Incubation temperature critical to successful stimulation of in vitro zygotic embryo growth in four Australian native Cyperaceae species

Many species of Western Australian Cyperaceae (sedges) are vital components of the indigenous flora but commonly display low seed set, poor seed quality and intractable seed dormancy. We report the effects of incubation temperature and in vitro growth media on whole seed germination compared with extracted zygotic embryo growth in Tetraria capillaris, T. octandra, Lepidosperma drummondii and L. tenue. No germination was observed from intact whole seeds of all test species regardless of the treatment evaluated. In contrast, excised zygotic embryos of all study species exhibited significant increases in growth when cultured at 15°C compared to embryos incubated at 25°C; however, optimal media for embryo growth were genera specific. Extracted embryos of T. capillaris and T. octandra exhibited maximum percentage growth (30 and 40%, respectively) at 15°C on ½ MS medium with no plant growth regulators required. In the case of L. drummondii and L. tenue 1 μM thidiazuron was a necessary addition to the ½ MS medium resulting in 40 and 77% growth of embryos (at 15°C), respectively. Incubation of extracted embryos at 25°C (regardless of medium treatment) resulted in <10% embryo growth for T. octandra and L. tenue, while the remaining two species (L. drummondii, T. capillaris) showed no embryo growth at 25°C on any medium treatment.     

Azoreductase activity in the hard clam, Mercenaria mercenaria (L.)

The ability of the hard clam Mercenaria mercenaria (L.) to metabolize compounds containing an azo linkage has been investigated. The hepatopancreas has azoreductase activity as evidenced by the reduction of 1,2-dimethyl-4-(p-carboxyphenylazo)-5-hydroxybenzene. This activity was higher at 37°C than at 22°C and the pH optimum was 8.0. The reaction was stimulated by the addition of flavin mononucleotide and inhibited by air. Activity was found in both the 105,000 g soluble and the microsomal fractions of the hepatopancreas.     

A quantitative study of phagocytosis by hemolymph cells of the pelecypods Crassostrea virginica and Mercenaria mercenaria

Fresh hemolymph cells of the pelecypods Crassostrea virginica and Mercenaria mercenaria were exposed to known concentrations of Bacillus megaterium, Escherichia coli, and Staphylococcus aureus in vitro and it was ascertained that all four types of cells of C. virginica and all three types of M. mercenaria became associated with the bacteria. Association is defined as either the first, i.e., contact and adherence, or second, i.e., engulfment, phase of phagocytosis. However, when the surfaces of each type of cell, as well as the percentages of each type in whole hemolymph, from both species of molluscs are taken into consideration, it is concluded that the granulocytes are the most important from the standpoint of phagocytosis.When hemocytes of M. mercenaria were exposed to Bacillus megaterium at 4°, 22°, and 37°C, it was found that the association indices were higher at the latter two temperatures. It is postulated, because of the results of Feng and Feng (1974), that nonself materials adhere with less frequency at 4°C and hence are not phagocytosed at this lower temperature.     

The influence of plankton composition and water quality on hard clam (Mercenaria mercenaria L.) populations across Long Island's south shore lagoon estuaries (New York, USA)

We conducted a two-year study to assess how plankton composition and water quality impacts the distribution, densities, condition, growth, biochemical composition and reproductive success of juvenile and adult Mercenaria mercenaria (L.) in Long Island's south shore estuaries (LISSE). Juvenile and adult hard clams were placed in suspended cages at 10 locations ranging from the ocean inlets to locations furthest from inlets in Shinnecock Bay (SB), the eastern-most barrier island estuary of LISSE, and Great South Bay (GSB), the western-most barrier island estuary of LISSE. Phytoplankton community composition, temperature, salinity, dissolved oxygen, and clam growth and condition were monitored bi-weekly. A benthic survey of M. mercenaria densities in both estuaries was also conducted. In both 2004 and 2005, juveniles in central bay locations had significantly faster growth rates, lower mortality rates, and higher lipid content relative to sites closest to the inlets. Adult hard clams closest to the Fire Island inlet also had significantly lower condition indexes compared to mid-bay stations and densities of wild M. mercenaria populations in both estuaries were lower near inlets compared to locations further from inlets. In addition to substantial spatial differences within each estuary, differences were also observed between the embayments as juvenile clams in SB grew approximately twice as fast as those in GSB and adults in SB had significantly greater condition indexes than clams in GSB. Instantaneous juvenile growth rates were highly correlated to temperatures below 24 °C (p < 0.0001) and were also significantly correlated with several indicators of suspended food quantity and food quality (centric diatoms, phytoplankton cells > 5 μm, and dinoflagellates (inverse correlation)) which co-varied independently of temperature. In sum, these results suggest tidal exchange in LISSE promotes a water quality regime (cold water, with low food concentration) which would reduce the growth of juvenile clams and the overall reproductive success of adult hard clams located near newly-formed ocean inlets. However, increased exchange for regions furthest from inlets could enhance juvenile clam growth rates by reducing summer peak temperatures (> 24 °C) and densities of poor food sources (dinoflagellates).     

Growth competition between Microcystis aeruginosa and Quadrigula chodatii under controlled conditions

Cyanobacteria are the dominant bloom-forming species in Lake Taihu. Understanding the competition among algae is important to control strategies for bloom formation and outbreaks in freshwater ecosystems. In this study, we demonstrate that the cyanobacterium Microcystis aeruginosa PCC7820 and the green alga Quadrigula chodatii FACHB-1080 exhibit a strong competitive inhibitory relationship under co-culture conditions, with the latter strain inhibiting the former. Several factors influence the competitive relationship between the two species, including nutrition, temperature, and organic/inorganic compounds. Q. chodatii strongly inhibited M. aeruginosa growth through the inhibition of nitrogen utilization during co-culture. Temperature was also an influential determinant of the competition capacity between the two species under eutrophic conditions: at lower temperatures (15 °C), M. aeruginosa grew better than Q. chodatii, but the difference was not significant (p?>?0.05), whereas at higher temperatures (25 °C, 35 °C), Q. chodatii grew significantly better than M. aeruginosa (p?<?0.05). Furthermore, the Q. chodatii filtrate strongly inhibited the growth of M. aeruginosa. An analysis of the crude extracts of the algae culture filtrates from uni- and co-cultures using gas chromatography mass spectrometry (GC/MS) indicated that algal metabolites, such as dibutyl phthalate and beta-sitosterol, might play a key role in the competition between algae.     

Short-term effects of temperature upon the growth of intertidal fucales

The growth rate of five species of intertidal Fucales (Pelvetia canaliculata (L.) Dec. et Thur., Fucus spiralis L., Fucus vesiculosus L., Fucus serratus L., Ascophyllum nodosum (L.) Le Jolis) was measured at temperatures from 2.5 to 35 °C. An increase in temperature immediately causes a high growth rate, and during the first hour it increases linearly with temperature; at 35 °C it is 20 times the control at 7 °C. This acceleration of growth is based mainly on stored photosynthate. After the first few hours the growth rate decreases rapidly, particularly at the highest temperatures. After 2–3 weeks a temperature optimum below 17.5 °C is indicated. High temperatures, 30–35 °C, were lethal to all species, with a survival time corresponding to their vertical zonation in the natural habitat.     

Effects of temperature on calcium deposition in the hard-shell clam, Mercenaria mercenaria

A radiographic technique was developed and employed to determine the effects of temperature variation on the rate and distributive pattern of calcium deposition in the shell of the marine clam Mercenaria mercenaria (Linne). Both the rate and pattern of calcification were found to be significantly affected by temperature variation. Two optimal temperatures for maximum overall shell growth were found at approx. 12.8–15.6 and 23.9°C. At all temperatures but the lowest one tested (4.4°C), a higher rate of calcification was found peripherally than centrally in the shell. The pattern of calcium incorporation in the central portions of the shell was irregular and often discontinuous.     

The food chain dynamics of the oyster,clam, and mussel in an aquaculture food chain

The food chain dynamics of the edible mussel Mytilus edulis L., the American oyster Crassostrea virginica (Gmelin) and the hard clam Mercenaria mercenaria (L.) were investigated in large experimental tanks with flowing, filtered sea water and controlled addition of phytoplankton. The feeding rate of the mussel (5.36 μg carbon removed/l/g C animal was higher than that of the oyster (3.92) and clam (3.03) but the ecological efficiencies (net production/ingested food) × 100 of the clam (23.69 %) and the oyster (18.38 %) were higher than that of the mussel (10.01 %).The food chain efficiencies (net production/available food) were lower than the ecological efficiencies, suggesting under-exploitation of the available food. The clam, although having a lower feeding rate, was more efficient in utilizing the food it filtered and so showed the highest net production.The rates (μg-at/l/g C animal) of regeneration of nutrients, especially total inorganic nitrogen (mussel, 2.1723 × 10^?3; oyster, 7.4270 × 10^?3; and clam, 8.1750 × 10^?3) along with reported high biodeposition rates of bivalves suggest that multi-species aquaculture systems would be more efficient and productive than one-species systems.     

Lilium candidum bulblet and meristem development

Lilium candidum L., commonly known as the Madonna lily, is a wild Lilium species with medicinal properties and excellent potential as an ornamental crop, but one that has been scarcely investigated. The aim of this research was to study (1) tissue culture propagation of L. candidum bulblets, (2) early bulblet development, and (3) the effect of temperature and bulblet weight on bulblet and plant growth and meristem development. An investigation of the effect of explant type and temperature on in vitro bulblet propagation showed that scales were the most efficient explants for in vitro propagation and that exposing the regenerating bulblets to 15°C for 4 wk increased bulblet weight but reduced the number of bulblets produced. For bulblets planted in soil after 12 wk of exposure to 15°C or 25°C, the fastest growth was observed in the bulblets that had been exposed to 15°C and that had a larger initial size. Histological examination showed that young in vitro-grown bulblets had a rudimentary meristem comprising few cells with no layer organization. After 12 wk of growth, all bulblets showed a layered meristem, regardless of bulblet size or exposure to 15°C. However, an increased amount of leaf primordia was detected in larger bulblets. Furthermore, the histological examination revealed that in L. candidum, as opposed to other lily species, there had been no real "phase change" in the meristem and that the phase change from juvenile to vegetative adult occurred at a much later stage in L. candidum than in other species.     

Photosystem II recovery in the presence and absence of chloroplast protein repair in the symbionts of corals exposed to bleaching conditions

Increased seawater temperature causes photoinhibition due to accumulation of photodamaged photosystem II (PSII) in symbiotic algae (genus Symbiodinium) within corals, and it is assumed to be associated with coral bleaching. To avoid photoinhibition, photosynthetic organisms repair the photodamaged PSII through replacing the PSII proteins, primarily the D1 protein, with newly synthesised proteins. However, in experiments using cultured Symbiodinium strains, the PSII repair of Symbiodinium has been suggested not to be related to the synthesis of the D1 protein. In this study, we examined the relationship between the recovery of PSII photochemical efficiency (F _V/F _M) and the content of D1 protein after high-light and high-temperature treatments using the bleaching-sensitive coral species, Pocillopora damicornis and Acropora millepora, and the bleaching-tolerant coral species, Montipora digitata and Pavona decussata. When corals were exposed to strong light (600 µmol photons m^?2 s^?1) at elevated temperature (32 °C) for 8 h, significant bleaching occurred in bleaching-sensitive coral species although an almost similar extent of reduced PSII function was found across all coral species tested. During a subsequent 15-h recovery under low light (10 µmol photons m^?2 s^?1) at optimal temperature (22 °C), the reduced F _V/F _M recovered close to initial levels in all coral species, but the reduced D1 content recovered only in one coral species (Pavona decussata). D1 content was therefore not strongly linked to chloroplast protein synthesis-dependent PSII repair. These results demonstrate that the recovery of photodamaged PSII does not always correspond with the recovery of D1 protein content in Symbiodinium within corals, suggesting that photodamaged PSII can be repaired by a unique mechanism in Symbiodinium within corals.     

The association between algae organisms and environmental factors in Hai-tan Strait of Fujian,China

27 points were surveyed, and then algae and seawater samples were collected in Hai-tan Strait. The correlation on HAB (harmful algae blooms) species and environmental factors were studied. Water temperature (T) and salinity (S) ranging from 11.9 °C to 27.8 °C and 20.4 to 33.7 in the year, respectively. Dissolved inorganic nitrogen (DIN) in surface water ranged from 0.098 to 0.776 mg·L^?1, PO₄-P ranged from 0.0016 to 0.0729 mg·L^?1. And Eutrophication index (E) ranged from 0.03 to 13.8, varied different. 102 species of algae belonging to 4 classes and 52 genera were identified. The diversity was increasingly from winter to summer, decreasingly from summer to autumn, highest in summer. 49 species of red tide organisms were found in Hai-tan Strait, main two classes were Bacillariophyta and Pyrrophyta. Ceratium tripos and Noctiluca scintillans were dominant species in spring, Skeletonema costatum was common, and was also mainly HABs dominant species in summer, autumn and winter. Pearson correlation and Canonical correspondence analysis (CCA) showed that environment factors had significant correlation with dominance HABs species in different extent, and the ordination result was that S(Salinity) > T(Temperature) > pH > E(Eutrophication index) > DO(dissolved oxygen) > DIN > PO₄-P. Prorocentrum donghaiense, Skeletonema costatum, Noctiluca scintillans and Karenia mikimotoi caused many times red tide in 2011 to 2016. However, Prorocentrum donghaiense and Karenia mikimotoi cell density was low in survey year. North of the strait and east coast of the southern strait were sensitive sea area of red tide. The work highlights for the first time ecological characteristic of HAB was studied in Hai-tan Strait. Further, the data and results of this study will help us to improve efficiency for controlling HAB. Even, it is worthwhile to the management and response to the red tide disaster. Ordination result can also be a good indicator of ecological risk.     

Effects of four constant temperatures on the development of two Bradysia (Diptera: Sciaridae) species

In this study, the effects of temperature on the growth, development, survival, fecundity and other population parameters of two local Bradysia species B. odoriphaga and B. impatiens were studied at four constant temperatures (25, 28, 31 and 34°C). The results show that 25°C is the optimum temperature for the growth and development of B. odoriphaga, while 28°C is more favourable for B. impatiens. The temperature of 31°C restricted the growth and development, while the temperature of 34°C inhibited the eggs hatching in both species, resulting in no egg survival and no subsequent development. High temperatures (>28°C) prolonged the 4th larval stage duration, mean generation time (T) and population doubling time (Dt) of both species. The high temperature of 31°C greatly shortened the female longevity, weakened the oviposition and reduced the survival of both species. Moreover, the life table parameters R₀, r_m and λ were also suppressed by this high temperature. However, the high temperature of 31°C had little impact on the egg survival, pupal weight and male longevity. In addition, at 31°C, the values of R₀, r_m and λ of B. odoriphaga were higher than those of B. impatiens, suggesting that B. odoriphaga is more tolerant to high temperature than B. impatiens. The differences between two Bradydsia species seem determined genetically. Our findings are important for better understanding their biological characteristics at a certain constant temperature and demonstrate the possibility to control and manage those two Bradysia species by increasing ambient temperature.     

Saccharomycomorpha psychra n. g., n. sp., a Novel Member of Glissmonadida (Cercozoa) Isolated from Arctic and Antarctica

A novel genus and species within the order Glissmonadida (Cercozoa, Rhizaria), Saccharomycomorpha psychra n. g., n. sp., is described from lichen in the Ny-Ålesund region (High Arctic) and moss in the Fildes peninsula of King George Island (Maritime Antarctica). Cells were spherical and did not appear to present flagella in organic-rich Potato Dextrose Agar medium where they were able to feed osmotrophically. Molecular phylogenetic analyses based on 18S rRNA gene sequence demonstrated that Saccharomycomorpha psychra belong to “clade T” within the order Glissmonadida (Cercozoa, Rhizaria). All three investigated strains could grow at 4 °C and had an optimum growth temperature of 12 °C, 20 °C, and 20 °C, while a maximum growth temperature of 20 °C, 20 °C, and 25 °C, respectively. In conclusion, we established the phenotypic identity of “clade T,” which until now was exclusively detected by environmental sequences, and erect a new family Saccharomycomorphidae for “clade T.” Nomenclatural, morphological and ecological aspects of this novel species are discussed.     

Thermal ecotypes of amphi-Atlantic algae. II. Cold-temperate species (Furcellaria lumbricalis andPolyides rotundus)

Two species of cold-temperate algae from the North Atlantic Ocean,Polyides rotundus andFurcellaria lumbricalis, were tested for growth and survival over a temperature range of −5 to 30 °C. In comparisons of eastern and western isolates, bothF. lumbricalis, a North Atlantic endemic, andP. rotundus, a species having related populations in the North Pacific, were quite homogeneous.F. lumbricalis tolerated −5 to 25°C and grew well from 0 to 25°C, with optimal growth at 10–15 °C.P. rotundus tolerated −5 to 27°C, grew well from 5 to 25°C, and had a broad optimal range of 10–25°C. Both species tolerated 3 months in darkness at 0°C. In neither case could any geographic boundary be explained in terms of lethal seasonal temperatures, suggesting that these species are restricted in distribution by strict thermal and/or daylength requirements for reproduction. The hypothesis that northern species are more homogeneous than southern taxa in terms of thermal tolerance was supported. A second hypothesis, that disjunct cold-temperate species should be more variable than pan-Arctic species, was not supported.     

Seasonal variation in light- and temperature-dependent growth of marine planktonic diatoms in in situ dialysis cultures in the Trondheimsfjord,norway (63°N)

Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from ?1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m^?2 · s^?1 (0.5 m depth), and the length of the days (I > 1 μE · m^?2 · s^?1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m^?2 · s^?1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day^?1 (July, 15–16°C).The three species exhibit different ecological behaviour. Skeletonema is eurythermal (Q₁₀ = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found.     

Japanese species of the Longibrachiatum Clade of Trichoderma

The Longibrachiatum Clade of the genus Trichoderma in Japan was examined, among which two new species and three new records are herewith reported. The new species, T. tsugarense and T. kunigamense were isolated from a bed log (cultivation of Lentinula edodes) and volcanic ash soil, respectively. These species are distinguished from closely related species by growth and morphological characteristics and in phylogenetic analysis. Additional species new to Japan were T. ghanense, T. parareesei and T. sinense. The significance of their distribution is discussed. Most species of the Longibrachiatum Clade are tropical rather than temperate in distribution. Their in vitro optimum growth tends to be >35 °C but the optimum temperature for some Japanese species was lower. Some species are endophytes of temperate plant species, some of which are endemic in Japan.     

Diatom-derived SSTs (Td′ ratio) indicate warm seas off Japan during the middle Holocene (8.2–3.3 kyr BP)

Regression analysis was performed between the ratio of warm- and cold-water diatoms (Td′ ratio) in 123 surface sediment samples in the northwest Pacific Ocean and the mean annual sea surface temperatures (SSTs) (°C) at the core sites, in order to calibrate this proxy for paleo-temperatures. Equations to derive annual SST (°C) from diatom analysis were somewhat different for the Tohoku area (y = 6.5711⁎ × ^0.273, r = 0.89946) than for the Japan Sea (y = 5.4069⁎ × ^0.26841, r = 0.89088). The annual paleo-SSTs (°C) in the Tohoku Area were in general higher than in the Japan Sea despite lower Td′ values, because the warm-water species Fragilariopsis doliolus is abundant only in the Tsushima Warm Current in the Japan Sea. The reliability of the equations is supported by our understanding of the ecology of recent diatoms. Td′-derived annual paleo-SSTs (°C) agree with alkenone-derived summer paleo-SST (°C) at a site off central Japan in the northwestern Pacific. In a south-to-north transect of cores around Honshu and Hokkaido, paleo-SSTs (°C) decreased when the Kuroshio and Tsushima Warm Currents weakened. The middle Holocene (8.2–3.3 cal kyr BP) was warmer by 1–2 °C than earlier and later parts of the Holocene, and mean annual paleo-SSTs (°C) show rhythmic fluctuations with durations of 1000 years and 400–500 years. These new data show that annual SSTs were warm in the northwestern Pacific at times that the northeastern Pacific was cold. In addition, oceanic warm- and cold-water species defined by Kanaya and Koizumi [Kanaya, T., Koizumi, I., 1966. Interpretation of diatom thanatocoenoses from the North Pacific applied to a study of core V20–130 (studies of a deep-sea core V20–130, part IV). Sci. Rep. Tohoku Univ., 2nd series (Geol.) 37, 89–130], and Koizumi et al. [Koizumi, I., Irino, T., Oba, T., 2004. Paleoceanography during the last 150 kyr off central Japan based on diatom floras. Mar. Micropaleontol. 53, 293–365] are illustrated.     

Effects of temperature on eggs and larvae of Anisakis simplex sensu stricto and Anisakis pegreffii (Nematoda: Anisakidae) and its possible role on their geographic distributions

Effects of temperature on development of eggs, recently hatched larvae and L3 larvae of the marine parasitic nematodes Anisakis simplex sensu stricto (s.s.) and A. pegreffii were examined in vitro. The eggs of A. simplex s.s. hatched at 3–25 °C and those of A. pegreffii hatched at 3–27 °C. Days before hatching varied between 2 days at 25 °C and 35–36 days at 3 °C in A. simplex s.s. and between 2 and 3 days at 27 °C and 65 days at 3 °C in A. pegreffii. Hatching rates of A. simplex s.s. were maintained high at temperatures between 3 and 25 °C but decreased to 0% at 27 °C. In contrast, those of A. pegreffii were lowest particularly at 3 °C, but also at 27 °C. The mean 50% survivals of hatched larvae ranged from 5.3 days at 25 °C to 82.3 days at 9 °C in A. simplex s.s., while in A. pegreffii it ranged from 1.2 days at 27 °C to 77.2 days at 9 °C. L3 larvae of A. pegreffii exhibited higher survival rates and activity than those of A. simplex s.s., particularly at 20 and 25 °C. These results suggest that the early stages of A. simplex s.s. are more adapted to lower temperatures whereas those of A. pegreffii are more tolerant to warm environments, which may correspond to their distribution patterns in Japan and Europe.     

Distances of dispersal of juvenile bivalves (Mya arenaria (Linnaeus), Mercenaria mercenaria (Linnaeus), Gemma gemma (Totten))

Although it is recognized that many species of benthic invertebrates continue to disperse after settlement, particularly in soft-bottom habitats, the scale over which movements of juveniles occur is not well known. This study combined laboratory flume experiments assessing the effects of clam size, species, and water velocity on rates and distances of dispersal of three species of juvenile bivalves with field measurements of loss rates and distances of dispersal of transplanted bivalves in the Navesink River estuary in New Jersey, USA. Dispersal distances measured in the laboratory ranged from an average of 1.6 to 40 cm h^− 1 depending on clam size, species, and flow speed. Distances and likelihood of dispersal were generally greater for Mya arenaria than for Mercenaria mercenaria or Gemma gemma, although differences between species were not consistent. As predicted, smaller (1.3 mm) M. arenaria tended to disperse more than larger (3.7 mm) ones, although no significant differences were detected between two sizes (1.8 and 3.4 mm) of M. mercenaria. The similarity of the erosion thresholds of dead clams across sizes and species suggests that burrowing behaviour plays an important role in determining variation in dispersal due to clam size and species. In the field, densities of clams (M.arenaria and M.mercenaria) were reduced to half of that in controls after 3.5-5 h, indicating high levels of dispersal and/or mortality. Some individuals were recovered up to 50 cm away from their initial locations. Overall, our results suggest that dispersal distances of these three species due to bedload transport are likely to be on the order of centimeters per hour. Although these dispersal distances are small, such movements are likely to occur frequently due to tidal currents and, consequently, may have profound impacts on patterns of abundance and distribution.     

High survival and growth rates of introduced Pacific oysters may cause restrictions on habitat use by native mussels in the Wadden Sea

Pacific oysters Crassostrea gigas (Thunberg, 1793) were introduced to the northern Wadden Sea (North Sea, Germany) by aquaculture in 1986 and finally became established. Even though at first recruitment success was rare, three consecutive warm summers led to a massive increase in oyster abundances and to the overgrowth of native mussel beds (Mytilus edulis L.). These mussels constitute biogenic reefs on the sand and mud flats in this area. Survival and growth of the invading C. gigas were investigated and compared with the native mussels in order to predict the further development of the oyster population and the scope for coexistence of both species. Field experiments revealed high survival of juvenile C. gigas (approximately 70%) during the first three months after settlement. Survival during the first winter varied between > 90% during a mild and 25% during a cold winter and was independent of substrate (i.e., mussels or oysters) and tide level. Within their first year C. gigas reached a mean length of 35-53 mm, and within two years they grew to 68-82 mm, which is about twice the size native mussels would attain during that time. Growth of juvenile oysters was not affected by substrate (i.e., sand, mussels, and other oysters), barnacle epibionts and tide level, but was facilitated by fucoid algae. By contrast, growth of juvenile mussels was significantly higher on sand flats than on mussel or oyster beds and higher in the subtidal compared to intertidal locations. Cover with fucoid algae increased mussel growth but decreased their condition expressed as dry flesh weight versus shell weight. High survival and growth rates may compensate for years with low recruitment, and may therefore allow a fast population increase. This may lead to restrictions on habitat use by native mussels in the Wadden Sea.