Publisher : Bulletin of Marine Science
Place of publication :
Publication year : 2004
Thematic : Coral Reef
Language : English
Note
Tropical and subtropical back reef habitats such as seagrass meadows, mangrove
prop-roots, and channels bisecting mangrove islands presumably serve as important
nursery areas for numerous fi shes. This study provides an initial step towards identifi
cation of the nursery role of specifi c habitats within multiple back reef habitats by
quantifying fi sh density, diversity, and size-structure, and was part of a larger study that
used aerial photographs, ground-truthing, and GIS software to map putative nursery
habitats in the Key West National Wildlife Refuge (KWNWR). Visual surveys assessed
fi sh density, diversity, and size-structure in the Lakes and Marquesas regions of the
KWNWR over a 3-mo period and across the marine habitats of concern (seagrass,
channels, mangroves, hardbottoms, patch reefs, offshore reefs). A combination of band
transects and 10-min surveys provided a more complete overall species assessment than
either method in isolation. Mangrove prop-root habitats contained the highest relative
mean density and diversity of fi sh, with abundant forage fi sh such as silverside minnows
(Atherinidae) and herrings (Clupeidae), as well as a high number of piscivores such as
gray snapper Lutjanus griseus (Linnaeus, 1758) and barracuda Sphyraena barracuda
(Walbaum in Artedi, 1792). Channel habitats contained the greatest diversity of microhabitats,
and contained a relatively high diversity of fi sh compared to seagrass. Channel
habitats typically harbored juvenile snappers (Lutjanidae), grunts (Haemulidae), and
forage fi sh (Atherinidae). Qualitatively, we observed greater numbers of relatively large
gamefi sh, as well as rare and threatened species in channel and mangrove habitats than
any other habitat. Conversely, seagrass contained higher fi sh densities than channels.
Increases in the size-frequency of certain species, such as S. barracuda, Pomacanthus
arcuatus (Linnaeus, 1758), and Gerres cinereus (Walbaum in Artedi, 1792), from backreef
habitats such as seagrass and mangroves, to channels and eventually patch and offshore
reefs were suggestive of ontogenetic patterns of habitat use. In contrast, the smallest
stages of L. griseus were found exclusively in seagrass, but remaining size classes,
including adults, were found at all of the habitats surveyed. In contrast, the smallest size
classes of Halichoeres bivitattus (Bloch, 1791), Lutjanis synagris (Linnaeus, 1758) and
Haemulon sciurus (Shaw, 1803) were found in nearly all of the habitats examined. We
found no relationship between fi sh density and diversity, or seagrass shoot density and
blade height. Inclusion of seagrass, mangrove, and channel habitats in future studies of
reef fi sh growth, survival, and emigration should produce a more complete picture of
their nursery role in tropical back reef environments.
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Keywords : Marine resources
Encoded by : Pauline Carmel Joy Eje
