Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

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The Ecology of Phytoplankton

This review provides an integrated synthesis with timelines and evaluations of ecological responses to eutrophi- cation in Chesapeake Bay, the largest estuary in the USA. Analyses of dated sediment cores reveal initial evidence of organic enrichment in ~200 yr old strata, while signs of increased phytoplankton and decreased water clarity first appeared ~100 yr ago. Severe, recurring deep-water hypoxia and loss of diverse submersed vascular plants were first evident in the 1950s and 1960s, respectively. The degradation of these benthic habitats has contributed to declines in benthic macro- infauna in deep mesohaline regions of the Bay and blue crabs in shallow polyhaline areas. In contrast, copepods, which are heavily consumed in pelagic food chains, are relatively un- affected by nutrient-induced changes in phytoplankton. Intense mortality associated with fisheries and disease have caused a dramatic decline in eastern oyster stocks and associated Bay water filtration, which may have exacerbated eutrophication effects on phytoplankton and water clarity. Extensive tidal marshes, which have served as effective nutrient buffers along the Bay margins, are now being lost with rising sea level. Although the Bay's overall fisheries production has probably not been affected by eutrophication, decreases in the relative contribution of demersal fish and in the efficiency with which primary production is transferred to harvest suggest funda- mental shifts in trophic and habitat structures. Bay ecosystem responses to changes in nutrient loading are complicated by non-linear feedback mechanisms, including particle trapping and binding by benthic plants that increase water clarity, and by oxygen effects on benthic nutrient recycling efficiency. Observations in Bay tributaries undergoing recent reductions in nutrient input indicate relatively rapid recovery of some ecosystem functions but lags in the response of others.

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Eutrophication of Chesapeake Bay: historical trends and ecological interactions

Effects of submersed macrophytes on ecosystem processes

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The Structuring Role of Submerged Macrophytes in Lakes

1. In river corridors, water plays a key role in connecting various landscape patches. This `hydrological connectivity' operates on the four dimensions of fluvial hydrosystems: longitudinal, lateral, vertical, and temporal. The present review focuses on: (1) lateral connectivity that links the main course of a river with floodplain waterbodies; and (2) vertical connectivity, the exchanges between the surface and groundwater via infiltration into the alluvial aquifer and exfiltration of phreatic water from the hillslope aquifer.



2. The biocomplexity of fluvial hydrosystems results from interactions between processes operating at various spatial and temporal scales. Differences in the nature and intensity of hydrological connectivity contribute to the spatial heterogeneity of riverine floodplains, which results in high alpha, beta and gamma diversity. Differences in connectivity also provide complementary habitats that are required for the parts of life cycles and life-cycles of some species. Hydrological connectivity also produces antagonistic effects, even within the same waterbody.



3. Two temporal scales are distinguished in connectivity dynamics. River level fluctuations within years lead to a pulsing connectivity that drives the functioning of floodplain ecosystems, namely the exchange of organic matter and inorganic nutrients and the shift between production and transport phases. On the scale of decades to centuries, the interactions between various processes increase the biocomplexity of floodplains; for example, river dynamics, which create highly connected waterbodies, compensate for succession that tends towards disconnection. Alternatively, river-bed incision leads to the reduction of fluvial dynamics and to the disconnection of waterbodies, although river incision may increase vertical connectivity where waterbodies are supplied by the hillslope aquifer.

Connectivity and biocomplexity in waterbodies of riverine floodplains

A mechanism to account for macrophyte decline in progressively eutrophicated freshwaters

The surfaces of aquatic plants are not metabolically inert, yet much evidence seems to suggest that they exert little influence on the composition of the periphytic algal communities associated with them. Other evidence indicates a specificity of the algal communities to particular macrophyte species. Evidence is given here, from a variety of studies, that the influence of host type in determining periphyton community composition is greatest in infertile lakes, but, that in progressively more fertile water, external environmental factors become more important.

The composition and ecology of periphyton communities in freshwaters

Diatom epiphytes were collected from six dyke sites and six Broad sites, of contrasting nutrient loadings, on three occasions during 1976. Diversity indices were higher in the Broad sites than in the dyke sites and the diversity indices in the Broad sites also increased from the first sampling date to the second and third sampling dates. The results are discussed with reference to diversity changes and mechanisms thought to occur in phytoplankton populations. Epiphyte density was higher in the dyke sites than in the Broad sites, probably due to increased nutrient loadings in the dykes. This result is discussed in relation to a recently constructed model to account for the decline of aquatic macrophytes in progressively enriched freshwaters.

https://www.tandfonline.com/doi/pdf/10.1080/00071617800650071

A comparison of diatom epiphytes, their diversity and density, attached to Myriophyllum spicatum L. in Norfolk dykes and Broads

(1978). A laboratory experiment to examine the effects of nutrient enrichment on macrophyte and epiphyte growth. SIL Proceedings, 1922-2010: Vol. 20, No. 1, pp. 82-87.

David Eminson

Papers

A mechanism to account for macrophyte decline in progressively eutrophicated freshwaters

The composition and ecology of periphyton communities in freshwaters

A comparison of diatom epiphytes, their diversity and density, attached to Myriophyllum spicatum L. in Norfolk dykes and Broads

A laboratory experiment to examine the effects of nutrient enrichment on macrophyte and epiphyte growth: With 3 figures and 1 table in the text