Sustainable? Threats to coral reefs and marine fish Part 1
There is little mystery that coral reefs around the world are being affected negatively by a barrage of factors. It is estimated that in the last few decades, 10% of the worlds coral reefs have been completely lost with an even higher percentage being degraded or weakened. Corals live in a world where the balance of temperature, salinity, pH, alkalinity, calcium, and light all play a vital role in their health. If any one of these parameters gets out of narrow band, their growth may slow, they may bleach, or simply be wiped out. Most live coral reefs and saltwater marine fish environments around the globe are being affected by these adverse conditions. The reasons for this may include ocean acidification, water nutrification, and in some respects, the overuse of these environments by humans.
With all the talk about global warming lately, scientists are only beginning to understand the far reaching impacts these increased CO2 levels are having in more areas than just our atmosphere. In the last few years, there have been a handful of studies (OSU) and (BIOS) which have studied the impacts of multiple higher levels of CO2 in coral environments. These studies are finding some interesting conclusions. First that most stony or what we would call SPS corals in the reef aquarium hobby exhibit lower levels of calcification when CO2 levels increase in the ocean. This reduced growth most likely will also leave the corals more vulnerable to other stresses that they may encounter. In other coral species it has been found that the corals are able to adapt to this changing water chemistry if the change in CO2 happens slowly over time. More research is needed to determine how this complex environment and the organisms within it will respond over time to this change in water chemistry.
Simply put, the increased nutrification of our coastal waters and nearshore marine environments over the last 50 or so years has had a unique impact on those environments as well as in the environments adjacent to these areas. Unfortunately, most coral reefs lie in these nearshore waters which tend to be more shallow and thus home to photosynthetic coral species. Most marine aquarists spend many hours and usually many dollars trying to remove nitrates (NO3) and (ortho) phosphates (PO4) from their marine reef tanks. If left unchecked, these compounds can have an adverse affect on the corals as well as also stimulating the growth of such nuisance algae as caulerpa, bryopsis, and derbesia. If there are not enough grazing animals ( snails, hermit crabs, tang surgeonfish, etc) in the marine tank, these macro algae can grow large using these nutrients as fuel. The forthcoming problem becomes these macro algae competing for light with the corals, as well as competing in a kind of chemical warefare with the corals for space on the reef to grow. An example of that may be seen in this picture from Coral magazine this month
It probably is no surprise that many coral reef and marine fish environments are suffering from the same overuse as many other parts of our planet. In the coral reef world, this overuse comes from a few sources. Overuse for commercial food fishing has not only over fished many reef environments, but some of the fishing practices like trawling can be hazardous to the corals, especially in deeper waters. Even the very marine hobby that many of us are a part of has a sizable impact on coral reefs. We need to remember that while each one of us holds the coral and fish that we keep in our tanks with the highest regard, we must also remember that many of those fish are caught in far away places, travel thousands of miles, and then are sold to marine aquarists with varying expertise. We cannot simply look the other way or tell people about what we have in our tanks without also educating them on where they come from and how we need to do a better job to protect them in the wild. These environments have been around many times longer than we have and their decline over such a short amount of time is a very humbling fact. There are always things that each individual can do to help and that combined effort seems to be exactly what needs to happen to prevent the loss of such a diverse part of our planet.