What are sea fleas? - briefly
Sea fleas are tiny marine crustaceans—most commonly copepods or amphipods—that propel themselves with rapid, flea‑like jumps and frequently attach to fish or other marine hosts. They occur throughout coastal waters and provide a significant food source for numerous larger organisms.
What are sea fleas? - in detail
Sea fleas are minute marine crustaceans belonging primarily to the copepod group. Their bodies measure from 0.5 mm to 5 mm, with a segmented thorax, a single median eye, and long, often jointed antennae that can be longer than the animal itself. The exoskeleton is chitinous, providing protection and a platform for muscle attachment. Appendages include swimming legs equipped with setae that generate thrust, allowing rapid vertical migrations in the water column.
Their life cycle comprises several naupliar stages, followed by copepodite phases before reaching adulthood. Development is temperature‑dependent; warmer waters accelerate molting cycles, while colder regions extend larval duration. Reproduction is typically ovigerous, with females carrying eggs in a brood sac until hatching. Some species exhibit diapause—a dormant period at depth—to survive unfavorable conditions.
Ecologically, sea fleas occupy the planktonic zone, where they feed on phytoplankton, microzooplankton, and detritus. Their feeding structures, including a specialized mandible and maxilliped, enable both filter‑feeding and raptorial capture. By consuming primary producers, they channel carbon up the marine food web, serving as prey for fish larvae, pelagic fish, and seabirds. Seasonal peaks in abundance often coincide with phytoplankton blooms, reflecting a tight coupling between primary productivity and their population dynamics.
Geographically, they are distributed worldwide, from polar to tropical seas. Species composition varies with temperature, salinity, and nutrient regimes. For instance, Calanus finmarchicus dominates the North Atlantic, while Acartia tonsa thrives in temperate coastal waters. Their tolerance ranges allow some taxa to inhabit estuarine environments, where they adapt to fluctuating salinity.
Physiologically, sea fleas possess a high surface‑to‑volume ratio, facilitating rapid gas exchange but also rendering them sensitive to changes in dissolved oxygen and pH. They regulate internal ion balance through specialized gills and excretory pores, maintaining homeostasis across variable marine conditions.
Key characteristics can be summarized:
- Small size (0.5–5 mm) with a chitinous exoskeleton
- Long antennae used for locomotion and sensory detection
- Complex life cycle: nauplius → copepodite → adult
- Feeding versatility: filter‑feeding, raptorial, detritivory
- Seasonal abundance linked to phytoplankton productivity
- Global distribution with species adapted to specific oceanic regions
Understanding these organisms is essential for marine ecosystem assessments, as their population fluctuations serve as indicators of environmental change and influence higher trophic levels.