Hong Kong has decades of data about red tides. Scientists have done much research into the algal blooms that cause them and have identified the types that are harmful to sea life, the fishing industry and health. An alert system warns when waters… are affected; we know that there were more in the first six months of this year than since 1988. For all the knowledge and opinions, though, we are still short of basic facts.
Known factors that cause the blooms to grow include high levels of nutrients in the water, low salinity and warmer-than-usual surface temperatures. Global warming is seen as a reason for the increase in red-tide numbers. But how many are naturally occurring and which are the result of pollution is not known. Some researchers point to the heavily polluted Pearl River as a major source; others blame our own agricultural run-off and sewage being dumped into the sea. While clean-up measures have apparently made red tides in Victoria Harbour a thing of the past, hundreds of thousands of cubic metres of sewage – raw, untreated and some only lightly so – are still finding their way into our surrounding waters.
There are many varieties of algal blooms, but only a handful are harmful. Those types can starve the water of oxygen or release toxins that can kill fish and shellfish; affected sea life, if eaten, can cause illness and in the most severe cases, death. People who swim in red tide-affected waters can sometimes suffer skin and eye allergies or respiratory irritations should winds be blowing on-shore. The costs to tourism and the fishing industry can be substantial – in 1998, 80 per cent of Hong Kong’s fish farm stocks were wiped out while more than two tonnes of fish suffocated off Tai O in 2011.
The blooms can also ruin a good day at the beach. They are most prevalent during summer when our shorelines are a pleasant place to escape the heat and humidity. But with 35 outbreaks of algal blooms in the first half of the year, the often-discoloured water seemed more dangerous than enticing. That is not necessarily the case, of course, which is why we need the best possible analysis to decide if harmful blooms are present.
More research is necessary, perhaps coupled with extra government funding, so that a solution can be found. There has to be regular cooperation with mainland scientists. With the threat of another outbreak like that in 1998 ever-present, Hong Kong needs more than an alert system; it also needs action.
Photo caption: An algal bloom turns water in Repulse Bay red. Photo: Edward Wong
View original article at: Action needed on red tides