A primary focus of coastal science during the past 3 decades has been the question: How does anthropogenic nutrient enrichment cause change in the structure or function of nearshore coastal ecosystems? This theme of environmental science is recent, so our conceptual model of the coastal eutrophication problem continues to change rapidly In this review, I suggest that the early (Phase I) con- ceptual model was strongly influenced by limnologists, who began intense study of lake eutrophication by the 1960s The Phase I model emphasized changing nutrient input as a signal, and responses to that signal as increased phytoplankton biomass and primary production, decomposition of phytoplankton- derived organic matter, and enhanced depletion of oxygen from bottom waters Coastal research in recent decades has identified key differences in the responses of lakes and coastal-estuarine ecosystems to nutrient enrichment The contemporary (Phase II) conceptual model reflects those differences and includes explicit recognition of (1) system-specific attributes that act as a filter to modulate the responses to enrichment (leading to large differences among estuarine-coastal systems in their sensitivity to nu- trient enrichment); and (2) a complex suite of direct and indirect responses including linked changes in: water transparency, distribution of vascular plants and biomass of macroalgae, sediment biogeochem- istry and nutrient cycling, nutrient ratios and their regulation of phytoplankton community composition, frequency of toxic/harmful algal blooms, habitat quality for metazoans, reproduction/growth/survival of pelagic and benthic invertebrates, and subtle changes such as shifts in the seasonality of ecosystem functions Each aspect of the Phase II model is illustrated here with examples from coastal ecosystems around the world In the last section of this review I present one vision of the next (Phase III) stage in the evolution of our conceptual model, organized around 5 questions that will guide coastal science in the early 21st century: (1) How do system-specific attributes constrain or amplify the responses of coastal ecosystems to nutrient enrichment? (2) How does nutrient enrichment interact with other stressors (toxic contaminants, fishing harvest, aquaculture, nonindigenous species, habitat loss, climate change, hydro- logic manipulations) to change coastal ecosystems? (3) How are responses to multiple stressors linked? (4) How does human-induced change in the coastal zone impact the Earth system as habitat for humanity and other species? (5) How can a deeper scientific understanding of the coastal eutrophication problem be applied to develop tools for building strategies at ecosystem restoration or rehabilitation?

https://www.int-res.com/articles/meps/210/m210p223.pdf

Our evolving conceptual model of the coastal eutrophication problem

Physical ecosystem engineers are organisms that directly or indirectly control the availability of resources to other organisms by causing physical state changes in biotic or abiotic materials. Physical ecosystem engineering by organisms is the physical modification, maintenance, or creation of habitats. Ecological effects of engineers on many other species occur in virtually all ecosystems because the physical state changes directly create nonfood resources such as living space, directly control abiotic resources, and indirectly modulate abiotic forces that, in turn, affect resource use by other organisms. Trophic interactions and resource competition do not constitute engineering. Engineering can have significant or trivial effects on other species, may involve the physical structure of an organism (like a tree) or structures made by an organism (like a beaver dam), and can, but does not invariably, have feedback effects on the engineer. We argue that engineering has both negative and positive effects on species richness and abundances at small scales, but the net effects are probably positive at larger scales encompassing engineered and nonengineered environments in ecological and evolutionary space and time. Models of the population dynamics of engineers suggest that the engineer/habitat equilibrium is often, but not always, locally stable and may show long-term cycles, with potential ramifications for community and ecosystem stability. As yet, data adequate to parameterize such a model do not exist for any engineer species. Because engineers control flows of energy and materials but do not have to participate in these flows, energy, mass, and stoichiometry do not appear to be useful in predicting which engineers will have big effects. Empirical observations suggest some potential generalizations about which species will be important engineers in which ecosystems. We point out some of the obvious, and not so obvious, ways in which engineering and trophic relations interact, and we call for greater research on physical ecosystem engineers, their impacts, and their interface with trophic relations.

Positive and negative effects of organisms as physical ecosystem engineers

Impacts of pollution on coastal and marine ecosystems including coastal and marine fisheries and approach for management: a review and synthesis.

Mollusk shells are abundant, persistent, ubiquitous physical structures in aquatic habitats. Using an ecosystem engineering perspective, we identify general roles of mollusk shell production in aquatic ecosystems. Shells are substrata for attachment of epibionts, provide refuges from predation, physical or physiological stress, and control transport of solutes and particles in the benthic environment. Changes in availability of these resources caused by shell production have important consequences for other organisms. Colonization of shelled habitat depends on individual shell traits and spatial arrangement of shells, which determine access of organisms to resources and the degree to which biotic or abiotic forces are modulated. Shell production will increase species richness at the landscape level if shells create resources that are not otherwise available and species are present that use these resources. Changes in the availability of resources caused by shells and the resulting effects on other organisms have both positive and negative feedbacks to these engineers. Positive feedbacks appear to be most frequently mediated by changes in resource availability, whereas negative feedbacks appear to be most frequently mediated by organisms. Given the diversity of species that depend upon resources controlled by shells and rapid changes in global shell production that are occurring due to human activities, we suggest that shell producers should not be neglected as a targets of conservation, restoration and habitat management.

Mollusks as ecosystem engineers: the role of shell production in aquatic habitats

Intertidal marine systems are highly dynamic systems which are characterized by periodic #uctuations in environmental parameters. Microbial processes play critical roles in the remineralization of nutrients and primary production in intertidal systems. Many of the geochemical and biological processes which are mediated by microorganisms occur within microenvironments which can be measured over micrometer spatial scales. These processes are localized by cells within a matrix of extracellular polymeric secretions (EPS), collectively called a ‘microbial bio"lma. Recent examinations of intertidal systems by a range of investigators using new approaches show an abundance of bio"lm communities. The purpose of this overview is to examine recent information concerning the roles of microbial bio"lms in intertidal systems. The microbial bio"lm is a common adaptation of natural bacteria and other microorganisms. In the #uctuating environments of intertidal systems, bio"lms form protective microenvironments and may structure a range of microbial processes. The EPS matrix of bio"lm forms sticky coatings on individual sediment particles and detrital surfaces, which act as a stabilizing anchor to bu!er cells and their extracellular processes during the frequent physical stresses (e.g., changes in salinity and temperature, UV irradiation, dessication). EPS is an operational de"nition designed to encompass a range of large microbially-secreted molecules having widely varying physical and chemical properties, and a range of biological roles. Examinations of EPS using Raman and Fourier-transform infared spectroscopy, and atomicforce microscopy suggest that some EPS gels possess physical and chemical properties which may hasten the development of sharp geochemical gradients, and contribute a protective e!ect to cells. Bio"lm polymers act as a sorptive sponge which binds and concentrates organic molecules and ions close to cells. Concurrently, the EPS appear to localize extracellular enzyme activities of bacteria, and hence contribute to the e$cient biomineralization of organics. At larger spatial scales, the copious secretion of speci"c types of EPS by diatoms on the surfaces of

/pdf/microbial-biofilms-in-intertidal-systems-an-overview-5cawhnq7ke.pdf

Microbial biofilms in intertidal systems: an overview

The effect of growth and carbohydrate production by the diatom Nitzschia cuwilineata on sediment erodibility was explored in laboratory flume experiments. Diatom cultures, incubated on sediment, were monitored daily for chlorophyll and carbohydrate concentrations and eroded in a recirculating flume at successive stages of growth. Because variations in erosion rate were far greater than variations in erosion threshold during the diatom growth period, erosion rate may be a more sensitive index of sediment stability. Erosion rate was negatively correlated with sediment chlorophyll (r2 = 0.759; P = 0.024) and bulk carbohydrate (r2 = 0.958; P = 0.001) concentrations. A strong negative correlation was found between the sediment bulk carbohydrate-to-chlorophyll ratio and erosion rate (r2 = 0.996; P < O.OOl), suggesting that this ratio would serve as a good indicator of sediment erodibility. The size of eroding particles or aggregates increased with the age of the biofilm, probably due to the pervasion of sediment with mucilage and changes in “stickiness” of the resulting sediment microfabric. Sediment stability increased throughout the stationary phase of growth regardless of lift forces produced by trapped bubbles within the biofilm and progressively smaller increases in sediment carbohydrate concentrations during this period. Knowledge of the physiological status of diatom biofilms is essential for the quantitative prediction of sediment transport, since diatom growth phase alters the behavior of sediment erosion.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1998.43.1.0065

The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment

Effects of suspended mussel culture (Mytilus spp.) on sedimentation, benthic respiration and sediment nutrient dynamics in a coastal bay

The threshold of sediment erosion by currents and waves (critical friction velocity, ) is an important predictive tool in sedimentology and coastal engineering1,2 owing to its use in entrainment and transport rate equations. The measurement of sediment transport is relevant to many concerns including dispersal of pollutants and dredge spoil, harbour and beach maintainence, geochemical fluxes and animal–sediment relations3. In marine sediments, biotic processes alter erosion criteria4, for instance through binding and stabilization of the sediment surface by the extracellular products of diatoms, bacteria and other benthic organisms5,6. Despite the widespread occurrence of benthic microbial mats and attendant sediment binding, prediction of erosion thresholds and transport rates in natural marine sediments has incorporated biotic variables only qualitatively5,7. We used a laboratory flume to erode intact sediment cores containing undisturbed mats of phototrophic purple sulphur bacteria. The pigment content of bacterial films (bacterio-chlorophyll a) was positively correlated with , increasing the erosion threshold as much as fivefold compared with sterile control cores. We demonstrate the profound influence of benthic micro-biota on prediction of erosion in marine sediments.

Prediction of coastal sediment stability from photopigment content of mats of purple sulphur bacteria

An ecological cascade effect: Migratory birds affect stability of intertidal sediments

The combined influences of intensive mussel aquaculture and watershed nutrient inputs on nitrogen dynamics in Tracadie Bay, Prince Edward Island, Canada, were examined using a nitrogen budget and an ecosystem model. Budget calculations, and inputs and parameters for the model were based on extensive field data. Both approaches showed that mussel aquaculture has a dominant influence on all aspects of the nitrogen cycle and dramatically alters pathways by which nitrogen reaches the phytoplankton and benthos. A large proportion of phytoplankton production is supported by land-derived nitrogen and this anthropogenic input is important for sustaining existing levels of mussel production. The amount of nitrogen removed in the mussel harvest is small com- pared with agricultural nitrogen inputs and the amounts excreted and biodeposited on the seabed. Mussel biodeposition greatly increases the flux of nitrogen to the benthos, with potentially serious eutrophication impacts. Results from the observation-based nitrogen budget and dynamic model were compared and both support the above conclusions. However, the ability of the model to test dif- ferent scenarios and to provide additional information (e.g. fluxes) over a finer spatial scale led to insights unattainable with a nitrogen budget. For example, food appears to be less available to mus- sels at the head of the Bay than at the mouth, despite the lower density of grow-out sites in the for- mer location. The number of fundamental ecosystem processes influenced by the mussels and the complexity of their interactions make it difficult to predict the effects of mussels on many ecosystem properties without resorting to a model.

/pdf/influence-of-mussel-aquaculture-on-nitrogen-dynamics-in-a-1f5n6azasf.pdf

Influence of mussel aquaculture on nitrogen dynamics in a nutrient enriched coastal embayment

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