figure 6 - Thermarces cerberus (http://www.deepseaphotography.com)
Thermarces cerberus (figure 6), a benthic predatory fish species found specifically at hydrothermal vent sites of the eastern pacific rise (Sancho et al 2005) has been found to be the top trophic predator in many pacific vent sites. This species belongs to the Zoarcidae family, which are deep sea predators/scavengers, typically being associated with cold seep, hydrothermal vent or whale carcass communities (Sancho et al 2005). There are approximately 220 species, ranging in size however none believed to be large, all primarily occupying deep sea habitats (Anderson 1994). The diet of such fish is not generally known however it is believed that they are dynamic feeders but most likely to be scavenging what is closest and easily accessible to them (Ferry 1996).
T.cerberus is a hydrothermal vent specialist. Feeding typically on mobile molluscs e.g. limpets (B. thermophilus) and some crustacean species, however opportunistic feeding strategies have been noted with disturbance from research vessels such as ALVIN on R.pachyptilia. Fragments of R.pachyptilia have been found within T.cerberus stomachs however due to the robust protective tube surrounding the majority of the organisms it is unlikely to be predated on by T.cerberus (Anderson 1994). Due to the specialized nature of all organisms found at hydrothermal vent sites and high toxicity, sulphides, T.cerberus has no great competition from outside predators and as such does not have to grow to large sizes (Sancho et al 2005) or compete over resources except with members of the same species. The distribution of this species is quite sparse, probably due to the diminished ability of such an ecosystem to support higher organisms such as this. T.cerberus is found largely between the R.pachyptilia tubes (Figure 7) however individuals have been noted to stray from this particular microhabitat. The Zoarcidae family are deep sea specialists however the majority of species within the family still rely on surface sourced bio material, meaning there dietary requirements are met by scavenging. T.cerberus diet however is contained within the vent site it inhabits. All marine vertebrates have a requirement for some specific fatty acids within their diets (Pond et al 2008) however analysis of the chemoautotrophic bacteria that form the base of the food chain, show they produce low abundances of such fatty acids. Yet mature individuals of T.cerberus have been found, at lowering levels to that normally associated with deep sea fish species, with significant concentrations of essential fatty acids within their liver and muscle tissue. It was found by Pond et al that due to trophic concentration a diet of certain prey species of T.cerberus could offer an explanation however further investigations were required. This species represents the highest trophic level found at hydrothermal vents, however due to a lack of external pressure from outside predators it has not had to make any adaptations in such a sense, this probably why low diversity in morphology is observed in varying sites. Adaptations have been made to optimise its success in such a habitat however in a generalized sense it is fairly similar to other species found within its family. Some research has recently been conducted on predator-prey relationships between the T.cerberus and other invertebrates however it is likely that due to the specialized nature of each feeding niche and the high abundances of some species found, that the strong trophic relationships observed in surface predator-prey interaction do not take effect (to the same extent) in such biomes
Figure 7 - Thermarces cerberus amonst Riftia (http://www.ifremer.com)