Martin A. Collins

Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell–Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño–Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.

The thermohaline expressway: the Southern Ocean as a centre of origin for deep-sea octopuses

Understanding how environmental forcing has generated and maintained large‐scale patterns of biodiversity is a key goal of evolutionary research and critical to predicting the impacts of global climate change. We suggest that the initiation of the global thermohaline circulation provided a mechanism for the radiation of Southern Ocean fauna into the deep sea. We test this hypothesis using a relaxed phylogenetic approach to coestimate phylogeny and divergence times for a lineage of octopuses with Antarctic and deep‐sea representatives. We show that the deep‐sea lineage had their evolutionary origins in Antarctica, and estimate that this lineage diverged around 33 million years ago (Ma) and subsequently radiated at 15 Ma. Both of these dates are critical in development of the thermohaline circulation and we suggest that this has acted as an evolutionary driver enabling the Southern Ocean to become a centre of origin for deep‐sea fauna. This is the first unequivocal molecular evidence that deep‐sea fauna from other ocean basins originated from Southern Ocean taxa and this is the first evidence to be dated.

The fate of cetacean carcasses in the deep sea: observations on consumption rates and succession of scavenging species in the abyssal north-east Atlantic Ocean

The fate of cetacean carcasses in the deep sea was investigated using autonomous deep–sea lander vehicles incorporating time–lapse camera systems, fish and amphipod traps. Three lander deployments placed cetacean carcasses at depths of 4000 to 4800 m in the north–east Atlantic for periods of 36 h, 152 h and 276 h before being recovered. The photographic sequences revealed that carcasses were rapidly consumed by fish and invertebrate scavengers with removal rates ranging from 0.05 to 0.4 kg h-1. In the longest experiment the carcass was skeletonized within five days. In each deployment, approximately an hour after emplacement, the grenadier Coryphaenoides (Nematonurus) armatus and large numbers of lysianassid amphipods had arrived at the food–fall. The initially high numbers of grenadiers declined once the majority of the bait had been consumed and a variety of other fish and invertebrates were then observed, some taking up residence at the site. None of the fish species appeared to consume the carcass directly, but preyed upon amphipods instead. Funnel traps recovered with the carcass indicated a succession in the species composition of amphipods, with the specialist necrophages such as Paralicella spp. being replaced by more generalist feeders of the Orchomene species complex.

The absence of sharks from abyssal regions of the world's oceans

The oceanic abyss (depths greater than 3000 m), one of the largest environments on the planet, is characterized by absence of solar light, high pressures and remoteness from surface food supply necessitating special molecular, physiological, behavioural and ecological adaptations of organisms that live there. Sampling by trawl, baited hooks and cameras we show that the Chondrichthyes (sharks, rays and chimaeras) are absent from, or very rare in this region. Analysis of a global data set shows a trend of rapid disappearance of chondrichthyan species with depth when compared with bony fishes. Sharks, apparently well adapted to life at high pressures are conspicuous on slopes down to 2000 m including scavenging at food falls such as dead whales. We propose that they are excluded from the abyss by high-energy demand, including an oil-rich liver for buoyancy, which cannot be sustained in extreme oligotrophic conditions. Sharks are apparently confined to ca 30% of the total ocean and distribution of many species is fragmented around sea mounts, ocean ridges and ocean margins. All populations are therefore within reach of human fisheries, and there is no hidden reserve of chondrichthyan biomass or biodiversity in the deep sea. Sharks may be more vulnerable to over-exploitation than previously thought.

Southern ocean cephalopods

The Southern Ocean cephalopod fauna is distinctive, with high levels of endemism in the squid and particularly in the octopodids. Loliginid squid, sepiids and sepiolids are absent from the Southern Ocean, and all the squid are oceanic pelagic species. The octopodids dominate the neritic cephalopod fauna, with high levels of diversity, probably associated with niche separation. In common with temperate cephalopods, Southern Ocean species appear to be semelparous, but growth rates are probably lower and longevity greater than temperate counterparts. Compared with equivalent temperate species, eggs are generally large and fecundity low, with putative long development times. Reproduction may be seasonal in the squid but is extended in the octopodids. Cephalopods play an important role in the ecology of the Southern Ocean, linking the abundant mesopelagic fish and crustaceans with higher predators such as albatross, seals and whales. To date Southern Ocean cephalopods have not been commercially exploited, but there is potential for exploitation of muscular species of the Family Ommastrephidae.

In situ comparison of activity in two deep-sea scavenging fishes occupying different depth zones

The activity of two scavenging deep–sea fishes occupying the same niche in overlapping depth zones were compared by in situ measurements of swimming speeds, tail–beat frequencies and by arrival time at baits. At 4800 m on the Porcupine Abyssal Plain, the grenadier Coryphaenoides (Nematonurus) armatus was the dominant scavenger, arriving at baits after 30 min, and swimming at relatively slow speeds of 0.17 body lengths (BL) sec-1. At 2500 m in the relatively food rich Porcupine Seabight both C. (N.) armatus and the blue–hake, Antimora rostrata, were attracted to bait, but A. rostrata was always the first to arrive and most of the bait was consumed before the C. (N.) armatus arrived. A. rostrata swam at mean speeds of 0.39 BL sec−1, similar to related shallow water species at equivalent temperatures. Observations on tail–beat frequency from video sequences confirmed the greater activity of A. rostrata. The data indicate that, given sufficient food supply, high pressure and low temperature do not limit activity levels of demersal deep–sea fishes. Low activity of C. (N.) armatus is an adaptation to poor food supply in the abyss, where these fishes dominate, but prevents it competing with the more active A. rostrata in shallower depths.

The Patagonian toothfish: biology, ecology and fishery

Patagonian toothfish (Dissostichus eleginoides) is a large notothenioid fish that supports valuable fisheries throughout the Southern Ocean. D. eleginoides are found on the southern shelves and slopes of South America and around the sub-Antarctic islands of the Southern Ocean. Patagonian toothfish are a long-lived species (>50 years), which initially grow rapidly on the shallow shelf areas, before undertaking an ontogenetic migration into deeper water. Although they are active predators and scavengers, there is no evidence of large-scale geographic migrations, and studies using genetics, biochemistry, parasite fauna and tagging indicate a high degree of isolation between populations in the Indian Ocean, South Georgia and the Patagonian Shelf. Patagonian toothfish spawn in deep water (ca. 1000 m) during the austral winter, producing pelagic eggs and larvae. Larvae switch to a demersal habitat at around 100 mm (1-year-old) and inhabit relatively shallow water (<300 m) until 6-7 years of age, when they begin a gradual migration into deeper water. As juveniles in shallow water, toothfish are primarily piscivorous, consuming the most abundant suitably sized local prey. With increasing size and habitat depth, the diet diversifies and includes more scavenging. Toothfish have weakly mineralised skeletons and a high fat content in muscle, which helps neutral buoyancy, but limits swimming capacity. Toothfish generally swim with labriform motion, but are capable of more rapid sub-carangiform swimming when startled. Toothfish were first caught as a by-catch (as juveniles) in shallow trawl fisheries, but following the development of deep water longlining, fisheries rapidly developed throughout the Southern Ocean. The initial rapid expansion of the fishery, which led to a peak of over 40,000 tonnes in reported landings in 1995, was accompanied by problems of bird by-catch and overexploitation as a consequence of illegal, unreported and unregulated fishing (IUU). These problems have now largely been addressed, but continued vigilance is required to ensure that the species is sustainably exploited and the ecosystem effects of the fisheries are minimised.

Distribution of deep-water benthic and bentho–pelagic cephalopods from the north-east Atlantic

The distribution of deep-water (150-4850 m) benthic and bentho-pelagic cephalopods in the northeast Atlantic is described, based on 592 specimens collected from commercial and research trawling. Thirty-six different species of cephalopod belonging to 14 families were identified, though problems remain with the taxonomy of some of the octopod genera. At the shallower depths (150-500 m) sepiolids were the most abundant group with five species identified. Sepiola atlantica, Sepietta oweniana and Rondeletiola minor were restricted to the shallow depths (<300 m), but Neorossia caroli (400-1535 m) and Rossia macrosoma (205-515 m) extended into deeper water. The squids Todaropsis eblanae and Loligo forbesi were also common in shallow areas (<250 m). Among the incirrate octopods, Eledone cirrhosa was found at depths of 208-490 m. Three putative species of Benthoctopus and two of Bathypolypus were identified occupying depths of 250-2700 m. Graneledone verrucosa was caught at depths of 1785-2095 m. Cirrate octopods dominated the cephalopod catch from the deeper areas, with Opisthoteuthis massyae occurring from 877 to 1398 m, O. grimaldii from 2165 to 2287 m, Stauroteuthis syrtensis from 1425 to 3100 m, Cirroteuthis muelleri from 700 to 4854 m, Cirrothauma murrayi from 2430 to 4850 m and Grimpoteuthis (five putative species) from 1775 to 4877 m. Abundance estimates of the more frequently caught species were calculated from swept areas of trawls and sledges in the Porcupine Seabight and on the Porcupine Abyssal Plain.

Behavioural observations on the scavenging fauna of the Patagonian slope

The scavenging fauna of the Patagonian slope (900–1750 m), east of the Falkland Islands was investigated using the Aberdeen University Deep Ocean Submersible (AUDOS), an autonomous baited camera vehicle designed to photograph scavenging fish and invertebrates. The AUDOS was deployed on ten occasions in Falkland waters. Nine experiments were of 10–14 h duration and baited with 800 g of squid and one experiment lasted six days, baited with a 10 kg toothfish ( Dissostichus eleginoides ). Analysis of photographs revealed considerable patchiness in the composition of the scavenging fauna. Hagfish ( Myxine cf. fernholmi ) dominated three of the shallower experiments including the 6-d experiment, arriving quickly from down-current, holding station at the bait and consuming the soft tissues first, with consumption rates of up to 200 g h −1 . In the other experiments, stone crabs (Lithodidae), the blue-hake ( Antimora rostrata ) and amphipods were the primary consumers, but the rate of bait consumption was lower. Patagonian toothfish ( D. eleginoides ) were attracted to the bait at each experiment, but did not attempt to consume the bait. The patchiness in the fauna may be a result of depth, substratum and topography, but in general the rapid response of the scavenging fauna indicates that carrion is rapidly dispersed, with little impact on the local sediment community.

Observations on Morphology, Age and Diet of Three Architeuthis Caught Off the West Coast of Ireland in 1995

Three specimens of the giant squid Architeuthis were by-caught in demersal trawls to the west of Ireland, between April and June 1995. All three specimens were mature males, of mantle length 975–1084 mm. Although some intraspecific variation in fin, beak and gill were noticed, all three specimens were tentatively assigned to the species A. dux. The three specimens had food remains in their stomachs and food items identified included Micromesistius poutassou, Trachurus trachurus, Nephrops norvegicus and Eledone cirrhosa . Age estimates were made by counting putative daily growth increments in ground statoliths, and ranged from 294–122 d, giving percentage daily growth rates of 2·96–4·25% indicating a short life cycle and extremely rapid growth.