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Mollusc aquaculture is advocated as a highly sustainable food source and may play an important role in future food security globally. With production increasing worldwide, it is timely to appraise all aspects of aquaculture when considering its expanding role as a food source. In this regard, one regularly overlooked aspect of mollusc aquaculture is waste generation: namely the production of calcareous shells. Shells from the aquaculture industry are widely regarded as a nuisance waste product, yet at the same time, calcium carbonate is mined in the form of limestone and viewed as a valuable commodity. In a time of increased awareness of the need for a circular economy, the aquaculture and seafood industry should consider shells as a valuable biomaterial that can be reused for both environmental and economic benefit. This review discusses the current waste shell issue and identifies large‐scale shell applications that are already in place. Further, it highlights proposed applications that have the potential to be scaled up to address the problem of waste shell accumulations and reduce our reliance on environmentally damaging incineration and landfill disposal. Of the plethora of shell valorisation techniques proposed in the scientific literature, this review will focus only on those that can incorporate large‐scale shell utilisation, and do not require high‐energy processing, and are thus; simple, sustainable and potentially economically viable. Further, this review questions whether, in many cases, shells can provide more inherent value being returned to the marine environment rather than being used in land‐based applications.

Chapelle, G. and Peck, L. S. 2004. Amphipod crustacean size spectra: new insights in the relationship between size and oxygen. Á/ Oikos 106: 167 Á/175.Oxygen availability limits the maximum potential size attainable in benthic gammaridean amphipods from the suborder to the generic level, while also influencing size within species. In this paper we investigate the effect of oxygen on 15 size spectra worldwide, established by compiling maximum length data of more than 2000 amphipod species. We used TS95/5 as a proxy for maximum size and defined this as the threshold size between the 95% smallest and the 5% largest species at any given site. Our data show that beside TS95/5, minimum, mean and modal sizes, as well as all 10% increment threshold sizes (from TS10/90 to TS90/10) also vary significantly with oxygen concentration. Size distributions are very similar in shape from one geographical area to another, whatever the width of the spectrum, hence if overall numbers of species stay constant more small species should coexist at low than at high latitudes. No amphipod species were found in water with an oxygen content lower than the minimum requirement predicted (175 mmol O 2 kg (1 ). Our data also show that minimum adult amphipod size is probably limited by the minimum possible egg size, whereas maximum size is set by the physico-chemic ceiling of oxygen availability.

Most molluscs possess shells, constructed from a vast array of microstructures and architectures. The fully formed shell is composed of calcite or aragonite. These CaCO3 crystals form complex biocomposites with proteins, which although typically less than 5% of total shell mass, play significant roles in determining shell microstructure. Despite much research effort, large knowledge gaps remain in how molluscs construct and maintain their shells, and how they produce such a great diversity of forms. Here we synthesize results on how shell shape, microstructure, composition and organic content vary among, and within, species in response to numerous biotic and abiotic factors. At the local level, temperature, food supply and predation cues significantly affect shell morphology, whilst salinity has a much stronger influence across latitudes. Moreover, we emphasize how advances in genomic technologies [e.g. restriction site‐associated DNA sequencing (RAD‐Seq) and epigenetics] allow detailed examinations of whether morphological changes result from phenotypic plasticity or genetic adaptation, or a combination of these. RAD‐Seq has already identified single nucleotide polymorphisms associated with temperature and aquaculture practices, whilst epigenetic processes have been shown significantly to modify shell construction to local conditions in, for example, Antarctica and New Zealand. We also synthesize results on the costs of shell construction and explore how these affect energetic trade‐offs in animal metabolism. The cellular costs are still debated, with CaCO3 precipitation estimates ranging from 1–2 J/mg to 17–55 J/mg depending on experimental and environmental conditions. However, organic components are more expensive (~29 J/mg) and recent data indicate transmembrane calcium ion transporters can involve considerable costs. This review emphasizes the role that molecular analyses have played in demonstrating multiple evolutionary origins of biomineralization genes. Although these are characterized by lineage‐specific proteins and unique combinations of co‐opted genes, a small set of protein domains have been identified as a conserved biomineralization tool box. We further highlight the use of sequence data sets in providing candidate genes for in situ localization and protein function studies. The former has elucidated gene expression modularity in mantle tissue, improving understanding of the diversity of shell morphology synthesis. RNA interference (RNAi) and clustered regularly interspersed short palindromic repeats ‐ CRISPR‐associated protein 9 (CRISPR‐Cas9) experiments have provided proof of concept for use in the functional investigation of mollusc gene sequences, showing for example that Pif (aragonite‐binding) protein plays a significant role in structured nacre crystal growth and that the Lsdia1 gene sets shell chirality in Lymnaea stagnalis. Much research has focused on the impacts of ocean acidification on molluscs. Initial studies were predominantly pessimistic for future molluscan biodiversity...

The influence of acclimation and substratum on the metabolism of the Antarctic amphipods Waldeckia obesa (Chevreux 1905) and Bovallia gigantea (Pfeffer 1888)

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The trend towards large size in marine animals with latitude, and the existence of giant marine species in polar regions have long been recognized, but remained enigmatic until a recent study showed it to be an effect of increased oxygen availability in sea water of a low temperature. The effect was apparent in data from 12 sites worldwide because of variations in water oxygen content controlled by differences in temperature and salinity. Another major physical factor affecting oxygen content in aquatic environments is reduced pressure at high altitude. Suitable data from high-altitude sites are very scarce. However, an exceptionally rich crustacean collection, which remains largely undescribed, was obtained by the British 1937 expedition from Lake Titicaca on the border between Peru and Bolivia in the Andes at an altitude of 3809 m. We show that in Lake Titicaca the maximum length of amphipods is 2-4 times smaller than other low-salinity sites (Caspian Sea and Lake Baikal).Keywords: size limits; oxygen availability; gigantism; temperature; amphipod Studies investigating the limits set by physical factors on animal size require many species inhabiting a given area. A large number of species living proximally causes selective pressures to drive some close to their maximum potential size. Amphipods meet these criteria better than most other taxa, and the existence of giant species at high latitude is well known (Saintemarie 1991;Poulin & Hamilton 1995). Until recently, only 11 species of amphipod crustaceans had been described from Lake Titicaca (Dejoux 1992). However, a minimum of 93 additional unnamed distinct morphotypes have been described from the 1937 expedition and at least 104 species clearly inhabit the lake (Crawford et al. 1993). The oxygen content of the water in Lake Titicaca is reduced because of its high altitude, and because its salt content is slightly higher than in most lakes (Iltis et al. 1992). The largest amphipod species present has a maximum length of 22 mm, and is yet to be named. This compares with the 90 mm Acanthogammarus grewingkii from Lake Baikal (salinity of 0 psu (practical salinity units)) and the 42 mm Gammaracanthus loricatus from the Caspian Sea (salinity of 13 psu size separating the smallest 95% of species from the largest 5% (hereafter termed TS95/5) as the measure of large size to overcome any potential sampling bias. For Lake Titicaca we measured the largest individuals of the 10 largest morphotypes, and used the threshold between species 5 and 6 as the TS95/5, which is 15.2 mm. This result falls very close to the overall relationship linking TS95/5 for amphipods and water oxygen content (Chapelle & Peck 1999) (figure 1). Thus, high altitude has a similar effect on size to high salinity and temperature because it reduces oxygen availability.It has been argued by Spicer & Gaston (1999) that the oxygen content of water should not affect size in aquatic organisms. They attributed to temperature the trends towards increased size with latitude, and pointed out that oxygen uptak...

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