Guano birds off Ecuador and Peru (guanay cormorant, Peruvian booby, tropical
penguins) can suffer massive mortalities, and flocks can be reduced 60% or more in a
single season when anchoveta have moved seaward and deeper than usual during El
Niño. It can take several cycles of normal conditions and mild El Niños for stocks of
these birds to recover. Seals do not simply shift poleward during El Niños, because of
fidelity to particular breeding and pupping sites along the coast. Seal pups off
southern California suffer high mortality during warm spells, and growth of larger
juveniles is sharply curtailed. El Niño-induced scarcity of fish can render seals so
malnourished that they cannot deposit enamel in the layers added annually to their
teeth. Thus, El Niño years are recorded in their teeth as abnormally thick dentin
deposits.
(^) It can be predicted, from the effects of El Niño on coastal biota, that longer-term
warming will produce more permanent shifts in the latitudinal limits of plankton and
nekton species. Tropical species will be displaced poleward; so will temperate and
boreal species. Probably the warming (accelerating metabolism) and enhanced water-
column stability due to warming (reducing nutrient supply from depth) will reduce
production over a wider latitudinal range. The richer, more productive temperate-
boreal communities will have smaller latitudinal ranges, reducing global marine
production overall. Less production means less fish, which means less fishery
production. While older, more resident animals like rockfish may be protected from
warming by their deep, cool habitat, their young usually must survive a period at the
surface. Warming and reduced production will reduce that survival, or shift the zone
of larval success poleward. Recent losses of Atlantic cod from sites at the warmer
limits of its range, like Georges Bank and the Grand Banks, while at least partly
caused by excessive fishing, may become permanent due to ocean warming. Just the
loss of a few such cod populations caused dramatic economic and social
displacements along the New England and Canadian coasts. If and as warming
continues, we can expect more such disruptions to our interaction with marine life.
Ocean Acidification
Unfortunately, this is something more to worry about (see for example, Vol. 22 of
Oceanography, a 2009 special issue on ocean acidification). Carbon dioxide newly
released into the atmosphere dissolves in the ocean and reversibly combines with
water, becoming carbonic acid. That dissociates, adding hydrogen ions and
bicarbonate to the water chemistry. The hydrogen ions (dashed line in the reaction
equations) reversibly combine with free carbonate to generate more bicarbonate. The