Ecosystem Engineers Flashcards
What are physical ecosystem engineers?
‘‘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. The ecological effects of engineering on other species occur because the physical state changes directly or indirectly control resources used by these other species.’’
Give two types of ecosystem engineering
Jones et al distinguished between Autogenic and Allogenic engineering, comparing them to trees and beavers • Autogenic; Trees change the availability of resources, influence light and availability, by changing their own structure and remain part of the engineered environment. • Allogenic; Beavers cut down trees, alter river flow rates, alter resource availability but are not part of the engineered habitat themselves. Structural complexity and architectural complexity are one way habitat engineers exert their impact.
Define a keystone species
Keystone species have a disproportionate impact overall on a habitat or community structure, but they do not physically modify the habitat themselves. Otters in Californian Kelp community.
How is seagrass a bioengineer?
Seagrass, promote sedimentation, stabilise sediment, and increase local sedimentation.
How are mearl beds bioengineers?
Mearl beds create complex habitats, promote diversity, change sedimentation flow rates, modifying the physical environment Maerl occur mostly on the south and west coasts of the UK. They are free living, red algae, calcareous nodules, which build up layers of Maerl beds. They create a complex habitat which can have a very high diversity.
WIDER READING: bioengineers effecting organism distribution
Lindsey et al, 2006. Lindsey, E., Altieri, A. and Witman, J. (2006). Influence of biogenic habitat on the recruitment and distribution of a subtidal xanthid crab. Marine Ecology Progress Series, 306, pp.223-231. · Investigates role played by biogenic habitats in influencing mud crab (Dyspanopeus sayi) distribution · Found that biogenic habitats (e.g. mussel beds) can have cascading effects on communities · Lab experiment: confirmed that the crab species will consume both M. edulis (mussels) and Crepidula spp. (slipper snails) · Field surveys revealed that crabs were significantly more abundant on beds of these organisms, however modules containing rocks demonstrated an even higher abundance, suggesting that structural complexity of the biogenic substrates I the primary factor in influencing recruitment, rather than their availability as prey · Both prey species recruit to conspecifics, meaning that both beds provide seasonal predictability as a food source · Biogenic habitats offer food sources and complex physical structure and so are particularly important in habitats where this is lacking, e.g. soft sediments.
What are biogenic reefs?
“Solid, massive structures which are created by accumulations of organisms, usually rising from the seabed, or at least clearly forming a substantial, discrete community or habitat which is very different from the surrounding seabed. The structure of the reef may be composed almost entirely of the reef building organism and its tubes or shells, or it may to some degree be composed of sediments, stones and shells bound together by the organisms.” Habitats Directive Annexe 1
Five UK species of biogenic reef builders
Sabellaria alveolata, the honeycomb worm, often solitary and will form tubes out of sediment. Occasionally, when the conditions are right, they will aggregate and form reef structures. They can form substantial populations and are very vulnerable to changes in temperatures, disturbances like dredging ect. They have a very particular group of species associated with them when they do aggregate.
Sabellaria spinulosa, Ross
Mytilus edulis, Blue Mussel, open coast reefs tend to be smaller 2-3cm and estuarine subtidal reefs (on mudflats) tend to be much larger. Open coast reefs can form denser, deeper mussel beds and support higher biodiversity.
Modiolus modiolus, Horse mussels, long lived. Reefs are quite large and incredibly diverse due to the longer timescales. Take a long time to build up due to being vulnerable to predation and having slow growth rates, but once well-established they can be quite persistent and long lived.
Serpula vermicularis, calcareous worm which only builds reefs in specific conditions. There has to be large amounts of shelter and hydrodynamic flow, ect. Few areas contain large reefs, but diverse interstitial fauna will occur when they do.
What are some htreats to biogenic reefs?
Bottom fishing (particularly S. spinulosa and M. modiolus)
Changes to sediment regime: Shoreline Management Plans
Trampling damage
Gravel extraction (S. spinulosa)
Pipelaying, trenching, oil rigs
Organic enrichment from aquaculture (enclosed sea lochs)
WIDER READING: Overexploiting marine ecosystem engineers:
Coleman and Williams (2002)
. Overexploiting marine ecosystem engineers: potential consequences for biodiversity. Trends in Ecology & Evolution, 17(1), pp.40-44.
Reviews fishing/overexploitation as ecosystem engineers and effects on biodiversity
Mass removal of engineering organisms can impact local biodiversity negatively, as well as alter important water-sediment biogeochemical processes
Importantly, studies have become more abundant on this topic, with a growing appreciation for the extent of the impact that’s had
This article encourages future policy makers to gain further knowledge before making decisions on fishing
Overfishing is a major environmental problem in the oceans. In addition to the direct loss of the exploited species, the very act of fishing, particularly with mobile bottom gear, destroys habitat and ultimately results in the loss of biodiversity. Furthermore, overfishing can create trophic cascades in marine communities that cause similar declines in species richness. These effects are compounded by indirect effects on habitat that occur through removal of ecological or ecosystem engineers. Mass removal of species that restructure the architecture of habitat and thus increase its complexity or influence the biogeochemistry of sediments could have devastating effects on local biodiversity and important water–sediment processes. The possible overexploitation of engineering species requires more attention because the consequences extend beyond their own decline to affect the rest of the ecosystem. This is particularly problematic in the deep ocean, where oil and gas exploration and fishing pressure are likely to increase.
WIDER READING: Whales
Roman et al, 2014
Roman, J., Estes, J.A., Morissette, L., Smith, C., Costa, D., McCarthy, J., Nation, J.B., Nicol, S., Pershing, A. and Smetacek, V., 2014. Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment, 12(7), pp.377-385.
Recent technological advancements have allowed us to further our research into functional roles of whales in ecosystems
Commercial whaling dramatically reduced biomass and abundance of baleen and sperm whales (aka the great whales)
Whales act as a horizontal and vertical vector, as well as a reservoir for nutrients; they facilitate the transfer of nutrients by releasing faecal plumes near the surface after feeding at depth and by moving nutrients from highly productive, high-latitude feeding areas to low-latitude calving areas
Deep sea whale carcasses provide a habitat and food source for many endemic invertebrates
The continued recovery of great whales may help to minimise the destabilising stresses that marine ecosystems face and could lead to higher rates of productivity in areas where whales aggregate to feed and reproduce
Mat forming autotrophs
Mat-forming autotrophs: coat the sediment, stabilise it, and alter the exchange of nutrients, water and gasses between the water column, the air and the sediments themselves.
Cyanobacteria, filaments, EPS
Diatoms
Green macroaglal mats (eutrophication)
