FACTORS

What are the factors that can affect seagrass growth/ cause seagrass loss?
How does the changing environment impact the seagrass?

Based on notes from Dr Len McKenzie’s Seagrass Workshop last year, here’s a general list of factors that can affect the growth of seagrass!

Factors affecting Seagrass Growth

• Sediment Quality        
• Water Depth        
•  Water Quality  
  • Temperature
  • Salinity
  • Clarity        
• Nutrients         
• Current & Hydrodynamic (water movement) processes ·        
• Interactions with other species (e.g. there must be epiphytes to prevent the seagrass from “sunburn”, but too much epiphytes will suffocate the seagrass.) 

(All this differs for different species types. ) 

*epiphyte: according to “http://en.wikipedia.org/wiki/Epiphyte”, ‘An epiphyte is an organism that grows upon or attached to a living plant.’ In this case, the living plant would be the seagrass.  

Also based on the Seagrass Workshop conducted last year, here’s a list of the factors contributing to seagrass loss

Causes for seagrass loss (due to environment/machinery) to seagrass meadows

• dredging: removes plants and reduces light availability        
• grazing (by turtles and dugongs): removes plants       
• bait & clam digging: physical disturbances of plants, removes plants       
• anchors & propellers: physical disturbances of plants (cuts up rhizomes, during storms, whole meadows can get uprooted)       
• flooding: lots of deepwater/freshwater input, sedimentation, herbicide input        
• increased sedimentation can lead to topography changes such as a raised seabed: overexposure to sunlight      
• loss of shelter : loss of protection from wind/wave action       
• Diseases: e.g. labyrinthula – slime mould·        
• Elevated nutrients: too much epiphytes can smother leaves        
• Poor catchment practices (diffuse & chronic inputs from modified catchment): sedimentation, herbicides
• Aquaculture: can result in increased algae blooms, increased sedimentation (block sunlight)       
• Coastal land development: runoff, acid sulphate soils (sulphuric acid, washed out to seagrass meadow, kills animals), sedimentation       
• Industrial ports: physical damage (ports often in protected areas, seagrass as well, they have to co-exist), change in topography and water flow, point source discharge (oil spills, sewage and industrial discharge)
• Shipping: physical damage from grounding, point source discharge        
• Trawling: physical damage from intensive trawling       
• Fishing: poisoning, blasting (high in phosphites, algae blooms), set nets (when they drag the nets to catch fish, they uproot sea grass) 
• Physical damage by ignorant children/ adults

   Finally, here’s a list of the impacts of climate change on seagrass. 

  Impacts of climate change on seagrass        

  • increase in temperature: burnoff, affects distribution and reproduction        
  • sea level rise, increasing water depth so exposure to light is reduced        
  • disturbances through increased number and intensity of hurricanes/cyclones·        
  • elevated flooding frequency and amplitude 
  • slight rise in temperature (1-2 degrees Celcius) even for short period breaks down the enzymes needed for photosynthesis.