6. E nvironmental Monitoring at the Mariculture Pa rk Zone scale

An output of the EU funded project PHILMINAQ “Mitigating impact from aquaculture in the Philippines,” was the development of 3 categories of environmental survey:

1. Simple survey for clusters of small farmers or medium sized farmers
2. Intermediate survey for large farms for aquaculture zones
3. Detailed survey for research purposes.
Regular Category 1 surveys are sufficient for monitoring physical and chemical parameters for mariculture parks (see below).
Category 1. Simple cheap, cost-effective survey aimed at LGU monitoring mariculture parks and medium sized farmer.
This survey measures the following parameters:
• Cage layout and sizes. Cage layouts and dimensions give crucial information for interpretation of survey results and also for modelling of the area.

• Hydrographic. Depth recordings provide inform ation to assist the sampling of the water column and seabed during the survey. Accurate depth measurements are also important for management of the site so that mooring ropes and nets can be set at the correct depth. Water depth below the net should be at least double the net cage net. Also, computer modelling of cages requires accurate depth measurements on the basis of the TROPOMOD supported with the physiochemical parameters and bathymetric data taken from the site assessment study.
• Condition of the seabed sediments. The condition of the seabed sediments is important as too much organic input to the seabed causes oxygen to be absent resulting in no fauna living there. If no fauna are living in the sediment, waste from the cages above is not eaten and it builds up on the seabed. This results in chemical reactions where gas bubbles from the sediments rise to the cages above and cause stress to the fish. It is important to monitor the biological and chemical condition of the seabed using sediment grabs or sediment cores to take samples for biological and chemical analysis.
• Oxygen levels in the water column. Oxygen levels in the water column (surface, mid-level column and bottom levels of the cage structure) are important as very low levels result in fish kills.
Also, low levels of oxygen stress the fish and cause poor growth. Oxygen levels in the water column are affected by many things, including water temperature, concentration of phytoplankton (algae), current and condition of the seabed as described above.
• Turbidity of the water column. Water turbidity is measured and monitored in two ways either using a secchi disk or depth transparency light emission instrument. The turbidity of the water column relates to how much algae and suspended solid material is in the water column. High turbidity may be linked to high levels of nutrients which cause excess algal growth or seasonal effects such as high suspended material from runoff caused by rain.
This is important as high concentrations of algae and suspended material (high turbidity) can lead to reduced oxygen in the water column if this material starts to decay.