There are nearly 400 different types of sharks, but only about 30 types have even been reported as attacking human beings.The chances of being attacked by a shark are very small compared to other dangers. Many more people drown(溺死)in the ocean every year than are bitten by sharks. The ...
Even though the majority of species are harmless, these protists are well known for causing algal blooms and accumulating in amounts coloring the water red-brown (‘red tides’). Blooms are harmful when the dinoflagellate produces toxins, such as those causing paralytic (PSP), diarrhetic (DSP...