Sediment selection: range-expanding fiddler crabs are better burrowers than their historic-range counterparts

Rj Wong,Jek Byrnes,Ms Roy

doi:10.3354/meps13811

Rj Wong, Jek Byrnes + Show 1 more

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https://doi.org/10.3354/meps13811

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Abstract

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.

Highlights

Global distributions of species are shifting due to warming temperatures (Crozier 2004, Sanford et al 2006, Ling 2008, Dawson et al 2010, Johnson 2014)
In contrast to our initial expectations, our experimental results show that Minuca pugnax collected from their expanded range (e.g. Plum Island Estuary (PIE)) are more capable of burrowing in compacted sediment than crabs collected from south of the cape (e.g. NAN) (Fig. 1)
Fiddler crabs from Nantucket were unable to dig in sediments with a. Such differences in burrowing abilities between these populations suggest that PIE crabs are better burrowers in higher sediment compactions than NAN counterparts

Summary

INTRODUCTION

Global distributions of species are shifting due to warming temperatures (Crozier 2004, Sanford et al 2006, Ling 2008, Dawson et al 2010, Johnson 2014). Fiddler crab densities are low in PIE (~3−6 crabs m−2) relative to salt marshes south of Cape Cod (~150 crabs m−2) (Martínez-Soto & Johnson 2020). One mechanism driving this low density could be partly due to an inhibition in burrowing ability by some physical barrier to survival and growth such as soil strength. Such low densities could shift burrowing behavior in PIE crabs relative to NAN crabs via reduced pressure for conspecifics to compete for space. We expected that burrows will be deeper ( having larger volumes) at intermediate soil strengths

MATERIALS AND METHODS

RESULTS

Findings

DISCUSSION