Our Biology Presentation Speech
On(03/9-10/09)&(17/9-24/09) there were red tides occur at Clear Water Bay First and Second Beach and Shuen Wan Hoi respectively. Although these two red tides not affect us as much as that one in 1999 ,But we still can’t ignore them . To take some precaution for prevent the same case occur , we may need to learn more about red tides. Let us give u a brief introduction of red tides
Firstly , u may ask why red tides called as red tides , but not other and what kind of substance made red tides being formed . Let me tell u step by step
Red tides’ a kind of algal blooms which microscopic , single-celled algae increased rapidly in aquatic system .They may recognized by discoloration of the water from the high density of pigmented cells . They may became green, reddish brown , etc
Red tides is caused by a combination of factors that encourage algal growth which include sunlight, nutrients, trace elements, salinity, water temperature and water flow. The continuation of any algal bloom is therefore dependent on the changes of these factors. Moreover , the red tides very active especially in March and April , this may due to the wet and humid weather
Now , let’s talk about the algal blooms in HK. Here is the region distribution of red tides from 1975-2003 in HK . This had shown that in the past thirty years , there are a large amount of red tides occur at different bays or sea in HK , especially at ( ), about 43% of cases were happened there .
Now, it’s a bar-chart that was about Seasonal distribution of red tide in Hong Kong from 1975-2003. Again in the past 30 years , most red tides occur in March and April . This may due to its wet and humid weather.
In general , A majority of the algal blooms or red tides are basically harmless. Only a few may cause fish kill, contaminate seafood or have harmful effects on humans Although algal blooms or red tides occur quite frequently in Hong Kong averaging about 20 - 30 incidents in a year, the blooms associated with harmful effects are not common and seldom caused large scale impact.
In HK , there are many causative Species of algae. Here are some of them.
When red tides occur , there must be some impacts on human or mariculture .Let’s talk about mariculture first. When red tides happened , this may risk of fish kill by oxygen depletion .For example ,Sometimes in sheltered bays or in very calm sea, the sufficient number of algae will consume a large amount of oxygen in the water during the night such that fish, especially those cultured in cages, will die of oxygen depletion.
To take some measures, we may increase the oxygen content in the water by aeration. For long-term mitigation, we must stop feeding the fish to reduce the oxygen requirement of the fish as well as the ecosystem
Second, risk of fish due to toxic or noxious algae. Some algal species may produce mucus or toxins which damage the fish gills and impair the fish's ability to respire. The fish may also die of suffocation.
We may move the fish further away to avoid the harmful algae. For short-term mitigation, enclose the fish cages with plastic sheets to separate fish from the harmful algae and aerate the water in the cage
The red tides also affect our health. Numbness of the lips, tongue or limbs, headache and dizziness commonly occur within 30 minutes after consumption of the contaminated seafood. If you experience poisoning symptoms mentioned above, you should seek medical advice as soon as possible
In addition , Some algae may produce biotoxins. Filter-feeding shellfish, particularly the bivalves, such as scallops, oysters and mussels, can accumulate these algal biotoxins such that they become toxic to humans. Avoid eating the viscera of shellfish where biotoxins, such as Paralytic Shellfish Poisoning toxins are concentrated.
You may ask is it save for us to swim in beaches then?
OF coz u can , because Only a few algae species produce chemical toxins that may affect swimmers by causing minor eye, nose or skin irritation and respiratory distress. When a red tide is sighted at a bathing beach, the Leisure and Cultural Services Department will close the beach, hoist the red flag to warn swimmers to avoid contact with red tide as a safety precaution. Leisure and Cultural Services Department will arrange water sample analysis for red tide organisms. Based on the algal species identified, Leisure and Cultural Services Department will consider re-opening the beach.