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Recent shifts in the geographic distribution of marine species have been linked to shifts in preferred thermal habitats. These shifts in distribution have already posed challenges for living marine resource management, and there is a strong need for projections of how species might be impacted by future changes in ocean temperatures during the 21st century. We modeled thermal habitat for 686 marine species in the Atlantic and Pacific oceans using long-term ecological survey data from the North American continental shelves. These habitat models were coupled to output from sixteen general circulation models that were run under high (RCP 8.5) and low (RCP 2.6) future greenhouse gas emission scenarios over the 21st century to produce 32 possible future outcomes for each species. The models generally agreed on the magnitude and direction of future shifts for some species (448 or 429 under RCP 8.5 and RCP 2.6, respectively), but strongly disagreed for other species (116 or 120 respectively). This allowed us to identify species with more or less robust predictions. Future shifts in species distributions were generally poleward and followed the coastline, but also varied among regions and species. Species from the U.S. and Canadian west coast including the Gulf of Alaska had the highest projected magnitude shifts in distribution, and many species shifted more than 1000 km under the high greenhouse gas emissions scenario. Following a strong mitigation scenario consistent with the Paris Agreement would likely produce substantially smaller shifts and less disruption to marine management efforts. Our projections offer an important tool for identifying species, fisheries, and management efforts that are particularly vulnerable to climate change impacts.

Population sizes of generalist consumers are increasing in many ecosystems because of various human activities, and it is critical to understand the trophic role of these generalist species if we are to predict how they may affect food web structure and ecosystem function. LionfishPterois volitans/mileshave spread throughout the Western Atlantic and Gulf of Mexico and they may have significant effects on native faunal communities. We characterized the trophic ecology of lionfish in back reef habitats on Abaco Island, Bahamas, drawing on recently developed analytical tools that employ both direct diet information and stable isotope data. Although δ15N and δ13C bi-plot data appeared to suggest substantial niche overlap with native gray snapper and schoolmaster snapper, Bayesian analytical tools suggested differences in core isotopic niches among the species. This was consistent with direct diet information, as lionfish fed almost exclusively on small prey fishes and snapper fed more commonly on crustaceans. When combining empirical isotope and diet data in a simulation model, individual lionfish appear to be more specialized in their diets than schoolmaster snapper. We suggest that this pattern may be driven by high site-fidelity of lionfish, in conjunction with distinct prey assemblages at the patch scale. Lionfish are widely considered to be generalist predators, and our data reveal aspects of this trophic generality that must be considered as the role of lionfish in their invaded habitats continues to be examined.

Caribbean seagrass habitats provide food and protection for reef-associated juvenile fish. The invasive seagrass Halophila stipulacea is rapidly altering these seascapes. Since its arrival in the Caribbean in 2002, H. stipulacea has colonized and displaced native seagrasses, but the function of this invasive seagrass as a juvenile fish habitat remains unknown. To compare diversity, community structure, and abundance of juvenile fish between H. stipulacea and native seagrass beds, fish traps were deployed in four nearshore bays around St. Thomas, U.S. Virgin Islands. Traps were deployed in Frenchman, Lindbergh, and Sprat Bays for 24 h intervals in patches of bare sand, patches of H. stipulacea and patches of the native Caribbean seagrasses Thalassia testudinum and Syringodium filiforme. Traps were then deployed in Brewers Bay for 12 h intervals in stands of H. stipulacea and S. filiforme. Relative and total abundances of juvenile fish, identified at least to family, were compared across treatment habitats for each trap deployment period. The catch from H. stipulacea, compared to native seagrasses, comprised a greater abundance of nocturnal carnivores Lutjanus synagris (family Lutjanidae) and Haemulon flavolineatum (family Haemulidae). Additionally, the herbivore species Sparisoma aurofrenatum (family Labridae) and Acanthurus bahianus (family Acanthuridae) and the diurnal carnivore species Pseudopeneus maculatus (family Mullidae) were relatively scarce in H. stipulacea. The catch from sand was much smaller, compared to vegetated habitats, and comprised only L. synagris, H. flavolineatum, and H. aurolineatum. These results provide evidence of reduced family diversity and altered juvenile fish assemblages in H. stipulacea, driven by an abundance of some nocturnal carnivores and scarcity of herbivores and diurnal carnivores. The findings from the present work underpin the need for further investigation and mitigation of this invasion, particularly where H. stipulacea is driving seascape-alterations of key juvenile fish habitats.

Artificial reefs provide critical habitat for fish in areas lacking benthic structure, yet our understanding of how artificial reefs function and develop is limited. Here, changes in fish community assemblages were monitored using baited remote underwater video (BRUV) surveys before and after a new artificial reef was deployed in the northern Gulf of Mexico. Movement of red snapper (Lutjanus campechanus) and gray snapper (Lutjanus griseus) between nearby oil and gas platforms (n = 3) and the new artificial reef was examined using acoustic telemetry, and residency was calculated for fish associated with both structure types. Fish community development at the artificial reef site was slow despite close proximity to existing habitat, and fish communities at the artificial reef site did not differ from control sites (unconsolidated substrate) one year after reef deployment. Residency of red snapper and gray snapper at the artificial reef was surprisingly low, with most tagged fish emigrating rapidly, and no tagged fishes from the surrounding platforms were detected moving to the artificial reef during the initial eight months following artificial reef deployment. While residency was much higher at the platforms, a major hurricane (Hurricane Ida) passed directly over the sites and led to large numbers of tagged fishes emigrating from the study area. Results highlight an artificial reef with limited fish community development and low residency after one year despite close proximity to existing habitats. Considering the presence of seasonal benthic hypoxia in this region, findings suggest that artificial reefs with limited vertical relief may offer sub‐optimal habitat for reef fish in comparison with the substantial vertical relief offered by standing platforms, reducing the potential benefits to reef fish. Given the rapid decommissioning of oil and gas infrastructure in the Gulf of Mexico, this study has significant implications for rigs‐to‐reefs programs as well as artificial reef siting and design.

In 2013–2014, remote video and diver surveys documented fish assemblages around 150 small oil platforms in nearshore federal waters off the entire Louisiana coast (≤ 18 m depth). Results were used to evaluate ecological processes driving differences in fish abundance and assemblages associated with platforms. The nearshore zone was characterized by high spatial and temporal environmental heterogeneity. Surveys documented 55 species of platform-associated fishes. Twenty-nine species were partially or wholly represented by young-of-the-year (YOY) or age 1–2 juveniles, including red, gray, and lane snapper (Lutjanus campechanus, Lutjanus griseus, and Lutjanus synagris), greater amberjack (Seriola dumerili), and gag grouper (Mycteroperca microlepis). Assemblages were compared among three coastal regions with different hydrography due to interactions between river discharge and bathymetry. Assemblage composition near platforms varied in a region × year interaction associated with inter-annual differences in river discharge and coastal distribution of Sargassum drifts. The probability of YOY L. campechanus occurrence increased with bottom DO saturation (1.40–124.3%) from 0.15 to 0.72. The probability of YOY L. synagris and M. microlepis respectively decreased and increased with depth (5.61–16.76 m) from 0.81 to 0.05 and from 0.03 to 0.68. The results show that fish assemblages around platforms in the nearshore zone experienced substantial regional inter- and inter-annual differences that were driven by hydrographic and recruitment variability. Platforms also provided suitable reef habitat for juvenile fishes in areas that experience widespread bottom water hypoxia and large freshwater inflows, highlighting the importance of nearshore platforms as nursery locations for juvenile fishes that represent a variety of early life-history strategies.

Indo-Pacific red lionfish (Pterois volitans) have invaded the western Atlantic, and most recently the northern Gulf of Mexico (nGOM), at a rapid pace. Given their generalist habitat affinities and diet, and strong ecological overlap with members of the commercially valuable snapper-grouper complex, increased density and abundance of lionfish could result in significant competitive interactions with nGOM commercially important species. We experimentally investigated the intensity of behavioral interactions between lionfish and indigenous, abundant and economically important juvenile nGOM red snapper (Lutjanus campechanus), and other increasingly abundant juvenile tropical snapper species (gray snapper-L. griseus and lane snapper-L. synagris) in large outdoor mesocosms to examine snapper vulnerabilities to lionfish competition. When paired with lionfish, red snapper swimming activity (i.e., time swimming and roving around experimental tank or at structure habitat during experiments) was significantly lower than in intraspecific control trials, but gray and lane snapper swimming activities in the presence of lionfish did not significantly differ from their intraspecific controls. Additionally in paired trials, red and lane snapper swimming activities were significantly lower than those of lionfish, while no significant difference in swimming activities was observed between lionfish and gray snapper. We found that red snapper prey consumption rates in the presence of lionfish were significantly lower than in their intraspecific 3-individual control trials, but when paired together no significant differences in prey consumption rates between red snapper and lionfish were observed. When paired with lane or gray snapper, lionfish were observed having comparatively higher prey consumption than snappers, or as observed in lionfish intraspecific 1-individual controls. However, lane and gray snapper consumption rates in the presence of lionfish did not significantly differ from those in intraspecific controls. These findings suggest that competition between juvenile snappers and invasive lionfish may be variable, with lionfish exhibiting differing degrees of competitive dominance and snappers exhibiting partial competitive vulnerability and resistance to lionfish. While the degree of intensity at which these interactions may occur in nGOM reefs may differ from those observed in our findings, this study enables greater understanding of the potential ecological effects of red lionfish on native reef fishes.

We tracked locations of three fish species in two bays with differing hydrology in SW Florida in 2018–2020 to test the hypotheses about fish residency, movements, and environmental variables. Due to extensive watershed modification, one bay receives less freshwater and the other receives more relative to natural conditions. Home range duration differed for gray snapper (54 ± 6 days), red drum (132 ± 39), and goliath grouper (226 ± 63). Distances between relocation movements were similar for gray snapper and red drum (~ 1.2 km), but farther for goliath grouper (2.3 ± 0.3 km). Relocations were primarily seaward for gray snapper (83%) but varied for the other species. Home range duration related to age for goliath grouper (< 100 days for 1–1.5-year-olds, 300–425 days for 4–4.5-year-olds). Generalized additive models marginally related probability of gray snapper relocating to salinity and temperature whereas relocations of the other species occurred during all environmental conditions. Movement simulations lacking environmental cues produced similar emigration patterns as observed in tagged fish. Overall, results suggest that movements here are not strongly linked to environmental conditions, will be resilient to watershed restoration that should moderate salinity, and have implications for understanding the impacts of localized depletion due to recreational fishing.

Artificial reefs continue to be added as habitat throughout the world, yet questions remain about how reef design affects fish diversity and abundance. In the present study, the effects of reef density were assessed for fish communities and sizes of economically valuable Lutjanus campechanus 13 km off Port Mansfield, Texas, at a reef composed of more than 4000 concrete culverts. The study spanned from May to June in 2013 and 2014, and sites sampled included natural reefs, bare areas, and varying culvert patch density categories, ranging from 1-190 culverts. Abundances of adults and species evenness of juvenile populations differed between the years. Fish communities did not significantly differ among density categories; however, highest species richness and total abundances were observed at intermediate culvert densities and at natural reefs. Whereas the abundance of L. campechanus did not differ among density categories, mean total lengths of L. campechanus were greatest at the lower density. Our findings suggest that reefs should be deployed with intermediate patch density of 71-120 culverts in a 30-m radius to yield the highest fish abundances.

Home ranges, activity patterns, and habitat preferences in and around no-take marine reserves (NTMRs) were evaluated for 5 exploited snapper-grouper species in diverse coral reef habitats in the Dry Tortugas, Florida. Movements of ultrasonic tagged reef fish were determined using a calibrated array of omnidirectional hydroacoustic receivers. Average home range sizes were 2.09 ± 0.39 km² (n = 28; total length, TL = 45 to 66 cm) for red grouperEpinephelus morio, 4.17 ± 1.75 km² (n = 5, TL = 48 to 55 cm) for yellowtail snapperOcyurus chrysurus, 1.44 ± 1.04 km² (n = 2, TL = 57 to 75 cm) for black grouperMycteroperca bonaci, and 7.64 km² (n = 1, TL = 70 cm) for mutton snapperLutjanus analis. Red grouper and yellowtail snapper moved moderate distances (from 700 to 900 m) with moderate frequency. Observed movements for black groupers were relatively small and infrequent. Mutton snappers appeared to make short, frequent movements. A tracked gray snapperL. griseusmade long-distance nocturnal migrations. Several exploited-phase groupers and snappers crossed into and out of reserve boundaries. They were most likely to do so in locations where boundaries were positioned over contiguous coral reef and close to home-range centers. We found that home ranges for red grouper, black grouper, and yellowtail snapper were relatively small in comparison to NTMR area. Our observations suggest that the Dry Tortugas NTMRs may reduce exposure to exploitation for these and other species with limited home ranges, especially where NTMR boundaries do not overlie contiguous reef.

Many fishes are thought to make diel, seasonal and/or ontogenetic migrations among seagrass, mangrove, and coral reef habitats. However, most evidence of such movement has been inferred from density and size structure differences among these habitats in tropical waters. The aim of the present study was to directly evaluate multiple habitat use by an ecologically and economically important reef fish, the gray snapper Lutjanus griseus, in subtropical waters. An integrated set of activities was conducted, including tagging and tracking of individuals and underwater video photography to examine the spatial and temporal dynamics of movements among neighboring mangrove, seagrass, and coral reef habitats in the northern Florida Keys, USA. Results of ultrasonic acoustic and mini-archival tagging indicated that L. griseus exhibits: (1) a distinct diel migration pattern, whereby shallow seagrass beds are frequented nocturnally and mangroves and other habitats with complex structure are occupied diurnally, and (2) bay-to-ocean movement, occurring during the known spawning season of L. griseus in this region. Video photography confirmed diel movement among seagrass and mangrove habitats. Results of this subtropical study corroborate direct and indirect evidence obtained in tropical waters of multiple inshore habitat use by L. griseus, as well as its seasonal movement into or towards offshore reefs. For resource managers charged with designing and implementing management plans for subtropical coastal habitats and fisheries, our findings provide direct support for the strategy of conserving both inshore seagrass and mangrove habitats as well as offshore coral reefs.