Subsea Environment

Surface and Mid-Ocean Areas

In the offshore oceanic environment, surface-schooling pelagic fish species such as tuna frequent the area, along with the occasional passage of large marine animals such as whales, dolphins and turtles.

The surface and mid-water levels are also known to be habitats for various species of plankton, small shrimps, fish and squid; many of which migrate through the water column between day and night and form the basis of the food chain. Species of tuna and squid were observed during ROV dives indicating depths (to hundreds of metres) to which some surface species (e.g., yellow fin tuna) can go in search of prey.

Hydrothermal Vents

Seafloor hydrothermal vents were first discovered in 1976 on the Galapagos Rift in the Pacific Ocean. Since then, hydrothermal vents have been found on the seafloor close to tectonic plate boundaries all over the world. Hydrothermal vents are of particular interest to biologists as they tend to support a much higher abundance of fauna compared to surrounding deep sea environments, although the biodiversity tends to be lower. Locations of some well studied hydrothermal vent sites are provided in the map below.

Subsea Environment at Solwara 1

Solwara 1 is located on the northwest flank of the active subsea volcano called North Su. North Su emits plumes of gas and sediment into the water which, depending on the current direction, usually settle over Solwara 1 or South Su. When present over Solwara 1, the plume is typically seen between 900 and 1,100 metres water depth. In many ways, the environmental setting at Solwara 1 is variable, and can fluctuate significantly over relatively short time frames. These observations are significant in characterising the existing seafloor habitats.


South Su, the proposed reference site for the Project, is located on the south-eastern flank of the North Su volcano. To see the location of Solwara 1, North Su and South Su relative to one another, please see the map below:

 

Vent Environment and Biology

Active hydrothermal areas have a number of fundamental characteristics that influence biology. The most important characteristics are the chemistry and temperature of the fluid emitted from the seafloor.

Some micro-organisms can make use of the chemicals from the fluid chemistry to produce energy (known as chemosynthetic primary production) (note: there is no photosynthetic primary production at these depths). Some animals consume the micro-organisms directly, while in others, the micro-organisms reside as endosymbionts, i.e., living within the host animal tissues to extract their source of energy. The animal communities around the vents typically include species of gastropods, bivalves and crustaceans. These endosymbiotic relationships enable the generation of extremely high biomass, and the animals are adapted for tolerance of sulphides and heavy metals at levels to which surface organisms are not typically exposed. Many of these animals are dependent on the micro-organisms that break down hydrogen sulphide and cannot exist away from the influence of vent activity.

Observations made at Solwara 1 between 2006 and 2008 showed that venting activity is variable. Some areas observed to be venting in the 2006 survey were not venting when re-surveyed during 2007, and vice versa. Some of these differences may be due to sampling or observation frequency but this pattern is also suggested on a macro-scale through regional plume studies that also show variability from year to year (Parr & Binns, 1997).

These observations are of significance in characterizing the existing seafloor habitats of Solwara 1 and South Su, and show that it is a dynamic system and there is no durable differentiation of active and inactive areas.