a series of sequential blooms of different phytoplankton species. Succession occurs because different species have optimal nutrient uptake at different ambient concentrations and reach their growth peaks at different times. Shifts in the dominant phytoplankton species are likely caused by biological and physical (i.e. environmental) factors. For instance, diatom growth rate becomes limited when the supply of silicate is depleted. Since silicate is not required by other phytoplankton, such as dinoflagellates, their growth rates continue to increase. For example, in oceanic environments, diatoms (cells diameter greater than 10 to 70 µm or larger) typically dominate first because they are capable of growing faster. Once silicate is depleted in the environment, diatoms are succeeded by smaller dinoflagellates. This scenario has been observed in Rhode Island, as well as Massachusetts and Cape Cod Bay. By the end of a spring bloom, when most nutrients have been depleted, the majority of the total phytoplankton biomass is very small phytoplankton, known as ultraphytoplankton (cell diameter <5 to 10 µm). Ultraphytoplankton can sustain low, but constant stocks, in nutrient depleted environments because they have a larger surface area to volume ratio, which offers a much more effective rate of diffusion. The types of phytoplankton comprising a bloom can be determined by examination of the varying photosynthetic pigments found in chloroplasts of each species. Variability and the influence of climate change Variability in the patterns (e.g., timing of onset, duration, magnitude, position, and spatial extent) of annual spring bloom events has been well documented. These variations occur due to fluctuations in environmental conditions, such as wind intensity, temperature, freshwater input, and light. Consequently, spring bloom patterns are likely sensitive to global climate change. Links have been found between temperature and spring bloom patterns. For example, several studies have reported a correlation between earlier spring bloom onset and temperature increases over time. Furthermore, in Long Island Sound and the Gulf of Maine, blooms begin later in the year, are more productive, and last longer during colder years, while years that are warmer exhibit earlier, shorter blooms of greater magnitude. Temperature may also regulate bloom sizes. In Narragansett Bay, Rhode Island, a study by Durbin et al. (1992) indicated that a 2 °C increase in water temperature resulted in a three-week shift in the maturation of the copepod, Acartia hudsonica, which could significantly increase zooplankton grazing intensity. Oviatt et al. (2002) noted a reduction in spring bloom intensity