Callianassa subterranea

Feeding method
Callianassa subterranea is a sub-surface deposit feeder. Feeding takes place entirely within the burrow and once a burrow is established, much of the subsequent burrowing activity is for the purpose of obtaining food. Although it has been suggested that Callianassa subterranea is also a facultative filter-feeder (Nickell & Atkinson, 1995) and may 'garden' bacteria within its burrow detailed behavioural studies reveal the species to be a genuine deposit feeder (Stamhuis et al., 1996). Sediment is processed before ingesting and so contains a larger silt fraction than the sediment.

Sociability
The density of Callianassa subterranea individuals varies between 2 and 60 shrimps per m² (Künitzer et al., 1992). Although population density of Callianassa subterreanea is often high, Rowden & Jones (1994) observed individual shrimps to be aggressive and intolerant of each other. The role of such aggressive behaviour may be important to the regulation of population density. It is also suggested that shrimp population density may control aspects of burrow morphology. In the laboratory, Callianassa subterranea showed self-inhibiting burrow construction. Burrows were smaller when individuals were present in high densities (Rowden & Jones, 1995).

• Callianassa subterranea is likely to be more widespread than records of adults suggest. Many observations of the deep-burrowing habit of the species indicate that the adults will usually be unavailable to conventional benthic sampling equipment (Atkinson & Nash, 1990) because of the depth of the shrimps burrows.
• Burrows in mud are relatively simple and deep (30-81cm) compared to those in sandier sediments which tend to be shallow and complex (Rowden & Jones, 1997). These differences may be related to the associated food content of the substratum.

• Female Callianassa subterranea brood eggs on their pleopods.
• Most sexually mature females collected from the southern North Sea were ovigerous in July and August suggesting a summer breeding season for Callianassa subterranea. The proportion of ovigerous females declined during April and September, and no females with eggs were collected in October (Rowden & Jones, 1994). Approximately one month after the peak occurrence of ovigerous females, post larval abundance is highest, implying that newly-hatched larvae have about four weeks in the plankton before being recruited to the benthic population. However, post larvae were also relatively abundant in April which supports evidence from Witbaard & Duineveld (1989) of a double reproductive cycle. Large or old females (9 mm carapace length, 2 years old) were ovigerous in February and post larvae common in April. Lindley (1987) found no Callianassa subterranea larvae in the North Sea plankton for late winter or early spring which also supports the suggestion of a double reproductive cycle. However, Rowden & Jones (1994) suggest that the absence of larvae between the two peaks may be because Callianassa subterranea adopts an alternative life-history strategy of direct benthic development during this period. Such benthic larval development has been observed for Callianassa kraussi in South Africa
• Rowden & Jones (1995) observed the influence of the sex of Callianassa subterranea upon burrow structure. Resin casts of burrows produced by females had consistently fewer surface openings than those of males. The reason for this difference is unknown.