B361 (Feb 28) – Lecture Outline. Open oceans: Adaptations
OPEN OCEANS: ADAPTATIONS
[Text reading: Thurman and Trujillo Ch. 13 pp 372-393; Ch. 15 pp 426-432]
1) Features of ocean waters – light, food, oxygen, temperature, salinity, pressure – change
markedly within short distances and affect zooplankton. Zooplankton form the ‘deep
scattering layer’ and make diel migrations from the mesopelagic zone to the photic zone
(~1000m). DSL organisms feed at surface during the night, and migrate deeper during the
day – following productivity and possibly escaping some visual predators. Diel migration
could also save energy by reduced metabolic rate in colder deeper water.
2) Main or prominent zooplankton types: Primary consumers, some are 2° or even 4°
consumers. e.g. Cnidarians, ctenophores, molluscs, chaetognaths, crustaceans, tunicates.
(internet field guides to ocean animals: http://www.oceanoasis.org/fieldguide/index.html)
3) Floatation: most tissues are more dense than water. Mechanisms animals use to compensate
so that energy is not spent keeping afloat are:
a) shape - e.g. Cestid Ctenophores
b) projections - e.g. spines on copepods
c) composition of tissues – e.g. mesoglea, oil droplets in medusae and siphonophores
d) gas – e.g. Hydrozoans: Velella velella – air filled chambers in ‘sail’; Physalia –
pneumatophore: N2 filled float; Gastropod mollusc: Janthina – captures air for bubble
float; Cephalopod mollusc: e.g. Nautilus – uses chambered shell.
 Three cephalopods use rigid gas containers for buoyancy – Sepia, Spirula, Nautilus
 Nautilus regulates buoyancy as it grows larger, by active absorption of solutes (ions)
from the siphuncle; water follows by osmosis, and space is filled with N2 and CO2 gases
from metabolism. Limit to depth is 600m, based on gases within spaces in shell.
 Deep sea squids: cranchiids (Heterocranchia) regulate buoyancy using ammonia.
4) Transparency: provides camouflage where there are no surfaces to match or hide behind.
Involves the whole organism; has evolved multiple times.
a) Transparency involves the choice of tissues that absorb but do not refract light; i.e. it
is a structural problem.
Solutions are sought to camouflage guts in transparent animals by using black (or light
absorbing tissue) or silver (or light reflecting tissue) over the gut.
b) Success in predator prey interactions depends on ‘sighting distance’ = the maximum
distance at which predator/prey are detected by an animal relying on visual cues.
c) Visibility depends more on contrast than size. Visual adaptations that increase
contrast of transparent organisms are: UV vision & Polarization vision – both
predator and prey have adapted. Prey may be transparent, but if their tissue is
birefringent, a predator with polarization vision will be able to target them easily.
[http://www.colorado.edu/physics/2000/polarization/polarizationI.html]
e.g. both adult and juvenile squid show increased detection of birefringent beads
over non-birefringent beads – Nature 1998 [see 2 page article as PDF]