A coupled, three-dimensional, time-dependent numerical model of water circulation, spectral light, plankton dynamics, nutrient/CDOM loadings, and zooplankton grazing provided an assessment of the factors affecting the growth and maintenance of red tides on the west Florida shelf (WFS). The coupled biophysical model consisted of state variable quantities for temperature, salinity, horizontal/vertical velocity components, turbulent diffusion, spectral light, colored dissolved organic matter (CDOM), dissolved organic and inorganic carbon, particulate silica, four dissolved inorganic nutrient pools (nitrate, ammonium, phosphate, and silicate), and four phytoplankton groups (diatoms, microflagellates, non-toxic dinoflagellates, and the red tide organism Karenia brevis). The model also included a complex grazing scheme that utilized thirteen different zooplankton groups to explore the effects of selective herbivory, feeding periodicity, diel vertical migration, fecal pellet egestion, and ammonium/phosphate excretion within a diverse zooplankton community. Over the shelf and slope of the eastern Gulf of Mexico, from the Mississippi River delta to the Florida Keys, four cases of the model were run during August -- November to explore the dynamics of red tide maintenance with respect to: (1) no refuge from grazing for K. brevis; (2) grazer avoidance of K. brevis during CDOM shading; (3) grazer avoidance of K. brevis in Case II waters; and (4) increased grazing stress on K. brevis competitors. NEGOM and ECOHAB data sets during July -- November 1999 were used to establish the initial/boundary conditions and provided validation data for the coupled model as well. Model results indicate that the red tide of 5.9 x 10 6 cells L-1 witnessed offshore Sarasota, Florida on 07 October 1999 was initiated by an inoculum of K. brevis observed in near-bottom waters above the 30 m isobath offshore Sarasota on 31 August 1999. Flowfields measured at moored ADCPs, observations from AVHRR satellite imagery, and west Florida shelf circulation models indicate that conditions of coastal upwelling existed during the period of bloom development, such that the K. brevis inoculum was delivered to the coast in the bottom Ekman layer. As a shade-adapted species capable of vertical migration, K. brevis cells aggregated near the bottom in order to escape photo-inhibitive light intensities in the overlying water column during the day and harvested the recycled nitrogen excreted by zooplankton grazers. This concomitant relaxation of light inhibition and nitrogen-limitation ultimately led to the growth and maintenance of the red tide, constrained in near-bottom waters during much of the day and preferentially advected inshore as a result of coastal upwelling. As K. brevis was advected inshore, self-shading, CDOM, and suspended inorganic particulates all contributed to the prevention of photo-inhibitive light intensities that, in combination with the excretion of recycled ammonium, ultimately led to the maintenance of a significant red tide at the coast.

No description available.

Blooms of nitrogen fixing cyanobacteria (NFC) occur in many freshwater and marine systems, including the Baltic Sea. By fixing dissolved nitrogen, they circumvent general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for non-diazotrophic primary producers and ultimately supporting secondary production. Elucidating trophic links between primary consumers and NFC is essential for understanding role of these blooms for secondary production. However, until recently, there was no reliable method to quantify individual prey species for zooplankter feeding in situ. The development of PCR-based methods to detect prey-specific DNA in the diet of consumers, including microscopic animals, allows identification and quantification of trophic linkages in the field. Using molecular diet analysis in combination with egg production measurements, biochemical markers of growth and condition; and stable isotope approach, we explored a possibility to determine (1) whether cyanobacteria are grazed and assimilated by mesozooplankters (Papers I and II), (2) which species/groups are particularly efficient consumers of cyanobacteria (Papers II and III), and (3) how feeding on cyanobacteria affects zooplankton growth and development (Paper I and III). Taken together, these laboratory and field observations, provided evidence that NFC contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment for the copepod nauplii (Paper I). The favorable growth conditions for juvenile copepods observed during NFC blooms were hypothesized to be mediated by picoplankton that take up bioavailable nitrogen exuded from cyanobacterial cells. This hypothesis found support in Paper II that provided quantitative estimates for the direct picocyanobacteria → mesozooplankton pathway, with highest weight-specific consumption observed in nauplii. Further, using field observations on zooplankton and phytoplankton development during a growth season in the northern Baltic proper, we found that NFC nitrogen is assimilated and transferred to zooplankton via both direct grazing and indirectly through grazing on small-sized phyto- and bacterioplankton (Paper III). Finally, these and other findings emphasizing the importance of NFC for Baltic Sea secondary production during growth season were synthesized to show that diazotrophic nitrogen enters food webs already at bloom initiation (Paper III) and is transferred via multiple pathways to pelagic and benthic food webs and, ultimately, to fish (Paper IV). / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted.</p>

The current rate of species extinction is higher than at any other time in Earth’s history. Despite our understanding of the causes and consequences of extinction and the development of numerous species conservation plans, it is surprising how little we know about the dynamics of extinction and recovery. Here, I explore the dynamics of population extinction and recovery across a range of meio-invertebrate species embedded in aquatic multi-trophic communities under external pressure. My results indicate that external mortality frequency has a negative impact on the dynamics of population extinction and recovery and suggest that it may be possible to predict patterns of population extinction from patterns of population growth as well as patterns of recovery from patterns of population collapse. My findings provide a valuable empirical basis from which we may increase our understanding of the factors influencing extinction risk and recovery potential to develop sustainable management strategies.

Freshwater ecosystems face unprecedented levels of human-induced stresses and it is expected that the invasion of non-indigenous species will cause the greatest loss of biodiversity in lakes and rivers worldwide. Bythotrephes longimanus is a predatory invertebrate that invaded North America in the early 1980s, first being detected in the Great Lakes, and then moving to a number of inland lakes in Ontario and the northern United States. Using experimental and survey-based approaches, I tested several hypotheses concerning the effects of Bythotrephes on native zooplankton community structure and function. My results indicate that Bythotrephes reduces total abundance, biomass, and richness of zooplankton, especially cladoceran taxa, throughout the ice-free season. As a result of high predation pressure by the invader, total seasonal and epilimnetic zooplankton production was also substantially reduced in invaded lakes, which may have important consequences for the transfer of energy to fish and other taxa that feed on zooplankton. Interestingly, there was some evidence that zooplankton shifted their reproduction in time and space to avoid Bythotrephes, which may buffer the effects of the invader on food web functioning. Other measures of ecosystem function were relatively unaffected by the invasion of Bythotrephes. In addition, Bythotrephes may interact in unexpected ways with other anthropogenic stressors, and act to slow down the process of recovery by preying on species that maintain community abundance during acidification, but also affecting species attempting to recolonize historically acidified lakes. Although dispersal of zooplankton may maintain some of the ecosystem functions provided by zooplankton communities, loss of biodiversity may be a permanent result of invasion. The effects of the continued spread of invasive species across the landscape may be profound, as the invader Bythotrephes has demonstrably altered zooplankton communities and may reduce the ability of freshwater ecosystems to respond to future environmental change and maintain ecosystem functioning. / Thesis (Ph.D, Biology) -- Queen's University, 2007-07-19 14:56:57.102

Climate change will affect all freshwater ecosystems via both direct physiological and indirect, biologically-mediated effects. Small lakes (< 10 ha) numerically dominate the Boreal Shield and represent an important habitat for aquatic biota. Small, shallow lakes are particularly responsive to climate-induced changes in thermal structure. Furthermore, biological interactions may be particularly important in small lakes where space, habitat heterogeneity, and thermal refugia are limited. Therefore, it is critical to understand and predict the consequences of climate change for community dynamics in small Boreal Shield lakes. Using 10 years of monitoring data and a field experiment I tested for differences in crustacean zooplankton community structure between warm and cool lake habitats. I classified years from a small, shallow Boreal Shield lake as ‘warm’ or ‘cool’ based on several characteristics of lake thermal structure. Since macroinvertebrates are often the main predators in small, shallow lakes, I further tested for potential interactions between lake thermal structure and spatially-dependent macroinvertebrate predation using in situ mesocosms. Body sizes of two ubiquitous crustacean zooplankton taxa, Leptodiaptomus minutus and Bosmina spp., were reduced in warm years, but no differences in abundance or diversity were detected at the annual scale. In contrast, in 15d enclosure experiments, crustacean zooplankton abundance and calanoid copepodid body size were reduced by the vertically-migrating predator Chaoborus punctipennis, but only in warm isothermal conditions. Zooplankton lowered their daytime depth distribution to avoid the surface-orienting notonectid predator, Buenoa macrotibialis, regardless of thermal habitat. No predation effect was detected in a hot (25ºC) isothermal habitat where both Chaoborus and notonectids were likely heat-stressed. Differences in abundance effects between the enclosure and monitoring data are likely due to the scales at which the analyses were conducted. Over short timescales predator-prey dynamics depended on lake thermal structure. However, over annual timescales zooplankton response was averaged across periods of seasonal change in thermal structure and biological processes, which may dampen the short-term effects associated with strong predation in isothermal conditions. Therefore, the importance of macroinvertebrate predators in regulating crustacean zooplankton community structure may increase if small lakes become progressively more isothermal with future climate change. / Thesis (Master, Biology) -- Queen's University, 2009-03-31 13:29:35.975

No description available.

The objective of this thesis was to construct general models to predict pollutant fluxes in limnoplankton by incorporating characteristics of the organism and the structures of the chemical. A two-compartmental pharmacokinetic model was used to quantify the pollutant uptake, depuration and intercompartmental exchanges. The model pollutants were phosphorus and 22 organic chemicals. / The rate constants of phosphorus uptake, excretion and intercompartmental changes by algae and cladocerans decreased with cell volume or body size raised to a power close to $-$0.25, except the intercompartmental exchanges for cladocerans which showed more negative slopes. In contrast, uptake, excretion and internal exchange rates per individual increased with cell size or body weight to a power similar to 0.75 with a similar exception for the cladoceran intercompartmental exchanges, which had slopes $<$0.75. / Bioconcentration factors, rate constants and flux rates of uptake and intercompartmental exchange from metabolic pool to structural pool of 22 $ sp{14}$C-labelled organic toxicants by Chlorella pyrenoidosa and Daphnia magna were positively correlated with the octanol/water partition coefficient, molecular weight, parachor, connectivity index, boiling point and melting point, and negatively with aqueous solubility. However, those of elimination and internal transfer from structural pool to metabolic pool showed opposite changes. Comparisons of pharmacokinetic parameters between Daphnia and Chlorella demonstrated that, although all kinetic parameters displayed similar patterns, the relative magnitudes of each corresponding parameters were significantly different between two species.

Interactions between multiple anthropogenic stressors can have unexpected synergistic or antagonistic effects, making it difficult to predict their combined effect using single stressor studies. The interaction between invasive consumers and nutrient enrichment is particularly important as both of these stressors frequently co-occur and their respective bottom-up and top-down effects have the potential to interact across multiple trophic levels. We conducted a mesocosm experiment that crossed an increasing nutrient addition gradient against an increasing zebra mussel invasion gradient. Native zooplankton communities were added to the mesocosms, and after three months we examined how the single stressor effects on available resources and the zooplankton community were altered by their multiple stressor interaction. Added nutrients had no effect on primary producer abundance, but increased the abundance and dominance of the top consumer, which likely increased predation pressure on the producers and so prevented their response to increased nutrients. Zebra mussels reduced total phytoplankton abundance by ~75%, rotifer abundance by ~80%, and shifted communities towards dominance of cladocerans and adult/juvenile copepods. When combined, the top-down control exerted by the mussels interacted antagonistically to prevent any bottom-up influence of nutrient enrichment on the zooplankton community. These results provide insight into the potential outcomes of nutrient and invasive consumer stressor interactions, and illustrate the need for researchers to consider single stressor problems in a multiple stressor context. / Thesis (Master, Biology) -- Queen's University, 2014-01-31 15:20:15.387

A high proportion of South Africa’s temporarily open/closed estuaries (TOCEs) occur along the coast of KwaZulu-Natal. Mouth breaching events have major impacts on the biological processes of an estuary, resulting in depletion of zooplankton via flushing and sediment scouring. Mouth closure, usually within weeks of a breaching event, initiates a new phase of stable physical conditions, leading to biological recovery. Therefore, the aim of this investigation was: (1) to monitor the recovery of zooplankton abundance and biomass following a breaching event in the Mdloti Estuary; (2) to compare the spatial and temporal patterns in zooplankton distribution in the lower (mouth), middle and upper reaches (head) of the Mdloti Estuary in terms of abundance and biomass just before, during and after a mouth breaching event; and (3) to determine the key environmental variables influencing zooplankton abundance and biomass during such a breaching event. The zooplankton community of the Mdloti Estuary was studied over a 3-month period (27 January to 26 April 2004). The estuary was artificially breached on 12 February 2004, due to a fish kill, and closed again naturally on 18 March 2004. Samples were collected twice a week in the lower, middle and upper reaches using a WP-2 net and an epibenthic sled. Upon breaching, 98% of zooplankton biomass was lost through sediment scouring and flushing. During the open phase, zooplankton biomass showed a temporary recovery, but due to continual sediment scouring and flushing, this was not sustained. One-way ANOVA revealed a significant difference in total zooplankton abundance and biomass between phases (d.f.2, 59 = 55.0; p < 0.001; d.f.2, 59 = 15.51; p < 0.001). ANCOVA revealed significant differences between zooplankton abundance and biomass (d.f.0.05;2,56=2.97, p = 0.05) at the different estuarine reaches (d.f.0.05;2,56=5.51, p < 0.01) . In both cases, the lower reaches recovered quicker than the middle and upper reaches. Thirty-five taxa were identified during the study, with only 10 contributing more than 1% of the total abundance or biomass. For the overall study, P. hessei was the dominant species, accounting for 42% of the total abundance and 58% of the total biomass. Keratella sp. 1 accounted for 17% and 11% of the total abundance and total biomass, respectively, while harpacticoid copepodites and Acartia natalensis contributed 11% and 10% to the total zooplankton abundance and 3% and 7% to the total zooplankton biomass, respectively. Pre-breaching levels of zooplankton were reached only 9 days after the closure of the mouth, during the recovery phase (mean 1.1 x 105 ± 6.5 x 104 SD ind.m3 and 2.4 x 102 ± 1.6 x 102 SD mg.m3). Zooplankton abundance and biomass reached a peak in the lower reaches after 19 days, in the upper reaches after 28 days and in the middle reaches after 35 days. The zooplankton biomass decreased slightly, but stabilised for the duration of the study. During the study the state of the mouth was primarily responsible for regulating the zooplankton abundance and biomass. However, the zooplankton in the different reaches did not recover in synchrony after mouth re-closure because abiotic factors and food availability were different in the three estuarine reaches. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.