12th Pacific Science Inter-Congress, 8-12 July 2013
University of the South Pacific, Laucala Bay Campus, Suva, Fiji
Trophic structure of mesophotic coral reef fish
assemblages of the Northwestern Hawaiian Islands
Randall Kosaki1 , Corinne Kane2, Richard Pyle3, and
Daniel Wagner4
1NOAA
Papahānaumokuākea Marine National
Monument, randall.kosaki@noaa.gov
2Washington State University, corinne.kane@wsu.edu
3B.P. Bishop Museum, deepreef@bishopmuseum.org
4NOAA Papahānaumokuākea Marine National
Monument, Daniel.wagner@noaa.gov
Mesophotic coral ecosystems, also known as the coralreef “twilight zone”, are receiving increased attention
from coral-reef ecologists and managers because of
their potential contributions to tropical biodiversity, and
their potential to serve as refugia for fishes that are
depleted due to anthropogenic activities on shallow
reefs. However, the composition and trophic structure
of these fish communities are poorly characterized. We
present the results of the first quantitative mesophotic
coral reef fish assemblage characterizations from the
Northwestern Hawaiian Islands (NWHI). Each fish
species recorded was assigned to one of six feeding
12th Pacific Science Inter-Congress, 8-12 July 2013
University of the South Pacific, Laucala Bay Campus, Suva, Fiji
guilds. When compared to shallow reefs (<30 m) of the
NWHI, the mesophotic reefs exhibited a near absence of
herbivores, and an abundance of planktivores. These
deep reef fish assemblages (50-80 m) were also found to
have the highest recorded levels of endemism of any
marine ecosystem, with endemic species comprising
>90% of the total assemblage at Midway and Kure
Atolls. High endemism was driven by the numerical
dominance of small-bodied, endemic planktivorous
fishes. This planktivore community is supported by
seasonal increases in planktonic productivity from the
high-chlorphyll waters of the Transition Zone
Chlorophyll Front (TCZF). The TCZF shifts far enough
south in the winter that the northern atolls of the NWHI
lie within its productive waters. Small increases in sea
surface temperatures may drive the TZCF slightly north,
depriving these planktivore-dominated, high-endemism
fish assemblages of this enhanced planktonic primary
productivity. Climate change may thus threaten the
trophic structure of these ecosystems and their
extraordinary levels of endemism.
Key Words: mesophotic, coral reef fishes, endemism,
Northwestern Hawaiian Islands