If you were on the beach over the weekend, you could not have missed the red tide that hit Lantau’s waters.
Red tide is a natural phenomenon caused by algal blooms during which algae become so numerous that they discolour coastal waters (hence the name “red tide”). The algal bloom may also deplete oxygen in the waters and/or release toxins that may cause illness in humans and animals. Depending on the pigments, the massive growth of algal cells may turn the water into pink, red, brown, reddish-brown, deep green or other colours.
As reported by SCMP, scientists warn that close contact with toxic algae could lead to pain in the limbs and reversed temperature sensations. Consuming marine life that had eaten the toxins could cause serious headaches, nausea and loss of balance, explains Dr Johnny Chan Chun-yin, clinical assistant professor of the medicine department at the University of Hong Kong’s Li Ka Shing Faculty of Medicine.
According to DB resident Gary Stokes, director for South East Asia at Sea Shepherd, “Diatoms and dinoflagellates are two common groups making up the phytoplankton community in Hong Kong and many of the red tide causative species belong to these 2 groups. There are however other groups of phytoplankton species also recorded to cause red tide in Hong Kong.”
Scientific experts explain that red tides might indicate that pollution is getting worse, and climate patterns are increasingly shifting. “The more algal blooms we have, the higher the probability that a toxic red tide will strike,” said Professor Rudolf Wu Shiu-sun, director of the University of Hong Kong’s school of biological sciences. “Even if they are not toxic, the blooms can still deprive the sea of oxygen and harm fish.”
The Agriculture, Fisheries and Conservation Department (AFCD) started to record the occurrences of red tide since 1975. From 1975 to 2015, a total of 907 red tide incidents were recorded in Hong Kong waters. Amongst these incidents, only 28 were associated with fish kills.
A total of 78 algal species have been recorded to form red tides in Hong Kong, but majority of them are harmless. 21 of these algal species are considered as harmful or toxic. Amongst these harmful/toxic algal species, 5 of them have brought about fish kills and two others have caused contamination of shellfish by toxins in Hong Kong. The red tide associated fish kill events were mostly recorded in the 80’s and early 90’s.
Photo credit: Jean-Luc Karlin, Renee McLean, Gary Stokes