John D M Gordon

Does Presence of a Mid-Ocean Ridge Enhance Biomass and Biodiversity?

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007–2010. The MAR, 3,704,404 km2 in area, accounts for 44.7% lower bathyal habitat (800–3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Deep demersal fish assemblage structure in the Porcupine Seabight (Eastern North Atlantic): results of single warp trawling at lower slope to abyssal soundings

The dynamics of clearance, segregation and elimination of a marine bacterium, Moraxella sp., by the shore crab, Carcinus maenas (L.) has been studied utilizing fluorescent and radiolabelling techniques. In addition to the gills, the hepatopancreas was a major site of bacterial accumulation with sequestration occurring within haemocyte clumps and groups of stationary cells in this organ. The heart, excretory organ and subcuticular tissues also incorporated bacteria, but to a lesser extent. By the first day post-injection, many of the segregated micro-organisms had been removed from the organs. This latter process was not due to the exodus of laden haemocytes or of intact cell clumps from the host but seemed to result from lytic action by the host blood cells. Little material arising from such bacterial/haemocytic interaction was, however, immediately excreted, and much was relocated in the general body tissues as well as the gill nephrocytes.

Long-term changes in deep-water fish populations in the northeast Atlantic: a deeper reaching effect of fisheries?

A severe scarcity of life history and population data for deep-water fishes is a major impediment to successful fisheries management. Long-term data for non-target species and those living deeper than the fishing grounds are particularly rare. We analysed a unique dataset of scientific trawls made from 1977 to 1989 and from 1997 to 2002, at depths from 800 to 4800 m. Over this time, overall fish abundance fell significantly at all depths from 800 to 2500 m, considerably deeper than the maximum depth of commercial fishing (approx. 1600 m). Changes in abundance were significantly larger in species whose ranges fell at least partly within fished depths and did not appear to be consistent with any natural factors such as changes in fluxes from the surface or the abundance of potential prey. If the observed decreases in abundance are due to fishing, then its effects now extend into the lower bathyal zone, resulting in declines in areas that have been previously thought to be unaffected. A possible mechanism is impacts on the shallow parts of the ranges of fish species, resulting in declines in abundance in the lower parts of their ranges. This unexpected phenomenon has important consequences for fisheries and marine reserve management, as this would indicate that the impacts of fisheries can be transmitted into deep offshore areas that are neither routinely monitored nor considered as part of the managed fishery areas.

Environmental and Biological Aspects of Slope-Dwelling Fishes of the North Atlantic

The environmental and biological aspects of slope dwelling fishes of the North Atlantic are discussed in the form of answers to the following questions. (1) How do the physical features of the continental slope and shelf compare? (2) How does the physical environment of the slope differ from that of the shelf? How do the demersal species assemblages on the shelf and slope differ from one another and are the latter basically different from the pelagic oceanic assemblage? (5) How do the basic distribution patterns (vertical and horizontal) of slope-dwellers compare with their shelf-dwelling counterparts? (6) How does the vertical distribution pattern of fish biomass correlate with the trophic input to the oceanic environment? (7) What is known about deep-sea fish population structure and breeding biology?

Fish communities on the slope of the eastern Norwegian Sea

Abstract Bottom trawl data from the depth interval 300–2050 m on the slope off Norway were analysed to study distribution of fish biomass and the associated species assemblages. It is hypothesised that the pronounced hydrographic front between the warm Atlantic Watermass and the cold Norwegian Sea Deepwater, combined with a declining food supply with depth and distance from the shelf, structure the assemblages on the continental slope of the eastern Norwegian Sea. From a high level at the shelf edge and upper slope, the fish biomass declined abruptly at about 720 m when crossing the 0 °C-isotherm associated with the hydrographic front. Beneath the frontal zone, the fish biomass was only 11 % of that above it and decreased further with increasing depth. In upper slope waters, the fish biomass increased with increasing latitude. Arctic species such as Lycodes frigidus and Paraliparis bathybius were dominant in the deep cold slope waters. The high fish biomass associated with the steep temperature gradient a...

Age-related trends in otolith chemistry of Merluccius merluccius from the north-eastern Atlantic Ocean and the western Mediterranean Sea

Sagittal otoliths of European hake obtained from five geographic locations in the north-eastern Atlantic and western Mediterranean were examined using laser ablation and inductively coupled plasma mass spectrometry. Otolith sections were analysed for the isotopes 24 Mg, 55 Mn, 66 Zn, 85 Rb, 86 Sr, 138 Ba and 208 Pb, measured relative to 43 Ca counts. These analyses considered only age 0 (core area) and ages 1 to 3. Age-related trends in otolith elemental composition were observed in hake from all areas, but were masked by variability between locations. Elemental concentrations generally decreased outside the core, with some increase at age 3. The composition of the otolith core was very distinct from that of the other growth increments. In the Mediterranean, part of this differentiation was a result of Mn, which was present in the core at high concentrations compared with the rest of the otolith. Mediterranean otoliths also had higher concentrations of Sr, Zn and Ba in the core. For most samples a similar trend was observed, although samples from one of the Mediterranean areas showed some differences, mainly in the concentrations of Mg and Sr. These results provide new empirical evidence of the variation in elemental concentrations across hake otoliths with age, at least throughout the first 3 years of life.

Deep-water ichthyoplankton of the Skagerrak with special reference to Coryphaenoides rupestris Gunnerus, 1765 (Pisces, Macrouridae) and Argentina silus (Ascanius, 1775) (Pisces, Argentinidae)

Abstract Two species, Coryphaenoides rupestris and Argentina silus, were abundant in the ichthyoplankton of the 150–550 m depth zone of the Skagerrak in 1992. Eggs of C. rupestris occurred only in October and December and a single yolk sac larva was caught in December. Postlarvae and juveniles occurred in all months (Feb, Apr, Jun, Oct, Dec) and showed a continuous increase in length through the year. This confirms earlier indications of a single late autumn spawning period. By October the juveniles had attained a demersal mode of life. Argentina silus eggs and larvae occurred year-round, but eggs were most abundant in the spring. Most of the other fish eggs and larvae were probably caught incidentally in surface layers. Exceptions may be four postlarval Atlantic halibut Hippoglossus hippoglossus L.

The trace metal ecology of ichthyofauna in the Rockall Trough, north-eastern Atlantic

Abstract The concentrations of Cu, Mn, and Ni in tissue samples from 230 fish from the Rockall Trough were determined by atomic absorption spectrophotometry. Concentrations of Cu, Mn and Ni were 0.02–23 μg g −1 , 0.02–6.5 μg g −1 and 0.02–10 μg g −1 respectively. Cu appeared to selectively accumulate in liver tissues while Mn accumulated in gill tissues. Ni was evenly distributed throughout all tissues examined. Concentrations of all three metals generally decreased with length. Inter-specific differences between teleosts were found to be related to differences in feeding behaviour. There was no apparent concentration of metals through the food chain from prey to sharks. Low concentrations of Cu, Mn and Ni were detected in the water column (Cu 86–103 ng l −1 , Mn −1 , Ni 210–224 ng l −1 ), suggesting that for sharks in the Rockall Trough, the uptake of metals from diet is of more importance than that from the water column. Metallothionein-like proteins were detected in liver samples from nine species of deep-water shark. Concentrations were similar in all species (8–10 μg g −1 ) and were independent of hepatic Cu and Cd. It is suggested that these proteins are involved in the homeostasis of essential trace metals.

The distribution and diet of the dominant, slope-dwelling eel, Synaphobranchus kaupi, of the Rockall Trough

INTRODUCTION The deep-sea eel, Synaphobranchus kaupi , is widely distributed on the continental slopes of the North Atlantic (Saldanha & Bauchot, 1986; Haedrich & Merrett, 1988). It was a dominant fish species in epibenthic sledge and semi-balloon otter trawl (OTSB) hauls on the West African slope (Merrett & Marshall, 1981; Merrett & Domanski, 1985). Also in the eastern North Atlantic, it was the most abundant species on the slopes of the Porcupine Sea Bight off south-west Ireland (Merrett et al., 1991; Priede et al., 1994). In the western North Atlantic, it was the dominant species on the middle and lower slopes of the Middle Atlantic States of the USA and on the upper slopes of the Grand Banks off Newfoundland (Sedberry & Musick, 1978; Houston & Haedrich, 1986).

Metallothionein-like proteins in the livers of squaloid and carcharhinid sharks

Abstract Liver extracts from three species of shark ( Etmopterus spinax, Galeorhinus galeus, Scymnorhinus licha ), were analysed using Differential Pulse Polarography. All three extracts gave significant polarographic responses, indicating the presence of cysteine containing proteins. On the basis of previous work, these proteins were considered to be metallothionein-like in nature. These results mark the first data on MT in natural populations of sharks and in mid- to deep-water species.