Native Mussels Research Articles

Mortality, movement and behaviour of native mussels during a planned water‐level drawdown in the Upper Mississippi River

Summary Managers in the Upper Mississippi River (UMR) are using reductions in the River's water levels during summer to mimic historical water regimes and rehabilitate habitats for vegetation and other species. Concerns for the unintended effects of these actions on mussel populations threatened to halt these projects. Our objective was to characterise the survival and movement of two mussel species in the UMR associated with a water level drawdown. During 2009 (no drawdown) and 2010 (0.3 m summer drawdown), we glued passive integrated transponder tags to 10 Amblema plicata and 10 Lampsilis cardium at each of 11 sites. Five sites were in shallow areas expected to be minimally affected by the drawdown (reference sites), and six sites were in shallow areas expected to be directly affected by the drawdown (treatment sites). About equal numbers of sites within both the reference and treatment areas had low and high slopes. Tagged mussels were randomly allocated across sites (within years). Recovery of tagged mussels was >88% in 2009 and 2010. Mortality was similar and low (mean, c. 5% in both species) among reference sites but was variable and relatively high (means, c. 27% in L. cardium and c. 52% in A. plicata) among treatment sites; variation in mortality among treatment sites appeared related to slope. The study found evidence of drawdown associations with net horizontal movements in A. plicata but not L. cardium. Weekly horizontal movements in both species were significantly correlated with changes in water elevation. We observed significant slope associations related to the drawdown for mortality and net horizontal movement in A. plicata. There were strong species‐specific differences in the effects of the drawdown on mortality, vertical movement and horizontal movement. These results suggest that A. plicata responded to the drawdown by vertical movement into the substratum, whereas L. cardium responded by horizontal movement to deeper water. No directionality of movement was observed in either species. Collectively, these data suggest that drawdowns can influence the mortality, movement and behaviour of mussels in the UMR. However, more information on spatial and temporal distributions of mussels is needed to better understand the magnitude of these effects. Results from this study are being used by resource managers to better evaluate the effects of this management tool on native mussel assemblages.

Zebra Mussel Colonization of Construction Materials, and Effectiveness of a Foul Release Coating

We compared zebra mussel (Dreissena polymorpha) colonization of six commonly used construction materials (PVC, concrete, steel, galvanized steel, pressure-treated wood, aluminum) plus a native unionid mussel shell, and examined effectiveness of the Intersleek® 970 Fluoropolymer Foul Release Coating system applied to the six materials in limiting colonization by this aquatic nuisance species. Coated and uncoated substrates were deployed in Marion Reservoir, Kansas, from April 2011 to August 2012. Density of colonizing zebra mussels was evaluated in July and November 2011, and durability of the substrates was monitored until August 2012. Mussels differentially utilized materials, with eight of the 13 substrates being colonized. PVC was colonized more heavily than galvanized steel and all surfaces coated with foul release fluoropolymer, which were largely mussel-free. Coating eventually showed signs of pitting, but did not delaminate from the materials to which it was applied. These results suggest that use of particular materials and coatings may aid management of some zebra mussel infestations.

Freshwater Mussel Population Status and Habitat Quality in the Clinch River, Virginia and Tennessee, USA: A Featured Collection

AbstractThe Clinch River of southwestern Virginia and northeastern Tennessee is arguably the most important river for freshwater mussel conservation in the United States. This featured collection presents investigations of mussel population status and habitat quality in the Clinch River. Analyses of historic water‐ and sediment‐quality data suggest that water column ammonia and water column and sediment metals, including Cu and Zn, may have contributed historically to declining densities and extirpations of mussels in the river's Virginia sections. These studies also reveal increasing temporal trends for dissolved solids concentrations throughout much of the river's extent. Current mussel abundance patterns do not correspond spatially with physical habitat quality, but they do correspond with specific conductance, dissolved major ions, and water column metals, suggesting these and/or associated constituents as factors contributing to mussel declines. Mussels are sensitive to metals. Native mussels and hatchery‐raised mussels held in cages in situ accumulated metals in their body tissues in river sections where mussels are declining. Organic compound and bed‐sediment contaminant analyses did not reveal spatial correspondences with mussel status metrics, although potentially toxic levels were found. Collectively, these studies identify major ions and metals as water‐ and sediment‐quality concerns for mussel conservation in the Clinch River.

Uptake of contaminants of emerging concern by the bivalves Anodonta californiensis and Corbicula fluminea.

Uptake of seven contaminants regularly detected in surface waters and spanning a range of hydrophobicities (log D(ow) -1 to 5) was studied for two species of freshwater bivalves, the native mussel Anodonta californiensis and the invasive clam Corbicula fluminea. Batch systems were utilized to determine compound partitioning, and flow-through systems, comparable to environmental conditions in effluent dominated surface waters, were used to determine uptake and depuration kinetics. Uptake of compounds was independent of bivalve type. Log bioconcentration factor (BCF) values were correlated with log D(ow) for nonionized compounds with the highest BCF value obtained for triclocarban (TCC). TCC concentrations were reduced in the water column due to bivalve activity. Anionic compounds with low D(ow) values, i.e., clofibric acid and ibuprofen, were not removed from water, while the organic cation propranolol showed biouptake similar to that of TCC. Batch experiments supported compound uptake patterns observed in flow-through experiments. Contaminant removal from water was observed through accumulation in tissue or settling as excreted pseudofeces or feces. The outcomes of this study indicate the potential utility of bivalve augmentation to improve water quality by removing hydrophobic trace organic compounds found in natural systems.

Differences in sperm ultrastructure between Mytilus chilensis and Mytilus galloprovincialis (Bivalvia, Mytilidae): could be used as a taxonomic trait

The sperm ultrastructure has been used to solve several systematic and phylogenetic problems in marine invertebrates. The sperm ultrastructure of the Chilean mussel Mytilus chilensis and Mytilus galloprovincialis corresponds to the ect-aquasperm type. Sperm from both taxa measured 55-60 µm between head (acrosome + nucleus), midpiece (only 5 mitochondria) and the flagellum which in its end piece has a smaller diameter tail. The differences between both taxa are clearly shown, in the structure of the acrosome and nucleus. Therefore, according to our results and those reported in the literature, we indicate that Chilean native mussel sperm is different from other species of the Mytilus complex (M. trossulus, M. galloprovincialis and M. edulis). These differences in sperm ultrastructure found in M. chilensis, are another trait that can be used to validate the taxonomic status of the species. Differences in sperm morphology are related with reproductive isolation, and probably will be useful to understand future data on speciation. Finally, we discussed the finding that Mytilus galloprovincialis sperm from Chile have an acrosome notoriously smaller than those reported for specimens from Europe and Africa, though they have a great similarity with specimens from Japan, as reported in the literature.

Preliminary estimates of consumption rates of Rapana venosa (Gastropoda, Muricidae); a new threat to mollusk biodiversity in the Río de la Plata

The veined whelk Rapana venosa (Valenciennes, 1846) is an active, Asian, invasive mollusk predator that has been present along the coastal zone of Maldonado, Uruguay since 2004. The feeding rate of R. venosa on native mussels was estimated in a laboratory experiment. A flume with a constant water flow was used, in which the mean (± SD) temperature was 25.4 ± 1.8 °C, the mean (± SD) salinity was 18.5 ± 1.6, and a 15:9 light-dark schedule was followed. Each experimental trial lasted 9 days and a constant prey supply was maintained. Three size classes of predators and three size classes of prey (Brachidontes rodriguezii and Mytella charruana), were used. For all sizes of predator combined, the average (± SD) absolute consumption rate was 0.88 ± 0.3 g day -1 , and the relative consumption rate was 0.057 ± 0.034 g g -1 day -1 . No significant differences were found between the number of prey and total grams consumed among the three size categories of snails. However, for the relative consumption rate, small snails consumed significantly greater (0.10 g g -1 day -1 ) amounts than intermediate and large snails (0.04 and 0.02 g g -1 day -1 respectively). All sizes of snails consumed significantly more intermediate- than small-sized mussels. This study provides important knowledge for future research to assess the impact of this invasive species on native bivalve resources.

Refocusing Mussel Watch on contaminants of emerging concern (CECs): The California pilot study (2009–10)

To expand the utility of the Mussel Watch Program, local, regional and state agencies in California partnered with NOAA to design a pilot study that targeted contaminants of emerging concern (CECs). Native mussels (Mytilus spp.) from 68 stations, stratified by land use and discharge scenario, were collected in 2009–10 and analyzed for 167 individual pharmaceuticals, industrial and commercial chemicals and current use pesticides. Passive sampling devices (PSDs) and caged Mytilus were co-deployed to expand the list of CECs, and to assess the ability of PSDs to mimic bioaccumulation by Mytilus. A performance-based quality assurance/quality control (QA/QC) approach was developed to ensure a high degree of data quality, consistency and comparability. Data management and analysis were streamlined and standardized using automated software tools. This pioneering study will help shape future monitoring efforts in California’s coastal ecosystems, while serving as a model for monitoring CECs within the region and across the nation.

Shifts from native to non-indigenous mussels: Enhanced habitat complexity and its effects on faunal assemblages

Ecosystem engineers such as mussels may affect strongly both the structure of benthic assemblages and the ecosystem functioning. The black-pygmy mussel Limnoperna securis is an invasive species that is spreading along the Galician coast (NW Spain). Its current distribution overlaps with the distribution of the commercial native mussel species Mytilus galloprovincialis, but only in the inner part of two southern Galician rias. Here, we analysed the assemblages associated with clumps of the two mussel species and evaluated if the invasive species increased complexity of habitat. To measure complexity of clumps we used a new method modified from the “chain and tape” method. Results showed that the identity of the mussel influenced macrofaunal assemblages, but not meiofauna. L. securis increased the complexity of clumps, and such complexity explained a high percentage of variability of macrofauna. The shift in dominance from M. galloprovincialis to L. securis may alter habitat structure and complexity, affecting the macrofaunal assemblages with unpredictable consequences on trophic web relations.

Development of sensitive and specific molecular tools for the efficient detection and discrimination of potentially invasive mussel species of the genus Perna

Marine mussels of the genus Perna include three species: P. canaliculus, P. viridis and P. perna. While P. canaliculus appears to be greatly restricted to its endemic range of New Zealand, P. perna and P.viridis introductions have been recorded outside their native ranges in several regions of the globe. Such introductions have often resulted in significant negative ecological, economic and social impacts. Perna perna and P.viridis are exotic to Australia and are listed under the Australian Government National System for the Prevention and Management of Marine Pest Incursions as high priority species. Rapid detection of marine pests such as Perna species remains fundamental to their effective containment and control. The present study reports on the development and validation of both conventional and real-time PCR assays suited to the rapid identification and discrimination of juvenile and adult specimens of P. viridis, P. canaliculus and P. perna. The development of a sensitive high-throughput real-time PCR assay offers further potential for the efficient detection of the presence of single Perna specimens in mixed populations of native mussel species, and for early detection of larval stages in ballast water and plankton samples. This assay offers considerable advantages over traditional identification methods and represents an important step in developing capacity for efficient identification and management of Perna species incursions in Australian waters.

Filtration activity of invasive mussel species under wave disturbance conditions

Self-purification is one of the most important ecosystem functions of rivers. Multiple human activities regularly impact this ecosystem service, consequently altering river morphology, hydrology, and the composition of biotic assemblages that contribute to self-purification. However, little quantitative information is available about the importance of such impacts. Hence, we tested how invasive mussel species contribute to self-purification under disturbed riverine conditions. In laboratory experiments, invasive mussel species equipped with magnetic sensors that recorded filtration activity were exposed to artificial waves of varying intensity that simulated the hydraulic effects of inland navigation. Our results suggest that invasive mussel species are more resistant to wave disturbance compared to native species, as estimated threshold values for initiating shell closure are very high (Dreissena rostriformis bugensis) or the duration (Corbicula fluminea) and degree of shell closing (D. rostriformis bugensis, C. fluminea) very low. Also we demonstrated that the invasive species D. rostriformis bugensis and C. fluminea continued filtering during wave impact, whereas Dreissena polymorpha did not behave significantly differently than previously studied native mussel species, based on the studied susceptibility parameters. Thus, D. rostriformis bugensis and C. fluminea appear to be pre-adapted to hydraulic or morphological disturbance, and may compensate against other losses regarding this important ecosystem function in rivers that are intensively used for inland navigation. However, as the dominance of invasive species in river systems may disrupt natural food webs, this compensation of filter-feeding activity may be accompanied by the loss of other ecosystem functions.

Biodiversity on the brink: an assessment of conservation strategies for North American freshwater mussels

The North America freshwater mussel fauna has suffered an inordinately high recent extinc- tion rate, and the small size and isolation of many remaining populations portends a continued diminish- ment of this fauna. Causes of extinction and imperil- ment are varied but revolve around massive habitat loss, deterioration, and fragmentation. The National Strategy for the Conservation of Native Mussels, published in 1997, has guided efforts to address this crisis. Considerable progress has been made toward several of the Strategies' goals, particularly increasing our knowledge of mussel biology, promoting mussel conservation, and development of techniques for captive mussel propagation. However, mussel conser- vation should focus more directly on reducing frag- mentation through bold and aggressive habitat restoration. In addition to dam removal, improvement in dam tailwater flows, and restoration of channelized streams, identification of factors that eliminated mussels from many otherwise intact streams is critical. Translocation and captive propagation will be key elements in reestablishing mussel assemblages in restored habitats, but these techniques should be used with caution and primarily to increase the occurrence of a species throughout its historical range. Conserving mussel diversity in an ever-changing world is depen- dent on promoting the natural, long-term sustainability and evolutionary potential of mussel populations.

Combined use of native and caged mussels to assess biological effects of pollution through the integrative biomarker approach

Native and caged mussels were used in combination for the monitoring of pollution biological effects through an integrative biomarker approach. Mussels (Mytilus galloprovincialis) were deployed in cages in two well-known model localities with different pollution levels in the Basque coast. After 3 weeks caged and native mussels were collected from each site and a suite of effect and exposure biomarkers (from molecular/cellular to organism level) was applied and chemical contaminants (metals, PAHs, PCBs, phthalates and nonylphenol ethoxylates) were analytically determined. Integrative biomarker indices and pollutant indices of tissues were calculated. Several biomarkers used herein responded similarly in native and caged mussels, whereas others exhibited significant differences. Overall, biomarkers in-a-suite depicted site-specific profiles useful for the diagnostic of mussel health status and therefore for ecosystem health assessment in marine pollution biomonitoring. On the other hand, biomarkers and bioaccumulation exhibited different response times, which was especially evident when comparing biomarker and pollutant indices of tissues. The suite of biomarkers was more sensitive after caging (short-term response), whereas tissue pollutant concentrations were more sensitive in native mussels (long-term response). Thus, the combination of native and caged mussels is highly recommended to monitor biological effects of pollution in mussels through the integrative biomarker approach, especially in chronically polluted sites.

The Mussel–Fish Relationship: A Potential New Twist in North America?

AbstractNorth American freshwater mussels are critically imperiled organisms that generally require fish hosts in order to complete their life cycle. Although numerous studies have focused on the parasitic relationship between mussels and fishes, few have examined the benefits that mussels provide to other organisms. During sampling of Altamaha River, Georgia, we observed foreign eggs occurring within body cavities of native mussels across a 253‐km reach of the river basin. Eggs were recovered from 6% of the 757 mussels examined among seven sites. Foreign eggs were present in 17% and 18% of examined mussels at two sites. Using molecular techniques, eggs were identified as American Shad Alosa sapidissima. This discovery appears to be the first documented occurrence of native fish eggs in live North American mussels. Further research into the nature and mechanism of this symbiosis is warranted to assess whether this relationship is amensalistic, mutualistic, or commensalistic as American Shad and many freshwater mussels are species of conservation concern. A commensalistic or mutualistic relationship between these taxa may result in restoration activities affecting one species facilitating restoration of others.

The effects of elevated water temperature on native juvenile mussels: implications for climate change

Native freshwater mussels are a diverse but imperiled fauna and may be especially sensitive to increasing water temperatures because many species already may be living near their upper thermal limits. We tested the hypothesis that elevated water temperatures (20, 25, 30, and 35°C) adversely affected the survival and physiology of 2-mo-old juvenile mussels (Lampsilis abrupta, Lampsilis siliquoidea, and Megalonaias nervosa) in 28-d laboratory experiments. The 28-d LT50s (lethal temperature affecting 50% of the population) ranged from 25.3 to 30.3°C across species, and were lowest for L. abrupta and L. siliquoidea. Heart rate of L. siliquoidea was not affected by temperature, but heart rate declined at higher temperatures in L. abrupta and M. nervosa. However, for both of these species, heart rate also declined steadily during the experiment and a strong temperature × time interaction was detected. Juvenile growth was low for all species in all treatments and did not respond directly to temperature, but growth of some species responded to a temperature × time interaction. Responses to thermal stress differed among species, but potential laboratory artifacts may limit applicability of these results to real-world situations. Environmentally relevant estimates of upper thermal tolerances in native mussels are urgently needed to assess the extent of assemblage changes that can be expected in response to global climate change.

Water and Sediment Temperatures at Mussel Beds in the Upper Mississippi River Basin

Native freshwater mussels are in global decline and urgently need protection and conservation. Declines in the abundance and diversity of North American mussels have been attributed to human activities that cause pollution, waterquality degradation, and habitat destruction. Recent studies suggest that effects of climate change may also endanger native mussel assemblages, as many mussel species are living close to their upper thermal tolerances. Adult and juvenile mussels spend a large fraction of their lives burrowed into sediments of rivers and lakes. Our objective was to measure surface water and sediment temperatures at known mussel beds in the Upper Mississippi (UMR) and St. Croix (SCR) rivers to estimate the potential for sediments to serve as thermal refugia. Across four mussel beds in the UMR and SCR, surface waters were generally warmer than sediments in summer, and were cooler than sediments in winter. This suggests that sediments may act as a thermal buffer for mussels in these large rivers. Although the magnitude of this effect was usually <3.0°C, sediments were up to 7.5°C cooler at one site in May, suggesting site-specific variation in the ability of sediments to act as thermal buffers. Sediment temperatures in the UMR exceeded those shown to cause mortality in laboratory studies. These data suggest that elevated water temperatures resulting from global warming, thermal discharges, water extraction, and/or droughts have the potential to adversely affect native mussel assemblages.

The ecology of freshwater bivalves in the Lake Sapanca basin, Turkey

Despite the ecological importance and globally threatened status of freshwater bivalves, the freshwater mussel fauna of Turkey has hitherto received little attention. The aim of this study was to describe the ecology of freshwater mussels of the Lake Sapanca basin (northwest Turkey) to provide baseline data against which to measure future trends. Five native mussel species belonging to 3 genera were encountered in surveys: Anodonta cygnea, A. anatina, Unio pictorum, U. crassus, and Dreissena polymorpha. In addition, an invasive species from Asia, A. woodiana, was recorded in the region for the first time. A. cygnea and U. pictorum were the most abundant species in the lake, while U. crassus was most abundant in the associated stream. Age and growth parameters were estimated for U. pictorum and U. crassus, and indicated that the latter species had a younger median age and faster growth rate than the former, possibly a function of exclusively occupying a nutrient-enriched stream. The bioecological features of the bivalve fauna of the Lake Sapanca basin, as well as the implications of the introduction of A. woodiana, are discussed.

Comparison of phototrophic shell-degrading endoliths in invasive and native populations of the intertidal mussel Mytilus galloprovincialis

The intertidal mussel Mytilus galloprovincialis is a successful invader worldwide. Since its accidental introduction onto the South African west coast in the late 1970s, it has become the most successful marine invasive species in South Africa. One possible explanation for this phenomenon is that M. galloprovincialis suffers less from phototrophic shell-degrading endoliths in its invasive than in its native range. We assessed photoautotrophic endolithic pressure on M. galloprovincialis in native (Portugal) and invasive (South Africa) ranges. Invasive populations were more heavily infested than native populations. In Portugal, only the biggest/oldest mussels displayed endolithic erosion of the shell and the incidence of infestation was greater at higher shore levels where more prolonged exposure to light enhances endolith photosynthesis. In South Africa, even the smallest size classes of mussels were heavily infested throughout the shore. In Portugal, endolithic-induced mortality was observed at only one location, while in South Africa it occurred at all locations and at significantly higher rates than in Portugal. Important sub-lethal effects were detected in infested native mussels, confirming previous studies of invasive populations and suggesting an energy trade-off between shell repair and other physiological constraints. We observed a positive relationship between infestation rates and barnacle colonization on mussel shells, suggesting possible facilitation of barnacle settlement/survival by shell-boring pathogens. Identification of endoliths revealed common species between regions. However, two species were unique in the invasive range while another was unique in the native region. Different levels of endolithic infestation in the invasive and the native range were not explained by the effect of major environmental determinants (Photosynthetically Available Radiation and wave height). The results reject our initial hypothesis, indicating that invasion success of M. galloprovincialis is not simply explained by escape from its natural enemies but results from complex interactions between characteristics of the invaded community and properties of the invader.

The impact of climate change on mediterranean intertidal communities: losses in coastal ecosystem integrity and services

As has been shown for other ecosystems, the ecological and socio-economic impacts of climate change on Mediterranean intertidal habitats are highly variable in space and time. We conducted field and laboratory mea- surements of cellular, ecophysiological and behavioural responses of selected intertidal invertebrates (mussels, gastropods and sponges) and completed a literature review to determine what is known of socio-economic consequences of these biological changes. Results suggest significant gaps in our knowledge that may impede a complete understanding of likely impacts (physical, bio- logical and socio-economic) and that sufficient data for such an analysis are available only for mussels. Application of ecological models for native mussels Mytilaster minimus and invasive Brachidontes pharaonis bivalves indicates that the current distribution of these species is linked to the availability of food and local temperature. Choosing Israel as a case study, the study focused on the identification of ecosystem services and goods provided by the Mediterranean rocky intertidal and on the assessment of conservation approaches. Intertidal systems were poorly represented in the socio-economic literature, and there was low awareness of the value of these ecosystems among stakeholders. Subsequently, conservation efforts for intertidal communities were minimal. While climate change will very likely continue

Regional assessment of PAHs contamination in SE Brazil using brown mussels (Perna perna Linnaeus 1758)

Cultured and native brown mussels (Perna perna Linnaeus 1758) were used to evaluate the contamination by PAHs in the SE Brazilian coastal zone. Mean concentrations of total PAH (38 parental and alkylated compounds) and cluster analysis revealed that: (i) mussel farms (32.7–70.1ngg−1) are located in uncontaminated areas; (ii) coastal rockyshore areas (89.7±25.8ngg−1) have low level of contamination; and (iii) the Guanabara Bay (760.9±456.3ngg−1) is chronically contaminated by hydrocarbons, which is consistent with previous results. PAH profiles and diagnostic ratios suggested mixed petrogenic and pyrolitic sources for group (ii) and petrogenic sources for group (iii). The levels of PAH in the cultured and native mussels are below threshold values for safe food, even in Guanabara Bay, and thus in such cases other contaminants and pathogens should be considered in order to evaluate the quality of shellfish for human consumption.

Allometric relationships in feeding and digestion in the Chilean mytilids Mytilus chilensis (Hupé), Choromytilus chorus (Molina) and Aulacomya ater (Molina): A comparative study

As a first attempt to explain the functional basis of the co-occurrence of three sympatric species of native mussels frequently found at the cold-temperate coasts of Chile, we tested the existence of potential morpho-functional differences operating at the feeding and digestive levels of Mytilus chilensis, Choromytilus chorus and Aulacomya ater. Clearance rate (CR (l h–1)), gill area (GA: mm2), dry weight of labial palps (WLP: mg), gut contents (GC: mg), weight of digestive gland (WDG: mg), specific (mg of maltose or tyrosine mg prot−1h−1) and total (mg of maltose or tyrosine digestive gland−1h−1) amylase, cellulase, laminarinase, xylanase and protease activities were measured in different size individuals of the three species collected from Corral Bay (Chile). Hydrolytic activity of digestive extracts towards natural substrates elaborated from different macrophyte was also tested for the 3 species. No significant differences between species were found for mass-exponents (b) scaling CR (b=0.744) and GA (b=0.803). However, size-specific CR and GA were found to vary between species, ranking as follows: M. chilensis>C. chorus>A. ater. WLP fitted to an inter‐specific common function (b=0.77). Regarding digestive parameters, no significant inter‐specific differences were found between mass-exponents for GC (b=0.434), WDG (b=1.067) and total enzyme activities (common b ranged from 0.904 to 1.212), except total amylase which was significantly higher in A. ater (b=1.838). Specific activities of digestive enzymes were size-independent except A. ater amylase, which increased with body-size, and protease in the three species which decreased with size. For a common body-size, GC and carbohydrase activities were significantly higher in M. chilensis than in C. chorus and A. ater. Inter‐specific differences were found in the composition of carbohydrase pool: amylase was the prevalent enzyme in M. chilensis (up to 44.5% of total carbohydrase) whereas the three carbohydrases had a similar contribution in C. chorus and A. ater. Sugar release from vascular plants was significantly higher in C. chorus.