4.4 Nekton & Benthos
Nekton are free-swimming organisms (fish, squid, marine mammals), while benthos live on or in the seafloor. Together they represent the larger, more familiar marine life.
Nekton
Fish
~35,000 species. Bony (teleosts) and cartilaginous (sharks, rays). Diverse ecology.
Cephalopods
Squid, octopus, cuttlefish. Intelligent invertebrates. Important prey for whales.
Marine Mammals
Whales, dolphins, seals. Air-breathing. Apex predators. Long lifespans.
Sea Turtles
Ancient lineage. Long migrations. Endangered. Nest on beaches.
Benthos
Epifauna
Live on substrate surface: crabs, sea stars, corals, sponges, anemones
Infauna
Burrow in sediment: polychaete worms, bivalves, burrowing shrimp
Demersal Fish
Bottom-dwelling: flatfish, cod, rays. Feed on benthos.
Deep-Sea Adaptations
Bioluminescence
90% of deep species
Giant Size
Deep-sea gigantism
Slow Metabolism
Food-limited environment
Python: Fish Diversity
#!/usr/bin/env python3
"""nekton_benthos.py - Marine fish diversity by habitat"""
import numpy as np
import matplotlib.pyplot as plt
# Approximate fish species by habitat
habitats = ['Coral Reefs', 'Pelagic', 'Deep Sea', 'Polar',
'Temperate Coastal', 'Estuarine']
species = [4000, 3000, 2000, 500, 8000, 1500]
plt.figure(figsize=(10, 6))
colors = ['coral', 'royalblue', 'purple', 'lightblue', 'green', 'brown']
bars = plt.bar(habitats, species, color=colors)
plt.ylabel('Number of Species (approx)')
plt.title('Marine Fish Diversity by Habitat')
plt.xticks(rotation=45, ha='right')
for bar, count in zip(bars, species):
plt.text(bar.get_x() + bar.get_width()/2, bar.get_height() + 100,
str(count), ha='center', va='bottom')
plt.tight_layout()
# Biomass estimation
fish_biomass_ocean = 0.8e9 # tonnes
ocean_volume = 1.335e18 # m³
concentration = fish_biomass_ocean * 1e6 / ocean_volume # g/m³
print(f"Average fish biomass: {concentration:.4f} g/m³")