. By increasing phytoplankton availability to M. sen- housia, such perturbations also indirectly affect eelgrass by acting to enhance mussel survival and growth, magnifying the negative effects of the mussel on Z. marina.

Ecological characteristics of the invasive Asian date mussel,Musculista senhousia, in the Sacca Di Goro (Adriatic Sea, Italy)

A population of the invasive musselMusculista senhousia was monitored bimonthly from May 1999 through April 2000 in the Sacca di Goro, a brackish lagoon of the Po River Delta, Northern Adriatic Sea, in order to give information on the gametogenic cycle, population dynamics, and secondary production of this successful invader. The gonad underwent 4 different stages: spent (December to February), developing (March to May), ripe (June to August), and spawning (September to November). The population was numerically dominated by a single cohort of individuals for most of the year. The mean size of this cohort rapidly increased to 24–25 mm shell length, after which growth slowed and mussels rarely grew larger than 30–32 mm. Summer anoxia may have greatly reduced mussel abundance; annual cohort mortality was 95%. No recruitment was registered on the bed until February 2000, and there was a large pulse of new recruits in April when two cohorts were clearly recognizable. The established bed was the primary site for new recruitment. Secondary production, calculated with two different methods, gave comparable estimates; P:B ratios were 1.5 and 1.7.M. senhousia beds seemed to facilitate the presence of other macrofaunal taxa: abundance of some species (a small gastropod, amphipods, and tube-building polychaetes) were significantly higher within mussel mats at two sites sampled in May 2000 than they were in soft-sediments ∼100 m away.

Effect of Food Concentration Inside Eelgrass Beds on the Energy Balance of the Invasive Mussel Musculista Senhousia

Samples of Musculista senhousia, 20 mm in length, were gathered from San Diego Bay and fed on three different food concentrations: 0.2, 0.4 and 0.8 mg AFDW L m 1, and their energy balance studied. Food concentration ranges were selected to reflect those observed in the field where the invasive mussel M. senhousia co-occurs with the angiosperm, Zostera marina. The lowest and intermediate concentrations correspond to concentrations described in and over large eelgrass patches, respectively. The upper concentration is equivalent to that occurring during the spring phytoplankton blooms. Ingestion rates varied between 81.6 µg AFDW h m 1 for the mussels fed on the lowest concentration, 191.2 µg AFDW h m 1 when the concentration rose to 0.4 mg AFDW L m 1, and 164.0 µg AFDW h m 1 for the highest concentration. Food concentration had a significant effect on absorption efficiency, which was approximately 70% at the intermediate and upper concentrations, but rose to over 80% at the lowest concentration. The food absorption rate varied with food concentration in a manner similar to that of the ingestion rate, i.e., with a maximum value of 142.34 µg AFDW h m 1 for the mussels fed on the intermediate concentration, this being higher than the values for both the highest concentration (114.72 µg AFDW h m 1) and the lowest (65.89 µg AFDW h m 1). Respiration rates were 54 µg O 2 h m 1 for the mussels fed on the lowest concentration and 74 µg O 2 h m 1 for those fed on the intermediate concentration. These results show a close relationship between respiration and ingestion rates, which can be fitted to the following equation: RR = e (m 0.42 + 0.10 IR) (r = 0.5703, R 2 = 32.53, p <0.01). Scope for growth (SFG) estimations were higher for those mussels fed at the intermediate and upper concentrations (1.95 J h m 1 and 1.50 J h m 1, respectively), between which no significant difference was observed (p > 0.05), whilst SFG for the lowest food concentration was only 0.69 J h m 1. The physiological rate with the greatest effect on growth was the absorption rate. Its relation to SFG is described by the equation SFG = 0.67 + 0.90AR (r = 0.977, R 2 = 95.56%, p <0.01). The discussion of these results is based on the growth rates that have been described for this mussel in its natural environment where habitat structure, such as the canopy provided by the eelgrass, can affect the success of the invasive mussel.

The effects of seagrass (Zostera japonica) canopy structure on associated fauna: a study using artificial seagrass units and sampling of natural beds.

The importance of seagrass canopy to associated fauna was assessed by comparing the species richness, abundance and diversity of the epi- and infaunal macroinvertebrate assemblages in a seagrass (Zostera japonica Ascherson and Graebner) bed and the adjacent unvegetated area in Hong Kong. Seagrass cover had significant effects on the composition and abundance of the associated fauna and the amount of detritus accumulated on the sediment surface. Detritus abundance was significantly higher in the seagrass bed, and was positively correlated with both the above- and belowground biomass of Z. japonica. Both the abundance and species richness of the epi- and infauna were significantly positively correlated with the belowground biomass of the seagrass and detritus standing crop. Macrofaunal species richness was higher (118) in the seagrass bed than the adjacent unvegetated areas (70), with a higher degree of similarity between the infauna than the epifauna of the two habitats. While all species recorded from the unvegetated areas were found in the seagrass bed, 48 species occurred only in the seagrass-covered areas. Species richness of epifauna was significantly higher in the seagrass bed, but there was no difference between infaunal species of the two habitats. On the contrary, faunal (epi- and infauna) abundance was significantly higher in seagrass areas. The seagrass bed also supported species of small tellinid bivalves previously not recorded from Hong Kong. Artificial seagrass units (ASUs, 0.2 m(2)) with four combinations of leaf density and leaf length and a control (bare sand) were placed at short distances from natural patches of Z. japonica. The composition, abundance and biomass of the epibenthos associated with the ASUs and the control were recorded after 3 months in the field. While species richness did not differ among the treatments, total abundance of epibenthos was significantly higher in the high density-long leaves (HL) treatment than in the control. Results of a discriminant analysis using log-transformed abundance data suggest that the gastropod Clithon oualaniensis, the mussel Musculista senhousia and the crab Thalamita sp. were important species distinguishing the assemblages in the various treatments. All the three species were significantly more abundant in the HL treatment than in the low density-short leaves (LS) treatment and the control. By contrast, there was no significant difference in the biomass of the epifauna, but discriminant analysis again separated the five treatments based on the composition of the biomass, with the same three species identified as the most important discriminating species. The species richness and abundance of the epifauna associated with the ASUs were similar to the adjacent unvegetated areas, but significantly lower than in the Zostera patches. The physical canopy structure of Z. japonica beds increased the abundance of the epibenthos, potentially through provision of canopy and indirectly through trapping of detritus.

Assessing invader roles within changing ecosystems: historical and experimental perspectives on an exotic mussel in an urbanized lagoon

It is often difficult to accurately assess the long-term effects of invaders because of a lack of data and the changing nature of ecosystems. However, available historical information can be used to make comparisons with current conditions and generate hypotheses that can be tested experimentally. This approach was used to examine changes in the bivalve community of Mission Bay, San Diego, California, USA. A 20-year dataset on subtidal bivalves shows a marked increase in abundance of the exotic mussel Musculista senhousia, and concomitant declines in species richness and the abundance of the native Solen rostriformis. Currently, Musculista also dominates the tidal creeks of a remnant salt marsh and an adjacent restored marsh, and is 100 times more abundant than any native bivalve species. A comparison of the bivalves now present in the remnant marsh creek to the community present 35 years ago demonstrates that while Musculista increased in abundance, the native Chione fluctifraga disappeared from the creek. In the same time frame, two other natives, Macoma nasuta and C. undatella, appeared in the system. Experiments demonstrate that the growth and survivorship of the surface-dwelling, suspension-feeding Chione spp. significantly decrease in the presence of Musculista, whereas the deeper-dwelling, deposit-feeding Macoma nasuta shows no such inhibition. Viewing these results in the broader context of physical change within the wetland explains some patterns of observed change and suggests effects due at least in part to Musculista, but also demonstrates the complexities associated with assessing long-term patterns in systems affected by multiple factors.

Habitat selection by wintering tufted ducks with special reference to their digestive organ and to possible segregation between neighboring populations

Habitat selection by tufted ducks (Aythya fuligula), a diving duck which swallows benthic prey organisms, was studied during winter at two neighboring lagoons (Lakes Nakaumi and Shinji, Honshu, Japan) which differ strongly in their benthic fauna and in their diving duck densities. The ducks fed overwhelmingly on the dominant bivalve found in each of the two lagoons, the mussel Musculista senhousia in L. Nakaumi and the clam Corbicula japonica in L. Shinji. In general, however, the ducks probably preferred the mussels to the clams because of: (i) their high (2.9 times) calorific content for their weight; (ii) their high digestibility; (iii) their greater accessibility; and (iv) their shorter handling time. An average tufted duck (850 g) was estimated to require 1.3 kg of mussels or 3.8 kg of clams to meet their daily energy requirements. As a result, the two wintering populations were estimated to consume 4970 t mussels and 4770 t clams during a single wintering season, amounting to some 20% of the standing clam crop. Throughout the winter the average gizzard weight (37 g), and gizzard–body mass ratio (4.2%) of the Lake Nakaumi population were half those of the Lake Shinji population (73 g, 8.1%, respectively), despite their significantly similar nutritive body condition (% body lipid &gt; 12%). The need to maintain a specialized gizzard mass in order to be able to cope with the different prey species results in little opportunity for ‘sampling’ movements of birds between lakes/prey types and as a result two subpopulations of ducks are indicated to be segregated.

Macrophyte Canopy Structure and the Success of an Invasive Marine Bivalve

In both terrestrial and aquatic environments introductions of non-indigenous species are continuing and represent one important component of global change. Negative biotic interactions by resident species may prevent successful invaders from becoming pests. Few experimental data are available on the presence and significance of such biotic resistance other than predation or competition. This study addresses the role of habitat structure provided by a native eelgrass (Zostera marina) canopy on growth and survival of the non-indigenous mussel Musculista senhousia, a habitat-modifying gregarious suspension feeder with strong effects on native infauna and eelgrass. In 2 southern California bays, a series of transplantation experiments using tagged mussels revealed that inside an eelgrass canopy, Musculista growth rates were reduced by more than half in 3 of 4 experiments compared to adjacent unvegetated areas. Musculista survival also decreased inside the vegetation in a 4-mo experiment. As one element of habitat structure, we tested the effects of eelgrass parch size, using natural (1 site) and planted (1 site) eelgrass patches of defined sizes. Growth rates of Musculista were highest outside the veneration and decreased as eelgrass patch size increased. As a potential mechanism for the canopy effects, we suggest that Musculista receives less food inside the vegetation. In the experimental plots, the presence and spatial extent of the macrophyte canopy strongly affected near bottom (10 cm) horizontal water flow assessed with a direct dye tracking method. Reduced mussel growth rates were linearly associated with lower water flow, and presumably, food flux. Over a period of 7 mo, food resources (particulate chlorophyll a) were consistently lower 1 and 5 cm above the sea floor inside eelgrass patches compared to the sand Aat. The reduction in food availability matched the growth reduction of Musculista. Also, mussel condition (dry flesh mass/shell mass) was worse in individuals growing in eelgrass than in the sand Aat. Previous experiments revealed that dense beds of Musculista impede the rhizome growth and vegetative propagation of eelgrass, yet mussels attain abundances sufficient for interference only if eelgrass beds are patchy. Thus, anthropogenic disturbances on eelgrass beds, which often result in meadow fragmentation, and the proliferation of Musculista may have synergistic negative effects on the persistence of eelgrass beds.

Variable responses of native eelgrass Zostera marina to a non-indigenous bivalve Musculista senhousia.

The transport and establishment of non-indigenous species in coastal marine environments are increasing worldwide, yet few studies have experimentally addressed the interactions between potentially dominant non-native species and native organisms. We studied the effects of the introduced mussel Musculista senhousia on leaf and rhizome growth and shoot density of eelgrass Zostera marina in San Diego Bay, California. We added M. senhousia over a natural range in biomass (0-1200 g dry mass/m2) to eelgrass in transplanted and established beds. The effects of the non-indigenous mussel varied from facilitation to interference depending on time, the abundance of M. senhousia, and the response variable considered. Consistent results were that mussel additions linearly inhibited eelgrass rhizome elongation rates. With 800 g dry mass/m2 of M. senhousia, eelgrass rhizomes grew 40% less than controls in two eelgrass transplantations and in one established eelgrass bed. These results indicate that M. senhousia, could both impair the success of transplantations of eelgrass, which spread vegetatively by rhizomes, and the spread of established Z. marina beds to areas inhabited by M. senhousia. Although effects on leaf growth were not always significant, in August in both eelgrass transplantations and established meadows leaf growth was fertilized by mussels, and showed a saturation-type relationship to sediment ammonium concentrations. Ammonium concentrations and sediment organic content were linear functions of mussel biomass. We found only small, non-consistent effects of M. senhousia on shoot density of eelgrass over 6-month periods. In established eelgrass beds, but not in transplanted eelgrass patches (≈0.8 m in diameter), added mussels suffered large declines. Hence, eelgrass is likely to be affected by M. senhousia primarily where Z. marina beds are patchy and sparse. Our study has management and conservation implications for eelgrass because many beds are already seriously degraded and limited in southern California where the mussel is very abundant.

Habitat alteration and community-level effects of an exotic mussel, Musculista senhousia

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 162:137-152 (1998) - doi:10.3354/meps162137 Habitat alteration and community-level effects of an exotic mussel, Musculista senhousia Jeffrey A. Crooks* Scripps Institution of Oceanography, La Jolla, California 92093-0218, USA *E-mail: jcrooks@ucsd.edu The mussel Musculista senhousia is capable of marked habitat alteration through the construction of byssal mats on the surface of soft sediments. Here I demonstrate the importance of this alteration on sedimentary properties and resident macrofaunal assemblages of a tidal flat in Mission Bay, San Diego, California, USA, where the mussel is exotic. In well-developed mats, percent fine sediments, percent combustible organic matter, and sediment shear strengths were increased relative to adjacent areas without mats. Comparisons of naturally occurring areas with and without mats of M. senhousia, as well as comparisons of the same tidal flat when mussels were seasonally present and absent, revealed that assemblages within mussel mats differ from those in sediments without mats. The primary effect of the mussel and its mats was facilitation of other organisms. Total densities of all macrofaunal individuals as well as species richness were typically higher inside than outside mussel mats. Two species that exhibited large enhancements of densities within mussel mats were the tanaid Leptochelia dubia and the gastropod Barleeia subtenuis. Oligochaetes, a numerically important component of the tidal flat, appear least facilitated by the presence of mats. A short-term, manipulative experiment that examined the effects of mussel mat mimics on the colonization of macrofauna suggested that the presence of physical structure alone can produce several of the patterns observed in naturally occurring mussel mats. These results highlight that alteration of habitats is an important effect of exotic species, and that these habitat alterations can have subsequent effects on resident biotic communities. Community structure · Exotic species · Habitat alteration · Ecosystem engineering · Benthic macrofauna · Facilitation · Musculista senhousia · Mission Bay Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 162. Publication date: February 12, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.