Mining on land very evidently leaves scars and long-term problems such as acid mine drainage. But what harm could it do to mine the sea bed? What sort of scarring would it leave?
One of the three main nutrients needed by crops is phosphate, found in sedimentary rock — South Africa's biggest source is at Phalaborwa.
Phosphate is also found in the sediment that lies on the continental shelf, the shallow plain extending beyond the shores of the continents before it drops off into the wonderfully named abyssal plain.
Currently, offshore mining for phosphates is under consideration at a couple of sites around the world. Early in November, Namibian Marine Phosphate was granted a licence (pending environmental approval) to mine phosphate in its Sandpiper project off Walvis Bay at depths of between 180 and 300 metres below sea level.
This buoyed the hopes of Chatham Rock Phosphate, a New Zealand company which has applications in to mine phosphate in New Zealand as well as in Namibia.
But the Nambian Hake Association is concerned about the impact on the industry. As are hake and other fishers in South Africa, where Green Flash Trading has applied for the right to prospect for phosphates over a total of 108 000km between Adam Se Baai and Table Bay, and off Cape Columbine and Infanta.
All the companies involved have played down concerns about the impact on the marine environment and the important hake fisheries.
What could the impact be?
Dr Warren Potts, senior lecturer in the department of ichthyology and fisheries science at Rhodes University, says: "Perhaps the first and most important thing to highlight is the importance of the continental shelf zone to people."
Around the world, the fertile, rich and biodiverse marine coastal zone provides goods and services valued at US$14-trillion, says Dr Potts, referring to a chapter he co-wrote in a 2011 book (James N, Hermes J (eds). Insights into impacts of climate change on the South African marine and coastal environment). To quote the book: "The zone is considered to be one of the most socio-economically and ecologically important ecosystems on the planet (Harley et al. 2006).
"The subtidal zone provides essential ecosystem services such as habitat and food for both resident and migratory animals, and both recreational and commercial opportunities for human populations.
"The marine coastal zone supports subsistence, small scale, artisanal, recreational and commercial fishing activities."
Dr Potts says that the South African continental shelf zone is no exception.
"Besides its enormous biodiversity value, the marine coastal zone provides fish resources for approximately 24 700 commercial, 750 000 recreational and 29 000 subsistence line fishers as well as approximately 2 000 small scale gillnet and seine net fishers."
Gillnet and seine net fisheries contribute about R15-million a year to the Western Cape economy, and although subsistence fishery has a low economic value, it is absolutely critical to the survival of many small communities on the coast.
So the consequences of phosphate mining could be significant and have a range of domino effects.
Assuming that the type of mining to be undertaken would be dredging, Dr Potts says: "There are a number of short-term and long-term environmental concerns with this method and they extend from direct local consequences to indirect, wider consequences. The dredging will impact the seafloor, the water column and the surface waters and all of their associated marine life.
"Direct and local consequences would include habitat destruction and the disruption of benthic species [creatures who live on the seafloor]. This could have long term impacts on biodiversity."
Sediments that settle back in the dredging area could smother the local sea-floor community, which is a crucial part of the marine food chain.
And it won't just be the sea floor that is affected: "The suspension of sediments will have consequences for water quality and animals in the water column. Filter feeding fishes will be impacted and in severe cases, sediments can clog their gills and cause mortality. This will not be a localised impact as over time, depending on the current speeds and size of the suspended sediment, large areas can be impacted. The location of the dredging is critical in this regard and every effort should be made to avoid migratory pathways or high use areas of pelagic fishes."
He adds that just obscuring the sunlight which filters into the ocean and provides the energy which drives productivity (such as the growth of marine plant life) will have impacts. "The suspension of sediments will also reduce light in the water column, which will have an impact on the ecosystem by reducing primary productivity. As the dredging continues, and the plume reaches a maximum size, this may have significant impacts on the productivity of the coastal ecosystem.
The location of the dredging is critical in this regard and every effort should be made to avoid areas with fine sediments (which would be remain in the water column for longer).
Areas with high current speed may also be problematic as sediments will remain suspended for longer and the impact would be far less localised in nature."
And then, of course, there are other possibilities for harm, including the stirring up of heavy metals and other pollutants which have been safely settled on the sea floor for centuries, the potential for oil or fuel spillage and other wastes from the dredging vessels.
"If the dredging/mining occurred in biodiversity hotspots or important migratory or holding areas for fishes, the conservation and fisheries impacts could be great. If the extent of the dredging is large, we might expect some significant ecosystem effects, such as large reductions in primary production and possibly heavy metal poisoning," Dr Potts says.
"An extremely thorough environmental impact assessment process would be required to identify areas and techniques that are the most environmentally benign, and recommend appropriate mitigation strategies." Saving our seas Just a few years ago, if you told a restaurateur that he was serving red-listed fish, he would probably simply have shrugged his shoulders.
Today, many in the South African retail and hospitality industries will hasten to assure you their fish is all green-listed, thanks to a Worldwide Fund for Nature South Africa (WWF-SA) initiative.
The Southern African Sustainable Seafood Initiative (Sassi) enables consumers to make their concerns about seafood known. Consumers can text the name of a fish to the FishMS service on 079 499 8795 and within seconds, receive a reply indicating whether the fish is a green (go for it), orange (think twice) or red (don't even think about it) species.
The text may also include a short paragraph of information, explaining why the fish has been allocated to a category.
Earlier this month, WWF-SASSI announced a new Blackberry app, with Android and iPhone versions in the works.
FishMS is a success story that has harnessed consumer power in the cause of saving South Africa's seas, which once seemed an inexhaustible resource but now face daunting threats.
Growing awareness of the fragility of seas has spurred consumers round the world to demand more information and make choices based on their understanding of threats to marine life.
The fisheries and retail industry in South Africa have responded.
Bronwen Rohland, sustainability and marketing director at Pick n Pay, says: "Food security is a key driver for our commitment to sustainable seafood sourcing.
"As one of the country's largest retailers, we cannot ignore the fact that seafood is inextricably linked to food security."
This is especially true for inshore resources, such as line-fish. Line-fish have hit such a parlous state that in the early 2000s, Valli Moosa, then minister of environmental affairs, declared a state of emergency, following scientific advice that 79% of South Africa's line-fish resources were over-fished or had completely collapsed, with enormous implications for the food security of many local communities that depend on these fish – or their sales — for survival.
Noble words aside, consumer power plays a huge role.
Rohland says: "As a business we are also aware that a significant and growing number of our customers want to be able to make sustainable purchasing decisions and we believe it is our duty to assist them in making informed purchasing decisions.
"As a significant role player in the seafood industry, we can help to drive positive change in fisheries by supporting and promoting sustainable seafood choices from legal and responsibly managed sources."
The retailer has committed to stocking only sustainably sourced fish by the end of 2015.
Chair of the Responsible Fisheries Association (RFA) and chief executive of the Oceana Group Francois Kuttel agrees that consumer pressure is an important driver.
"The advancement of communication technology has allowed consumers greater access to information and the ability to share information on a global scale. Combined with this is scientific evidence that points to the fact that every individual or organisation needs to adopt a more sustainable way of living and operating in order to protect and preserve the planet for future generations."
"But not all operators embrace sustainable business practices and they, unfortunately, tarnish the entire industry. Poaching of specific fish species like lobster and abalone is a huge concern and definitely unsustainable."
The big operators in South African fishing have grasped the notion of a shared resource and a shared risk, and are working together to go beyond the letter of law and really ensure a sustainable industry, says Dr Samantha Petersen, senior manager of the marine programme at WWF-SA.
"Industry is even lobbying for improved regulations. They have understood that you can't manage the oceans in silos, as we've traditionally done. Integrated management is crucial to making optimal use of the goods and the services the sea provides to society."
A key to protecting South Africa's marine species, both fish and fowl, is protected areas where commercial fishing activities are limited and recreational or subsistence exploitation is strictly controlled.
South Africa has 21 marine protected areas, from iSimangaliso Wetland Park butting up against the Mozambique border, to Langebaan Lagoon and Sixteen Mile Beach, which form part of the West Coast National Park and stretch for 66km.
iSimangaliso is an important nursery for loggerhead and leatherback turtles, while Langebaan supports very rich bird life and is Ramsar listed.
Protected areas like Stilbaai in the Western Cape or Dwesa-Cwebe on the Wild Coast contain estuaries are important as nurseries for fish.
Protecting spawning grounds or nurseries is a crucial role marine protected areas play. For example at Dwesa-Cwebe, the inshore area north of the Mbashe river is a white steenbraas spawning area, one of just two breeding sites of this species in South Africa.
The first marine protected area, Tsitsikamma, was listed in 1964. The latest, the Amathole Marine Protected Area, was promulgated in September 2011.
It comprises three separate marine areas, the Gxulu, Gonubie and Kei areas, running parallel to nature reserves inland and protecting the inshore marine habitat and biodiversity of the Eastern Cape.
There are nearly 6 000 marine protected areas around the world (which amounts to less than 2% of the oceans), most proclaimed within the last half century. They have proven benefits for restocking over-fished species in the protected areas themselves as well as boosting stock in the adjacent areas.
Recent research has shown that eggs and larvae spawned within a reserve like Goat Island Bay in New Zealand drift long distances, creating a positive impact in unprotected areas near and far.
One, two, three red lights
Among the fish that have ended up as "red" species are some favourites familiar to restaurant-goers from the abundant days of yore, including our national fish, galjoen.
Galjoen (Dichistius capensis) is a line-fish caught by recreational angling or spearfishing right round the coast of South Africa. Unfortunately, it is also often caught illegally in gillnets, and this has played a role in putting it on the red list.
Once a very popular restaurant fish, it is now only legally fished by recreational fishers with a permit, outside of the closed season (from October 15 to the end of February). Recreational fishers by definition may not sell their catch.
Marine Protected Areas are vital to the conservation of this badly overfished species.
All of the three species of kob, also known to South Africans as kabeljou, have ended up on the red list when caught as bycatch by inshore trawl fisheries.
All of them have fallen to single-digit percentages of their previous populations, but the dusky kob (Argyrosomus japonicas) is perhaps worst off, at between 1 and 4.5% of the unexploited population.
So you have to know how your kabeljou was caught to be able to enjoy it with a clear conscience.
Red steenbras (Petrus rupestris) is also off the menu.
The largest of the seabream family, and endemic to South Africa, this huge game fish, which can weigh as much as 70kg and measure 2m long, has declined by over 90% in 25 years.
Like so many other threatened fish, it is a slow grower (a fish of about 1.4m is estimated to be 33 years old) and only matures sexually at between seven and nine years.
Trawlers targeting hake and East Coast sole on occasion scoop up steenbras as bycatch.
On the green list, Sassi has, among others: angelfish, dorado, gurnard, mackerels, sardines, snoek, trout and skipjack tuna.