Several studies have demonstrated that coastal marine areas with high populations of bivalves/polychaetes/ascidians are characterized by population filtration capacities often exceeding the overlying water column volume several times a day. This may lead to insufficient vertical water mixing in the field and may thereby uncouple the suspension feeders from the overlying water column, ultimately preventing them from grazing on the phytoplankton. In such a case, mesocosm and field investigations were performed in the benthic boundary layer at different temperatures to assess phytoplankton depletion caused by suspension-feeding Nereis diversicolor populations. The capability of the worms to deplete the phytoplanktons in the bottom water was demonstrated to be highly correlated with temperature-dependent filtration as well as water pumping capacity. In unstirred water, the worm population (57 g m^-2 dry wt) was capable to deplete the phytoplankton in the water column to a maximum height of 26 cm at an optimum temperature of 17.8 °C.  A combination of the clearance activity of the worms and the strength of vertical water mixing generated by the water jets elected from the worm tubes controlled the height of the algal depleted area. In this study, within 2-4 h, the algal concentration in the boundary layer was depleted from an initial of 7000 to l0000 Rhodomonas cells ml^-1 to a minimum of 1500 to 3000 cells ml^-1. The maximum height of the phytoplankton depleted zone in the field was only 4-8 cm, but considerable phytoplankton depletion (20-40%) occurred in the bottom layer. This happens even at moderate to high wind speeds (6 to 8 ms^-1). During the investigation, for approximately 70% of the season (March to August 1995), the wind speeds were less than 8 ms^-1 and as such in the shallow Odense Fjord, Denmark, algal depletion above dense population of suspension-feeding N. diversicolor may occur frequently. Therefore, in spite of a considerable increment in filtration capacity from 17 to 69 m³ m^-1 d^-1 (3 to 14 times the water column a day) from March to August 1995, N. diversicolor was not able to control phytoplankton biomass at the field site in Odense Fiord due to the presence of an algal depleted boundary layer.

For more details please visit: Phytoplankton depletion by Nereis diversicolor

The formation, alteration, and maintenance of habitats by organisms through the production of physical structures or the transformation of existing ones is known as ecosystem engineering. In one of these cases, the role of Alitta virens (Sars) as an ecosystem engineer in pristine sediments was assessed. Nereidid polychaetes are able to exploit vacant niches and pristine sediments owing to their ability to swim, crawl, and burrow as well as to be carried passively by currents. They engineer their own environment by burrowing, feeding and respiring, and produce a diverse array of potential sedimentary and endobenthic habitats for other organisms. Changes in the burrowing behavior and modifications of the event beds by the burrowing nereidid were examined using laboratory microcosms with either abiotic sediments or organic-rich mud and pristine sand. In all the microcosms, modification of the environment by the nereidids to permit long-term residence was observed. Moreover, the nereidids demonstrate different behavioural strategies and burrow morphologies based on sediment characteristic and nutrient availability. Alitta virens used a variety of feeding strategy viz. scavenging, surface deposit feeding, suspension feeding, microbial gardening, deposit feeding at depth, and cannibalism. Many nereidids are known to employ suspension feeding using mucus but has never been documented before for A. virens. The extended use of suspension feeding may indicate low availability of biotic sediments for deposit feeding. Though A. virens characteristically produced burrows similar to Arenicolites and Skolithos, burrow morphologies similar to Polykladichnus, Planolites, Palaeophycus, and Thalassinoides were formed under differing sedimentary conditions and over different time scales. According to the rock record, such ichnological diversity might be interpreted as indicating paleoeco- logical diversity, rather than the response of one taxon to changing conditions. On the whole, Alitta virens is an allogenic ecosystem engineer, changing the physical and geochemical characters of its environment by its behaviour. These changes, combined with the widespread occurrence and population longevity of A. virens, demonstrate that burrowing polychaetes are important ecosystem engineers in shallow marine environments, and are likely to have been so over geological time scales.

for more details please visit: Ecosystem Engineer

In the aquaculture sector, wastewater generated is one of the main problems impacting the surrounding environment. Increased aquaculture production implies an increased in waste production and the relevance of these wastes is highly unexploited. Polychaetes might effectively consume these wastes and convert them into high-value nutritional biomass. In such a study exploring the uses of aquaculture generated-waste, the growth and nutritional composition of the polychaete worm Hediste diversicolor (O.F. Muller, 1776) were analyzed. In addition, the capability of H. diversicolor to utilize waste from land-based salmon smolt farms for growth and the nutritional composition of H. diversicolor cultivated on salmon smolt waste was evaluated. The worms were cultured for a period of 30 days and fed on iso-carbonic diets viz. fish feed, smolt waste, microalgae paste, and a 1:5 mixture (based on carbon content) of microalgae paste and smolt waste. It was found that H. diversicolor fed on fish feed grew significantly faster (wet weight basis) than worms grown on the other diets (SGR=0.025 d⁻¹). The least growth was observed in worms fed with a mixture of smolt waste and microalgae (SGR=0.003 d⁻¹). The groups fed on smolt waste and microalgae paste did not show any significant differences in their growths (0.012 d⁻¹vs. 0.014 d⁻¹, respectively). In all the treatments the lipid content ranged between 12 and 16% of DW, where polyunsaturated fatty acids (PUFA) comprise approximately 45% of the total fatty acids. The most abundant fatty acids in the worms were Palmitic acid (C16:0) and eicosapentaenoic acid (C20:5 n-3; EPA). The content of Docosahexaenoic acid (C20:6 n-3; DHA) was found to increase significantly from 1.5% to 4.6–7.8% of the total fatty acids during the experiment for all treatments. In all the treatments, the protein content ranged between 54 and 58% of DW, and the most abundant essential amino acids (EAA) were found to be lysine and leucine. Moreover, the authors calculated that 8% of the smolt production might be accounted for by the potential polychaete biomass produced via recycling smolt waste nutrients. On the whole, this study implies that not only H. diversicolor can be successfully reared on waste sludge from land-based salmon smolt aquaculture, but they also have the ability to convert and accumulate high valuable compounds. Therefore, they can be used to increase the protein and lipid availability and in parallel help in decreasing the harmful environmental impacts due to aquaculture practices.

For more details please visit: Growth and nutritional composition of the polychaete Hediste diversicolor (OF Müller, 1776) cultivated on waste from land-based salmon smolt aquaculture

Two species of macroalgae (Undaria pinnatifida and Gracilaria vermiculophylla) collected from the Russian Far-East were evaluated in laboratory experiments to determine their potential as biofilters. For this purpose, their nutrient uptake potential and their physiological response to wastewater effluents from a maricultural rearing system (mussels’ culture) were measured.

8 g (fresh weight) of macroalgae were placed by replicate in 2 L containers with a continuous flow of wastewater. Water samples were taken to measure the ammonium- and phosphate concentrations and calculate the nutrient uptake rate. During the experiments, the temperature was maintained at 15°C, the irradiance was fixed at 130 µmol photons m^-2 s^-1, and the aeration was supplied continuously.

The results obtained indicated that both species of macroalgae can reduce the nutrient concentrations in the water (up to 70-90% of ammonium and 35-82% of phosphates). Besides, any negative effect on the growth and physiological conditions of both macroalgae species were found.

The study suggests that both species have great potential as a biofilter. Furthermore, the macroalgae species tested have great economic potential, being another good reason to use in IMTA.

For more details please visit: Skriptsova and Miroshnikova (2011). Laboratory experiment to determine the potential of two macroalgae from the Russian Far-East as biofilters for integrated multi-trophic aquaculture (IMTA). Bioresource Technology 102, 3149-3154.

The absorption efficiency of the orange-footed sea cucumber Cucumaria frondosa was evaluated in order to examine its potential as organic-matter extractive species for IMTA systems. For this reason, laboratory and field trials were conducted. In the laboratory, the sea cucumbers were exposed to three different diets: (i) commercial algal diet of T-iso (Isochrysis galbana) or shellfish diet (mix of different microalgae), (ii) modified algae diet (a mixture of diatomaceous earth) and T-iso and (iii) mixture of particles found at local salmon farms. For the field trial, sea cucumbers were maintained in three different locations exposed to natural conditions.

Cucumaria frondosa (source: Peabody Museum of Natural History)

The absorption efficiency estimated in the field trial was 70%, while in the laboratory trials ranged between 68 to 85%. Sea cucumbers were able to consume aquaculture waste in both kinds of experiments. The results obtained in the present study demonstrated that C. frondosa presents the capacity to reduce the organic matter from aquaculture wastes and it has the potential to be used as an organic-matter extractive species in IMTA systems.

For more details visit Nelson et al. (2012). The absorption efficiency of the suspension-feeding sea cucumber, Cucumaria frondosa, and its potential as an extractive integrated multi-trophic aquaculture (IMTA) species. Aquaculture 370–371, 19–25.