Stable isotope analysis has emerged as one of the primary means for examining the structure and dynamics of food webs, and numerous analytical approaches are now commonly used in the field. ...Techniques range from simple, qualitative inferences based on the isotopic niche, to Bayesian mixing models that can be used to characterize food‐web structure at multiple hierarchical levels. We provide a comprehensive review of these techniques, and thus a single reference source to help identify the most useful approaches to apply to a given data set. We structure the review around four general questions: (1) what is the trophic position of an organism in a food web?; (2) which resource pools support consumers?; (3) what additional information does relative position of consumers in isotopic space reveal about food‐web structure?; and (4) what is the degree of trophic variability at the intrapopulation level? For each general question, we detail different approaches that have been applied, discussing the strengths and weaknesses of each. We conclude with a set of suggestions that transcend individual analytical approaches, and provide guidance for future applications in the field.
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.
The ongoing invasion of non-native Indo-Pacific lionfish (Pterois spp.) represents a significant ecological threat throughout the Western Atlantic and Caribbean. As a generalist species, lionfish ...have been able to rapidly colonize a wide variety of ecosystems, including coral reefs, seagrass beds, mangroves, the sea floor at depths as great as 300 m, and even brackish estuaries. While lionfish have been encountered in a number of estuarine systems, the spatial distribution of lionfish in estuaries is likely limited by the species’ ability to tolerate low salinities. Here, we experimentally identify minimum salinity tolerance in lionfish by measuring survival salinity minimum—the lowest salinity at which all individuals survive for 48 h. Additionally, we examine whether long-term exposure to low (but sub-lethal) salinities has negative effects on lionfish. Field observations in the Loxahatchee River estuary (Jupiter, FL) showed that lionfish can survive brief exposure to salinities as low as 1 ‰. At one estuarine location, fish survived exposure to salinity fluctuations of ~28 ‰ every 6 h for several days. In laboratory trials, survival salinity minimum for lionfish was 5 ‰; however, some individuals survived at 4 ‰ for up to 94 h before dying. Lionfish that were held at 7 ‰ for 28 days showed no differences in mortality, behavior or growth, when compared to control fish held at 35 ‰ (typical ocean salinity). This broad salinity tolerance may allow lionfish to colonize estuaries throughout their invaded range, and may facilitate dispersal across the Amazon-Orinoco plume. Because of the ecological and economic importance of estuaries, this facet of the lionfish invasion warrants further study.
Many species of tropical marine fish aggregate to spawn, and the dynamics of these aggregations make them especially susceptible to overfishing and habitat loss. Spawning aggregations tend to attract ...reproductive adults from a large geographic area, sites are traditionally used across generations, and larval dispersal can help supply regional fish stocks. Thus, anthropogenic impacts to spawning sites can have population-level consequences over local and regional scales. A critical component in the challenge to conservation of aggregation-spawning species is identification and subsequent protection of spawning sites. Here we summarize fieldwork conducted to create a protocol for identification of pre-spawning aggregation sites for bonefish,
Albula vulpes
, in The Bahamas. The mixed-methods, field-based protocol includes Traditional Ecological Knowledge, assessment of spawning readiness, tracking using acoustic telemetry, behavioral observations, and mark-recapture, that combined meet the requirements for identifying pre-spawning aggregation sites. Pre-spawning site identification, in conjunction with information on other life stages and habitats, is essential for successful spatial management strategies. Since bonefish and many other tropical fishes that form spawning aggregation are ‘data poor’ and occur in regions where enforcement of fishery regulations is lacking, spatial management is often the best conservation strategy. This protocol builds upon similar previous efforts to identify spawning sites for groupers and snappers, and will contribute to information needs for conservation is an essential component in the conservation of aggregation-forming species such as bonefish across broad spatial scales.
Water filtration is one of the most important ecosystem services provided by sessile organisms in coastal ecosystems. As a consequence of increased coastal development, human-made shoreline ...structures (e.g., docks and bulkheads) are now common, providing extensive surface area for colonization by filter feeders. We estimate that in a highly urbanized sub-tropical estuary, water filtration capacity supported by filter feeding assemblages on dock pilings accounts for 11.7 million liters of water h−1, or 30% of the filtration provided by all natural oyster reef throughout the estuary. Assemblage composition, and thus filtration capacity, varied as a function of piling type, suggesting that the choice of building material has critical implications for ecosystem function. A more thorough depiction of the function of coastal ecosystems necessitates quantification of the extensive ecosystem services associated with human-made structures.
Understanding how individuals within a population of invasive organisms disperse during various life history stages has obvious implications for long term population dynamics in the invaded range. ...With the rapid expansion of the invasive Indo-Pacific lionfish (Pterois volitans and Pterois miles) in the western Atlantic and Caribbean, it has become increasingly important to understand how individuals move following initial recruitment, as this may have critical implications for population control and management. We conducted a 10-month mark–recapture study in the lower Loxahatchee River estuary (Florida, USA) to identify movement patterns and site fidelity in juvenile and young adult lionfish. We tagged 55 lionfish, ranging in size from 45 to 185mm standard length (66–256mm total length). Eighty percent of the tagged fish were recaptured at least one time during the course of the study. Lionfish in this system exhibited extremely high site fidelity over extended periods of time and across multiple size classes. Maximum range occupied by individuals along the shoreline of the estuary was small (mean=28m, asymmetrical 95% CI: 10 to 51m), and did not vary with lionfish size. The majority of lionfish recaptures (74%) occurred at or near (0–10m) the previous capture site, even after weeks or months at liberty. In systems where lionfish exhibit extremely high site fidelity and small maximum ranges, localized population control may be feasible, since lionfish removed from a given habitat would be replaced largely through larval recruitment rather than migration of older individuals. However, since lionfish grow extremely rapidly (averaging 0.46mm/day, but reaching as high as 0.78mm/day in one individual), localized control efforts would need to be carried out frequently in order to maintain a younger, smaller population. Localized control may be less effective if lionfish exhibit greater movement and lower site fidelity in other invaded systems.
► Lionfish exhibit extremely high site fidelity over extended periods of time. ► Many tagged individuals remained in the same location throughout the study period. ► Home range did not vary with body size for the size range we examined. ► High site fidelity may facilitate local population control in certain habitats.
As human development in coastal areas increases, the role of anthropogenically-created habitats in the life history of marine organisms is becoming increasingly important. We examined the diet of ...age-0 tarpon, Megalops atlanticus, in and around man-made mosquito control impoundments along the Indian River Lagoon in east-central Florida, with a particular focus on identifying dietary patterns associated with tarpon size and nursery habitat type (i.e., between perimeter pool habitats in established impoundments and newly-created restoration marsh habitats). Age-0 tarpon were found to consume a wide variety of prey organisms, and exhibited considerable dietary variation among study sites. Smaller juvenile tarpon consumed a limited number of small prey taxa, while larger individuals fed on a greater range of prey taxa and sizes. Overall, copepods and fishes were the dominant prey items; however, the consumption of these organisms varied considerably among size classes and sites. There was no clear difference in tarpon diet between the two types of habitat we examined. The ability of juvenile tarpon to utilize such a diverse range of prey organisms may allow populations to inhabit a variety of habitats, including man-made marshes. When natural systems have been degraded or destroyed, human-altered habitats can assume a nursery role for the species.
Restored oyster reefs support diverse communities of motile benthic organisms (small fishes and macroinvertebrates). These communities represent a critical component of estuarine food webs and ...frequently include juveniles of ecologically and economically important species that utilize oyster reefs as nurseries. Oyster-related metrics are commonly used to quantify restoration success, yet it is also important to examine communities of oyster-associated organisms when attempting to identify ecological convergence between natural and restored oyster reefs. Here, we compare the community composition of motile benthic organisms over time at one restored and three natural oyster (Crassostrea virginica) reefs in the Loxahatchee River estuary (Florida, USA) as one means of assessing restoration success. We also examine the effects of vertical relief on motile benthic organisms following restoration. The community of motile benthic organisms at the 1.93-ha restoration reef gradually began to resemble natural communities in the months following reef construction. Within ~22 months, biomass and community composition were similar between natural and restored habitats. At that point, the mean biomass of motile benthic organisms at the restoration site had reached 83.6 g/m2 (versus 89.8 g/m2 at nearby natural reefs), and the restored reef supported >1600 kg of small, motile, oyster-associated organisms. Biomass values increased more rapidly in high-relief sections of the restored reef (30 cm vs. 15 cm reef height), particularly during the first year following restoration. High-relief areas were also characterized by increased oyster densities, greater oyster-generated rugosity, and decreased sedimentation. Our findings suggest that small differences in reef design can have important implications for restoration success as well as food web structure and dynamics via shifts in community composition.
•Motile benthic organisms are one important metric for assessing restoration success.•Convergence between restored and natural motile oyster reef communities took <22 mo.•Juvenile organisms were largely responsible for initial colonization of restored reef.•Small increases in vertical relief greatly increased biomass at restored oyster reef.•High-relief areas = greater oyster growth, higher rugosity, and reduced sedimentation.
The invasion by lionfish Pterois volitans and P. miles throughout the western Atlantic and Caribbean is emerging as a serious ecological problem. While lionfish have been identified on coral reefs ...and in other marine systems, additional ecosystems may be affected as the invasion spreads. Here we identify the first estuarine intrusion by lionfish in their invasive range. Lionfish (n = 211) were captured in the Loxahatchee River estuary (Florida, USA) between August 2010 and April 2011, with some individuals located as far as similar to 5.5 km from the ocean. Multiple size classes were documented (standard lengths ranged from 23 to 185 mm), and post-settlement juveniles were present throughout the sampling period. All individuals were found in close association with anthropogenically created habitats (e.g. docks, sea walls, submerged debris), suggesting that human-driven changes in habitat availability may facilitate estuarine invasion. Fifteen prey taxa were found in lionfish stomachs, with diets dominated by small shrimp. Since estuaries are already highly threatened by human impacts, and provide critical habitat for numerous commercially, recreationally, and ecologically important species, establishment of lionfish in these ecosystems is of particular concern.
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