GEOL 388: Field Natural History of the Galápagos Islands
Summer Semester I 2006
The Community of Marine Organisms
Many differences between land and sea in general:
- Multiple clades of primary producers rather than just green plants: marine primary producers include both algae (attached) and phytoplankton
- Existence of food in suspension: allows for suspension feeding forms which just capture food "on the fly" (not really possible
in most terrestrial environments)
- More diverse, and larger bodied, sediment feeding community
- More diverse overall: majority of clades are marine
Marine realm can be divided into many different divisions:
- Photic Zone vs. Aphotic Zone: Presence or absence of transmitted light,
with all that means for photosynthesis
- Intertidal/Littoral: Exposed to air twice daily. Inhabitants must be adapted to
change of environment
- Pelagic vs. Benthic: above the sea floor vs. along the sea floor
Marine organisms life habits:
- Planktonic: floating
- Nektonic: swimming
- Benthic: bottom dwelling, including:
- Epifaunal (surface dwellers) vs. infaunal (sediment dwellers)
- Motile (moving) vs. sessile (non-moving)
- "Marine realm" also include fliers, waders, and other terrestrial forms which feed within
marine food webs
In Galápagos, we will primarily see Intertidal community, Shallow Sublittoral
community, and Shallow Pelagic organisms.
Intertidal Community of the Galápagos
- Tough to live in full time, as varies between air and water.
- Of course, some motile animals simply move back and forth with the tides. But sessile forms and infaunal forms have to deal with temporary exposure.
- Distinct zonation due to relative amount of exposure, temperatures, etc.
- Lacking big muddy component (either siliciclastic or carbonate) compared to
continental coasts or some islands, benthic community is not terribly diverse.
- Also, lacking coral reefs (temperature rather low, and very young islands to begin
with), not as many microniches for benthic organisms to inhabit.
- However, nektonic organisms are fairly diverse.
Bases of intertidal community are phytoplankton and algae (a life habit, not a clade!).
Most conspicuous is a green alga
Ulva lobata (sea lettuce): main food of marine iguanas. Also abundant are various red
algae and brown algae.
Benthic suspension feeders:
Benthic suspension feeders in the intertidal zone need to be able to retract their feeding organs (and other tissue) inside a durable watertight
covering for that period if time in which they are exposed.
Benthic grazers (a marine "grazer" is an animal that eats sessile organisms, which might
be algae or sessile animals):
(snails): some are temporarily exposed to air
- Fireworms (polychete annelids)
- Sea urchins (echinoids), whose broken up skeletons sometimes form a major type
of sediment on Galápagos beaches
- Crabs, including:
iguanas (Amblyrhynchus cristatus), the only living marine lizard. It feeds
mostly on sea lettuce and brown algae. As cold-blooded animals, they get their heat primarily
from the sun, so they can't stay in the cool Galápagos waters for long. On land they spend
their time basking on rocks. In order to deal with the salt water they take in, they have evolved
very efficient glands to extract the salt and "sneeze" it out as a highly-concentrated brine.
Bodies of marine iguanas are crusted with the salt they've sneezed out since their last trip into
the water. Like other iguanas, they nest on land.
Sediment feeders, most importantly sea cucumbers (holothuroids), including
pepinos (local name for Stichopus fuscus)
Nearshore predators include:
- A great variety of sea stars
- Sea stars, aka starfish, aka asteroids, are actually very fearsome predators to slower moving and sessile animals!
- Shore and Wading birds, such as
- Cone shells (Conus spp.):
A gastropod (snail) with a phenomenally-poisonous sting. Some species hunt fish: their poison is equally deadly to us "land fish" (aka tetrapods).
Pretty to look at, though.
Shallow Sublittoral Community of the Galápagos
Nearshore nektonic organisms, and those that prey on them (note that some of these also include the nektonic component of the intertidal community):
- Humungous diversity of actinopterygians (ray-finned fish). Here are
just a very few highlights:
- Damselfish (
various species within the
Pomacentridae): grazers which tend to patrol a particular algae patch. Juveniles are typically brilliantly colored relative to adults.
- Parrotfish (Scarus spp.): large grazers (up to 90 cm long). They and their
relatives the wrasses (various species within Labridae) have at least three
sexual morphs: males, females, and supermales (which may have been females earlier in their life). Supermales have extraordinarily extravagent coloration.
- Probers like Moorish idols (Zanclus cornutus),
barberfish (Johnrandallia nigrirostris), and yellow-tailed surgeonfish
(Prionurus laticlavius): these feed on algae and small invertebrates that hide in the cracks of the hard substrates
- Various pufferfish species
- Classic sharks, including white-tipped and black-tipped reef sharks, and hammerheads
- Stingrays, golden cownose rays,
and spotted eagle rays:
- Rays are sharks adapted to life as bottom feeders. They suck up infauna and mash
them with their flattened plate-like teeth.
- World class diversity of Sea Birds:
- Galápagos penguin (endemic) (Spheniscus mendiculus), wing swimmer
- Tube-nosed birds (Procellariformes), with specialized salt-glands allowing them
to drink sea water & excrete waste through tube in snout. Major procellariforms in Galápagos include:
- Waved albatross (Phoebastria [formerly Diomeda] irrorata):
nearly entire population breeds on Española (some in Isla de la Plata off Ecuador),
one of the largest flying birds in the world
- Petrels &
Storm-petrels: feed by "pattering" (dipping feet on surface to attract fish)
- Pelecaniformes, with totipalmate feet (all four digits on the ground, and all in web)
- Brown pelican (Pelecanus occidentalis urinator): shallow diver, gulping
water & fish)
- Frigate birds: steal fish from other birds as well as catching it themselves.
Males have big inflatable throat sacs. Two local species:
- Great Frigatebird (Fregata minor ridgwayi), mostly on Genovesa and
San Cristábal, males have slight greenish-sheen on back, more oceanic
- Magnificent Frigatebird (Fregata magnificens magnificens), throughout Archipelago,
males have slight purplish-sheen on back, more coastal
- Boobies (Sulidae): deep divers, catch fish on way back up. In Galápagos, the three species (which partition their niches by roosting sites and
by feeding environments) include:
- Red-footed booby (Sula sula), smallest, make honest-to-goodness nests,
live only on edges of archipelago (since they fed far offshore on squid)
- Blue-footed booby (Sula nebouxii excisa), very complex display behaviors,
nests near shore and feeds near shore
- Nazca booby (Sula granti), formerly included within Masked booby species,
largest of the Galápagos boobies
- Flightless cormorant (endemic) (Nannopterum harrisi), very fast swimmer,
lives only on westernmost islands (near upwelling zone of Cromwell current), foot swimmer. (Elsewhere, flying cormorants feed by shallow diving.)
- Red-billed Tropicbird (Phaethon aethereus), fast flyers, spending most of their time
on the wing or in their cliff-side nests. (Tropicbirds have traditionally been considered unusual pelecaniforms, but recent work suggests that they
are either closer to procellariforms or are an entirely separate radiation of seabirds).
- Gulls, including:
- Swallow-tailed gull (essentially endemic) (Larus furcatus), one of the
few night-feeding gulls in the world
- Lava gull (endemic) (Larus fuliginosus), very rare
- Brown noddy (Anous stolidus galapengis), infamous as
thieves from pelicans. (Noddies are close kin to the gulls.)
- Green sea turtles (Chelonia mydas agassizi): young are pelagic nektonic
carnivores, while adults are more grazers (especially when hanging out near islands).
- Marine mammals:
- Galápagos sea lion (Zalophus wollebaeki), coming
from coastal North American ancestors
- Galápagos fur sea lion (Arctocephalus galapagoensis), coming
from coastal South American ancestors
- These two show niche partitioning in terms of resting habitat: sea lions prefer sandy beaches, while fur sea lions like rocky sites
Shallow Pelagic Community of the Galápagos
We will see some marine life out at sea cruising between islands. In fact, we have a better chance of seeing large fish and marine mammals in the
archipelago than if we were 100 km farther east: the shallow pelagic realm is generally very sparsely inhabited except where upwelling or other
disturbance brings a lot of nutrients up to the photic zone. While out in the open seas, we might see:
- Sea birds that feed far from land, such as Great Frigatebirds, Swallow-tailed gulls, etc.
- Pelagic suspension-feeding rays: Mobula rays (Mobula munkiana) and their gigantic relatives
the Manta rays (Manta birostris). (If we see either of these, it would be because they were
jumping out of the water,
possibly to clear parasites.)
- Big sharks, such as the Scalloped hammerhead (Sphyrna
lewini, a predator), the awesome Basking shark (Cetorhinus maximus,
a suspension feeder), and the utterly spectacular
Whale shark (Rhincodon typus), also a suspension-feeder
and largest living fish.
- Large actinopterygians, such as the oceanic sunfish (Mola mola)
and the Wahoo (Acanthocybium solandri:
incidentally, this image was of "eco-tourists" that were fishing illegally in the Galápagos with the help of an "ecotourism" outfit...).
On the high seas, we will commonly see sea birds that feed far from land. Also, we might
notice some big, conspicuous fish, like wahoos.
- Flying fish (various species within Exocoetidae): use their
huge pectoral fins to glide through the air as an aid to escape swimming predators.
- Cetaceans (16 species of large whale, and 7 dolphins, are known to occur in the Galápagos: some only seasonally). These range from
giants such as the Sperm (Physter catodon),
Humpback (Megaptera novaeangliae), and
Bryde's (Balaenoptera brydei) whales, to medium-sized
killer whales (Orcinus orca) to smaller Bottle-nosed (Tursiops truncatus) and
Common (Delphinus delphis) dolphins.
Last modified: 18 June 2008