P. Kamermans

Competition in deposit- and suspension-feeding bivalves: experiments in controlled outdoor environments

Experiments were carried out in an intertidal and a subtidal outdoor flow-through basin. The effect of bivalve density on growth and survival was studied in the facultative deposit feeder Macoma balthica (L.) and the obligate suspension feeder Cerastoderma edule L. Patches of 0.2 m2 with densities of maximal 2480 bivalves per m2 were used. In C. edule growth was density independent, whereas in M. balthica growth decreased with density, indicating intraspecicic competition in M. balthica, but not in C. edule. These different feeding in C. edule. In mixed populations, C. edule and M. balthica did nopt clearly influence each others growth and survival, indicating that interspecific competition did not occur between the two species. Our experiments support the hypothesis of levinton (1972), that, on local scale, competition is expected more readily in deposit-feeding communities than in suspension-feeding communities.

Shrimp (Crangon crangon L.) browsing upon siphon tips inhibits feeding and growth in the bivalve Macoma balthica (L.)

Abstract The influence of siphon browsing on the feeding behaviour and growth of Macoma bclthica, a deposit-feeding bivalve, was studied in three manipulative experiments. Browsing was simulated by removing part of the inhalant siphon with scissors, or studied by exposing the bivalves to shrimps (Crangon crangon). Smaller siphons resulted in a reduction of the sediment surface area that could be grazed, and a decrease in siphon activity in M. balthica. Disturbance of the siphons by shrimps also reduced siphon activity. Siphons were reduced in size in the presence of shrimps. Immunological analyses of the stomachs of C. crangon identified this species as a consumer of siphon tips. Growth of M. balthica was negatively influenced by siphon browsing, probably due to three interactive factors: extra energy needed for siphon regeneration, less time available for feeding, and a smaller area from which to collect food. Burying depth was reduced in M. balthica with smaller siphons. However, individuals with similar siphon size were buried less deep in the sediment when not exposed to siphon browsing, suggesting an immediate response to absence of browsers.

Morphological differences in Macoma balthica (Bivalvia, Tellinacea) from a Dutch and three southeastern United States estuaries

Abstract Field collections of the bivalve Macoma balthica in the Dutch Wadden Sea and three southeastern United States estuaries revealed morphological differences between populations of the two sides of the Atlantic Ocean. Individuals of the same age showed much larger shell lengths at the American stations. In addition, bivalves of the same body weight had higher siphon weights at the American stations than at the Dutch stations. This difference in siphon size was related to their burying depths. The American population, which invested more in heavier siphons, was able to burrow much deeper into the sediment (up to 30 cm). Deep burial may be an adaptation to avoid exposure to the high southern temperatures. Furthermore, it may serve as a refuge from blue crab predation. The results of our comparison between the southern American population and the European support the suggestion that populations of M. balthica living in these two regions should be considered separate and sibling species.

The feasibility of offshore aquaculture and its potential for multi-use in the North Sea

Following the Blue Growth ambition of the European Commission, the interest in the potential of offshore is growing. This paper aimed to contribute to the discussion on the feasibility of offshore aquaculture development and its potential for multi-use with other maritime activities. A review of national and international projects forms the basis of the paper, where the Dutch North Sea is used as a case-study area. Analysis of technical, economic and ecological boundaries indicated that the potential of fish culture is limited, that seaweed cultivation is likely to gain potential when challenges related to processing will be overcome and that mussel culture has the highest potential in the near future. The North Sea is an area where many stakeholders claim space, which might set boundaries to the number of sites available for mussel culture. Competing claims are a potential source of conflict but may also lead to mutual benefits when smart combinations are sought, e.g. with wind parks, fisheries and nature conservation; especially, the possibility of combining mussel culture in or around wind parks is worthwhile to be further explored. A spatial distribution model adapted for the Dutch North Sea conditions demonstrated that offshore mussel production in wind farms can be profitable. Yet, the commercial interest for offshore development of mussel culture is still limited. Actions required to stimulate further development of the offshore mussel industry are presented for the government, the private sector, research institutes and civil society organizations.

Blue mussel hatchery technology in Europe

Abstract: To date, European mussel culture has relied entirely on wild seed from suspended collectors or mussel beds. One problem faced by blue mussel producers is the unpredictability of seed supply, the amounts of wild seed available being extremely variable from year to year. A second problem is that recently spawned mussels cannot be sold due to insufficient meat. Hatcheries can complement wild seed supply. Hatcheries also allow triploid induction that produces non-maturing mussels. In this chapter, the different steps in hatchery production of mussel seed are described. A final section addresses future trends.

Culturing Chaetoceros muelleri using simplified media with different N sources: effects on production and lipid content

Land-based bivalve aquaculture depends on large-scale cultures of live microalgae for food. The intensity of large-scale microalgal production is important for cost-effectiveness. Using Walne’s medium as the control, simplified media containing nitrogen, phosphorus, silica, iron, manganese and vitamins were designed to determine the impact of nitrogen source and molar N:P ratio (sodium nitrate, NO3 9:1, ammonium chloride, NH4 9:1 and NH4 25:1) on growth, dry-weight biomass, culture longevity and lipid content of Chaetoceros muelleri, a diatom commonly used in shellfish aquaculture. During the exponential phase (day 6), dry-weight production in simplified media was similar to controls, indicating that this microalga can grow successfully on simplified media and use ammonium as the nitrogen source. The cultures grown on nitrate or ammonium differed in their time-course. Low nitrogen concentration in cultures grown with nitrate caused the collapse of these cultures within 11–13 days, after a short stationary phase. Cultures grown with ammonium had a longer stationary phase and were still alive on day 20, in spite of the low nitrogen concentrations observed after day 13 in cultures grown with NH4 9:1. During stationary phase (day 18) there was an increase in lipid content of algae under conditions of low nitrogen availability (NH4 9:1) and extended low phosphorus availability (NH4 25:1). Considering dry weight production, culture longevity, nutrient efficiency and lipid composition, simplified media containing ammonium, phosphorus, silica, iron, manganese and vitamins are a viable and profitable choice for batch culture of C. muelleri. In the exponential phase, the simplified medium NH4 9:1 was as effective as the control. Overall, both of the simplified media using ammonium are effective and suitable, depending on the purpose of the cultures and whether lipid contents (NH4 9:1), dry weight biomass (NH4 25:1) or nitrogen input and output (NH4 9:1) are desired.

European flat oysters on offshore wind farms: additional locations: opportunities for the development of European flat oyster (Ostrea edulis) populations on planned wind farms and additional locations in the Dutch section of the North Sea

To determine the relative suitability for development of self-sustaining European flat oyster (Ostrea edulis) beds, potential areas for offshore wind farms in the Dutch Exclusive Economic Zone (EEZ) were analysed following Smaal et al (2017). The studied locations are the new wind farm zones “Hollandse Kust (“noordwest”, “west” and “zuidwest”)”, “IJmuiden Ver” and the remaining lot of the North of the Frysian Islands Wind Farm Zone, but also 13 additional potential locations on the EEZ (i.e. CP4-CP6 and CP9-17) and, in addition, the nature area location Borkum Reef Ground (Borkumse Stenen). This research is performed within EZ-program Beleidsondersteunend Onderzoek (BO). Biotic and abiotic factors of importance for flat oyster survival, growth, reproduction and recruitment, were compared for the 8 wind farm locations of Smaal et al. (2017) and the 18 new locations. For the locations on the Dutch EEZ the following habitat factors are important for flat oyster beds: shear stress, suspended sediment, larval retention, temperature, sediment composition and food availability. Presence in historic distribution area was used as a verification. Average shear stress, suspended sediment and temperature are within the range considered suitable for the development of an oyster bed at all locations. Thus, these factors do not discriminate between locations. Maximum shear stress is too high at one location and the sediment is too silty at 7 locations. However, habitat restoration efforts may make the environment more suitable, e.g. by placing shell material or 3D structures which elevate the oysters from the bottom. Based on the analysis described in this report we recommend to select the following locations that are suitable for flat oyster restoration. 1. Best: Borssele Wind Farm Zone, Buitengaats (part of the Gemini wind park) and CP9 (within historic distribution and high larval retention); 2. Very good: Hollandse Kust (zuidwest) Wind Farm Zone (high larval retention); 3. Good: Offshore Windpark Egmond aan Zee, Prinses Amalia Windpark, Windpark Eneco Luchterduinen, Hollandse Kust (zuid) Wind Farm Zone, Hollandse Kust (noord) Wind Farm Zone (medium larval retention); 4. Suitable: the remaining lot of the North of the Frysian Islands Wind Farm Zone, Zee-energie (part of the Gemini wind park), Borkum Reef Ground (Borkumse Stenen) (within historic distribution, medium or high larval retention, but locally too high maximum shear stress or too silty); 5. Suitable with introduction of substrate: CP5, CP6 (medium or high larval retention, but too silty without introduction of substrate).

Recirculation nursery systems for bivalves

In order to increase production of bivalves in hatcheries and nurseries, the development of new technology and its integration into commercial bivalve hatcheries is important. Recirculation aquaculture systems (RASs) have several advantages: high densities of the species can be cultured resulting in a cost-effective production system; optimal temperature maximizes production and allows rapid turnover of the product; stable water quality improves growth rate and minimizes stress and potential loss by diseases. Pilot RAS systems were developed for seed rearing of oysters (Crassostrea gigas), scallops (Pecten maximus), mussels (Mytilus edulis) and clams (Ruditapes decussatus). Optimal feed addition and waste matrix were determined. Based on this, system flow rates were designed. Seed growth in the pilot RAS systems was compared at different renewal rates and with growth in flow-through systems (FTS). All four species can be reared in RAS and showed similar growth in RAS and in FTS or in RAS with a higher renewal rate. RAS can keep O2, nitrogen and pH within the desired range. Temperature was generally higher in RAS than in FTS, probably due to heat induced by the pump circulating the water. The supply of sufficient amount of food in combination with a desire to reduce the renewal rate calls for use of concentrated feed in RAS.