Temperature-influenced variations in speciation and chemical composition of marine phytoplankton in outdoor mass cultures

Abstract

Between September, 1976 and July, 1977 Phaeodactylum tricornutum Bohlin was replaced as the dominant species by Skeletonema costatum (Grev) Cleve as temperatures fell below 10°C in the fall in an outdoor pond supplied with a mixture of waste water and sea water. Phaeodactylum tricornutum returned in the spring as the major species when temperatures rose above 10°C. In an adjacent pond in which only nitrogen and phosphorus were added in excess, however, P. tricornutum dominated throughout the entire study period even through the temperature varied between 0 and 25°C. We suspected that the difference inspecies dominance in the two ponds occurred because Skeletonema costatum requires silicon, which was present in sufficient quantities only in the waste-water-enriched pond. whereas Phaeodatylum tricornutum does not have a specififc requirement for this nutrient. The cellular chemical composition of P. tricornutum varied in a U-shaped fashion with changing temperature: minimum values for the cellular carbon, nitrogen, and chlorophyll contents were displayed at 15–20°C and maximum values at 3 and 15°C. Both the cellular carbon: nitrogen and carbon: chlorophyll ratios by weight were invariant with changing temperatures at ≈6: 1 and 50: 1 respectively, indicating nutrient saturation. Only under conditionsof nutrient saturation, which can be established in various ways, can the influence of temperature on phytoplankton physiology be separated from nutrient-related factors.