Global warming has a direct impact on the water body by increasing its surface water temperature. The increase in the kinetic energy of the water results in decrease in solubility of oxygen in the water and results to low dissolved oxygen. The waters of Lagos lagoon was studied between January, 2007 and December, 2008 to assess the impact of increased temperature and turbidity on the dissolved oxygen. Subsurface water and benthic samples were collected monthly between 0800h and 1200h and analysed in standard laboratories to investigate the impact of temperature and dissolved oxygen on the benthic macroinvertebrate fauna community of the area. The nereid polychaete, Nereis diversicolor was dominant in highly hypoxic study stations and about a hundred individuals of this species were collected, preserved in ice and transported to a laboratory in France for studies on their respiratory physiology. Two other nereid species Perinereis cultrifera and Platynereis dumerilii were collected from Roscoff coast of the English Channel in France at low tide for some comparative studies. The nereid haemoglobin was isolated and purified with ammonium sulphate and Fast Protein Liquid Chromatography respectively while the respiratory functional properties of the haemoglobin at different temperatures and pH were determined in the oxygen diffusion chamber. The result of the analysis of the haemoglobin shows that the nereid polychaetes have evolved a high oxygen-affinity haemoglobin that enables them cope with hypoxia in their environment.