B361 (Mar 2, 2006) – Lec14 Outline. Open oceans: feeding & mating
OPEN OCEANS: FEEDING (AND MATING)
Feeding:
1. Food in the open ocean consists of 1° productivity (phytoplankton) and 1° and other consumers.
Feeding involves herbivory and carnivory
 filter feeding/ raptors (predators)
2. Filter feeders: both large and small animals use filters or sieves to feed.
(a) Vertebrate sieves: e.g. Basking sharks &Whale sharks – filter plankton using gill rakers
(6000 l/hr – whale shark; 50m pool/hr – basking shark); Blue whales & Grey whales – are
gulp feeders, sieve plankton through baleen.
(b) Invertebrate sieves – can be large animals, or can be numerous: e.g. Pyrosomes & Larvaceans
(Urochordates) [http://jellieszone.com/tunicates.htm]. Pyrosomes are colonies of individual
ascidians that feed on microplankton that gets caught in mucous moving over the branchial
basket (pharynx); Larvaceans make an elaborate house of mucous with filters to concentrate
food. Can make a new house every 2-3 hours.
(c) Crustaceans – e.g. Copepods are examples of both filter feeders and raptors. Copepods detect
prey, predators, and mates by organizing the fluid medium they live in:
 when swimming a copepod barely leaves a trace
 it creates a laminar feeding current using fine setae on the second antennae; lines of
equal speed of fluid are called isotachs.
 Setae on the antennae are oriented to detect water-borne signals in 3 dimensions: x, y, z
and a fourth dimension, time.
 Planktonic, filter feeders, use the maxillae to capture the phytoplankton that comes in with
the ‘feeding’ or ‘gliding’ current, glues it into mucous, and passes it to the mandibles.
3. Raptors:
(a) Crustaceans – predatory copepods use the organized fluid medium to detect prey and to detect
their own predators:
i. Small disturbances to the fluid medium = prey
ii. Large disturbances = predators
(b) Other examples of planktonic raptors are Chaetognaths & Polychaetes
(c) Ambush predators: cnidarians and ctenophores occur in vast numbers (8 colonies/m3) and
some can be 30 m in length. Small animals (15 cm) long have tentacles that stretch out 3-4 m;
so they form a formidable fishing net in the ocean. E.g.
 Nanomia (siphonophore) nematocyst batteries
 Euplokamis (ctenophore) tentilla
4. Large pelagic predators: Best known are sharks – fast, agile swimmers (30-50 km/hr), with
excellent senses. Bottom dwellers feed on crabs, shrimp, even ‘garbage’! Pelagic species (e.g.
white sharks, hammerhead) feed on fish and squid.
 Lateral line system – can detect sound waves and disturbances in the water. These are
water filled canals that connect to nerves
 Ampullae of Lorenzini – jelly-filled pores connected to nervous system – detects minute
fluctuations in the electric field.
Mating: Copepods use the organized fluid field to detect other copepods for mating
The trace of a hovering copepod is detected by conspecifics; a male will follow the trail of a female,
first following hydrodynamic changes, then a chemical trail.