Hatching phenology of the brown shrimp Crangon crangon in the southern North Sea: inter-annual temperature variations and climate change effects

Crangon crangon is a key species in the southern North Sea and the most valuable target of coastal fisheries. Recruitment and stock development are highly variable. As recruitment is based on larval production, we determined the timing of larval release in relation to the annual temperature course and the winter water temperature. The annual temperature courses over 50 years (1961–2010) showed a strong inter-annual variation but also a continuous increase in winter water temperatures. The share of ovigerous C. crangon females starts to increase in October/November, reaches a maximum in May, and decreases continuously towards September/October. During cold winters (0°C), egg development is strongly retarded and hatching of larvae culminates in a sharp peak in early June. Warm winters (6°C) facilitate embryogenesis and the earliest larvae hatch in January and February. The temperature sums from November to April correlated significantly with the lowest winter water temperatures. Consequently, the lowest winter water temperatures provide a good indication for the appearance of C. crangon larvae and an estimate for the match or mismatch with the spring bloom and the production of microzooplankton, the preferred food of C. crangon larvae

Extracellular phosphoesterases of invertebrate origin: underrated actors in phosphorus recycling?

Extracellular enzymes contribute substantially to the remineralisation of organic matter in aquatic systems. Marine invertebrates release endogenous enzymes through activities such as sloppy feeding or egestion, but the significance of such processes is widely unexplored. We compared functional key properties such as activity, stability, and apparent molecular masses of extracellular phosphatases from faeces of the marine crustaceans Idotea balthica, Palaemon varians, and Homarus gammarus with those of their digestive organs. A fluorescent substrate was used to examine enzyme activity qualitatively on agarose plates and quantitatively in microplate assays. Apparent molecular masses and enzyme stability were examined by native substrate gel electrophoresis (NSGE). Active extracellular phosphatase were present in the faeces of all tested species. NSGE activity band patterns were similar in digestive tissue extracts and faeces extracts. The initial enzyme activity retained for about 2 days, but thereafter rapidly decreased. Activity band patterns of digestive organs and faeces of I. balthica remained consistent for up to 72 h. Antibiotic treatment did not reduce phosphatase activity in the faeces of I. balthica and H. gammarus but in the faeces P. varians. Because of the comparatively high activities in the faeces, the electrophoretic similarity between faeces and digestive organs, and the limited durability of the enzymes in faeces extracts, we conclude that the studied crustaceans release predominantly endogenous, rather than bacterial phosphatases through faeces. These can substantially contribute to the pool of active extracellular phosphatases and the recycling of phosphorus in aquatic systems. The wider physiological and ecological context is discussed

Does microplastic induce oxidative stress in marine invertebrates?

In the last decades the production of plastic increased continuously. Simultaneously, environmental pollution by plastic became a rising issue. Marine litter can have adverse effects on animals. Some species may get trapped in lost fishing nets or they may starve to death upon ingestion of plastic which may clog their digestive tracts. Degradation of plastic items generates a continuously increasing number of smaller-sized particles. Microplastic, finally ranging in the µm-size classes can have adverse effects on marine invertebrates upon ingestion. Most of these effects can be attributed to the cellular level. How can particles in the microscale harm organisms? In this study the ingestion of microplastic by marine invertebrates and, moreover, the possible transfer into cells of the digestive tract will be examined. As model species we chose the Atlantic ditch shrimp (Palaemon varians). This species inhabits coastal regions, estuaries, and brackish water systems which are most affected by anthropogenic pollution. Effects will be determined in the cells of the midgut gland of P. varians. Measuring the formation of reactive oxygen species (ROS) is a suitable method to detect cellular stress. Quantification of ROS-formation will be done by confocal laser scanning microscopy and the aid of the fluorogenic substrates Dihydroethidium (DHE) and 2’, 7’ - Dichlorodihydrofluorescin diacetate (DCFDA). The results will help to identify cellular reactions after exposure to microparticles and indicate the toxicological impact on cells and whole organisms

Lipolytic enzymes in the gastric fluids of Cancer pagurus are capable of hydrolyzing biodegradable plastic

The pollution of the environment by plastics is a perpetual problem that poses a great challenge to mankind. A promising strategy to counteract the increasing pollution is the innovation and development of biodegradable materials. However, biodegradable plastics reach into the marine environment in the same way as conventional plastics and can also be ingested by marine organisms. There is a wide variety of different polymers that are used in biodegradable materials, such as polylactic acid (PLA), polybutylene succinate (PBS) or polyhydroxyalkanoates (PHAs). Those compounds are known to be enzymatically degradable by several enzymes under certain conditions. Once ingested by marine organisms such as crustaceans, the highly active mixture of enzymes in their digestive tracts may break down compounds and facilitate degradation. In this study, the hydrolytic activity of gastric fluids from Cancer pagurus on different biodegradable and conventional plastics was evaluated with pH Stat titration. The enzymes capable of hydrolyzing biodegradable plastics were isolated from the gastric fluid and characterized using several analytical methods. Separated protein fractions with a high amount of lipolytic enzymes showed the highest potential on hydrolyzing biodegradable plastics

Bioplastics in the Sea: Rapid In-Vitro Evaluation of Degradability and Persistence at Natural Temperatures

The progressive substitution of petroleum-based polymers, such as polyethylene, polyvinylchloride, or polyethylene terephtalate, by so-called bioplastics facilitated the development and production of many new materials. The continuously refined properties of bioplastic compounds and their blends enable various applications. With growing production and utilization of bioplastic products, these materials are increasingly discarded into the environment. Although many of these materials are labeled biodegradable, there is limited information about their degradability under environmental conditions. We tested the enzymatic degradability of five bioplastic compounds with the rapid pH-Stat titration assay at environmentally relevant seawater temperatures between 5 and 30°C and pH 8.2. These plastics, issued from the European Horizon 2020 Project ´Bioplastics Europe´, are based on polylactic acid (PLA), polybutylene succinate (PBS), and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV). Suspensions of microparticles (< 200 µm) were incubated with each of the three hydrolytic enzymes, protease, lipase, and esterase. A PLA-based compound blended with polybutylene adipate terephthalate (PBAT) showed the highest hydrolysis rate of 30 nmol·min-1 when incubated with lipase at 30°C. All other materials showed low hydrolysis rates of less than 10 nmol·min-1. Below 20°C, hydrolysis almost ceased. Plate clearing assays with the same enzymes at 37°C and pH 5 and pH 8, respectively, largely confirmed the results of the pH-Stat titration assays. Our findings indicate that there is a potential degradation of most of the materials with at least one of these hydrolytic enzymes. Nonetheless, the rate of enzymatic degradation under environmentally relevant conditions is low, which indicates only a marginal degradability of bioplastics in the marine environment