Habitat engineering by the invasive zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas) in a boreal coastal lagoon: impact on biodiversity

Habitat engineering role of the invasive zebra mussel Dreissena polymorpha (Pallas) was studied in the Curonian lagoon, a shallow water body in the SE Baltic. Impacts of live zebra mussel clumps and its shell deposits on benthic biodiversity were differentiated and referred to unmodified (bare) sediments. Zebra mussel bed was distinguished from other habitat types by higher benthic invertebrate biomass, abundance, and species richness. The impact of live mussels on biodiversity was more pronounced than the effect of shell deposits. The structure of macrofaunal community in the habitats with >10³ g/m² of shell deposits devoid of live mussels was similar to that found within the zebra mussel bed. There was a continuous shift in species composition and abundance along the gradient ‘bare sediments—shell deposits—zebra mussel bed’. The engineering impact of zebra mussel on the benthic community became apparent both in individual patches and landscape-level analyses.     

The state of zooplankton in the cooler reservoir of the Chernobyl Nuclear Power Plant and in the upper part of the Kiev Reservoir

The results of studies on the zooplankton in the cooler reservoir of the Chernobyl Nuclear Power Plant following the 1986 disaster are presented. The study region also included the waterbodies and watercourses situated within the 30-km-wide right-of-way zone. Species composition, vertical and horizontal distribution, abundance, and biomass have been studied. A total of 101 species of invertebrates were found: 43 species of rotifers, 42 cladocerans, and 16 copepods. Among all the species found, almost 90% of the total zooplankton abundance and biomass were composed of indicator species: representatives of g. Brachionus, Asplanchna priodonta, Synchaeta spp., Euchlanis dilatata, Chydorus sphaericus, Bosmina longirostris, and Acanthocyclops americanus. The veligers of zebra mussel were found in the plankton of the investigated water-bodies. In the Kiev Reservoir, their abundance during the summer period may be high: >1 million spec./m³).     

Feeding,development, and growth of juvenile perch <Emphasis Type="Italic">perca fluviatilis</Emphasis> in mesocosms in the presence of filter-feeding zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> pallas

Quantitative and qualitative changes in the feeding spectra and growth patterns are studied in the larvae and juveniles of perch in artificial water ecosystems (mesocosms) in the presence of a filter-feeding zebra mussel. At a stocking density of 0.75 kg/m², the presence of a zebra mussel leads to a change in the feeding conditions of zooplankton, to a decrease in its abundance in regards to critical values for fish feeding, to an increase in the abundance of organisms of macrobenthos in the food, and to the rapid transition of the fish to feeding on chironomids. As a result of these changes, the growth rate of perch larvae decreases, their development at step D ₁ is delayed, the differentiation of the juveniles by size is accelerated, their size and weight variability increases, and individual predators (cannibals) appear.     

The influence of pre‐settlement and early post‐settlement processes on the adult distribution and relative dominance of two invasive mussel species

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Phosphorus recycling by zebra mussels in relation to density and food resource availability

Using flow-through microcosms, we examined phosphorus (P) recycling by zebra mussels under conditions of nearly constant food resource supply and varying zebra mussel population densities (600–5200 ind./m²). At all density levels, zebra mussels filtered substantial algae, measured as chlorophyll biomass. Because chlorophyll biomass inputs were low throughout the study, zebra mussel biomass-specific rates of chlorophyll filtration declined with increasing density, suggesting food resource limitation at the higher densities. We observed net total P export and high zebra mussel biomass-specific rates of P recycling over time in microcosms at high zebra mussel densities. In systems with a low zebra mussel density, net total P export did not occur over time. Our results suggest the occurrence of P remineralization by zebra mussels and net loss associated with emaciation during periods of temporary starvation. These findings have implications for P dynamics since zebra mussels can be subjected to periods of starvation over seasonal and annual time scales.     

Fast response of freshwater consumers to a new trophic resource: Predation on the recently introduced Asian bivalve Limnoperna fortunei in the lower Paraná river,South America

Abstract Comparison of Limnoperna fortunei numbers and biomass in screened (5, 15 and 40 mm) and unscreened cages deployed for 18 months in the lower Paraná delta indicates that predators harvest 26–79% (numbers), or 20–85% (biomass) of the mussel population. Predation impact decreases with mussel size. On average, 6 kg of whole live mussel × m⁻² × year⁻¹ (0.36 g of dry mussel tissue × m⁻² × day⁻¹) were eliminated from the unscreened cages. Cages with 15 and 40 mm screens lost between 1 and 2 kg × m⁻² × year⁻¹. Aquatic mammals, birds, and especially fish, are probably the main consumers of large mussels. Small L. fortunei are most probably eaten by fish and also by several invertebrates, including crustaceans, leeches and gastropods. It is suggested that L. fortunei intercepts a significant fraction of the organic carbon that the Paraná‐Uruguay rivers flush into the ocean, locally boosting numbers of benthophagous animals, deposit feeders and, indirectly, higher level predators. Our results indicate that only 15 years after its first introduction in South America this invasive species is very actively consumed by local predators, but predatory suppression of the mussel seems very unlikely. Comparisons with the effects reported for the zebra mussel (Dreissena polymorpha) in Europe and North America suggest that L. fortunei is consumed more actively and that its negative impact on the local fauna is more restricted. These differences are attributed to the fact that while D. polymorpha feeds chiefly on plankton, a limited resource, L. fortunei feeds on detrital particulate organic matter, whose supply in these large South American rivers largely exceeds consumption.     

Distribution, abundance, and roles of freshwater clams (Bivalvia, Unionidae) in the freshwater tidal Hudson River

1. An extensive series of PONAR grabs was used to determine the distribution and abundance of unionid clams in the freshwater tidal Hudson River. 2. The five species of unionids collected were distributed very unevenly within the river. Mean river-wide density and biomass of unionids were 8.0m^?2 and 6.2 g DM m^?2 (shell-free)., respectively. 3. The environmental variables that we measured (water depth, distance from shore, sediment granulometry and organic content, presence or absence of macrophytes, and the chlorophyll a and particulate organic matter content of the water) explained little of the variation in abundance of unionids. 4. The distributions of the various species of clams did not differ significantly with respect to the environmental variables measured. 5. We estimate that unionids filter a significant amount of water (0.14m³ m^?2 day^?1, on average) in the Hudson River estuary, roughly equivalent in magnitude to downstream flushing. 6. We project that unionids will serve as a major substratum for the settlement of the zebra mussel (Dreissena polymorpha), which is now invading the estuary. We emphasize that unionids may play important non-trophic roles in large river ecosystems.     

Age-dependent zonation of the periwinkle Littorina littorea (L.) in the Wadden Sea

On sedimentary tidal flats near the island of Sylt (German Bight, North Sea) abundance and size distribution of periwinkles, Littorina littorea L., were studied in low intertidal and in shallow and deep subtidal mussel beds (Mytilus edulis L.). In low intertidal mussel beds, surveys revealed that high densities (1,369±571 m^–2) of juvenile snails (≤13 mm) were positively correlated with strong barnacle epigrowth (Semibalanus balanoides L. and Balanus crenatus Bruguière) on mussels. A subsequent field experiment showed that recruitment of L. littorea was restricted to the intertidal zone. Abundances of periwinkles (213±114 m^–2) and barnacles abruptly decreased in the adjacent shallow subtidal zone, which served as a habitat for older snails (>13 mm). L. littorea was completely absent from disjunct deep (5 m) subtidal mussel beds. Snail abundance varied seasonally with maxima of >4,000 m^–2 in low intertidal mussel beds in October and minima in July, just before the onset of new recruitment. I suggest that the presence of cracks and crevices among the dense barnacle overgrowth in intertidal mussel beds favoured recruitment and survival of juvenile snails. Larger (older) specimens are assumed to actively migrate to the less favourable adjacent subtidal. Therefore, intertidal mussel beds are considered as nurseries for the population of L. littorea in the Wadden Sea. Received in revised form: 25 September 2000 Electronic Publication     

Quantitative trends of zebra mussels in Lake Balaton (Hungary) in 2003–2005 at different water levels

During the extremely dry period between 2000 and 2003, the water level of Lake Balaton decreased by 82 cm and 80% of the stony littoral, an important habitat for the zebra mussel (Dreissena polymorpha), became dry. A recovery period started in 2004 due to intense precipitation, which increased water levels in the lake. Seasonal and spatial variations of the relative abundance, population density, population structure and biomass of the zebra mussel and the relative abundance of the amphipod Chelicorophium curvispinum were monitored in the period of 2003–2005 at four different shoreline sections and in two different portions (on the bottom and near the surface portion of the rip-rap) of Lake Balaton. Along with these studies, a quantitative survey of mussel larvae found in the plankton and of the abundance of mussel feeding diving ducks were made. As a consequence of the water level fall, on the dried part of the stony littoral, numerous zebra mussel druses perished. Following the dry period in early 2004, the relative abundance of the mussel on the bottom stones was smaller than in 2003 and the bottom community was dominated by C. curvispinum. By the end of 2004 and during 2005, the water level returned to normal and the surfaces of the reinundated stones were conducive to the successful colonization of zebra mussels. Hence, they returned as the dominant fauna in 2005. The stones near the surface might provide a new substrate for the recruitment of zebra mussels, probably offering more suitable substrata for the settlement in 2005 than in 2003. Therefore, the new substrata available in 2005 may have encouraged better and more rapid zebra mussel colonization than before. Zebra mussels may be better competitors for new space than C. curvispinum. A minor change of water-level fluctuation in 2005 and the reduction in population size of the mussel feeding waterfowl could have contributed to the intensive spread of zebra mussel by 2005.     

The American slipper limpet <Emphasis Type="Italic">Crepidula fornicata </Emphasis>(L.) in the northern Wadden Sea 70 years after its introduction

In 1934 the American slipper limpet Crepidula fornicata (L.) was first recorded in the northern Wadden Sea in the Sylt-R?m? basin, presumably imported with Dutch oysters in the preceding years. The present account is the first investigation of the Crepidula population since its early spread on the former oyster beds was studied in 1948. A field survey in 2000 revealed the greatest abundance of Crepidula in the intertidal/subtidal transition zone on mussel (Mytilus edulis) beds. Here, average abundance and biomass was 141 m^–2 and 30 g organic dry weight per square metre, respectively. On tidal flats with regular and extended periods of emersion as well as in the subtidal with swift currents in the gullies, Crepidula abundance was low. The main substrate of attachment was live mussels. Compared with the years following their initial introduction, Crepidula is more abundant today and has shifted from the now extinct oyster beds to the epifaunal community of the mussel beds. Their present abundance is considerably lower than at more southern European coasts where the species may dominate the epifauna. Low winter temperatures are suggested to have limited the population expansion in the northern Wadden Sea until now. Electronic Publication     

Retention of N and P by zebra mussels (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis> Pallas) and its quantitative role in the nutrient budget of eutrophic Lake Ekoln,Sweden

We quantified cover, population densities, size distribution and biomass of zebra mussels along 7 transects in eutrophic Lake Ekoln (Sweden). We also analyzed the elemental (C, N, P) composition of zebra mussel soft tissue and computed their retention rates of N and P their quantitative role in the lake’s nutrient budget. We hypothesized that zebra mussels play an important role in the nutrient budget of the lake and speculate that the successive harvesting of cultured mussels could contribute to the lake’s rate of recovery from cultural eutrophication. At depths exceeding 5 m, mussels covered consistently less than 5% or were absent. Similarly, mean densities were 3,158 ± 2,143 ind m⁻² between 2 and 4 m, but rapidly declined at larger depths. Calculated clearance rates averaged 19.4 ± 2.3 km³ y⁻¹, implying the entire lake is filtered every 8–10 days. Concentrations of N and P in mussel soft tissue averaged 100.9 ± 1.5 mg N g⁻¹ DW and 9.3 ± 0.2 mg P g⁻¹ DW. The lake population was estimated to 22.2 ± 2.6 × 10¹⁰ mussels, corresponding to a standing stock biomass of 362 ± 42 ton DW, or conservative estimates of 36.6 ± 4.3 ton N and 3.4 ± 0.4 ton P. Assuming a life span of 2–3 years gives a retention estimate of 1.2–1.8 ton P y⁻¹ by mussels, corresponding to 50–77% of the annual P influx from Uppsala sewage treatment plant to the lake. Similarly, annual N-retention by zebra mussels makes up 13–20 ton N y⁻¹, largely equaling the annual N-deposition from atmospheric sources on the lake’s surface. These retention rates correspond to only a few percent of the annual P-load from agricultural sources, but we argue that the quantitative role of zebra mussels in nutrient budgets is much larger if these budgets are adjusted for the bias introduced by coarse estimates of N and P pools that include a large share of refractory P.     

Long-term demography of a zebra mussel (Dreissena polymorpha) population

1. We used long‐term data and a simulation model to investigate temporal fluctuations in zebra mussel populations, which govern the ecological and economic impacts of this pest species. 2. The size of the zebra mussel (Dreissena polymorpha) population in the Hudson River estuary fluctuated approximately 11‐fold across a 13‐year period, following a cycle with a 2–4 year period. 3. This cycling was caused by low recruitment during years of high adult population size, rapid somatic growth of settled animals, and adult survivorship of 50% per year. 4. Adult growth and body condition were weakly correlated with phytoplankton biomass. 5. The habitat distribution of the Hudson's population changed over the 13‐year period, with an increasing proportion of the population spreading onto soft sediments over time. The character of soft‐sediment habitats in the Hudson changed because of large amounts (mean = 34 g DM m^?2) of empty zebra mussel shells now in the sediments. 6. Simulation models show that zebra mussel populations can show a range of long‐term trajectories, depending on the balance between adult space limitation, larval food limitation, and disturbance. 7. Effective understanding and management of the effects of zebra mussels and other alien species depend on understanding of their long‐term demography, which may vary across ecosystems.     

Rapid range expansion of the invasive quagga mussel in relation to zebra mussel presence in The Netherlands and Western Europe

Since its appearance in 2006 in a freshwater section of the Rhine–Meuse estuary (Hollandsch Diep, The Netherlands), the non-indigenous quagga mussel has displayed a rapid range expansion in Western Europe. However, an overview characterising the spread and impacts of the quagga mussel in this area is currently lacking. A literature study, supplemented with field data, was performed to gather all available data and information relating to quagga mussel dispersal. Dispersal characteristics were analysed for rate and direction and in relation to hydrological connectivity and dispersal vectors. To determine ranges of conditions suitable for quagga mussel colonisation, physico-chemical characteristics of their habitats were analysed. After its initial arrival in the freshwater section of the Rhine-Meuse estuary and River Danube, the quagga mussel demonstrated a rapid and continued range expansion in Western Europe. Quagga mussels have extended their non-native range to the network of major waterways in The Netherlands and in an upstream direction in the River Rhine (Germany), its tributaries (rivers Main and Moselle) and the River Meuse (Belgium and France). The calculated average quagga mussel dispersal rate in Europe was 120 km year^?1 (range 23–383 km year^?1). Hydrological connectivity is important in determining the speed with which colonisation occurs. Dispersal to water bodies disconnected from the freshwater network requires the presence of a suitable vector e.g. pleasure boats transferred over land. Upstream dispersal is primarily human mediated through the attachment of mussels to watercraft. The relative abundance of quagga mussel to zebra mussel has greatly increased in a number of areas sampled in the major Dutch rivers and lakes and the rivers Main and Rhine and the Rhine–Danube Canal leading to a dominance shift from zebra mussels to quagga mussels. However, evidence for displacement of the zebra mussel is limited due to the lack of temporal trends relating to the overall density of zebra and quagga mussel.     

Subtidal and intertidal mussel beds (Mytilus edulis L.) in the Wadden Sea: diversity differences of associated epifauna

In 1997 and 1998, surveys were performed to compare species composition, abundance and diversity of non-attached epifauna (>1 mm) in low intertidal and adjacent shallow subtidal zones of three mussel beds (Mytilus edulis L.) near the island of Sylt in the North Sea. The community structure was similar when compared within tidal zones: no significant differences in species numbers and abundances were recorded between locations and between years. A comparison between tidal zones, however, revealed higher diversity, species densities and total species numbers in the subtidal (per 1,000 cm²: H ′=2.0±0.16; 12 ±1 species density; 22 species) than the intertidal zone (per 1,000 cm²: H ′=0.7±0.27; 6±2 species density; 19 species). Abundances significantly dropped with increasing submergence from 2,052 (±468) m^–2 to 1,184 (±475) m^–2. This was mainly due to significantly higher densities of both juvenile periwinkles, Littorina littorea, and crabs, Carcinus maenas, in intertidal mussel beds. However, many less dominant species were significantly more abundant in subtidal mussel beds. This study revealed that in the non-attached epifaunal community of mussel beds the tidal level effect within metres was strong, whilst the spatial variability in a much wider (kilometre) range but the same tidal level was negligible. The high epifaunal diversity in the subtidal zone suggests that the protective measures for mussel beds against the effects of mussel fishery should be extended from the intertidal to the subtidal zone, if the integrity of the mussel bed community in the Wadden Sea National Park is to be maintained. Electronic Publication     

Predation on invasive zebra mussel, Dreissena polymorpha, by pumpkinseed sunfish, rusty crayfish, and round goby

The enemy release hypothesis states that invasive species are successful in their new environment because native species are not adapted to utilize the invasive. If true for predators, native predators should have lower feeding rates on the invasive species than a predator from the native range of the invasive species. We tested this hypothesis for zebra mussel (Dreissena polymorpha) by comparing handling time and predation rate on zebra mussels in the laboratory by two North American species (pumpkinseed, Lepomis gibbosus, and rusty crayfish, Orconectes rusticus) and one predator with a long evolutionary history with zebra mussels (round goby, Neogobius melanostomus). Handling time per mussel (7 mm shell length) ranged from 25 to >70 s for the three predator species. Feeding rates on attached zebra mussels were higher for round goby than the two native predators. Medium and large gobies consumed 50–67 zebra mussels attached to stones in 24 h, whereas pumpkinseed and rusty crayfish consumed <11. This supports the hypothesis that the rapid spread of zebra mussels in North America was facilitated by low predation rates from the existing native predators. At these predation rates and realistic goby abundance estimates, round goby could affect zebra mussel abundance in some lakes.     

Summer bacterio- and zooplankton in coastal waters of Svalbard

The distribution of bacterio- and zooplankton was studied in West Spitsbergen (Svalbard) coastal waters in August 2009. The bacterial abundance and biomass varied from 110 to 3360 × 10³ cells/ml and from 0.66 to 44.93 mg C/m³, respectively. These values were the highest in the surface water layers and decreased with depth. The greatest abundance of bacteria (5099 individuals/m3) was found in the freshened and warm water layer in Isfjorden. The highest biomass of zooplankton (182.41 mg C/m³) was registered in the zone of interaction of coastal and transformed Atlantic waters in the archipelago inner shelf. The spatial variations of abundance and biomass of the planktonic communities were related to the thermohaline characteristics of the water masses and, probably, to microalgal blooms.     

Impacts of zebra mussels (Dreissena polymorpha) on isotopic niche size and niche overlap among fish species in a mesotrophic lake

Zebra mussels (Dreissena polymorpha) filter feed phytoplankton and reduce available pelagic energy, potentially driving fish to use littoral energy sources in lakes. However, changes in food webs and energy flow in complex fish communities after zebra mussel establishment are poorly known. We assessed impacts of zebra mussels on fish littoral carbon use, trophic position, isotopic niche size, and isotopic niche overlap among individual fish species using δ¹³C and δ¹⁵N data collected before (2014) and after (2019) zebra mussel establishment in Lake Ida, MN. Isotope data were collected from 11 fish species, and from zooplankton and littoral invertebrates to estimate baseline isotope values. Mixing models were used to convert fish δ¹³C and δ¹⁵N into estimates of littoral carbon and trophic position, respectively. We tested whether trophic position, littoral carbon use, isotopic niche size, and isotopic niche overlap changed from 2014 to 2019 for each fish species. We found few effects on fish trophic position, but 10 out of 11 fish species increased littoral carbon use after zebra mussel establishment, with mean littoral carbon increasing from 43% before to 67% after establishment. Average isotopic niche size of individual species increased significantly (2.1-fold) post zebra mussels, and pairwise-niche overlap between species increased significantly (1.2-fold). These results indicate zebra mussels increase littoral energy dependence in the fish community, resulting in larger individual isotopic niches and increased isotopic niche overlap. These effects may increase interspecific competition among fish species and could ultimately result in reduced abundance of species less able to utilize littoral energy sources.

     

Effects of zebra mussels on phytoplankton and ciliates: a field mesocosm experiment

Many observational studies in North American lakes have documenteddecreases in phytoplankton abundance after the invasion of thezebra mussel (Dreissena polymorpha). However, few field experimentshave examined in detail the effect of zebra mussels on phytoplanktonabundance and species composition over an extended period. Replicatedin situ mesocosms were used to evaluate the impact of naturaldensities of zebra mussels on phytoplankton and ciliate biovolume,and algal species composition over a 5-week period in a habitatthat lacked extant mussel populations. Mussel biomass used inthe experiment was determined using a regression model basedon a data analysis that predicts zebra mussel biomass from totalphosphorus concentration. Within 1 week, zebra mussels decreasedphytoplankton biovolume by 53% and ciliate biovolume by 71%.The effect of zebra mussels on ciliate biovolume was sustainedthroughout the study. However, the effect of zebra mussels onphytoplankton abundance gradually waned over the remaining 4weeks of the experiment, such that the declining effect of zebramussels could not be explained by a shift towards less edibleand/or faster growing algal species. The mussels’ decliningcondition could help to explain the effect observed over thecourse of the experiment.     

Impact of the zebra mussel Dreissena polymorpha invasion on the budget of suspended material in a shallow lagoon ecosystem

The role of the zebra mussel Dreissena polymorpha in redistribution of total particulate material (TPM) between the water column and bottom sediment was estimated using the TPM budget for a mussel bed in the Curonian lagoon, the Baltic Sea. Seasonal clearance rates were derived from the TPM budget assuming two resuspension scenarios: no resuspension and full resuspension of biodeposits. Estimated clearance rates for both scenarios were compared with the rates calculated from the population clearance rate model. Seasonal clearance rates estimated using the population model (1.1 and 11.8 l g⁻¹ SFDW day⁻¹) fitted well into the interval of seasonal clearance rates calculated from TPM budgets assuming no resuspension of biodeposits (3.2 and 21.4 l g SFDW⁻¹ day⁻¹). In the scenario with biodeposits resuspension clearance rates were much higher (57.4 and 148.9 g SFDW⁻¹ day⁻¹). The ratio of clearance to residence time was highly dependent on the fate of biodeposits. Therefore its use in interpretation of the species impact on TPM was limited. An alternative measure based on the ratio of the amount of TPM biodeposited to TPM transported into the bed was used. It was found that zebra mussels are able to deposit between 10 and 30% of the incoming TPM, and the amount of biodeposited material was correlated with water residence time. Results indicate that the impact of zebra mussels on TPM in the lagoon is small relative to the high transport rates of TPM over the bed. However, annual biosedimentation rate (~590 g m⁻²) in the mussel bed was higher than physical deposition rate (~380 g m⁻²) in accumulation areas devoid of large suspension feeders. We suggest that a local impact due to enhanced availability of organic material to other trophic groups of associated benthic organisms may be more significant than effects on TPM pathways at an ecosystem scale.     

AN “ENVIRO‐INFORMATIC” ASSESSMENT OF SAGINAW BAY (LAKE HURON,USA) PHYTOPLANKTON: DATA‐DRIVEN CHARACTERIZATION AND MODELING OF MICROCYSTIS (CYANOPHYTA)1

Phytoplankton and Microcystis aeruginosa (Kütz.) Kütz. biovolumes were characterized and modeled, respectively, with regard to hydrological and meteorological variables during zebra mussel invasion in Saginaw Bay (1990–1996). Total phytoplankton and Microcystis biomass within the inner bay were one and one‐half and six times greater, respectively, than those of the outer bay. Following mussel invasion, mean total biomass in the inner bay decreased 84% but then returned to its approximate initial value. Microcystis was not present in the bay during 1990 and 1991 and thereafter occurred at/in 52% of sample sites/dates with the greatest biomass occurring in 1994–1996 and within months having water temperatures >19°C. With an overall relative biomass of 0.03 ± 0.01 (mean + SE), Microcystis had, at best, a marginal impact upon holistic compositional dynamics. Dynamics of the centric diatom Cyclotella ocellata Pant. and large pennate diatoms dominated compositional dissimilarities both inter‐ and intra‐annually. The environmental variables that corresponded with phytoplankton distributions were similar for the inner and outer bays, and together identified physical forcing and biotic utilization of nutrients as determinants of system‐level biomass patterns. Nonparametric models explained 70%–85% of the variability in Microcystis biovolumes and identified maximal biomass to occur at total phosphorus (TP) concentrations ranging from 40 to 45 μg · L^?1. From isometric projections depicting modeled Microcystis/environmental interactions, a TP concentration of <30 μg · L^?1 was identified as a desirable contemporary “target” for management efforts to ameliorate bloom potentials throughout mussel‐impacted bay waters.