The effect of the sinking spring diatom bloom on digestive processes of the cold‐water protobranch Yoldia hyperborea

Abstract

Periodic sampling from April 1997 to December 1998 of a population of the deposit-feeding protobranch Yoldia hyperborea from the deep depositional zone (250 m) of Conception Bay, Newfoundland, indicated that this species was exposed to subzero temperatures (Ϫ0.63ЊC) throughout the year. However, the standing stock of phytoplankton in the photic zone showed strong seasonal fluctuations with primary peaks always occurring in April (4.26 and 5.09 g L Ϫ1 chlorophyll a in 1997 and 1998, respectively). In addition, sediment chlorophyll a started to increase (from a low of ϳ6 ng mg Ϫ1 dry weight of sediment) as the sinking of a smaller, secondary bloom, reached the bottom in the first 2 months of 1997 and 1998, although higher concentrations were reached by mid-April and May 1997 (21.32 ng mg Ϫ1 sediment) and remained relatively high until February 1998. An increase of digestive cell height and protein content occurred as soon as sinking organic material from the spring bloom reached the benthic zone, suggesting storage of metabolic energy during spring and summer. Sharp increases in digestive enzyme activity occurred primarily in early spring of each year, coinciding with the timing of the primary spring bloom fallout, suggesting activation of the formerly depressed digestive system after a prolonged period of low food availability (i.e., late summer to autumn). Results suggest that Y. hyperborea strongly depends on the input of fresh algal material despite the high availability of organic matter in the sediment.Carbon supply to the aphotic benthic zone of the sea is largely based on the timing of climatic events (e.g., snow and ice melt, rainfall), tidal exchange, and, most importantly, the sinking of phytoplankton blooms (Wassman 1991;Graf 1992). The organic fraction of the particle input to the sediment is a potential energy source for benthic organisms. It is well established that in shallow water the input of fresh organic matter of high nutritional value from primary production creates a burst of activity in the benthic population (Clarke 1988;Boon et al. 1998). Graf et al. (1982) showed that the response to organic matter input is more rapid in those species that utilize the organic matter directly rather than those species that feed on meiofauna and sediment. However, the availability of food particles decreases with increasing depth and becomes more episodic at higher latitudes, imposing specific constraints on the organisms, which must be able to withstand periods of reduced food availability. Thus energy-demanding metabolic processes such as growth and reproduction are often restricted to periods of high food abundance. For example, antarctic suspension feeders show a marked seasonal variation in feeding rates, with the highest activity occurring in the short but very productive summer, whereas most animals cease feeding during

Absorption efficiency, ingestion rate, gut passage time and scope for growth in suspension- and deposit-feeding Yoldia hyperborea

“…Conception Bay, Newfoundland). However, field data indicate that on one occasion during 1998, significant Y. hyperborea mortality occurred after an unusually high particle load was detected in the water column and near the sediment surface of Conception Bay (Stead & Thompson 2003a), which may be explained through the results obtained here.…”

“…Yoldia hyperborea were obtained by dredge from the deepdepositional zone of Conception Bay, Newfoundland (250 m, 47°34.0' N, 53°08.1' W) (Stead & Thompson 2003a) and placed in sediment within a refrigerated holding tank (0.0 ± 1.0°C; ambient temperature) at the Ocean Sciences Centre in Logy Bay. Since most physiological rates vary with body size, only large Y. hyperborea of similar size were used for feeding experiments (mean shell length = 28.96 mm, SD = 2.14, n = 96).…”

“…However, SFG also depends on the organic content of food, and the estimations obtained here are for sediments containing around 12% POM. Seasonal values for organic matter from Conception Bay sediments range between 8 and 13% DW (Stead & Thompson 2003a), with the highest POM values typically found after the fallout of the spring-bloom, and the lowest values between the end of summer and late winter. Thus the SFG of Y. hyperborea from Conception Bay probably varies with the organic content of the sediment.…”

“…Seasonal variation should also be observed in the AE of Y. hyperborea, as sediments from Conception Bay contain a high proportion of algae from the spring-bloom fallout during a short period in May and June of each year. During this time, high AE values are expected, but should decline thereafter as food quality decreases (Stead & Thompson 2003a).…”

Decline of Microcystis aeruginosa FACHB-905 under four stress conditions

“…在棕囊藻(Phaeocystis)死亡后, 异养细菌对浮游植物衰亡所引发的环境改变做 出了快速响应, α-变形菌纲和拟杆菌门立即出现, 原生动物生物量也剧增 [4][5] . 浮游植物的下沉还会促进 底栖生物的消化系统消化能力, 引起食物网传递链的改变 [6] . 第二, 在细菌作用下, 死亡藻细胞被降解, 水体有机质含量急剧增加, 也导致水体溶氧的急剧下降, 使水体中对低溶氧敏感的生物窒息而亡, 造成 巨大经济损失 [7] .…”