Red snapper excavate sediments around artificial reefs: observations of ecosystem-engineering behavior by a widely distributed lutjanid

Pockmarks are abundant seafloor features worldwide and, in West Florida Shelf waters <110 m deep, are thought to be sites of sediment excavation primarily by red grouper Epinephelus morio, although red snapper Lutjanus campechanus also excavate sediment. During 2014-2017, side-scan sonar (445 kHz) was used to locate and deploy stereo-baited remote underwater video arrays within view of 202 such excavations in waters 17-110 m deep on the West Florida Shelf off the Florida Panhandle and Peninsula. Three excavation habitat classes included 73 isolated excavations on open sand, 74 associated with low-relief hard bottom, and 55 associated with artificial reefs. Physical characteristics of excavations varied between regions, among habitats, and with depth; mean diameter (±1 SE) was 9.9 ± 0.3 m (range: 3-24.6 m). Excavations not around artificial reefs contained 6.9 ± 0.5 m2 (0-27.7 m2) of exposed rock, and epibenthic growth covered 33 ± 2% of the interiors. Members of 99 fish genera were identified. Fish abundance was greatest at isolated excavations which showed similar evenness to excavated artificial reefs; diversity was higher at excavated low-relief hard bottom. L. campechanus was much more common in Panhandle waters, especially at excavated artificial reefs which had subsided 0.8 ± 0.1 vertical meters below the seafloor (i.e. 48 ± 4% of the structure). These biotic and abiotic characteristics of excavations highlight the importance of E. morio’s ecosystem-engineering services and provide new insight into the contributions of L. campechanus in creating or maintaining excavations at natural and anthropogenic habitats.

Artificial reefs are one of a number of tools that should be considered by scientists and managers when planning coastal zone restoration and/or mitigation projects. In this article, the details of one project from the West Florida Shelf are presented. Two types of artificial reefs were used to mitigate pipeline construction impacts on natural hardbottom ledges in the eastern Gulf of Mexico. The project's primary objective was to avoid the paradigm of building artificial reefs as fish attraction devices, and to instead implement a design that would mimic, not augment, natural hardbottom conditions. Fish assemblage parameters (species richness and commercial fish abundances) were compared between the artificial habitats and natural hardbottom reference sites. Results indicate that species richness trends are similar among artificial and natural reefs, while certain commercial fish abundances are significantly higher on the artificial reefs. Recommendations for future restoration/mitigation projects using artificial reefs are discussed.

Energy exploration in the Gulf of Mexico (hereafter, Gulf) has resulted in the addition of numerous oil and gas production platforms that create structurally complex habitat in an area otherwise dominated by barren mud/sand bottom. How these artificial structures affect fish populations is largely unknown, and there is ongoing debate regarding their value as surrogate habitats for ecologically and economically important reef fish species. Thus, the purpose of this study was to characterize trends in Red Snapper Lutjanus campechanus reproductive potential in the western Gulf at oil and gas platform reefs relative to reproductive potential at natural banks. Red Snapper (n = 1,585) were collected during 2013–2015 from standing platforms, decommissioned platform artificial reefs, and natural banks by using standardized vertical line gear. Comparisons of gonadosomatic index, male : female ratios, batch fecundity, annual fecundity, spawning frequency, and number of spawning‐capable individuals indicated that Red Snapper reproductive biology was similar among natural bank, standing platform, and artificial reef habitats. These results suggest that in terms of reproductive output, fish inhabiting artificial reefs are functionally similar to similar‐aged fish on natural banks. This work can be used to make informed management decisions and suggests that there are benefits to converting decommissioned platforms into designated artificial reefs. Future studies should consider site‐specific characteristics, such as depth, vertical relief, and proximity to other structures, to elucidate how habitat characteristics may influence reproduction, ultimately improving future artificial reef deployments for fisheries enhancement in the western Gulf.

In 2011, an intensive, multiple-gear, fishery-independent survey was carried out in the northern Gulf of Mexico (GOM) to collect comprehensive age and length information on Red Snapper Lutjanus campechanus. Based on this synoptic survey, we produced a spatial map of Red Snapper relative abundance that integrates both gear selectivity effects and ontogenetically varying habitat usage. Our methodology generated a spatial map of Red Snapper at a 10-km2 grid resolution that is consistent with existing knowledge of the species: Red Snapper occurred in relatively high abundances at depths of 50–90 m along the coasts of Texas and Louisiana and in smaller, patchy “hot spots” at a variety of depths along the Alabama coast and the west Florida shelf. Red Snapper biomass and fecundity estimates were higher for the northwestern GOM than for the northeastern GOM, as the latter area contained mostly smaller, younger individuals. The existence of similar surveys on petroleum platforms and artificial reefs also enabled us to calculate their relative contribution to Red Snapper distribution compared with that of natural habitats. We estimated that for the youngest age-classes, catch rates were approximately 20 times higher on artificial structures than on natural reefs. Despite the high catch rates observed on artificial structures, they represent only a small fraction of the total area in the northern GOM; thus, we estimated that they held less than 14% of Red Snapper abundance. Because artificial structures—particularly petroleum platforms—attract mostly the youngest individuals, their contribution was even lower in terms of total population biomass (7.8%) or spawning potential (6.4%). Our estimates of Red Snapper relative abundance, biomass, and spawning potential can be used to design spatial management strategies or as inputs to spatial modeling techniques.

Artificial oyster reefs seek to restore reef ecosystem services, such as water filtration, shoreline protection, and habitat for nekton. This study established three objectives to address the dispersed nature of artificial reef information in the Gulf of Mexico (GoM) and lack of post-construction monitoring assessments. First, to document the extent of activities in the GoM, we developed a database of all inshore artificial oyster reefs created for restoration purposes. Of the 422 reefs in the resultant database, a third or less provided records of entities involved (27%), restoration goals (24%), area (20%), monitoring efforts (15%), relief (9%), and costs (8%). Material (89%) and age (66%) records showed reefs were primarily built with rock (48.6%, limestone or concrete) or shell (12.8%) materials; a quarter of projects (26%) occured after Hurricane Katrina (2005). Second, in a field study we examined the success of artificial subtidal reefs using the presence of (a) living oysters and (b) hard substrate as indicators of success. This field study sampled historic (N=7) and artificial shell (N=5) and rock (N=8) reefs in 8 bays along the northern GoM. Rock artificial reefs were more successful on average than shell, providing significantly higher mean adult oyster density and hard substrate volume. In addition to material effects, design (i.e., relief) and placement specific environmental variations (i.e., hydrodynamics) may have affected success. Lastly, to assess artificial reef use by nekton communities, we sampled nekton assemblages with 3 gear types (gillnet, castnet, and shrimp trawl), during 4 trips in summer 2011. Overall, abundance, richness and diversity were similar between historic reefs and both artificial reef materials (shell, rock). It is probable that biophysical variations may have affected nekton use, more than reef structure. Of the reefs sampled, only 65% of the artificial reefs were fully successful in providing reefs with hard substrate and living oysters, while all reefs provided similar nekton support. This project highlights the need to better track restoration projects in order to inform future activities. Identifying aspects of design and/or location that influence reef success is critical for improving restoration activities.

The Red Snapper Lutjanus campechanus is an economically and ecologically important species in the northern Gulf of Mexico, where it often dominates the reef fish community in shallow to mid water depths along the continental shelf. The affinity of Red Snapper for artificial and natural reefs is well established; however, this affinity appears to vary with age. We used a multigear survey that targeted all age‐classes of Red Snapper to determine the distribution by age‐class on artificial reefs, natural reefs, and unconsolidated mud–sand bottom across the shallow‐water (<100 m) portion of the north‐central Gulf of Mexico continental shelf. Bottom trawl, remotely operated vehicle (video), vertical longline, and bottom longline surveys were conducted in randomly selected 2‐km × 2‐km grids that were previously surveyed with side‐scan sonar to yield a synoptic understanding of habitat use by age‐class. Zero‐ and 1‐year‐old Red Snapper (collected from trawls) were found primarily in shallow water (~20–40 m deep) on unconsolidated muddy bottom in the northwestern portion of the survey area. Vertical longline catch per unit effort was highest at artificial reef sites, followed by natural reef sites and lastly sites with unstructured bottom. The vertical longline surveys collected 2–8‐year‐old Red Snapper near artificial and natural reefs, yet the mean age and size of these fish did not differ between the two habitats. Older Red Snapper (5–42 years old) were collected on bottom longlines, away from reef structures on unstructured bottom throughout all depth strata. Our results demonstrate ontogenetic changes in habitat use for Red Snapper (from unstructured bottom areas to artificial or natural reefs and back to unstructured bottom areas), but unlike the results from previous studies they do not show a strong trend toward increases in the prevalence of older Red Snapper with increasing depth.

<em>Abstract</em>.—Visual census scuba surveys (<em>n </em>= 87) were used to compare fish assemblages among three artificial reef types: big reefs (e.g., ships), tank reefs (i.e., U.S. Army tanks) and small reefs (e.g., metal cages and concrete pyramids), over three locations on the continental shelf (inner shelf, 18–26-m depths; mid-shelf, 26–34-m depths; outer shelf, 34–41-m depths) from April 20, 2012 to November 30, 2015 in the northeast Gulf of Mexico. These surveys identified 66 fish taxa (lowest taxon: 58 species, five genera, three families), and 65 taxa were used in community comparisons. Artificial reefs were dominated by Red Snapper <em>Lutjanus campechanus </em>(35.3% of total fish observed), Tomtate <em>Haemulon aurolineatum </em>(22.4%), Vermilion Snapper <em>Rhomboplites aurorubens </em>(19.5%), Atlantic Spadefish <em>Chaetodipterus faber </em>(7.0%), Greater Amberjack <em>Seriola dumerili </em>(3.0%), and Gray Triggerfish <em>Balistes capriscus </em>(1.8%). These six most abundant species comprised 89% of the total number of individuals observed. Red Snapper and Greater Amberjack mean sizes (total length mm) were larger at big reefs, Vermilion Snapper and Atlantic Spadefish were larger at tank reefs, and Tomtates were larger at small reefs. Red Snapper, Atlantic Spadefish, and Greater Amberjacks were larger at reefs on the outer shelf, and Red Snapper, Tomtates, Vermilion Snapper, Atlantic Spadefish and Greater Amberjacks were larger in the spring. Richness and Shannon–Wiener diversity indices were higher on big reefs and tank reefs compared to small reefs. Evenness, richness, and Shannon–Wiener diversity were lower in winter compared to other seasons. Fish assemblages, based on Bray–Curtis similarities, were different among reef type, location, and season, but no interactions effects were identified. In the present study, fish assemblages on big reefs were more similar to assemblages on tank reefs in comparison to small reefs. The larger size, longer life span, and relative stability of the big reefs and tank reefs were the reef attributes most likely responsible for these assemblage associations. Similarly, more stable conditions at deeper depths (less affected by tropical storms) and proximity to deepwater reef fish communities (e.g., pinnacle reefs) most likely influenced the increased assemblage diversity on the artificial reefs at outer-shelf locations. Diversities and densities were highest during the fall. This was most likely due to increased recruitment of tropical species and new age-0 recruits that were spawned during the same year. The attributes of all artificial reefs are not identical; consequently, it is important for managers to consider how reef type, shelf location, and season affect each species’ affinity and association with artificial reefs.

<em>Abstract</em>.—Florida boasts an abundance of natural and artificial reefs that support a large and diverse recreational fishery off the Gulf of Mexico coast. Recent efforts to mitigate the effects of the <em>Deepwater Horizon </em>oil spill have increased the number of artificial reefs deployed off Florida’s Gulf Coast. Fisheries-dependent data are needed to assess whether artificial reef programs are meeting intended objectives and to understand changes in recreational angler behavior, which may influence catch per unit effort and biomass of landed fish. The objective of this study was to quantify the use of artificial reefs by recreational anglers targeting reef fishes in the Gulf of Mexico off the west coast of Florida. We utilized an existing survey designed to monitor recreational fishing effort by anglers that target reef fishes from private boats. Over a 20-month period, an estimated total of 776,026 (SD ±27,540) angler trips targeted reef fishes off the Gulf Coast of Florida, of which 46% utilized artificial reefs. Approximately two-thirds of all reef angling trips took place nearshore in state-managed waters, and 70% of trips that utilized artificial reefs occurred in this area. Regionally, the highest proportion of angler trips targeting reef-associated species on artificial reefs took place in the panhandle of Florida, where Red Snapper <em>Lutjanus campechanus </em>are most abundant. Seasonally, state and federal fishing regulations also had an apparent influence on fishing effort and artificial reef use by recreational anglers. The method of assessment we present here could be useful for monitoring future trends in recreational fishing effort with respect to artificial reefs.

Habitat quality of natural and artificial reefs for red snapper (Lutjanus campechanus) in the northwestern Gulf of Mexico (Gulf) is important as this area is home to the majority of the Gulf’s artificial reef system, in the form of oil and gas platforms, in addition to the largest extent of high vertical relief natural habitat. This study sought to assess habitat quality of natural reefs of varying habitat complexity and an artificial reef complex located on the LA continental shelf. Habitat quality was assessed by comparing red snapper diets and foraging patterns, and nutritional condition using the liver-somatic index (LSI) and caloric densities. The diets at the natural reefs consisted of primarily fish, while the diets at the artificial reefs consisted of primarily fish and zooplankton. Size class was not an important factor for the diets at the natural reefs, but the diet varied between size classes at the artificial reefs. The natural reefs were found to offer a wider diversity of prey items, and reef-dependent species were found only in the diets at the natural reefs. Differences between diets at the natural and artificial reefs reflected differences between the substrates found at each habitat. Red snapper at the natural reefs were found to feed on and above the reef, while feeding at the artificial reefs was predominantly along the surrounding seafloor and water column. Site-specific temporal patterns in both the LSI and caloric density were evident. The LSI of females at the natural reefs was greater than the LSI of females at the artificial reefs. While caloric density statistically differed between habitats and sizes, the differences between values may not be biologically significant. Female red snapper at the natural reefs appear to be in a better nutritional condition than females at the artificial reefs. Results of this study indicate that natural reefs on the LA continental shelf provide high habitat quality for red snapper. To maximize reproductive output, the better-quality foraging and nutritional condition of red snapper at the natural reefs should be taken into account when evaluating potential areas for the Flower Garden Banks National Marine Sanctuary status.

<em>Abstract</em>.—Reef-fish assemblage structure was compared among multiple artificial and geologic (i.e., naturally occurring hard bottom) habitats in the northeastern Gulf of Mexico during 2014–2016 as part of a larger fishery-independent survey. Baited remote underwater video systems equipped with stereo cameras were deployed (<em>n </em>= 348) on 11 habitat types, classified through interpretation of side-scan sonar imagery. In the video samples, 11,801 fish were enumerated. Nonparametric analysis of reef-fish assemblages detected four clusters related to habitat; assemblages associated with geologic habitats were distinct, whereas the remaining three clusters represented groupings of artificial habitats of different size, scale, and complexity. While many species, including Vermilion Snapper <em>Rhomboplites aurorubens </em>and Red Snapper <em>Lutjanus campechanus</em>, were observed in greater numbers on artificial reef habitats, most species were observed in all habitats sampled. Among artificial reef habitats, the habitat cluster consisting of unidentified depressions, unidentified artificial reefs, construction materials, and reef modules was similar to geologic habitats in supporting larger individuals, specifically Gray Triggerfish <em>Balistes capriscus </em>and Red Snapper. In contrast, the habitat cluster consisting of smaller, generally solitary chicken-transport cages was inhabited by smaller individuals, including smaller Red Snapper. Although geologic reefs are the predominant reef habitat throughout much of the eastern Gulf, artificial reefs are important locally, especially in the Florida Panhandle. Accordingly, continued incorporation of artificial reef habitats within large-scale fishery-independent monitoring efforts is critical to the accurate assessment of the status of reef-fish stocks on broad spatial scales.

The northern Gulf of Mexico has been an important source for crude oil and natural gas extraction since the 1930s. Thousands of fixed platforms and associated equipment have been installed on the Gulf of Mexico continental shelf, leading to a pervasive ‘ocean sprawl’. After decommissioning, hundreds of these structures have been converted to artificial reefs under the federal ‘Rigs-to-Reefs’ program, in addition to artificial reefs specifically designed to enhance fisheries and/or benefit the recreational diving industry. Apart from a few natural banks, which reach to approximately 55 ft below the surface, artificial reefs provide the only shallow-water hard substrate for benthic organisms in the deeper waters of the northern Gulf of Mexico. This vast expansion in available habitat has almost exclusively occurred over a relatively short span of time (~ 50 years). The ecological interactions of artificial and natural reefs in the northern Gulf of Mexico are complex. Artificial reefs in general, and oil and gas structures in particular, have often been invoked as stepping stones for non-native and invasive species (e.g. Tubastrea cup corals, lionfish). The pilings are covered with fouling communities which remain largely unstudied. While the risks of these fouling organisms for invading natural reefs are being broadly discussed, other impacts on the ecological and economic health of the Gulf of Mexico, such as the potential to facilitate jellyfish blooms or increase the incidence of ciguatera fish poisoning, have received less attention. Artificial reefs also provide ecosystem services, particularly as habitat for economically important fish species like red snapper. Here we revisit the potential role of artificial reefs as ‘stepping stones’ for species invasions and for fisheries enhancement. Beyond concerns about ecological effects, some of these topics also raise public health concerns. We point out gaps in current knowledge and propose future research directions.

Modeling the spatial distribution of commercially important reef fishes on the West Florida Shelf

Red Snapper Lutjanus campechanus were sampled at 33 natural and 27 artificial reef sites in the northern Gulf of Mexico prior to (2009–2010) and after (2010–2011) to examine potential diet and trophic shifts following the Deepwater Horizon (DWH) oil spill. We dissected 708 stomachs for gut content analysis and processed 65 muscle tissue samples for stable isotope ratio-mass spectrometry analysis of δ13C, δ15N, and δ34S. Forty-eight percent of stomachs contained identifiable prey, which we grouped into seven categories: fish, decapods, cephalopods, stomatopods, gastropods, zooplankton, and other invertebrates. Based on these categories, Red Snapper diet was significantly different following the DWH oil spill, and was differentially affected by fish size. The interaction between habitat (natural versus artificial reefs) and DWH oil spill effects was also significant. Significant differences in diet among Red Snapper size-classes were due to low trophic position prey, such as pelagic zooplankton, being more abundant in the diet of larger (>500 mm) Red Snapper, while decapods and fish constituted a higher proportion of the diet of smaller individuals. Red Snapper consumed higher amounts of decapods at artificial (21.9% by mass) versus natural (14.8%) reef sites, but the habitat effect on diet was not significant. The habitat × DWH timing interaction was driven by a decrease in zooplankton consumed at both habitat types, increased benthic prey at natural reefs, and increased fish consumption at artificial reefs in post-DWH oil spill samples. Stable isotope data indicated a postspill increase in Red Snapper trophic position (15N enrichment) and an increase in benthic versus pelagic prey (34S depletion), both consistent with observed dietary shifts. Overall, results indicate shifts in Red Snapper diet and trophic position occurred following the DWH oil spill, thus the relative abundance of prey resources likely changed. Received May 30, 2014; accepted February 3, 2015

Structural differences alter residency and depth activity of red snapper (Lutjanus campechanus) at two artificial reefs

<em>Abstract.</em>—Red snapper, <em>Lutjanus campechanus</em>, (<em>n </em>= 4,317) were captured and tagged at 14 experimental artificial reefs of two designs during quarterly research cruises (<em>n </em>= 17) off coastal Alabama between January 1999 and October 2002. Six-hundred and twenty nine recaptures were reported, representing 578 tagged red snapper. Sixty-five percent of recaptures (<em>n </em>= 412) were made at the site of release on subsequent research cruises, while 217 recaptures were reported by fishers. Eighty-six percent of individuals with known recapture locations moved 2 km or less from the site of release; mean and maximum distances moved were 2.1 km and 201 km, respectively. Nine red snapper moved greater than 80 km. Mean dispersion rate from release sites was 8.6 m d<sup>⁻1</sup>. Annual site fidelity of tagged fish was estimated using nonlinear decay models. Estimated annual site fidelity ranged from 48% to 52% year<sup>⁻1</sup> and was not significantly affected by artificial reef design, reef fish biomass at the site of release, or artificial reef densities surrounding each tagging site. Growth rates were estimated by regressing the change in red snapper total length versus the days a fish was at liberty. Mean growth rate for all recaptured fish was 0.206 mm d<sup>⁻1</sup>. Growth rates were significantly affected by reef size (faster at larger experimental reefs) and reef fish biomass (slower at tagging sites supporting low reef fish biomass), but were not affected by artificial reef density. Moderate site fidelity and low dispersion rates during our study provide support for the hypothesis that artificial reefs off Alabama are suitable habitat for adult red snapper. However, characteristics of artificial reefs, such as reef size and standing stock biomass, may affect red snapper growth. Furthermore, ratios of instantaneous growth in weight to total mortality (<EM>G/Z</EM>) suggest artificial reefs off Alabama serve as net sinks (i.e., <EM>G/Z </EM>< 1) of red snapper biomass under current fishing mortality rates.