What is a sea flea? - briefly
A sea flea is a minute marine copepod, usually 0.5–2 mm long, that propels itself with a single large antenna and consumes microscopic plankton. It inhabits coastal and open‑ocean waters, providing a primary food source for fish and other marine predators.
What is a sea flea? - in detail
Sea fleas, commonly referred to as marine harpacticoid copepods, are small crustaceans inhabiting coastal and estuarine waters worldwide. Their bodies measure 1–5 mm, with a segmented thorax bearing swimming legs and a compact abdomen ending in a tail spine. The exoskeleton, composed of chitin, provides protection and structural support.
Physiology includes a pair of compound eyes that detect light intensity, facilitating vertical migration. Respiratory gas exchange occurs across a thin cuticle, while a simple open circulatory system transports hemolymph. Feeding mechanisms involve setae‑lined appendages that filter microscopic algae, detritus, and bacteria from the surrounding water.
Reproduction is characterized by separate sexes; females carry eggs in a brood pouch until hatching. Development proceeds through six naupliar and several copepodid stages, each marked by molting. Life cycles are rapid, often completing within weeks under favorable temperature and food conditions.
Ecological roles encompass:
- Primary consumer of phytoplankton, linking primary production to higher trophic levels.
- Prey for fish larvae, seabirds, and larger invertebrates, supporting food‑web dynamics.
- Contributors to nutrient recycling through excretion and decomposition of dead individuals.
Adaptations for a pelagic lifestyle include:
- Strong swimming legs for active locomotion and escape responses.
- Sensory hairs that detect water currents, aiding in predator avoidance.
- Ability to enter dormant states during adverse conditions, enhancing survival.
Human interest in sea fleas arises from their use as bioindicators of water quality and as model organisms in marine ecology research. Their sensitivity to pollutants, temperature shifts, and salinity changes provides valuable data for monitoring coastal environments.