Bythograea thermydron (William 1980)

Feeding Strategy: Scavenging and Predation
Bythograea therymdron are carnivores that prefer to consume mussels and vestimentiferans rather than limpets and mobile grazers found around vent sites (Micheli et al., 2002; Dittel et al.¸2005; Dittel et al., 2008). Although B. thermydron will occasionally eat gastropod grazers, amphipods are never part of their diet; amphipods swim at speeds of 5-10cm s1 which, when teamed with water currents, may be too quick for B. thermydron to capture, despite swimming in swarms (as shown in Fig. 1)(Van Dover et al., 1992).

amphipod swarm
Figure 1: A swarm of amphipod that is commonly encountered in a hydrothermal vent environment; it shows that they are in high abundance and densities. Regardless, Bythograea thermydron do not eat any amphipod species. (Dover et al., 1992)

Like many other species, the diet of B, thermydron changes with ontogenic development so that the zoeae and megalopae larval stages have different diet compositions than juvenile and adult crabs (Dittel et al., 2005). Dittel et al. (2005) suggested that the larval stages of B. thermydron feed on mostly zooplankton or small benthic organisms that are derived from surface waters that are show phytoplanktonic production rather than chemosynthetic production. This could be the result of its physiology (Fig. 2). Likewise, it is believed that it is with metamorphosis of and through juvenile stages that see the diet of B. thermydron shifting towards indigenous hydrothermal vent prey such as Riftia pachyptila.

larvae
Figure 2: The larvae of Bythograea thermydron has cheliped which allow it to catch and eat zooplankton as well as bethic invertebrates. However, its diet is largely from shallow-water surface phytoplanktonic production.

Despite the carnivorous nature of hydrothermal vent crabs, they are not always predators as they will sometimes scavenge on already dead mussels or vestimentiferan worms (Micheli et al., 2002). However, they do also actively predate on prey species, and they do this by ‘nipping’ at the plumes and siphons, of the R. pachyptila and Bathymodiolus species respectively, which effectively kills the organism. Occasionally, Micheli et al. (2002) observed that the crabs would ingest the prey whole and whilst it was still alive.

References
Dittel, A.I., Epifanio, C.E. & Perovich, G. (2005) Food sources for the early life history stages of the hydrothermal vent crab bythograea thermydron: A stable isotope approach. Hydrobiologia, 544, 339-346.

Dittel, A.I., Perovich, G. & Epifanio, C.E. (2008) Biology of the vent crab bythograea thermydron: A brief review. Journal of Shellfish Research, 27, 63-77.

Micheli, F., Peterson, C.H., Mullineaux, L.S., Fisher, C.R., Mills, S.W., Sancho, G., Johnson, G.A. & Lenihan, H.S. (2002) Predation structures communities at deep-sea hydrothermal vents. Ecological Monographs, 72, 365-382.

Mills, S. (2014) Bythograea thermydron larvae (figure 1). Available: http://www.whoi.edu/page.do?pid=80696&i=11903 [09/12/2014, 2014]

Van Dover, C.L., Kaartvedt, S., Bollens, S.M., Wiebe, P.H., Martin, J.W. & France, S.C. (1992) Deep-sea amphipod swarms. Nature, 358, 25-26.

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