Explain how biodiversity may be considered at different levels.
The St. Lawrence river contains many aquatic mammal species, particularly whales. During spring, thousands of whales travel from the Atlantic ocean into the St. Lawrence river. Thirteen whale species have been recorded there. One is the blue whale, Balaenoptera musculus. Fig. 1.1 shows a blue whale.
State the two sources of phenotypic variation in the blue whale population.
Suggest one reason why determining the actual population size of the blue whale is difficult.
The St. Lawrence river passes through heavily industrialised regions. It also has many ports for cargo ships, a strong fishing industry and numerous whale-watching boat trips for tourists. Many decades of whale hunting led to a major fall in whale population sizes. Even after whale hunting was banned, whale populations did not recover. Seven of the thirteen whale species in the St. Lawrence river have been classed as endangered species. Suggest two reasons why whale populations have not recovered since the ban on whale hunting.
Fat samples from beneath the skin of individual whales from several different species were collected. These were analysed and the concentrations of the toxins DDT and PCBs were measured. Suggest why whales were found to have accumulated very high concentrations of DDT and PCBs in their fatty tissues.
Algal blooms sometimes occur in the part of the Atlantic ocean near the St. Lawrence river. These are caused by the rapid increase in population of unicellular algae such as Alexandrium tamarense.
A. tamarense produces saxitoxin, a neurotoxin that brings about muscle paralysis by acting on voltage-gated sodium ion channels in neurones. Saxitoxin can kill whales. Suggest how saxitoxin leads to the death of a whale.
Algae such as A. tamarense used to be placed in the kingdom Plantae, but they are now put in the kingdom Protoctista. State one reason why A. tamarense is classified in the kingdom Protoctista and not in the kingdom Plantae.