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Abstract Species across the planet are shifting or expanding their ranges because of climate change. These are climate migrants. Although climate migrants are well documented, their impacts on recipient ecosystems are not. Climate migrants that are also ecosystem engineers (species that modify or create habitats) will likely have profound effects on ecosystems. The Atlantic marsh fiddler crab,Minuca pugnax, is a burrowing crab that recently expanded its range into the northeastern United States. In its historical range,M. pugnaxenhances the aboveground growth of the cordgrassSpartina alterniflora, a plant critical to marsh persistence. In a control‐impact study, however, we found thatSpartinaaboveground biomass was 40% lower whenM. pugnaxwas present. Thus, the positive effect ofM. pugnaxonSpartinaaboveground biomass flipped to a negative one in its expanded range.Spartinabelowground biomass was also 30% lower on average when crabs were present, a finding consistent with what is seen in the historical range. These impacts onSpartinaare likely due to burrowing byM. pugnax.Benthic microalgae was, on average, 45% lower when crabs were present. Fiddler crabs eat benthic microalgae, and these results suggest that fiddler crabs can control algal biomass via grazing. Because fiddler crabs reduced the biomass of foundational primary producers in its expanded range, our results imply thatM. pugnaxcan influence other saltmarsh functions such as carbon storage and accretion as they expand north. Most strikingly, our results suggest that as species expand or shift their range with climate change, not only can they have profound impacts in their new ranges but those impacts can be the inverse of what is seen in their historical ranges.
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Sediment selection: range-expanding fiddler crabs are better burrowers than their historic-range counterparts
Climate change plays a large role in driving species range shifts; however, the physical characteristics of an environment can also influence and alter species distributions. In New England salt marshes, the mud fiddler crab Minuca pugnax is expanding its range north of Cape Cod, MA, into the Gulf of Maine (GoM) due to warming waters. The burrowing lifestyle of M. pugnax means sediment compaction in salt marshes may influence the ability of crabs to dig, with more compact soils being resistant to burrowing. Previous studies indicate that salt marshes along the GoM have a higher sediment compaction relative to marshes south of Cape Cod. Physical characteristics of this habitat may be influencing the burrowing performance of M. pugnax and therefore the continuation of their northward range expansion into the GoM. We conducted a controlled laboratory experiment to determine if compaction affects the burrowing activity of M. pugnax in historical and range-expanded populations. We manipulated sediment compaction in standardized lab assays and measured crab burrowing performance with individuals collected from Nantucket (NAN, i.e. historical range) and the Plum Island Estuary (PIE, i.e. expanded range). We determined compaction negatively affected burrowing ability in crabs from both sites; however, crabs from PIE have a higher probability of burrowing in higher sediment compactions than NAN crabs. In addition, PIE crabs were more likely to burrow overall. We conclude that site level differences in compaction are likely altering burrowing behavior in the crab’s expanded-range territory by way of local adaptation or phenotypic plasticity.
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- Award ID(s):
- 1637630
- PAR ID:
- 10374194
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 674
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 163 to 171
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Abstract The Atlantic marsh fiddler crab, Minuca pugnax (Smith, 1870), is a climate migrant that recently expanded its range northward into the Gulf of Maine. We tracked the M. pugnax population within the Great Marsh, in northeastern Massachusetts, USA, since it was first detected in 2014 using burrow counts. Because burrow counts can overestimate fiddler-crab density, we used camera traps to determine the relationship between burrow densities and fiddler-crab densities in 2019. The burrow count surveys show a six-fold increase in the density of M. pugnax in the Great Marsh from 2014 to 2019. Results indicates that the fiddler-crab population in the expanded range is established and growing. Based on burrow counts, however, the density of M. pugnax in the expanded range (6 burrows m–2) remains much lower than those found in the historical range (up to 300 burrows m–2). Based on the camera traps, we determined that burrow counts overestimated fiddler-crab densities by 47% in 2019. There was, on average, one crab detected for every two burrows observed. This result suggests that estimates of densities of M. pugnax based on burrow counts should be reduced by half. Minuca pugnax is an ecosystem engineer that can influence saltmarsh functioning and the magnitude of that influence is related to its density. Our results imply that the populations of M. pugnax in the expanded range are currently having minor impacts on marshes relative to larger populations in the historical range, but their impact will increase as the populations grow.more » « less
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When a species colonizes a new range, it can escape enemies found in its original range. Examples of enemy escape abound for invasive species, but are rare for climate migrants, which are populations of a species that colonize a new range due to climate-driven range shifts or expansions. The fiddler crab Minuca (= Uca ) pugnax is found in the intertidal salt marshes of the US east coast. It recently expanded its range north into the Gulf of Maine as a result of ocean warming. We tested the hypothesis that M. pugnax had escaped its parasite enemies. Parasite richness and trematode intensity were lower in populations in the expanded range than in populations in the historical range, but infection prevalence did not differ. Although M. pugnax escaped most of its historical parasites when it migrated northward, it was infected with black-gill lamellae (indicative of Synophrya hypertrophica ), which was found in the historical range, and with the trematode Odhneria cf. odhneri , which was not found in the historical range. To our knowledge, this is the first time that O. cf. odhneri has been reported in fiddler crabs. These results demonstrate that although M. pugnax escaped some of its historical parasites when it expanded its range, it appears to have gained a new parasite ( O. cf. odhneri ) in the expanded range. Overall, our results demonstrate that climate migrants can escape their enemies despite colonizing habitats adjacent to their enemy-filled historical range.more » « less
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null (Ed.)Abstract It is well known that species across the world are expanding or shifting their ranges because of climate change. Yet, we know little about their impact on the habitats they colonize. In an observational study, we examined the effect of the fiddler crab Minuca pugnax (Smith, 1870) on benthic microalgal biomass in salt marshes in its expanded range (northeastern Massachusetts, USA). We found that plots with M. pugnax had, on average, 74% lower diatom biomass and 77% lower cyanobacteria biomass than plots without M. pugnax. Our results indicate that this climate migrant can impact saltmarsh functioning by limiting benthic microalgal biomass.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps13811
