Benthic faunal energy flow and biological interaction in some shallow marine soft bottom habitats

Abstract

Infauna, including macrofauna and temporary meiofauna, and mobile epibenthic fauna have been quantitatively investigated in more than 15 shallow (0 to 1.5 m) soft bottom areas from 1977 to 1982 on the Swedish west coast. The areas are grouped into 3 types of habitats having little or no vegetation: (1) exposed, (2) semi-exposed, (3) sheltered, and 1 habitat (4) where vegetation dominates. Results are presented mainly from 4 intensively studied areas, representative of each of the habitats. Infaunal annualproduction varies between and within habitats depending on temperature, recruitment strength, available space and predation pressure. Comparisons with lower salinity areas in the Baltic show lower infaunal production and production/biomass ratios there than on the Swedish Skagerrak coast. Epibenthic faunal annualproduction is similar within habitats; highest in vegetated areas (about 6 g AFDW m-2) followed by semi-exposed areas (4 to 5 g AFDW m-2). It is suggested that each habitat has a carrying capacity for epibenthic faunal production. Epibenthic faunal production is 5 to 10 times higher in semi-exposed habitats on the Skagerrak coast than in similar habitats on the Baltic coast. As production of the epibenthic fauna is similar between years within habitats despite significant interannual variations of infaunal production, food is not likely to be a limiting factor for epibenthic faunal production in summer-autumn in Swedish Skagerrak shallow waters. In most years 51 to 75 % of production o f dominant infaunal prey organisms is consumed by epibenthic carnivores in semiexposed unvegetated habitats. However, in years with heavy infaunal settlement the percentages are much lower. In an exposed area consumption exceeds infaunal production and epibenthic carnivores also prey upon semi-pelagic mysids. In a sheltered area about 10 % of the infaunal production is eaten and the fate of the remainder is unknown. In a vegetated area the epibenthic faunal consumption is about 4 times that of infaunal production. Here about 75 % of the food consumed by the dominant carnivore Palaemon adspersus is non-carnivorous epifauna, mainly amphipods. Thus, infauna is the quantitatively most important food category for epibenthic carnivores in exposed, semi-exposed and sheltered habitats with little or no vegetation, while in vegetated habitats non-carnivorous epifauna is the dominant prey. Energy flow through the 4 different shallow habitats is discussed in general terms and presented diagramatically for 2 of them. Exposed and semi-exposed shallow unvegetated habitats are largely fuelled by phytoplankton produced offshore, utilized by suspension feeders. In vegetated habitats the primary food is largely produced within the area and detritus and 'small' herbivores are important in this energy flow. Sheltered unvegetated habitats are largely based on detritus as food. In all these habitats a significant part of the animal production during summer and autumn is later transferred to deeper waters by migration and there constitutes a valuable food resource for coastal fish populations.