Factors influencing aggregation patterns in the sand crab Emerita analoga (Crustacea: Hippidae)

Abstract

Aggregation patterns in Emerita analoga (in southern California) are delineated with respect to their spatial, daily, and seasonal components. Both abiotic and biotic factors are found to be associated with patterns of aggregation. Spatially, E. analoga aggregates from March through September to a significantly greater degree in the upper one-third area of the wash zone where exposure to wave shock and fish predation are probably decreased. Sand crabs are more aggregated on a daily basis during low tides than at high tides. This may be due to differential rates of migration caused by a decrease in the beach slope angle. Two seasonal peak periods of aggregation are present, one in the early spring, and one in the late summer. These periods occur during the times of highest reproductive female abundance. High seasonal intensities of aggregation probably function to facilitate mating through the maintenance of close proximity between males and females. Visual methods and/or quantitative sampling based on visual observations do not adequately reflect patterns of aggregation in E. analoga.

Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis

“…On a finer scale, intertidal organisms may experience sorting by alongshore swash circulation resulting in aggregations. Concentration in cusps (spaced undulations of the beach face) has been documented in several sedentary filter feeders (Cubit 1969, Dillery & Knapp 1969, Perry 1980, McLachlan & Hesp 1984, Giménez & Yannicelli 2000. Sorting by cusp swash circulation tended to concentrate less motile forms in the bays, where patches were composed of more small individuals compared to those on promontories (Donn et al 1986, James 1999.…”

First record of an epibiosis between the sand crab Emerita analoga (Stimpson, 1857) (Decapoda: Hippidae) and the mussel Semimytilus algosus (Gould, 1850) (Bivalvia, Mytilidae) in southern Peru

“…Contreras et al 1999), and is a characteristic specie of the swash zone (Jaramillo et al , 2001Contreras et al 1999). It can appear in high abundance forming aggregations at certain water temperatures, food availability and beach morphodynamics (Perry 1980;Dugan 1994;Contreras et al 1999). The combination of substrate generalist characteristics and the unique orientation and swimming ability of E. analoga may be a key to its high abundance and wide distribution in the intertidal zone of exposed sandy beaches (Dugan et al 1994(Dugan et al , 2000.…”

Parasite infection and sand coarseness increase sand crab (Emerita analoga) burrowing time

“…However, these costs may be mitigated by micro-scale habitat choice; for example, large, infected females may be better able to burrow further in the surf than smaller infected females, thereby utilizing a micro-habitat that may afford protection from bird predators (MacGinitie, 1938). Quantitative field studies of micro-scale distribution patterns of E. analoga (e.g., Perry, 1980) representing different size classes, reproductive condition, and infection status would be worthwhile given the complex interplay among biotic and abiotic factors involved. It is also worth examining whether parasite infection affects burrowing depth, potentially further compounding the risks of predation if incomplete burial makes crabs more visible to birds or more likely to be washed into the open ocean (see Edelaar et al, 2003 for an example involving a bivalve).…”

“…Reproduction occurs during the first and second years, and the lifespan is typically two to three years (Oliva et al, 2008;Sorte et al, 2001). E. analoga is important prey for near-shore fish and marine birds (MacGinitie, 1938;Perry, 1980). The crabs thrive by burrowing especially rapidly (Dugan et al, 2000;Faulkes and Paul, 1998;Trueman, 1970) and by migrating with the tides to maintain position in the swash zone (Dillery and Knapp, 1970;Gibson, 2003;Trueman, 1970).…”