Quantifying Tidal Movements of the Shore Crab Carcinus maenas on to Complex Epibenthic Bivalve Habitats

Abstract

Many subtidal predators undertake regular tidal migrations into intertidal areas in order to access abundant prey. One of the most productive habitats in soft bottom intertidal systems is formed by beds of epibenthic bivalves such as blue mussels (Mytilus edulis) and Pacific oysters (Crassostrea gigas). In the Dutch Wadden Sea, these bivalves might face substantial predation pressure by the shore crab (Carcinus maenas), which increased considerably in numbers during the last 20 years. However, the quantification of this species on bivalve beds is challenging, since most methods common for quantifying animal abundance in marine habitats cannot be used. This study investigated the potential of two methods to quantify the abundance of C. maenas on 14 epibenthic bivalve beds across the Dutch Wadden Sea. The use of the number of crabs migrating from subtidal towards intertidal areas as a proxy of abundance on bivalve beds yielded unreliable results. In contrast, crabs caught with traps on the beds were correlated with the abundance assessed on the surrounding bare flats by beam trawl and therefore provided usable results. The estimates, however, were only reliable for crabs exceeding 35 mm in carapace width (CW). The application of these estimates indicated that crab abundances on bivalve beds were influenced by the biogenic structure. Beds dominated by oysters attracted many large crabs (> 50-mm CW), whereas abundances of medium-sized crabs (35-50-mm CW) showed no relationship to the oyster occurrence. The combination of traps and trawls is capable of quantifying crab abundance on bivalve beds, which offers the possibility to study biotic processes such as predator-prey interactions in these complex structures in more detail.

Prey size selection in invasive (Hemigrapsus sanguineus and H. takanoi) compared with native (Carcinus maenas) marine crabs

“…These habitats generally harbour only small juvenile C. maenas (Thiel & Dernedde, 1994). Adult C. maenas may frequent these habitats occasionally during migrations from subtidal zones onto intertidal areas at high tide (Waser et al ., 2018). Hemigrapsus species seem to be superior to juvenile C. maenas in competition for shelter and adult crabs also predate more heavily on juvenile C. maenas than is the case the other way around (Jensen et al ., 2002; Griffen & Byers, 2006; Geburzi et al ., 2018).…”

Variability in Carcinus maenas Fecundity Along Lagoons and Estuaries of the Portuguese Coast

“…Carcinus maenas (Linnaeus 1758), the European green crab, is a widely distributed epibenthic species inhabiting both hard and soft intertidal habitats in coasts and estuaries (Baeta et al 2005). Worldwide, it is one of the most ecologically prominent benthic predators in marine and estuarine intertidal areas (Waser et al 2017). Despite its native spatial distribution being the Northeast Atlantic, from Mauritania to Norway, and including Iceland (Crothers 1967;Carlton and Cohen 2003;Rewitz et al 2004;Young et al 2017), during the last two centuries this species spread its geographic distribution settling in five major regions of the globe: Northeast, Northwest and Southwest of the Pacific Ocean, and Communicated by Paul A. Montagna Northwest and Southeast Atlantic Ocean (Thresher et al 2000;Young and Elliott 2020).…”

Life History and Population Dynamics of Green Crabs (Carcinus maenas)

“…Passive nets are sometimes used but this method trusts to the currents and wandering crabs to enter the net so may be equally unreliable as a population density estimate. Trawling may be used if the bottom conditions are suitable [256] but often they are not due to the crab's preference for bivalve beds or other geometrically complex areas. Lastly, a common method for estimating population numbers of a mobile species is tag and recapture.…”