The species associated with this article are major components of the successionary communities arising around bathyal whale carcasses (though by no means the only whale-fall associated species).
A whale carcass arriving on the bathyal sea-floor (roughly 700-1000m depth) represents a massive influx of nutrients to an otherwise nutrient-poor ecosystem (Lundsten et al 2010a; Lundsten et al 2010b; Smith and Baco 2003). The background rate of carbon deposition to the deep-sea floor is on the order of tens of kilograms per hectare per year (Smith and Baco 2003); an adult whale can weigh up to 160 tons. Consequently, it has long been thought that whale carcasses must represent a significant source of nutrients for sea-bed communities. Additionally, since the discovery of deep-sea hydrothermal vents and cold seeps, it has been hypothesized that whale-falls may serve as stepping stones for the dispersal of organisms between chemosynthesis-dominated bottom communities (Smith and Baco 2003).
The community observed to spring up around whale carcasses has been characterized as having three major successionary stages (Danise et al 2012):
-Mobile scavenger stage: large, mobile detritivores consume the flesh of the whale.
-Enrichment opportunist stage: slow-moving or sessile organisms colonize the nutrient-enriched area in and around the carcass.
-Sulphophilic stage: a chemosynthesis-dominated system based on the sulfides released by anaerobic decomposition of bone lipids.
The duration of the first stage depends largely on the mass of the whale, ranging from a few months to up to one and a half years. Initially the community is dominated by large detritivores such as sleeper sharks and hagfish, but as the amount of flesh available decreases, smaller scavengers such as rattails, amphipods, and and lithodid crabs begin to replace them. Once the bulk of the tissue is removed from the skeleton, the community begins to shift to phase two. At this point, extremely dense populations of dorvilleid worms and other polychaetes, as well as crustaceans and gastropods colonize the area around the carcass, exploiting the rich organic material in the surrounding sediments. The rapid recruitment of these organisms suggests they may be opportunistic whale-fall specialists. Over time, without a discrete boundary, sulphide emission from anaerobic decay of bone lipids in the whale skeleton begins to support a chemosynthetic fauna similar to that found around cold seeps and hydrothermal vents, including bacteria, organisms with endosymbiotic bacteria, bacterial grazers, and small predators. This community may linger for up to several decades (Smith and Baco 2003). Fossil evidence suggests that a similar pattern of succession has been evolving since the late Miocene, and may even have operated on the carcasses of Cretaceous plesiosaurs (Danise et al 2012).
As always in ecology, this picture is somewhat oversimplified. In two 2010 articles, Lundsten et al observe that in addition to chemosynthetic fauna and whale-fall specialists, whale carcasses are often characterized by increased density of the background sea-floor organisms, particularly as time passes since the fall of the whale. Lundsten et al and Glover (2010) additionally found that there is a notable depth gradient in community structure, with fully sulphophilic ecosystems only developing on large, deep carcasses.
The function of whale-falls as stepping stones between cold seeps and hydrothermal vents remains unproven, but there is evidence for relatively large numbers of whale-fall specialist species, especially in the enrichment opportunist and sulphophilic stages (Smith and Baco 2003). Nearest-neighbor analyses of whale falls based on whale populations and the probability of a carcass sinking suggest that carcasses are distributed such that most organisms found in the latter two stages could easily disperse larvae between whale-fall sites. Unfortunately, this ecosystem may be endangered by declining whale populations and may even have already lost a great deal of diversity, as 19th century whale-fall density was likely up to six times higher than that in the present day (Smith and Baco 2003).
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:950
Specimens with Barcodes:929
Species With Barcodes:167
Grenadiers or rattails (less commonly whiptails) are generally large, brown to black gadiform marine fish of the family Macrouridae. Found at great depths from the Arctic to Antarctic, members of this family were amongst the most abundant of the deep-sea fish.
The Macrouridae are a large and diverse family with some 34 genera and 383 species recognized (well over half of which are contained in just three genera, Caelorinchus, Coryphaenoides, and Nezumia). They range in length from about 10 cm (3.9 in) in the graceful grenadier (Hymenocephalus gracilis) to 1.5 m (4.9 ft) in the giant grenadier, Albatrossia pectoralis. An important commercial fishery exists for the larger species, such as the giant grenadier and roundnose grenadier, Coryphaenoides rupestris. The family as a whole may represent up to 15% of the deep-sea fish population.
Typified by large heads with large mouths and eyes, grenadiers have slender bodies that taper greatly to very thin caudal peduncles or tails (excluding one species with no tail fin): this rat-like tail explains the common name 'rattail' and the family name Macrouridae, from the Greek makros meaning "great" and oura meaning "tail". The first dorsal fin is small, high, and pointed (and may be spinous); the second dorsal fin runs along the rest of the back and merges with the tail and extensive anal fin. The scales are small.
As with many deep-living fish, the lateral line system in grenadiers is well-developed; it is further aided by numerous chemoreceptors located on the head and lips, and chemosensory barbels underneath the chin. Benthic species have gas bladders with unique muscles attached to them. The animals are thought to use these muscles to "strum" their gas bladders and produce sound, possibly playing a role in courtship and mate location. Light-producing organs, photophores, are present in some species; they are located in the middle of the abdomen, just before the anus and underneath the skin.
Living at depths from 200 to 6,000 m (660 to 19,690 ft), grenadiers are the most common benthic fish of the deep (however, two genera are known to prefer the midwater). They may be solitary or may form large schools, as with the roundnose grenadiers. The benthic species are attracted to structural oases, such as hydrothermal vents, cold seeps, and shipwrecks. They are thought to be generalists, feeding on smaller fish, pelagic crustaceans such as shrimp, amphipods, cumaceans and less often cephalopods and lanternfish. As well as being important apex predators in the benthic habitat, some species are also notable as scavengers.
As few rattail larvae have been recovered, little is known of their life histories. They are known to produce a large number (over 100,000) of tiny (1–2 millimetres or 0.039–0.079 inches in diameter) eggs made buoyant by lipid droplets. The eggs are presumed to float up to the thermocline (the interface between warmer surface waters and cold, deeper waters) where they develop. The juveniles remain in shallower waters, gradually migrating to greater depths with age.
Spawning may or may not be tied to the seasons, depending on the species. At least one species, Coryphaenoides armatus, is thought to be semelparous; that is, the adults die after spawning. Nonsemelparous species may live to 56 years or more. The Macrouridae in general are thought to have low resilience; commercially exploited species may be overfished and this could soon lead to a collapse of their fisheries.
- Subfamily Bathygadinae
- Subfamily Macrourinae
- Genus Albatrossia (monotypic)
- Genus Asthenomacrurus (two species)
- Genus Cetonurichthys
- Genus Cetonurus
- Genus Coelorinchus (114 species)
- Genus Coryphaenoides
- Genus Cynomacrurus
- Genus Echinomacrurus
- Genus Haplomacrourus
- Genus Hymenocephalus (26 species)
- Genus Hymenogadus (2 species)
- Genus Kumba (eight species)
- Genus Kuronezumia
- Genus Lepidorhynchus
- Genus Lucigadus
- Genus Macrosmia
- Genus Macrourus
- Genus Malacocephalus
- Genus Mataeocephalus
- Genus Mesobius
- Genus Nezumia
- Genus Odontomacrurus
- Genus Pseudocetonurus
- Genus Pseudonezumia
- Genus Sphagemacrurus
- Genus Spicomacrurus
- Genus Trachonurus
- Genus Ventrifossa
- Subfamily Macrouroidinae
- Subfamily Trachyrincinae
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