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ACCESS NUMBER: 30660-19961
The waters within platforms had higher abundance and diversity of larval and juvenile
fishes than waters immediately down-current of the platform. Clupeiforms (clupeids and
engraulids) and synodontids were consistently collected in higher abundance within the
platform than off-platform. Taxa collected primarily in waters down-current of the
platforms included scombrids and possibly carangids. Reef fish were occasionally
found in higher abundance within-platform, yet pomacentrids and the blenniid
Hypsoblennius invemar were often found in higher abundance off-platform. These
specimens, though, were collected at settlement-size and may represent individuals
settling to the platforms.
The larval and juvenile reef fishes collected at platforms exhibited distinct temporal
patterns of abundance. Most of the reef taxa were collected during months when
surface water temperatures were at their highest, i.e., June-August. There were strong
differences in the numbers and developmental stages collected between new and full
moons. Many preflexion reef larvae were collected in higher numbers on either new or
full moons. Postflexion larvae, however, were almost exclusively collected on new
moons, which was consistent with the peak periods of settlement for many reef fishes.
Coefficients of variation calculated from the mean light trap catches per sampling night
and sampling trip, indicated pulses in the catches of several dominant taxa. Blenniids
and pomacentrids, in particular, were primarily found in very discrete pulses that
included the majority of settlement-size fishes collected at platforms. The occurrence of
these pulses during darker moon phases (i.e., first quarter and new moons) further
suggests that they were settlement-related.
Examination of the length frequency and developmental stages of reef taxa collected at
platforms provided indirect evidence of the potential spawning and nursery/recruitment
habitat provided by platforms. Recently-hatched and preflexion blenniids, holocentrids,
labrid, lutjanid, scarid and serranid larvae were collected at every platform. The
preponderance of platforms, as compared with natural hard bottom habitat, within the
transport envelope of the larvae makes platforms the most probable source of these
larvae. Blenniids and pomacentrids were the most common settlement-size reef taxa
collected at platforms while settlement-size larvae of other reef taxa were relatively rare,
except for possibly lutjanids at the mid-shelf platforms. Because blenniids and
pomacentrids are benthically-spawned, as compared with other reef taxa that spawn
pelagic eggs, their larvae may have shorter larval durations and limited dispersal and,
therefore, may be able to remain in areas where suitable settlement habitat (i.e.,
platforms) is more available.
STUDY PRODUCT(S): Shaw, R.F., D.C. Lindquist, M.C. Benfield, T. Farooqi and J.T.
Plunket. 2002. Offshore Petroleum Platforms: Functional Significance for Larval Fish
Across Longitudinal and Latitudinal Gradients. A final report for the U.S. Department of
Interior, Minerals Management Service Gulf of Mexico OCS Region, New Orleans, LA.
Contract No. 14-35-0001-30660-19961. 122 pp.
*P.I.'s affiliation may be different than that listed for Project Manager(s).