1. Introduction  
2. Plankton Imaging  
2.1. Imaging Instruments  
3. Automatic Plankton Recognition  
3.1. Feature Engineering  
3.2. Convolutional Neural Networks  
4. Challenges in Plankton Recognition  
5. Existing Solutions  
5.1. Challenge 1: Limited Amount of Training Data  
5.2. Challenge 2: High Class Imbalance  
5.4. Challenge 4: Domain Shift Between Datasets  
5.5. Challenge 5: Previously Unseen Classes and Unknown Particles  
5.6. Challenge 6: Label Uncertainty  
5.7. Challenge 7: Large Image Size Variation  
5.8. Challenge 8: Low or Varying Image Quality  
5.9. Challenge 9: Massive Amount of Data  
6. Summary and Future Directions