Live coral cover has declined precipitously on Caribbean reefs in recent decades. Acropora cervicornis coral has been particularly decimated, and few Western Atlantic Acropora spp. refugia remain. ...Coral Gardens, Belize, was identified in 2020 as a long-term refugium for this species. This study assesses changes in live A. cervicornis coral abundance over time at Coral Gardens to monitor the stability of A. cervicornis corals, and to explore potential threats to this important refugium. Live coral cover was documented annually from 2012-2019 along five permanent transects. In situ sea-surface temperature data were collected at Coral Gardens throughout the study period and compared with calibrated satellite data to calculate Maximum Monthly Mean (MMM) temperatures and Degree Heating Weeks (DHW). Data on bathymetry, sediment, substrate, herbivore abundance, and macroalgal abundance were collected in 2014 and 2019 to assess potential threats to Coral Gardens. Live coral cover declined at all five transect sites over the study period. The greatest loss of live coral occurred between 2016 and 2017, coincident with the earliest and highest maximum average temperatures recorded at the study site, and the passage of a hurricane in 2016. Structural storm damage was not observed at Coral Gardens, though live coral cover declined after the passage of the storm. Uranium-thorium (230Th) dating of 26 dead in situ fragments of A. cervicornis collected in 2015 from Coral Gardens revealed no correlation between coral mortality and tropical storms and hurricanes in the recent past. Our data suggest that several other common drivers for coral decline (i.e. herbivory, predation, sedimentation, pH) may likely be ruled out for Coral Gardens. At the end of the study period, Coral Gardens satisfied most criteria for refugium status. However, the early onset, higher mean, and longer duration of above-average temperatures, as well as intermittent temperature anomalies likely played a critical role in the stability of this refugium. We suggest that temperature stress in 2016 and perhaps 2015 may have increased coral tissue vulnerability at Coral Gardens to a passing hurricane, threatening the status of this unique refugium.
Nonindigenous lake trout (
Salvelinus namaycush)
expansion in Yellowstone Lake has led to a large decline in the native Yellowstone cutthroat trout (
Oncorhynchus clarkii bouvieri
) population. We ...assessed whether otolith microchemistry could be used to identify subbasin natal origins and long-term use by lake trout as a potential tool for optimizing removal efforts.
87
Sr:
86
Sr and Sr:Ca ratios in otolith cores were used to assess natal origins and
87
Sr:
86
Sr ratios in otolith transects were used to assess movement patterns. Water chemistry was similar throughout the lake, ranging from 0.70634 to 0.70642 and 3.94 to 4.38 mmol/mol for
87
Sr:
86
Sr and Sr:Ca ratios, respectively. Lake trout otoliths also showed little variation in
87
Sr:
86
Sr and Sr:Ca ratios of the natal region and
87
Sr:
86
Sr across otolith transects. Thus, we found that microchemical differences among Sr isotope and Sr:Ca elemental ratios in otoliths were insufficient to detect the natal origin or extensive within-lake movement that has been established from telemetry investigations. Detailed analysis of other elements or isotopes in hard-part microchemistry, in combination with other tools for detecting movement, may improve detection of natal origin and life history movement among fishes within freshwater lentic systems.
Quantifying the scale of offspring dispersal is essential for understanding demographic connectivity across landscapes and rates of population spread. However, characterizing natal dispersal in ...fishes is complicated by the difficulties of tracking origins and movement during early life-history stages. We combined direct observation of natal dispersal based on otolith chemistry with indirect estimates of dispersal from population genetics to quantify intergenerational dispersal of smallmouth bass (Micropterus dolomieu) inhabiting a river network. Average parent-offspring dispersal was estimated as 7.7 km from genetic isolation-by-distance and demographic population data. Otolith chemistry indicated that adults were captured an average of 8.3 km from their natal tributary, supporting the genetics-based estimate. Our estimate of intergenerational dispersal is higher than previous estimates for lotic fishes and considerably higher than estimates for smallmouth bass in lake systems. Differences in availability of seasonal habitats for smallmouth bass may account for the contrasting scales of dispersal between lake and river populations. The large intergenerational dispersal distance of riverine smallmouth bass should be considered in conservation of fisheries or efforts to control invasive populations in river networks.
Quantifying the scale of offspring dispersal is essential for understanding demographic connectivity across landscapes and rates of population spread. However, characterizing natal dispersal in ...fishes is complicated by the difficulties of tracking origins and movement during early life-history stages. We combined direct observation of natal dispersal based on otolith chemistry with indirect estimates of dispersal from population genetics to quantify intergenerational dispersal of smallmouth bass (Micropterus dolomieu) inhabiting a river network. Average parent–offspring dispersal was estimated as 7.7 km from genetic isolation-by-distance and demographic population data. Otolith chemistry indicated that adults were captured an average of 8.3 km from their natal tributary, supporting the genetics-based estimate. Our estimate of intergenerational dispersal is higher than previous estimates for lotic fishes and considerably higher than estimates for smallmouth bass in lake systems. Differences in availability of seasonal habitats for smallmouth bass may account for the contrasting scales of dispersal between lake and river populations. The large intergenerational dispersal distance of riverine smallmouth bass should be considered in conservation of fisheries or efforts to control invasive populations in river networks.
1. Establishment and spread are central in weed invasion. In this study we quantified the impact of harvest and weed management practices on these processes in row-crop agriculture. Quantifying the ...dynamics of patch expansion can direct management aimed at containment of weed populations. 2. We assessed annual patterns of common sunflower Helianthus annuus seedling recruitment to determine the influence of management on seed dispersal and patch expansion. Weed seed banks were sowed at three initial densities and exposed to either high or low intensity weed management. Fields were maintained in a maize-soybean crop rotation, with cultivation and harvest orientated in a single direction. We analysed spatial pattern in annual seedling recruitment using geostatistics and an integro-difference model to determine treatment effects on spatial dynamics. 3. The two spatial analyses allowed us to separate and quantify the contributions of natural and anthropogenic dispersal to seedling emergence and patch expansion. Expansion was predominantly isotropic, and estimated rates of isotropic spread (i.e. diffusion) were consistent between analysis methods. 4. We also confirmed that directional management practices can effect significant anisotropy on dispersal and expansion. Crop rotation had the greatest impact on expansion; anisotropy in patch expansion was more pronounced in maize compared with soybean. However, the scale of weed seed dispersal by machine (combine harvester) was greater following harvest of soybean. Simulation of patch dynamics indicated that harvest can increase expansion rate nearly fourfold. 5. Synthesis and applications. Patches of H. annuus originating from intermediate and high seed bank densities had the potential to spread rapidly from the source population. Patches with a low initial seed bank experienced extinction when subjected to high levels of chemical weed management. The combined approach of spatial modelling and geostatistics was particularly effective for quantifying admixed modes of dispersal from sequential data of population distribution. Independence of the two methods provided a system for cross-validating model assumptions and estimated parameters. The scales of spatial dynamics we assessed were well suited to these methods. The results of the analysis underscore the importance of managing populations in order to keep local populations at low densities. Helianthus annuus is difficult to manage and once intermediate or high local densities are reached, the rate of spread is accelerated, distributing this weed widely across fields. A targeted site-specific approach to maintaining populations at low levels would reduce the necessity for more costly field-wide management.
Yellowstone cutthroat trout inhabiting Yellowstone Lake have declined substantially over the past 25 years as a result of predation by invasive lake trout, the presence of whirling disease, and ...periods of persistent drought. We used otolith microchemistry to assess whether cutthroat trout recruitment patterns have changed in response to these environmental stressors. Though water chemistry variation among the 22 sampled spawning tributaries was low, we identified 9 distinct spawning stream clusters. Random forest models were developed for assessing relative recruitment, yielding a high classification accuracy of 84.4% for known-origin cutthroat trout fry otoliths and 79.0% for simulated otolith signatures based on water chemistry. Proportion of recruitment varied significantly between pre- and post-stressor samples (X
2
= 15.40,
P
= 0.03). The majority of pre- (0.84) and post-stressor (0.77) recruitment occurred in the same three stream clusters, but there was a notable decrease in recruitment in streams with high whirling disease prevalence, and a notable increase from the tributary cluster without whirling disease and with low lake trout predation risk. Conservation efforts should be focused on protecting important spawning tributaries and improving cutthroat trout recruitment in spawning streams that in the past likely contributed much greater numbers of fish.
In estuarine and coastal systems, anthropogenic activities and directional changes in global air temperatures have led to increased water temperatures, as well as increased frequency and severity of ...episodic hypoxia. These alterations have had population-level effects on aquatic organisms, including changes in species-specific distributions. Because physiology is the transfer function connecting environmental conditions to individual behaviors and eventually to population-level effects, we used individual-based models (IBMs) that incorporate changes in metabolic scope as motivation for movement. Our objective was to investigate the effects of temperature and hypoxia on the distribution of Atlantic croaker and spot in Chesapeake Bay. We compared the predicted monthly fish distributions from the IBMs with apparent fish distributions recorded by the VIMS Juvenile Fish Trawl Survey during 1988–2014. IBMs failed to reproduce accurately the apparent spatial distributions of Atlantic croaker and spot. More specifically, compared with the trawl survey, IBMs predicted larger proportions of these two species would be captured in the lower regions of Chesapeake Bay and smaller proportions in the York and Rappahannock rivers. We postulate that, because similar thermal and oxygen conditions were occupied by fish in the IBMs and in the wild, temperature may not be the most important factor motivating the movement of Atlantic croaker and spot in Chesapeake Bay, and other spatial factors (e.g., prey availability) act in concert with temperature and hypoxia to determine the spatial distributions of Atlantic croaker and spot in Chesapeake Bay. Alternatively, surveys used to estimate species occurrences could be biased if gear vulnerability is affected by temperature or oxygen conditions (or both). Additional research is needed to clarify which condition is true or if a combination of these factors (and others) led to discrepancies between predicted and apparent fish distributions based on trawl survey data.
A kinesis model driven by high‐resolution sea surface temperature maps is used to simulate Atlantic bluefin tuna movements in the Gulf of Maine during summer months. Simulations showed that ...individuals concentrated in areas of thermal preference. Results are compared to empirical distribution maps of bluefin tuna schools determined from aerial overflights of the stock during the same time periods. Simulations and empirical observations showed similar bluefin tuna distributions along fronts, although interannual variations in temperature ranges occupied suggest that additional foraging factors are involved. Performance of the model is further tested by simulating the relatively large‐scale annual north–south migrations of bluefin tuna that followed a preferred thermal regime. Despite the model’s relatively simple structure, results suggest that kinesis is an effective mechanism for describing movements of large pelagic fish in the expansive ocean environment.
Understanding large‐scale migratory behaviours, local movement patterns and population connectivity are critical to determining the natural processes and anthropogenic stressors that influence ...population dynamics and for developing effective conservation plans. Atlantic tarpon occur over a broad geographic range in the Atlantic Ocean where they support valuable subsistence, commercial and recreational fisheries. From 2001 through 2018, we deployed 292 satellite telemetry tags on Atlantic tarpon in coastal waters off three continents to document: (a) seasonal migrations and regional population connectivity; (b) freshwater and estuarine habitat utilization; (c) spawning locations; and (d) shark predation across the south‐eastern United States, Gulf of Mexico and northern Caribbean Sea. These results showed that some mature tarpon make long seasonal migrations over thousands of kilometres crossing state and national jurisdictional borders. Others showed more local movements and habitat use. The tag data also revealed potential spawning locations consistent with those inferred in other studies from observations of early life stage tarpon leptocephalus larvae. Our analyses indicated that shark predation mortality on released tarpon is higher than previously estimated, especially at ocean passes, river mouths and inlets to bays. To date, there has been no formal stock assessment of Atlantic tarpon, and regional fishery management plans do not exist. Our findings will provide critical input to these important efforts and assist the multinational community in the development of a stock‐wide management information system to support informed decision‐making for sustaining Atlantic tarpon fisheries.
The corals
Acropora palmata
and
A. cervicornis
are important Caribbean reef-builders that have faced significant mortality in recent decades. While many studies have focused on the recent demise of ...these species, data from areas where
Acropora
spp. have continued to thrive are limited. Understanding the genetic diversity, recruitment, and temporal continuity of healthy populations of these threatened
Acropora
spp. and the hybrid they form (“
Acropora prolifera
”) may provide insights into the demographic processes governing them. We studied three reef sites with abundant
A. cervicornis
,
A. palmata
, and hybrid
Acropora
populations offshore of Ambergris Caye, Belize at Coral Gardens, Manatee Channel, and Rocky Point. Samples were collected from all three
Acropora
taxa. We used microsatellite markers to determine: (1) genotypic diversity; (2) dominant reproductive mode supporting local recruitment; (3) minimum and maximum genet age estimates for all three acroporids; and (4) the history of hybrid colonization at these sites. We found that
Acropora
populations were highly clonal with local recruitment primarily occurring through asexual fragmentation. We also estimated the ages of 10
Acropora
genets using recent methodology based on somatic mutation rates from genetic data. Results indicate minimum ages of 62–409 yr for
A. cervicornis,
187–561 yr for
A. palmata
, and 156–281 yr for the
Acropora
hybrids at these sites. Our data indicate that existing
A. cervicornis, A. palmata,
and
Acropora
hybrid genets persisted during the 1980s Caribbean-wide
Acropora
spp. collapse, suggesting that these sites have been a refuge for Caribbean
Acropora
corals. Additionally, our data suggest that formation of extant hybrid
Acropora
genets pre-dates the widespread collapse of the parent taxa.
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