As of 2001, there were approximately 4,500 oil and gas structures in the northern Gulf of Mexico. While the adult fish aggregation value of oil and gas structures is well-recognized in the northern Gulf, little is known about interactions between the reef fish early life history stages and these artificial habitats. With this research, I wished to provide more basic biological information on the early life history stages of reef fish collected at oil and gas platforms, e.g., larval, postlarval, and juvenile taxonomy, seasonality, lunar periodicity, distribution (vertical and across-shelf), and relative abundance. I also wished to evaluate the ecological significance that this artificial habitat building, which has occurred on an unprecedented scale in the northcentral Gulf, may have had on the early life stages of fish, particularly reef-associated and reef-dependent fishes.

A cross-shelf transect of three petroleum platforms and a coastal rock jetty (another hard-substrate, artificial habitat) was sampled. The ichthyoplankton and juvenile fish assemblages were sampled at an outer shelf platform (230 m depth), a mid-shelf platform (60 m depth) and an inner shelf platform (20 m depth) with passive plankton nets and light-traps and at a coastal rock jetty (3-5 m depth) with a light-trap and a plankton pushnet. At all sites clupeiform fishes dominated samples, comprising 59-97% of the total catch. Reef-dependent (e.g., pomacentrids, scarids, chaetodontids and labrids) and reef-associated (e.g., serranids, lutjanids, blenniids and holocentrids) taxa were relatively rare in the collections compared to coastal pelagic (scombrids and carangids) and demersal taxa (sciaenids), which are also often associated with petroleum platforms as adults.

Across the shelf, taxonomic richness and diversity was highest at mid-shelf platform, possibly a result of its proximity to a high density of upstream and surrounding platforms which may create generally favorable conditions for the recruitment of reef taxa. Relatively low abundances of reef fish larvae and juveniles at the outer shelf platform may be due to a combination of depth, distance from other natural/artificial reefs (sources), and oligotrophic, open ocean waters devoid of possible recruits. Similarly, the close proximity of the inner shelf platform to the coastal boundary current and hydrologic interactions with the Mississippi River plume (e.g., low salinity and high turbidity), may result in fluctuating conditions generally unfavorable for most reef-associated or reef-dependent fishes.

Though relatively rare, preflexion and early larval stages of reef-dependent and reef-associated fishes were collected at all platforms, suggesting nearby spawning or local supply. Similarly, settlement-sized reef fishes were collected at all platforms. While platforms may not equal natural hard-bottom banks in terms of settlement area or suitable porosity/rugosity, they potentially serve as a settlement site for fishes that otherwise might be "lost" from the system. With the limited amount of hard-substrate habitat available in the northern Gulf, the addition of artificial habitats (platforms) may increase the chances of finding suitable spawning or settlement habitat. However, the lack of small-scale, structural complexity at the platforms, combined with high predation pressures, generally results in a habitat that is not very suitable for settlement. Some opportunistic settlement events undoubtedly occur, as evident by the presence of settlement-sized juveniles at the platforms and by the presence of sedentary, reef-dependent adult species (e.g., chaetodontids and labrids). However, the major value of oil and gas platforms as artificial habitat probably lies in their increased carrying capacity for adult fishes and potential as spawning habitat.