1) Ecohydrodynamics studies the physical constraints of ecosystems based on time and spatial scales, and incorporates the water characteristics surrounding marine environments. 2) The ecohydrodynamic conditions around cold-water coral reefs determine food and larvae supply through interactions between currents, internal waves, and topography. 3) A 3D ocean model of the Mingulay Reef complex in the Sea of Hebrides shows tidally-driven currents and downwelling of surface waters delivering pulses of food to the reefs every six hours.

1. Ecohydrodynamics of cold-water coral.
Juan Moreno Navas.
Heriot -Watt University. UK

2. Ecohydrodynamics
The determination of the hydrodynamic constraints on
ecosystems with different time and length scale has
been coined by the term Ecohydrodynamics.
This concept also encompasses the physical, chemical
and biological characteristics of the water bodies
surrounding marine ecosystems.

3. Ecohydrodynamics of cold-water coral.
• The Ecohydrodynamic conditions around the coral reefs determine the
supply of food particles and larvae.
• The interactions between currents, internal waves,
upwellings/donwelllings and the topography creates suitable conditions
for the development of suspension-feeding cold water corals.
• The lateral and vertical advection of particles may therefore play an
important role in the functioning of coral ecosystem.
• The suspension-feeding cold-water coral communities rely on the delivery
of phytoplankton, zooplankton and organic matter derived from near-
surface primary productivity.

4. Located to the east of the island of Mingulay in
the Sea of Hebrides, UK.
Each reef is formed by seabed mounds up to
five metres high that likely have been growing
since the early Holocene (Roberts et al. 2005).
High dynamic area
Barra
Sea of the
Hebrides
Mingulay
Reef mounds

5. Ecohydrodynamics. Sea of the Hebrides
(a) (b) (c)
Analysis of colour fronts using 23-30 Apr. 2011 MERIS FR composites: (a) Chl-a;
(b) enhanced colour; (c) simplified Chl-a front map.

6. Ecohydrodynamics. Sea of the Hebrides
%
Mean all-seasons : (a) thermal fronts; (b) 300m Chl-a fronts; (c) 1km Chl-a fronts

7. Ecohydrodynamics of Mingulay Reef complex
• Previous studies revealed two dominant food supply
mechanisms to the reefs, a regular rapid downwelling of
surface water delivering pulses of warm water and periodic
advection of high turbidity bottom waters(Davies et al. 2009).
• A 3D ocean model has been applied to provide an adequate
assessment of the water circulation, water exchange and
renewal in the Mingulay Reef complex.

8. Mathematical model
The Mass and Momentum equations solutions.
Momentum equation - x
u1 u j u1 1 pa
f u2 g dz
t x 
 x x1 x
Tim e derivative j coriolis 
z 1   
1
barotropic atmospheric
advective

baroclinic
pressure
u1 1 S11 z 1 S12 z
Kj
xj xj x1 x2
  
 
turbulent diffusion radiation stresses (waves)
Mass equation – 3D
Mass equation – 2D
U1 U2
D u1 u2 u3
0 0
t x1 x2 t x1 x2 x3

9. Initial condition. Vertical & horizontal discretization.
Physical parameter Numerical value
Time step: 2s
Grid mesh: 300, 100m
3D Sigma coordinate with Horizontal cells (x,y): 193, 244
4 layers
Vertical coordinate: Sigma
Vertical Vertical layers: 8
Horizontal Eddy Viscosity: 4.3810
Vertical Eddy viscosity: 0.001
Drag coefficient: 0.0025
River discharge: No
Salinity: 35 psu
Temperature: 11c
Forced: Tide from FES2004
Horizontal

10. Ecohydrodynamics of Mingulay Reef complex
3D ocean model : two different grid resolution.
Mingulay 1
A
300 m
A
B Mingulay 5
100 m animation slices

11. 3D ocean model results.
Currents are tidally driven
Time scale: tidal cycle
Lenght scale: 20x20 Km

12. 3D ocean model results.
High turbulence in the Reefs area. High turbidity bottom waters(Davies et al. 2009).
Mingulay 1
Mingulay 5

13. 3D ocean model results.
Mingulay 1
Mingulay 5

14. 3D ocean model results.
Mingulay 1

15. Downwelling of surface water delivering pulses of warm
water.
Scanfish data
Dmitry Aleynik & Mark Inall (SAMS)
Murray Roberts (Heriot-Watt

16. 3D ocean model results.
Downwelling of surface water delivering pulses of warm water (Davies et al. 2009)
and high particle delivery to the bottom every 6 hours.

17. 3D ocean model and GIS.
This modelled information has been integrated into a 3D GIS
Mingulay 1
Mingulay 1
Mingulay 5

18. 3D ocean model and GIS.
Colour-coded habitat classification map
(Roberts et al. 2005)
The significant decline in richness with easting
(Henry et al 2010)

19. Conclusions
The model and remote sensing techniques provide the
spatial and temporal aspect of water circulation in the reef
complex (turbulence, Downwelling).
The model will provide better understanding of food supply,
larvae transport, community composition and sediment
dynamics.
This modelled information has been integrated into a 3D GIS,
thus providing a user interface for visualization interrogation of
results and as an input into other spatial and ecological
modeling projects.