Realm: Marine
Climate: Temperate
Biome: Temperate shelf and seas ecoregions
Central latitude: 49.000000
Central longitude: -16.500000
Duration: 12 years, from 1989 to 2011

563 records

50 distinct species

Across the time series Amperima rosea is the most frequently occurring species

Methods

2.1. Study area - The Porcupine Abyssal Plain is situated off the southwest coast of Ireland in the Northeast Atlantic. All the samples were collected between 1989 and 2005. Most samples were taken within a 20 nautical mile (37 km) radius of a central position for time series studies (48?50?N and 16?30?W) (Fig. 1 and Table 1). This site became known as the ?BENGAL Station? following a major European project on seabed biology and geochemistry that focussed its work there (Billett and Rice 2001). The site is now known as the Porcupine Abyssal Plain Sustained Observatory (PAP-SO). The site was chosen to be as far as possible from the influence of the continental slope to the east and the foothills of the Mid-Atlantic Ridge to the west. The aim was to reduce perturbations caused by slope-related process on the continental margin and the ocean ridge to a minimum. This allowed processes linking the sea surface to the abyssal seabed through the transfer of organic matter to be studied. The seabed depth at the sampling site ranges between 4800 and 4850 m. The site was a level area of seabed with little topographic and environmental heterogeneity. It had a strong seasonal signal in the flux of organic material (phytodetritus) (Billett et al. 1983). 2.2. Sampling - Sampling for megafauna was undertaken using a semi-balloon otter trawl (OTSB14). The wing-end spread was 8.6 m and the net height was approximately 1.5 m from the footrope to the headline. Towing speed was a nominal 0.75 ms?1. The net was constructed of a 44 mm stretch mesh in the main part a 37 mm stretch mesh in the central part and a 13 mm stretch mesh liner in the cod-end. Contact of the net with the seafloor and hence an estimate of the area fished was assessed by changes in wire tension during trawling operations. The acoustic beacon used with trawls between 1989 and 1999 to monitor performance was unavailable from 2000 onwards. We are nevertheless confident that our estimates of seafloor area fished remain consistent throughout the time series. On completion of a trawl samples were sorted into major taxonomic groups on board the ship before being fixed in 5% borax-buffered formaldehyde in seawater. The samples were transferred into 80% methylated spirit once the samples were returned to the laboratory. The samples were then sorted into finer taxonomic groups and wet weight and length was measured for each individual. Apart from sampling at the time series station in the middle of the Porcupine Abyssal Plain a number of other stations were sampled over the years to give spatial relevance (ca. 40?100 nm from PAP-SO). Specific sampling was undertaken deeper than 4800 m to the southeast east and north of the time series station (Fig. 1 Table 1). In addition advantage was taken of other trawling at abyssal depths closer to the base of the continental slope as part of science programmes conducted by the Oceanlab University of Aberdeen and the National Oceanography Centre Southampton. The samples came mainly from close to the mouth of the Porcupine Seabight (Fig. 1). This area had been sampled many times during the IOS Deep-Sea Biology Programme from 1976 to 1989 (Rice et al. 1991). Some of the larger abundant holothurians collected in the trawls namely Psychropotes longicauda O. mutabilis Pseudostichopus villosus and Paroriza prouhoi were enumerated and weighed at sea (fresh wet weight biomass) before the samples were used for other analyses in the years 1998 and 1999. Where this occurred the fresh wet weights were converted to preserved wet weight by applying a factor of 0.6 to the fresh wet weight in order to allow a comparison of wet weight biomass over the whole time series. Conand (1989) has shown that holothurians lose about 40% of their wet weight on preservation. Trawl sampling OTSB14 Unit of abundance = CountPerSqM, Unit of biomass = Weight

Citation(s)

Billett, D., Bett, B., Reid, W., Boorman, B. & Priede, I. (2010) Long-term change in the abyssal NE Atlantic: The ‘Amperima Event’revisited. Deep Sea Research Part II: Topical Studies in Oceanography, 57, 1406-1417.
Billett, D., Bett, B., Rice, A., Thurston, M., Galéron, J., Sibuet, M. & Wolff, G. (2001) Long-term change in the megabenthos of the Porcupine Abyssal Plain (NE Atlantic). Progress in Oceanography, 50, 325-348.