Biogeomorphology of coastal systems

From Coastal Wiki
(Redirected from Bio-geointeraction)
Jump to: navigation, search

Biogeomorphology concerns two-way interactions between organisms and landform development: geomorphology determines the physical habitat of organisms, while organisms modify hydrodynamics, sediment transport, erosion and deposition and thereby alter morphology. These interactions can generate feedbacks through which biological and morphological patterns develop together. Understanding biogeomorphic feedbacks is important for nature-based coastal management. Restoration succeeds only when the physical environment allows ecosystem engineers to establish and when their subsequent effects on hydrodynamics, sediment transport and morphology reinforce rather than undermine persistence of the restored ecosystem.


Introduction

Biogeomorphology considers the interactions between the ecology and geomorphology of a system. Ecology is the study of relationships between the biota and their environment, while geomorphology examines landforms and how they are formed. Biogeomorphology can be studied in terrestrial as well as aquatic systems. Within aquatic systems, biogeomorphological relationships can be found for both hard substrates (rocky shores / coral reefs) and soft substrates (muddy / sandy coastal sediments). Biota can alter geomorphology by creating hard substrates (e.g. coral reefs) or by modifying the stability or erodibility of soft substrates. Key species in the benthic communities of sedimentary shores can influence the geotechnical properties of their sedimentary environments by acting as biostabilizers or biodestabilizers of sediment. Besides acting on substrate stability, biota can promote or impede sediment avalanching or slumping along submarine slopes, mix sediments, stimulate deposition and affect flow patterns[1]. The impact of organisms on coastal morphology can be both dramatic (e.g. coral reefs, saltmarshes, mussel beds) and more subtle by modifying rates of sediment erosion and accretion. Biota are not only influenced by various environmental factors (abiotic – physical & chemical; biotic – other organisms; anthropogenic – humans), but organisms also act as ecosystem engineers and modify their environment (physical, chemical and biological aspects). Ecosystem engineers create valuable habitats (e.g. coral reefs and saltmarshes) that are important for fish and birds and provide natural coastal protection by attenuating waves and currents, reducing erosion and, in some settings, accumulating sediment fast enough to contribute to adaptation to sea-level rise

Essential concepts

The term biogeomorphology was first used in the eighties (Viles, 1988[2]), although earlier studies focused on the topic without using this term. In coastal systems biogeomorphological interactions are clearly demonstrated in shallow, productive waters and various sedimentary environments. Examples of biogeomorphological interrelationships include sand dune development, tidal flats, salt marshes, mangrove systems and coral reefs.

Relevant geomorphological factors in coastal systems are bathymetry, bed composition (rock, gravel, sand, silt), and the transport of sediment. It also includes factors that drive morphological processes, such as water flow and wave energy. The biota involved in coastal biogeomorphology[3] include plants and animals, ranging from very small (microorganisms) to very large (feeding pits of whales).

Fig. 1. Surface disturbance by Arenicola marina, including the production of casts and feeding funnels, increases bed roughness and promotes sediment resuspension.

The geomorphologyl directly affects biota through its influence on habitats. Coastal morphology and geomorphological processes define the gradients between high and low, between wet and dry and between sedimentation and erosion. These gradients and the processes that cause them determine the gradients in grain size, nutrient levels, organic matter levels and water content. Plants and animals are adapted to specific conditions and will therefore be found and abundant at specific locations (often forming habitats).

The biological influence on geomorphological processes is through the ability of biota to create, maintain or transform their geomorphological surroundings. This is demonstrated by the influence of vegetation and macrofauna on water flow, sediment erosion and deposition, or by the influence of fauna on sediment characteristics through bioturbation and biostabilization (Fig. 1).

In some cases morphological processes are dominant over biological processes and therefore it is necessary for biota to adjust to their environment. In other cases biological processes are dominant (e.g. coral reefs, salt marshes). The most interesting are those cases where there is a mutual interaction that leads to feedback coupling of processes. When looking for these cases, it is important to examine the spatial and temporal scales of the mutually interacting processes.

Biogeomorphological feedbacks can reinforce ecosystem development, but they can also reinforce degradation; for example, loss of sediment-stabilizing vegetation can increase erosion or turbidity and thereby make vegetation recovery more difficult.

Biogeomorphology for hard substrates

On rocky shores and coral reefs the typical community of organisms modifies the erosion of substrate. Influenced by abiotic factors such as wave energy, splash water, inundation frequency and -period, depth, desiccation and substrate type, a clear zonation of various cyanobacteria, (macro-)algae, fungi, lichens, molluscs, sponges, worms, sea urchins, fish, etc. can be found. Some of these organisms dwell on the surface of the substrate, while others live within the substrate. Organisms can enhance breakdown of the substrate through chemical processes (biocorrosion) or mechanical removal by boring, scraping and grazing (bioabrasion), but biological cover can also protect rock surfaces against weathering and erosion.

Coral reefs

Coral reefs provide a conspicuous example of biogeomorphological feedback on hard substrates. Reef-building organisms produce a carbonate framework that modifies waves, currents and sediment transport and thereby creates habitat for the reef community itself[4]. Reef morphology reflects the balance between carbonate production and its incorporation into the reef framework, and losses through bioerosion, dissolution and physical breakage[5]. A reef can therefore remain biologically inhabited while losing its capacity to maintain or increase its surface elevation if carbonate losses exceed production. Coral reef ecosystems are dealt with in the article Coral reefs.

Rocky shores

Biogeomorphological feedbacks between rocky shores and biota include:

  • Microbial biofilms that modify substrate properties and influence settlement[6]
  • Boring, scraping and other forms of bioerosion that modify surface roughness and create microhabitats[7]
  • Biological cover by mussels, barnacles, algae and other organisms, which can increase habitat complexity and modify temperature, moisture, wave exposure and weathering of the rock[8].

Rocky shore habitats are dealt with in the article Rocky shore habitat.

Biogeomorphology for soft substrates

In soft coastal systems, the interrelationships between geomorphological factors and biota mainly apply to benthic fauna and flora. The presence of benthic species is affected by hydraulic and morphologic conditions, such as water depth or elevation on the shore, current velocity, wave action, salinity and grain size. The biota responsible for changes in geomorphology of soft substrates can be divided into two functional groups, namely biostabilizers and biodestabilizers. Biostabilization leads to increased sediment stability and a reduction in erosion potential, whereas biodestabilization leads to reduced sediment stability and an increase in erodibility.

Biostabilization by plants

Fig. 2 Seagrass meadow.

On tidal flats, small algae (diatoms) are capable of affecting the geomorphology. Microphytobenthos, especially benthic diatoms, can form surface biofilms and produce extracellular polymeric substances (EPS) that bind sediment particles and substantially increase resistance to erosion .

Seagrass is dependent on clear water, it needs sunlight to grow. A seagrass meadow (Fig. 2) slows down the current velocity near the bed, therefore reducing the resuspension of sand and silt, and this in turn helps to maintain clear water. Their root system also promotes binding of the substrate. Seagrass requires sufficient light for growth. A seagrass meadow slows near-bed currents and reduces sediment resuspension, thereby increasing water clarity and improving the light conditions for its own growth. This positive seagrass–sediment–light feedback can help maintain established meadows.

Seaweeds and salt marsh plants are capable of modifying their physical environments by damping down wave energy and tidal currents. Salt marsh vegetation can also promote sediment deposition resulting in a gradual elevation of the marsh on the upper shore. The resulting change in inundation conditions feeds back on vegetation growth and further sedimentation, allowing the marsh morphology and vegetation pattern to develop together. Other stabilizing effects result from cementation of beach-rock by cyanobacteria and stromatolite formation by algae. Research by Temmerman et al. (2005[9], 2007[10]) points out that the interaction of vegetation growth, tides and sedimentation is crucial in the formation of the typical levee-basin configuration of the saltmarsh landscape.

Fig. 3 Upper shore salt marsh with creek system and evidence of benthic diatoms stabilizing mudbanks.


Biostabilization by animals

Fig. 4 Example of biostabilization by animals.

Some macrozoobenthos can actively filter sediment particles from the water column and deposit them on the bed. The presence of a mussel bank, for example, will alter the bed in different ways. Mussels at high densities will protect the underlying sediment from erosion by waves and currents (armouring effect). In addition, mussels are filter feeders and actively remove small suspended particles from the water column and any inorganic material (e.g. silt) is rejected as faeces and pseudofaeces. Some of this material will get deposited and incorporated into the bed, causing a shift in the composition to finer sediments and an increase in bed-level.

The burrows of the polychaete worm Nereis (Hediste) diversicolor, ubiquitous in muddy tidal environments, increase sediment permeability and accelerate dewatering and compaction of freshly deposited muds, thus increasing the critical erosion shear strength. These and other worms exert pressures that compress and compact the surrounding sediment skeleton. Sediment removed from the burrows forms small asperities ('tubes') on the sediment bed. A single tube increases the total drag force between the water and the sediment (skin friction), due to the downward displacement of high momentum fluid. Where tubes are rare, local erosion is likely. In contrast, where tubes are abundant, sediment accretion is more likely. Dense stands of animal tubes protruding from the sediment surface can protect the deposit from erosion by so-called skimming flow, in which the water passes over but not through the stand (Fig. 1). An analogous situation exists with seagrasses and saltmarsh vegetation. Accumulation of fine particles and organic matter between the tubes, mucus production by the community of microorganisms, meiofauna and macrofauna between the tubes may also contribute to sediment stability. Colonization of newly deposited sediment by burrowing species, such as Nereis diversicolor and Corophium volutator, contributes to stabilization and promotes the development of large-scale mud banks[1].

The same broad type of biological activity—burrowing or tube building—can stabilize or destabilize sediment depending on how it changes bed structure and near-bed flow.

Biodestabilization

Fig. 5 Example of bioturbation.

Benthic animals may destabilize the substrate by their burrowing and surface deposit feeding activity (e.g. bivalves, snails and crustaceans; Fig. 5). The constant mixing and recycling of sediment in the top centimeters of the bed, known as bioturbation, results in a change in the vertical particle size profile. Selective uptake of preferred particle sizes and their subsequent defaecation results in sorting and pelletizing of sediments. Together, the burrowing and the constant movement within the substrate, results in the generation of a surface micro-relief that has a higher hydraulic roughness, which increases turbulence and increases the potential for erosion. Bioturbators also interact with biostabilizers, by destabilizing the sediment as a result of grazing on biostabilizers such as microalgae (Montserrat et al. 2008[11]). On the other hand, bioturbators may promote the microphytobenthos growth by organically enriching the sediment via biodeposition. Furthermore, bioturbation affects the sediment water content, porosity and sediment cohesion[12].

Fig.6 Illustrates how biota act as ecosystem engineers and influence sediment stability and morphology in the intertidal zone.

Mesocosm experiments by Cozzoli et al. (2020[13]) show that the effect of bioturbation by bivalves mainly occurs in muddy sediments and is strongest at moderate flow rates, which are insufficient to erode a cohesive sediment bed, but strong enough to suspend sediment particles when the cohesive bonds have been broken by bioturbation. These experiments also show that the degree of bioturbation is mainly related to the metabolic activity of the individual bioturbators. Metabolism is related to body mass, but increasing body mass does not increase metabolism in the same proportion[14]. A large number of small bioturbators thus produce more bioturbation than a smaller number of larger bioturbators with the same total mass. In order to estimate correctly the effect of bioturbation on the sediment balance, models must therefore be able to simulate the spatial distribution of the size classes of benthic animals[13]. Because the density of bioturbators is usually greatest in the intermediate-high part of the mudflat, their activity counteracts further upward growth of the mudflat[15].

Some marine vertebrates strongly disturb the seabed during foraging. Excavations are produced, for example, by tilefish (Lopholatilus chamaeleonticeps), loggerhead turtles (Caretta caretta), walruses (Odebenus rosmarus), Grey whales (Eschrichtius robustus) and sea otters (Enhydra lutris). They produce significant sediment suspension, but it is unlikely that these large fauna have comparable impact as the considerably more abundant communities of invertebrate macrofauna, meiofauna and microflora[1].

Research of Paarlberg et al. (2005[16]) has shown that impacts of (de)stabilizing biota on mudflat morphology and bed composition can be significant and can be quantified by adding a limited number of algorithms to existing hydro-morphological models. Borsje et al. (2008[17]) show that the influence of (de)stabilizers might extend beyond the mudflat scale to the estuary scale in cases of meso-tidal highly productive systems, such as the Wadden Sea. Biogeomorphic effects are not necessarily local: by changing sediment availability and transport pathways at one location, ecosystem engineers can alter morphology and ecosystem development elsewhere in the coastal system.

Zoning

Biogeomorphic effects vary systematically across the intertidal zone because organisms occupy different ranges of elevation, salinity, inundation and hydrodynamic stress. This biological zonation feeds back on sediment stability and transport, so that spatial patterns of organisms and morphology are partly co-produced. Figure 6 illustrates examples of biota acting as ecosystem engineers across the intertidal zone. Key biota are divided into two functional groups, the bio-stabilisers and bio-destabilisers, with varying spatial distribution along estuarine gradients (both axial and vertical).

Related articles

Benthos
Meiofauna of Sandy Beaches
Coastal and marine sediments
Spatial and temporal scales in biogeomorphology
Salt marshes
Spatial and temporal variability of salt marshes
Nature-based shore protection
Biogenic reefs of Europe and temporal variability
Dynamics, threats and management of biogenic reefs
Dynamics, threats and management of salt marshes
Seagrass meadows


References

  1. ↑ 1.0 1.1 1.2 Murray, J.M.H., Meadows, A. and Meadows, P.S. 2002. Biogeomorphological implications of microscale interactions between sediment geotechnics and marine benthos: a review. Geomorphology 47: 15–30
  2. ↑ Viles H.A. (ed.) 1988. Biogeomorphology. Oxford: Basil Blackwell Ltd.
  3. ↑ Baptist M.J. 2005. Biogeomorphology. In: Schwartz, M. (Ed.). Encyclopaedia of Coastal Science, pp. 192-193. ISBN 1-4020-1903-3
  4. ↑ Lange, I.D., Perry, C.T. and Alvarez-Filip, L. 2020. Carbonate budgets as indicators of functional reef “health”: A critical review of data underpinning census-based methods and current knowledge gaps. Ecological Indicators 110, 105857
  5. ↑ Perry, C.T., Murphy, G.N., Kench, P.S., Smithers, S.G., Edinger, E.N., Steneck, R.S. and Mumby, P.J. 2013. Caribbean-wide decline in carbonate production threatens coral reef growth. Nature Communications 4, 1402
  6. ↑ Dobretsov, S. and Rittschof, D. 2020. Love at first taste: induction of larval settlement by marine microbes. International Journal of Molecular Sciences 21, 731
  7. ↑ Thompson, R. C., Wilson, B. J., Tobin, M. L., Hill, A. S. and Hawkins, S. J. 1996. Biologically generated habitat provision and diversity of rocky shore organisms at a hierarchy of spatial scales. Journal of Experimental Marine Biology and Ecology 202: 73-84
  8. ↑ Coombes, M.A. 2014. The rock coast of the British Isles: weathering and biogenic processes. In: Kennedy, D.M., Stephenson, W.J. & Naylor, L.A. (eds), Rock Coast Geomorphology: A Global Synthesis. Geological Society, London, Memoirs 40: 57–76
  9. ↑ Temmerman, S., Bouma, T. J., Govers, G., Wang, Z. B., De Vries, M. B. and Herman P. M. J. 2005. Impact of vegetation on flow routing and sedimentation patterns: Three-dimensional modeling for a tidal marsh. J. Geophys. Res. 110, F04019.
  10. ↑ Temmerman, S., Bouma, T.J., Van de Koppel, J., Van der Wal, D., De Vries, M.B. and Herman, P.M.J. 2007. Vegetation causes channel erosion in a tidal landscape. Geology 7: 631-634
  11. ↑ Montserrat, F., Van Colen, C., Degraer, S., Ysebaert, T. and Herman, P.M.J. 2008. Benthic community-mediated sediment dynamics. Mar. Ecol. Prog. Ser. 372: 43–59
  12. ↑ Cozzoli, F., Gjoni, V., Del Pasqua, M., Hu, Z., Ysebaert, T., Herman, P.M.J. and Bouma, T.J. 2019. A process based model of cohesive sediment resuspension under bioturbators' influence. Science of The Total Environment 670: 18-30
  13. ↑ 13.0 13.1 Cozzoli, F., Gomes da Conceicao, T., Van Dalen, J., Fang, X., Gjoni, V., Herman, P.M.J., Hu, Z., Soissons, L.M., Walles, B., Ysebaert, T. and Bouma, T.J. 2020. Biological and physical drivers of bio-mediated sediment resuspension: A flume study on Cerastoderma edule. Estuarine, Coastal and Shelf Science 241, 106824
  14. ↑ Vladimirova, I., Kleimenov, S. and Radzinskaya, L. 2003. The relation of energy metabolism and body weight in bivalves (Mollusca: Bivalvia). Biol. Bull. 30: 392–399
  15. ↑ Wood, R. and Widdows, J. 2002. A model of sediment transport over an intertidal transect, comparing the influences of biological and physical factors. Limnol. Oceanogr. 47: 848–855
  16. ↑ Paarlberg, A. J., Knaapen, M. A. F., de Vries, M. B., Hulscher S. J. M. H. and Wang, Z. B. 2005. Modelling of the biological influence on the morphology and bed composition of an intertidal flat. Estuarine Coastal and Shelf Science 64 (4): 577-590
  17. ↑ Borsje, B.W., de Vries, M.B., Hulscher S.J.M.H. and de Boer, G.J. 2008. Modeling large scale cohesive sediment transport affected by biological activity. Estuarine, Coastal and Shelf Science 78: 468-480


The main author of this article is Widdows, John
Please note that others may also have edited the contents of this article.
Citation: Widdows, John (2026): Biogeomorphology of coastal systems. Available from http://www.coastalwiki.org/wiki/Biogeomorphology_of_coastal_systems [accessed on 3-09-2026]




Retrieved from "https://www.coastalwiki.org/w/index.php?title=Biogeomorphology_of_coastal_systems&oldid=82389"