We can agree to disagree in our opinions but we do need to be sure that we are working with the same set of facts.
In order to understand it, you need to look at the whole picture, not just single aspects taken out of context and interpreted according to a set of parameters based on personal bias.
We will pretend that you do not have personal bias, but I do.
There is some deposition directly beneath the farms but it is undergoing a continuous process of breaking down to constituent elements; that breakdown is accelerated by site fallowing. If there are creatures that find the environment less than ideal, they simply move 100m to an environment essentially unaffected by the deposition; consequently, diversity in the benthic substrate immediately under the pen is somewhat reduced but overall diversity within an area is unaffected. That is not a permanent condition, nor one that is particularly harmful, nor one that affects the seabed a stone's throw from the pens.
This, of course, assumes that the surrounding area can support the additional organisms and that the carrying capacity of the surrounding area is not already reached.
Arguing precisely how many farms fit into Stanley Park is a sidetrack that has nothing to do with the point being made, though having done the actual calculation of area occupied by the farms in the past, I'll stand by my assertion that all farms will fit within the Park. The point, once again, is that the farms use an extremely small area of the coast and that because of oceanographic conditions, physical principles, biological principles and the nature of the materials being deposited, the depositions are not causing harm nor are they a cause for concern.
Again, if it is true that the deposits are not causing harm and are not a concern, why the recommendations from scientists, like Pusceddu et al, that farm be located at a minimum of 2k from vulnerable sites? While I totally understand your argument that the affected area is small compared to the overall size of the coastal sea bed, but I have a hard time understanding how a reduction of abundance and biodiversity in an ecosystem is not harmful. If the micro-, meio- and macrobenthic organisms are reduced in number or diversity, that is going to have an impact on the mega faunal organisms further up the food chains as the organisms that might feed on these organisms are reduced and the organisms that feed on those organism are reduced and so on. So while it is fine to say that "creatures that find the environment less than ideal . . .[can] simply move 100m to an environment essentially unaffected by the deposition," the reality is this may not always be possible, and this itself would have an impact on those neighbouring areas, which would now see an increase in populations that may exceed its own carrying capacity. If I clearcut a forest ecosystem, I can make the same argument that the organisms (ie: squirrels) that find the clear cut "unsuitable" can all just move over to the neighbouring forests, but we know that is not necessarily the simple move you make it out to be, as the surrounding forest may already have reached its carrying capacity for food, shelter, etc. Furthermore, while you insist that the current number of farms is not going to increase, and therefore the area that they affect is going to remain low and "insignificant," I still do not accept that there will be no expansion of salmon farming. I simply wonder at what point is the area affected no longer "insignificant"? How will we know when that point is reached? Will farmers be willing to close up shop at that point? This is why I used the reference to how we once viewed the oceans and atmosphere. We all understand that throwing a glass of freshwater into the ocean is not going cause a measurable effect, and I see that this is how you currently view the impact of salmon farms on the coast sea floor (you admit there is an impact, but it is "insignificant" when viewed in the context of the total sea floor). However, what happens when the atmosphere warms to a point where the Antarctic ice sheet all melts and that freshwater is added to the oceans? Is there a measurable impact? Just ask the billions that live within 50m of sea level. I see the same for salmon farms. You may be right that the loss of biodiversity due to the salmon farms is insignificant today, that there is enough biodiveristy in the surrounding seafloor to make any losses caused by the farms to be "insignificant," a cost of doing business, but then where do you draw the line? How many more farms can be added before their impact becomes "significant"?