Glass sponges are enigmatic members of the deep-sea fauna that inhabit shallow waters in only a few locations world-wide. In order to understand what factors influence the distribution of glass sponges, patterns of distribution and abundance of reef and non-reef forming hexactinellids in fjords of British Columbia, Canada, were analyzed from photographs and transcripts recorded on dives undertaken by the 'Pisces IV' manned submersible during the 1980s. Hexactinellids are widely distributed throughout all fjords from 16 to 650 m depths, and in some fjords abundances reach 240 individuals in 10 m 2 . In all fjords hexactinellids were most abundant at depths of 20 to 260 m, even where water depths exceeded 500 m. Glass sponges were rare in regions of inlets where oxygen levels fall below 2 ml l -1 , or in areas of high sediment deposition. Highest abundances coincided with water conditions of high dissolved silicate, low light, temperatures between 9 and 10°C and low suspended sediments. Extensive glass sponge skeletons in the inner basin of Howe Sound reflect past stress in this fjord that may include oxygen deficit, sediment loading from a mine and contamination from industrial sites. The observations from 'Pisces IV' suggest that glass sponges may be sentinel species for current and past seawater conditions in coastal British Columbia.
Plate I, Figs, The mortalities and subsequent recolonization of a rocky shore in S.W. Ireland following a bloom of the toxic dinoflagellate, Gyrodinium aureolum in 1979 are described. Selective mortalities of key animal species notably grazing gastropods were followed by a marked increase in fucoid algae. Enteromorpha spp. blooms were a feature of vertical surfaces only. In general planktonic recruiting gastropods exhibited the most rapid recovery. Forty-two months after the red tide, fucoid algae still dominate both vertical and horizontal surfaces at the study area. M
Changes in the diversity of fish populations have been monitored during a period of improving water quality in the Mersey estuary. Historically the Mersey estuary supported a wide range of locally important fisheries, particularly for salmon, mullet, sturgeon, eels and smelt (sparling). With the advent of the Industrial Revolution, increased quantities of sewage and industrial wastes discharged to the Mersey from the Manchester area dramatically reduced the water quality and led to the depletion of fish stocks in the upper estuary. By the time the Manchester Ship Canal opened in 1894 the R. Mersey and its tributaries were heavily polluted, salmon were effectively eradicated and the fisheries in the upper estuary severely limited. By 1920 the commercially important fisheries, for shrimp and flounder, had been displaced downstream to the middle part of the estuary. The dramatic increase in industrial development around the estuary itself in the 1940s caused further deteriorations such that throughout the 1950s and early 1960s anoxic conditions in the estuary were common and fish were reportedly absent from the upper estuary for much of the time. At this time major efforts were made to improve the river and its tributaries upstream of the estuary, and within a decade the quality of river water had improved markedly ( Fig. 1). This led to some improvement in estuarine water quality such that, for example, by 1976 less than 2% of samples from the upper estuary contained no detectable dissolved oxygen compared to nearly 20% of samples taken in 1963 (Fig. 2).In 1976 the North West Water Authority instituted a regular monitoring programme by collecting fish from two industrial intake screens at Stanlow and Runcorn on the Manchester Ship Canal, which has intermittent influxes of water from the estuary. Surveys in the middle and upper estuary with a 2-m beam trawl began in 1981, and electrofishing surveys of tributaries/streams around the estuary shortly afterwards. Within one year the intake screen monitoring programme recorded 19 different species of fish of which four were freshwater species, the remainder typically estuarine or marine. By 1987 the total had risen to 40 species, ten of which were freshwater (Fig. 1). The number of different species observed in any one year ranged from nine to 17. Most of the species were encountered rarely, 33 species being seen on fewer than 5% of occasions and only three species observed on more than 50% of sampling occasions when fish were taken. This pattern was confirmed by the results of the beam trawling which produced a total of 14 different species, a maximum of seven in any one year. Both the commercial intake screen and beam trawl samples were dominated by the same species, ' whitebait ' (predominately sprat, Sprattus sprattus, with lesser numbers of young herring, CIupea harengus) and sand-goby, Pomatoschistus minutus. All species caught by beam trawling had previously been recorded from the intake screens (Figs 3,4). Other species including codling, salmon and grey mullet a...
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