Biogenic Habitat & Engineers

Nota:

• Biogenic engineers directly or indirectly control the availability of  resources to other organisms by changing the biotic and abiotic resources available 
• physical ecosystems engineers do this by physical modification, maintenance, or creation of habitats 

Nota:

• Autogenic are organisms that change the environment by their actual bodies and structure such as corals or tube worms 
• Allogenic change the environment by their behaviour such as beavers creating dams for shelter 

1. structural complexity increases Biodiversity
   1. thompson et al 1996, harley 2006
   2. it allows many more systems to become apart of the ecosystem so produces micro habitats, such as mussels and hard substrate for palnts that need places to lock onto. they also provied cover

Nota:

• Predator refugee  stress relief  protection from flow rates  refugee from sedmentation  encourages sedimentation  hard substrate for settlement 

1. seagrasses
2. oyester beds
3. Maerl

   Nota:

   • free calcareous Algae - they reomve sediment under moderate flow = when they die they support fauna 

Nota:

• massive structures made up of entirely biogenic engineers either by thier own bodies such as tubes and shells or by sediment and rocks held together by substances secreted by said organisms, it is discrete from the substrate usually rising from it.

1. Sabellaria alveolata

   Nota:

   • this is a polycheate live up to 4-5 years  they have tube like structures that aggriate together  they are very fragile and conditions for them are unknown  things attached to them and promotes diversity 
2. Sabellaria spinulosa

   Nota:

   • less common then its cousin species, but is home to the shrimp Pandulose montagui 
3. Modiolus modiolus

   Nota:

   • its a slow growing species with a 25 year life span, it becomes reproductively active at ages 3 to 5 onceestablished they are stable strutures - extremely rich communitys, embeded into the sediment 
4. Mytilus edulis

   Nota:

   • these are small organisms in the uk but they form dense sea beds with verdiverse communities due to thier hard substrate and binding gel creating a micro habitat 
5. Serpula vermicularis

   Nota:

   • prevented at low depth due to lack of O2, they are normally found in semienclosed scottish locks - allowing groeth 

Nota:

• these are all anthropogenic impacts  - bottom fishing  - changes in sedimentation from management  - trampling  - gravel extraction  - pipelaying, trenching, oil rigs  - aquaculture enrichment 

Nota:

• soft sediment habitats cosist of 90% of the sea floor  we know very little about this as it is very different to terrestrial environments if we knew the process we could see the evolution of these bioengineers 
• soft sediments are alot more ort livid then rocky shores  so biogenic engineers basically stablise the sediment 

1. sediment habitats

   Nota:

   • these are influence greatly by engineers due to  - particle size and sorting  - sedment quality - decreasing toxicity and om content  - depth  - improves attchment  alter sedjiment properties  -alters currents  

Nota:

• he studied wether small groups or single tubes effected the area more they found that single tubes just lead to destablisation where as dense aggregation led to stablisation 
• so for single the sediment was more flowing making it easier for isopods and amphipods to move and forage and became a better nursing are for polycheates 
• also single worms created a piston effect wich lowered the oxygenic layer in the sediment 

Nota:

• mat-forming autotrophs  sliming motile benthos  burrows as habitats  sediment reworking and irrigation by infuana