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The Spring Bloom Awakens the Waters of Long Island Sound

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Phytoplankton from water sample taken from Long Island Sound during the spring bloom under microscope. Photo credit: NOAA Fisheries/Dr. Judy Li

While spring still seems a long way off, recently the waters of Long Island Sound awoke with new life. The spring bloom has begun - an ecologically important annual occurrence in the temperate North Atlantic Ocean, sub-polar regions, and coastal waters.

As the days begin to grow longer, more light is available and surface waters warm. This stratifies the water column, holding phytoplankton in the layer of water most exposed to sunlight. The nutrients that phytoplankton need have recently been replenished due to winter’s churning effect on the water. As they convert sunlight into food using photosynthesis external link, these are perfect conditions for phytoplankton to grow, and the plant-like organisms flourish in their newfound abundance.

The spring bloom is a relatively brief pulse that fuels much of the productivity of temperate marine ecosystems. In fact, the bloom can be tracked at the macro scale via changes in ocean color detected by satellite imagery. Phytoplankton are the base of most aquatic food webs. In the late winter/early spring, marine grazers, including copepods and other zooplankton, haven’t yet entered the scene to eat them. Eventually, grazing zooplankton will begin to feast on the phytoplankton and multiply.

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Monthly chlorophyll a generated from the MODIS-Aqua satellite sensor. Raw data obtained from the NASA Ocean Biology Processing Group, statistics and images produced by Northeast Fisheries Science Center.

As the water warms, filter feeders such as oysters and clams come out of dormancy and feed on phytoplankton. Forage fish such as Atlantic herring will chow down on zooplankton, and soon enough, larger fish such as striped bass will arrive to eat those forage fish. Some of these fish and shellfish will find their way onto our dinner plates. All of this life depends on mighty phytoplankton, single-celled organisms too tiny to see with the naked eye!

Diatoms dominate the spring bloom in Long Island Sound. They move with water currents, and live in houses made of glass. These 'glass houses' are actually hardened cell walls made out of silica (a major component of sand and glass) called "frustules."

Diatoms come in a large variety of shapes and sizes; some having frustules with very ornate and intricate patterns. These patterns are symmetrical and geometric, allowing species to be identified and inspiring both nanotechnology external link and art external link. While diatoms are single-celled, some varieties form colonies (see Asterionellopsis glacialis) or chains (see Skeletonema sp.).

The photo at the top of the page, taken by Research Ecologist Dr. Judy Li with a light microscope, shows the contents of a water sample taken from Long Island Sound on January 29th, which was teeming with photosynthetic life. Dr. Li specializes in phytoplankton dynamics at the Science Center’s Milford Lab.

For more information, see A Student’s Guide to the Phytoplankton of Long Island Sound external link.

Can you find the following common diatoms in the photo at the top of the page?

Skeletonema sp.

  • Sometimes grazers slurp up the whole chain like a strand of spaghetti.
  • Common primary producer found everywhere in Long Island Sound. Critical component of the Sound’s food web.
  • Size: individual cells are 2-21 micrometers* in width (smallest of the three diatoms).

Ditylum brightwellii

  • Shaped like a capsule with a toothpick on either end.
  • Produces resting spores which survive the harsh winter months.
  • Size: 25-100 micrometers in diameter, 8-130 micrometers long.

Asterionellopsis glacialis

  • Triangle-shaped cells with a long spine sticking out from one end, often joined at the wide end to form star-shaped colonies.
  • The first part of its name means "little star;" the latter part means "glacier-like." Although found worldwide, they are most abundant in cold to temperate waters.
  • Size: From wide end to end of outer spine, 30-150 micrometers.

Photos courtesy of Dr. Judy Li, Melissa Krisak, and David Veilleux
*One micrometer = 1×10−6 meter

Answer Key:
4 chains of Skeletonema sp.
1 colony of Asterionellopsis glacialis
3 cells of Ditylum brightwellii