Algal Identification

Harmful Algal Blooms

Harmful Algal Blooms in Maryland

Brown Tide Bloom Index
(Gastrich & Wazniak, 2002)

Category 1: <35,000 cells/ml Aureococcus anophagefferens

  • No observed impacts


Category 2: > 35,000 to < 200,000 cells/ml Aureococcus

  • Reduction in growth of juvenile hard clams, cblife/benthos/hard_shell_clam.html Mercenaria mercenaria;
  • Reduced feeding rates in adult hard clams;
  • Growth reduction in mussels (Mytilus edulis) and bay scallops (Argopecten irradians).


Category 3: > 200,000 cells/ml Aureococcus

  • Water becomes discolored yellow-brown;
  • Feeding rates of mussels severely reduced;
  • Recruitment failures of bay scallops;
  • No significant growth of juvenile hard clams;
  • Negative impacts to eelgrass due to algal shading;
  • Copepod production reduced and negative impacts to protozoa.


For a complete description of the Brown Tide Bloom Index see:

Gastrich, M.D. and C. E. Wazniak. 2002. A Brown Tide Bloom Index based on the potential harmful effects of the brown tide alga, Aureococcus anophagefferens. Aquatic Ecosystem Health and Management, 5(4):435-441.