ABSTRACT The invasive macroalga, Nitellopsis obtusa (‘ N. obtusa ’), commonly known as starry stonewort, is rapidly expanding across North American freshwater systems. This study assessed the spatial distribution and abundance of N. obtusa over time in coastal wetlands of the Laurentian Great Lakes (hereafter ‘Great Lakes’) using data collected from the Great Lakes Coastal Wetland Monitoring Program. In this study, a total of 511 wetlands were compared across two 5‐year sampling cycles (2015–2019 and 2020–2024). The number of wetlands in the Great Lakes with N. obtusa increased significantly from 8% of wetland sites in 2015–2019 to 15% in 2020–2024. Lake Ontario exhibited a significant increase in site‐level detections (25% to 31%). While Lake Superior and Lake Huron had no detections in the first sampling cycle, new occurrences were documented in the second. Lake Michigan and Lake Erie showed no significant change in the number of sites with N. obtusa between the two sampling cycles. Quadrat‐level analyses revealed similar patterns; the number of quadrats with N. obtusa increased significantly across the Great Lakes, along with the number of quadrats where N. obtusa covered ≥ 50% of the quadrat. Notably, Lake Ontario experienced significant increases in the number of quadrats with N. obtusa present and high‐cover quadrats (≥ 50%), whereas Lake Erie showed no significant changes overall. These findings suggest rapid colonization and proliferation of this invasive species. This study highlights key areas for future monitoring and emphasizes the importance of coordinated management strategies, early detection and more awareness to support the conservation of Great Lakes wetland ecosystems.
ABSTRACT Ephemeral wetlands can radically change the ecology of arid landscapes but are difficult to robustly survey when flooded, challenging conservation management. The Fortescue Marsh ( Martuyitha ) is one of the largest water features of northwest Australia, with significant cultural and ecological value. Our aim was to develop a repeatable aerial waterbird survey methodology allowing systematic counts across years with different flooding extents, and accounting for differences in species responsiveness to the aircraft (i.e., detectability). We carried out systematic helicopter surveys of the marsh, flying georeferenced 1‐km‐spaced transects to proportionally cover the entire flooded area. We estimated the distance to bird observations using markings on the aircarft windows, which were calibrated at regular intervals and accounting for aircraft flight height. Data demonstrated both an effect of transect strip width and position on raw waterbird counts and community composition, reflecting species differences in responsiveness to the aircraft. Detectability ( p ) for 15 waterbird species (average p = 0.79 ± 0.17), together with three other bird taxa, was positively correlated with group size and body mass. Distance sampling was used to estimate population sizes (), which were strongly correlated with maximum counts for each of 15 waterbird species ( p < 0.001), but averaged 1.45 times greater than maximum counts recorded for these species. Significant differences in waterbird counts and community composition due to transect width and position undermine confidence in interpretation of raw counts, highlighting the importance of carrying out statistical correction for species' detectability. We present a practical, field‐ready approach to carrying out data collection suitable for Distance sampling analysis.
ABSTRACT Mangrove tree populations of Rhizophora mucronata and Avicennia marina in the Western Indian Ocean (WIO) comprise distinct evolutionary significant units (ESUs) with contrasting dispersal histories between remote islands and the eastern African coastline. Because earlier genetic surveys across the Indo‐West Pacific revealed strong population differentiation in Bruguiera gymnorhiza , we hypothesised the presence of comparable ESUs within the WIO mangroves. Therefore, we investigated the phylogeography of B. gymnorhiza using complete chloroplast genomes and nuclear ribosomal DNA sequences from 14 provenances spanning the granitic Seychelles, Aldabra Atoll, Madagascar and the African coast. Maximum‐likelihood phylogenies and haplotype network analyses identified three ESUs corresponding to the Seychelles, Aldabra and Africa/Southwest Madagascar, highlighting a within‐species conservation issue. WIO populations were more differentiated from Asian B. gymnorhiza than B ruguiera cylindrica is from B ruguiera hainesii . Approximate Bayesian computation suggested that remote island populations diverged from African lineages approximately 26,000–31,000 generations ago and from each other about 6000 generations ago, corresponding to Mid‐ and Late‐Pleistocene periods, respectively. These divergence times are consistent with independent colonisation events inferred for other mangrove taxa. Chloroplast genomes of extant B. gymnorhiza lineages were more differentiated than those of R. mucronata or A. marina , suggesting an earlier arrival and longer time persistence of Bruguiera lineages in the WIO mangrove ecosystems. Our results demonstrate deep historical structure among B. gymnorhiza populations across the WIO region. A geographic concordance of genetic barriers with other mangrove species highlights the importance of conserving isolated island populations as unique evolutionary units of mangrove ecosystems.
ABSTRACT Bycatch is the biggest threat to marine mammals globally. To estimate bycatch and investigate bycatch drivers for Irrawaddy dolphin ( Orcaella brevirostris ), Indo‐Pacific humpback dolphin ( Sousa chinensis ), Indo‐Pacific finless porpoise ( Neophocaena phocaenoides ) and dugong ( Dugong dugon ) in Cambodia, questionnaires were conducted with 449 vessels (gillnet, trap, longline, trawl and surrounding net) across Cambodia's coastline between September and October 2023. Collected data included the number of species‐specific bycatch events per vessel, for 1‐ and 5‐year periods. Fishery effort data were obtained from the Cambodian 2018 Fishing Vessel Census. A ratio‐based approach was used to estimate annual bycatch. Bycatch drivers were investigated for Irrawaddy dolphin (only species with sufficient data) by modelling bycatch presence–absence per vessel per 5‐year period as a function of candidate explanatory covariates (e.g., gear and target catch). Bycatch was estimated to 286 Irrawaddy dolphins year −1 (95% CI 149–464), with gillnets contributing to 66.6% of total bycatch. Gillnets were significantly associated with a higher probability of Irrawaddy dolphin bycatch presence per vessel per 5‐year period (0.18, 95% CI 0.13–0.24) compared to traps (0.03, 95% CI 0.01–0.10). Bycatch was estimated to 60 humpback dolphins year −1 (95% CI 10–146), 101 finless porpoises year −1 (95% CI 1–201) and seven dugongs year −1 (95% CI 0–14), with trawls contributing most to total bycatch for the three species. The results represent the first bycatch estimates for marine mammals in Cambodia and the initial evidence needed to guide further research and conservation action to reduce bycatch.
ABSTRACT Holocephalans, together with sharks and rays, form the oldest lineage of jawed vertebrates, yet they remain severely understudied and basic biological knowledge is lacking for most species. The American elephantfish ( Callorhinchus callorynchus ) is a coastal holocephalan species distributed along the South American continental shelf. It is classified as Vulnerable by the IUCN Red List of Threatened Species due to a combination of extensive fishing pressure from both industrial and local artisanal fisheries, and limited regulatory oversight. To inform stock assessment and aid transnational management and conservation, we investigated population structure and genetic diversity of this species across most of its distribution using genome‐wide single nucleotide polymorphisms generated through double‐digest restriction‐site associated DNA (ddRAD) sequencing. In addition, we reconstructed the species' recent demographic history to infer potential glacial refugia during the last glacial maximum (LGM). We detected three weakly differentiated population units in Peru, Chile and Argentina. These results point to the need for country‐specific conservation, as local population depletion may lead to the loss of region‐specific genetic variation and the reduction of the species' evolutionary potential to respond to future environmental change. Demographic modelling indicated that present‐day populations possibly originated from a single Pacific refugium in northern South America, when coastal habitats were strongly reduced along the southern Pacific and Atlantic margins, followed by postglacial expansion after the LGM. Current spatial sampling did not allow robust inference of the processes shaping genetic differentiation (e.g., isolation‐by‐distance vs. isolation‐by‐environment), and future studies including denser sampling could improve our understanding of these processes across the species' range.
