Microplastics, plastics particles <5 mm in length, are a widespread pollutant of the marine environment. Oral ingestion of microplastics has been reported for a wide range of marine biota, but uptake into the body by other routes has received less attention. Here, we test the hypothesis that the shore crab (Carcinus maenas) can take up microplastics through inspiration across the gills as well as ingestion of pre-exposed food (common mussel Mytilus edulis). We used fluorescently labeled polystyrene microspheres (8–10 μm) to show that ingested microspheres were retained within the body tissues of the crabs for up to 14 days following ingestion and up to 21 days following inspiration across the gill, with uptake significantly higher into the posterior versus anterior gills. Multiphoton imaging suggested that most microspheres were retained in the foregut after dietary exposure due to adherence to the hairlike setae and were found on the external surface of gills following aqueous exposure. Results were used...

Uptake and retention of microplastics by the shore crab Carcinus maenas.

Hemoglobin (Hb) occurs in all the kingdoms of living organisms. Its distribution is episodic among the nonvertebrate groups in contrast to vertebrates. Nonvertebrate Hbs range from single-chain globins found in bacteria, algae, protozoa, and plants to large, multisubunit, multidomain Hbs found in nematodes, molluscs and crustaceans, and the giant annelid and vestimentiferan Hbs comprised of globin and nonglobin subunits. Chimeric hemoglobins have been found recently in bacteria and fungi. Hb occurs intracellularly in specific tissues and in circulating red blood cells (RBCs) and freely dissolved in various body fluids. In addition to transporting and storing O2 and facilitating its diffusion, several novel Hb functions have emerged, including control of nitric oxide (NO) levels in microorganisms, use of NO to control the level of O2 in nematodes, binding and transport of sulfide in endosymbiont-harboring species and protection against sulfide, scavenging of O2 in symbiotic leguminous plants, O2sensing in ...

Nonvertebrate Hemoglobins: Functions and Molecular Adaptations

In this article, an attempt is made to review the presently known, completely identified crustacean neuropeptides with regard to structure, function and distribution. Probably the most important progress has been made in the elucidation of a novel family of large peptides from the X-organ-sinus gland system which includes crustacean hyperglycemic hormone (CHH), putative molt-inhibiting hormone (MIH) and vitellogenesis (=gonad)-inhibiting hormone (VIH). These peptides have so far only been found in crustaceans. Renewed interest in the neurohemal pericardial organs has led to the identification of a number of cardioactive/myotropic neuropeptides, some of them. unique to crustaceans. Important contributions have been made by immunocytochemical mapping of peptidergic neurons in the nervous system, which has provided evidence for a multiple role of several neuropeptides as neurohormones on the one hand and as local transmitters or modulators on the other. This has been corroborated by physiological studies. The long-known chromatophore-regulating hormones, red pigment concentrating hormone (RPCH) and pigment-dispending hormone (PDH), have been placed in a broader perspective by the demonstration of an additional role as local neuromodulators. The scope of crustacean neuropeptide research has thus been broadened considerably during the last years.

Crustacean neuropeptides: structures, functions and comparative aspects.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones.

7 – Biochemistry of Digestion

Contrary to previous reports, oxygen consumption is maintained over a wide range of external oxygen tensions in the lobster Homarus americanus . In animals acclimated to the experimental conditions this response is mediated by increased branchial pumping, increased effectiveness of oxygen uptake by the gills and an increased contribution by the respiratory pigment to the oxygen delivered to the tissues. Circulatory blood oxygen levels are generally high in lobsters resting in well-aerated water. Mechanisms for detection of hypoxia and possible control mechanisms are discussed.

Respiratory and Circulatory Responses to Hypoxia in the Lobster Homarus Americanus

Periods of simultaneous apnoea and bradycardia lasting for up to 20 min have been recorded from specimens of Homarus americanus isolated under experimental conditions but otherwise exposed to no direct stress. The onset of the response and the resumption of normal activity occurred abruptly and simultaneously in both respiratory and circulatory parameters. A study of the response leads the authors to propose a central control area which can inhibit both branchial and cardiac pumps simultaneously. Blood oxygen tensions were monitored during the response and possible mediating effects of oxygen are discussed.

Simultaneous apnoea and bradycardia in the lobster Homarus americanus

1. Changes in the rate and force of scaphognathite beating, irrigation volume, oxygen utilization, oxygen consumption and heart rate during acclimation in response to the experimental conditions and in response to long-term hypoxic exposure have been measured in the crayfish Orconectes virilis .

2. Immediately following placement in the experimental chamber the animals exhibited very high levels of respiratory and circulatory performance. These levels decreased slowly and stable minimal performance levels could be measured only after 2-3 days. A 3-day acclimation period under normoxic conditions thus routinely preceded hypoxic experiments to ensure measurement of unmasked hypoxic responses.

3. Two responses to hypoxia were routinely observed: an initial hyperirrigation response maintained oxygen consumption by increased branchial water flow. This response was not maintained, but oxygen consumption remained at pre-hypoxic levels while pumping rates decreased.

4. Possible mechanisms of acclimation to hypoxia are discussed.

Respiratory Responses to Long-Term Hypoxic Stress in the Crayfish Orconectes virilis

1. The movements of the scaphognathites of the lobster, Homarus americanus , and the resulting thrust, were resolved in two dimensions accompanied by attack angle changes. Correlation of these scaphognathite and related body movements with branchial hydrostatic pressures during forward and reversed pumping were effected by simultaneously recording on video tape.

2. Forward pumping maintains a negative pressure within the branchial chambers of 2·5-10 mm H2O superimposed on a maintained negative pressure relative to the outside of 0-5 mm H2O. The scaphognathite, by assuming a negative attack angle to the water during the upstroke of the beat, produces the positive pressure of reversals.

3. Contraction of the epimeral attractor muscle appears to contribute to the reestablishment of branchial negativity following each reversal. This muscle inserts on the epimera and by contraction enlarges the branchial chamber.

4. The role of reversals is discussed and it is concluded that their primary function is to clean foreign material from the border of hairs which filter incurrent water. Reversed beating may be a general response to all unusual stimuli to the respiratory system.

5. The pattern of water flow into and through the gill chambers was determined. The relative volume of water entering each incurrent aperture between the legs was calculated and indicated that approximately equal volumes of water entered each aperture. It is concluded that forward pumping adequately irrigates all gill surfaces.

J. L. Wilkens

Papers

Respiratory and Circulatory Responses to Hypoxia in the Lobster Homarus Americanus

Simultaneous apnoea and bradycardia in the lobster Homarus americanus

Respiratory Responses to Long-Term Hypoxic Stress in the Crayfish Orconectes virilis

Aspects of branchial irrigation in the lobster Homarus americanus. I. Functional analysis of scaphognathite beat, water pressures and currents.

Cardiac and ventilatory responses to stress and to neurohormonal modulators by the shore crab, Carcinus maenas