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 impact of suspended mussel culture (Mytilus edulis, M. trossulus) on the benthos of a small Nova Scotia cove (7 m depth) was assessed using meehods involving both benthic metabolism and community structure. Due to deposition of mussel feces and pseudofeces, sedimentation rate was higher under the mussel culture lines than at an adjacent reference site of similar sediment texture. Porewater profiles of sediment sulfate and sulfide indicated greater anaerobic metabolism at the mussel site than at the reference site, but sulfide was absent from the upper centimeters of sediments under the mussels. Seasonal measures of sediment oxygen demand showed little change between sites, but maximum rates of ammonium release at the mussel site were twice the highest rates measured at the reference site. Abundance of benthic macrofauna was higher at the reference site, but biomass was generally lower. Biomass at the mussel site was dominated by molluscs (Ilyanassa spp. andNucula tenuisulcata), that were attracted to mussels fallen from the culture and/or enriched organic matter due to biodeposition. Species diversity was lower at the reference site due to the dominance of the polychaeteNephtys neotena. Abundance-biomass comparisons (ABC method) of faunal analysis did not indicate any impact of biodeposition at this site: however, disturbance did not result in a typical assemblage of small opportunistic species anticipated with this method. Cluster analysis of macrofauna usually provided a clear separation between the sites. Since the contruction of a causeway (1968), foraminifera species composition showed a temporal response to temperature changes in the cove by shifting toward calcareous species, but assemblages downcore showed little or no relationship to aquaculture impacts. Although there is a shift toward anaerobic metabolism at the mussel lines, the impact of mussels falling to the sediments was more noticeable in benthic community structure than was any impact due to organic sedimentation or hypoxia. In general the impact of aquaculture on the benthos appeared to be minor. Furtyher assesment of these consequences may mandate both taxonomic and energetic approaches to impact assessment.

A multidisciplinary approach to evaluating impacts of shellfish aquaculture on benthic communities

/pdf/effects-of-suspended-mussel-culture-mytilus-spp-on-ycj8sc5pn6.pdf

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

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

Field and laboratory flume studies were used to examine the stabilization of intertidal sands by diatom mucus films. Films were delineated by analyzing colloid carbohydrates, chlorophyll, and by scanning electron microscopy on intact sediment samples. In the field, diatom films were patchy on a scale of centimetres, corresponding to the structure of sand ripples. Films were present on the sediment surface after calm weather and absent after storms. Extracellular polysaccharides accounted for a maximum of 20% of microalgal carbon. Erosion of intact cores in the flume showed that although films stabilized local areas of the bed, portions of the film were also washed away or buried. Stabilized areas of the bed were transposed to new ripple locations as the bedform moved ‘through’ the film. This observation explained the heterogeneous distribution of films with respect to ripple topography in the field. SEM showed diatom cells attached between sand grains with mucus strands, particularly in samples from the films. Mucus attachment due to protozoa, fungi, and other organisms was also observed. In the flume, diatom cells were washed away leaving mucus strands behind. A flume core with diatom films lost smaller amounts of chlorophyll than a core without films, under similar stages of erosion. At the highest flow, many grains were cleaned of mucus coatings; the grains appeared similar to those from sites of active transport (crests) in the field. We conclude that sediment stabilization by biofilms must be studied on a spatial scale of centimetres, and a temporal scale of days to weeks. The most important effect of microbial binding of sediments may be their role in the transfer of organic matter between the sediment and the water column.

The interaction between benthic diatom films and sediment transport

https://bdigital.ufp.pt/bitstream/10284/289/2/Mathematical%20modelling%20to%20assess%20the%20carrying%20capacity%20for%20multi-species%20culture%20within%20coastal%20waters.pdf

Jonathan Grant

Papers

A multidisciplinary approach to evaluating impacts of shellfish aquaculture on benthic communities

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

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

The interaction between benthic diatom films and sediment transport

Mathematical modelling to assess the carrying capacity for multi-species culture within coastal waters