Area 1    Pago Pago Harbor

5.  Other Invertebrates:

     The predominant benthic macroinvertebrates of the harbor environment of Area 1 were
sessile, suspension-feeding organisms.  Of the seven areas designated in this survey, Pago
Pago Harbor exhibited the lowest species diversity.  In general, species abundance and
diversity decreased with increasing depth.  
     Nonscleractinian cnidarians comprised the principal macroinvertebrate assemblage,
with alcyonaceans exhibiting both greatest abundance and greatest species diversity. 
Although colonies of Sinularia spp. were abundant on oblique limestone substrates of the 6-m
isobath, the colonies tended to be clustered rather than evenly distributed.  Likewise, colonies
of Lobophytum spp. were commonly found among the Sinularia colonies at this depth, but
more than 50 percent of all those observed were grouped in a single cluster.  With the
exception of the zoanthid Palythoa tuberculosa, which was common, other nonscleractinian
cnidarian taxa were represented by solitary observations.
     Sponges are an important component of the suspension feeding community of the
harbor.  Although both species were common on the 6-m isobath, Stylotella agminata
outnumbered Cinachyra spp. by ratio of 5:1.  An unidentified yellow sponge, tentatively
assigned to the Class Calcarea, was encountered only occasionally.
     Suspension feeding organisms other than cnidarians were present in lower abundance. 
Crinoids were represented by two cryptic species, Comaster multifidus and Comanthus
parvicirrus.  
     Deposit feeding organisms were present but not abundant in the harbor.  Principal
among these were the holothurian Stichopus chloronotus, which was commonly observed on
the 6-m isobath.  Feeding tentacles of the spaghetti worm Loimia medusa could be observed
extending from the worms' burrows.
     Two species of browsing herbivorous invertebrates were encountered on the 6-m
isobath.  The turbinid snail Astraea rhodostoma was found occasionally in crevices of
coralline algae-encrusted reef rock.  The sea urchin Echinothrix diadema was common in
larger crevices among the rocks.
     The substrate of the 18-m isobath was characterized by a reduced slope bearing a
greater sediment load. Slightly more than half of the species encountered along the 6-m
isobath were also found on the 18-m isobath, but in lower abundance.  
     Sarcophyton spp. was the predominant soft coral along this isobath, inhabiting large
fragments of reef rock that has slumped down from the fringing reef above.  Lobophytum spp.
were encountered only occasionally.  Sinularia spp. were not observed at this depth, and
Dendronephthya sp. was found only at this depth.  Cladiella sp. and gorgonian spp. increased
slightly in abundance in the deeper zone.