Estuaries are highly productive and serve as vital habitats for numerous decapod crustacean species. However, the environmental conditions within estuaries are often highly dynamic and subject to large changes in salinity and temperature that occur on seasonal and tidal scales. Not all of the species occupying these habitats are adept in coping with changes in these environmental conditions. This dissertation describes the influence of low salinity conditions on the 1) habitat preference, 2) feeding behaviour and 3) digestive physiology of crustaceans inhabiting estuaries. I have primarily focussed on a weak osmoregulator, the Dungeness crab, Cancer magister , but have also compared some aspects with the blue crab, Callinectes sapidus , an efficient osmoregulator. Recordings of temperature, salinity and depth using archival data tags affixed to crabs in the field showed that adult Cancer magister spent the majority of time in deep water where they were not subjected to stressful salinity or temperature conditions. When crabs did enter into the estuary, these forays often corresponded to times of increased food abundance and crabs avoided challenging temperature and salinity conditions by exploiting the estuary during nocturnal high tides when salinities were higher and temperatures lower. In the laboratory, experiments in temperature and salinity gradients showed that Cancer magister alters thermal and salinity preference behaviour in response to a food stimulus. Thus, while Cancer magister primarily avoids challenging environmental conditions, they may forage in these areas during times of increased food abundance. Since crabs may be foraging in low salinity, the effects of low salinity and starvation on feeding behaviour of Cancer magister were examined. The likelihood of feeding, the amount of food consumed and the time spent feeding were all reduced in low salinity. However, these responses were partially overridden by starvation. Removal of the sinus gland (the potential source of inhibitory hormones that regulate feeding) revealed that changes in feeding behaviour result from hormonal regulation rather than physiological limitation. Although crabs regulate food intake in response to hyposaline exposure, they may be exposed to low salinity conditions at any point in the digestive cycle. Therefore the effects that low salinity has on digestive physiology and how these effects were influenced by osmoregulatory ability were examined. In Cancer magister , exposure to low salinity post-feeding resulted in a prioritization towards the responses to low salinity, resulting in a reduction in oxygen uptake that corresponded to a reduced rate of gut contraction and an increase in gastric evacuation time. These reductions also corresponded with a delay in digestive enzyme secretion and a subsequent reduction in the post feeding increase in circulating free amino acids in the hemolymph. In contrast, Callinectes sapidus , an efficient osmoregulator, displayed a summation of the metabolic responses to low salinity exposure and digestion. Accordingly, digestive processes continued unabated in low salinity, resulting in a build up of free amino acids in the hemolymph.
Curtis, Daniel Luke, "Integrated responses of crustaceans inhabiting estuaries to the challenges of feeding and digestion in low salinity" (2009). UNLV Theses, Dissertations, Professional Papers, and Capstones. 91.
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Abstract: Dynamic marine environments can shape complex spatial and temporal patterns in the population connectivity of marine species, and this is often exemplified in species with long larval phases. In this paper, researchers used a genotyping-by-sequencing (GBS) approach to examine fine-scale spatial and temporal genomic variation among Dungeness crab Cancer magister larval recruits sampled in the California Current Ecosystem.
Specifically, they compared samples collected during expected- and late-season recruitment time periods within two consecutive years (2017 and 2018) at two sites in Oregon, USA (Yaquina Bay and Coos Bay). Evidence was found for high gene flow between the expected- and late-season recruits within each year and at both sites based on 1389 neutral loci. In contrast, strong genetic differentiation was observed between these two groups within each year and at both sites based on variation at two putatively adaptive loci. Contrary to prediction, the magnitude of genetic differentiation between these two seasonal groups was greater in 2017 when the Pacific Decadal Oscillation was stronger, upwelling was weaker, and the spring transition was later. Spatial genetic variation was not observed within 2017 or 2018. Comparing across years, expected- and late-season groups were differentiated at putatively adaptive loci.
Interestingly, strong genetic differentiation was also observed between late-season groups across the years. Researchers found no evidence for cohesive larval dispersal among recruits based on genetic relatedness estimates. Overall, findings provide evidence for high connectivity within Dungeness crab, but suggest that selective pressures and ocean conditions influence the genetic composition of larval recruits both intra- and inter-annually.
Pestilens est morbus contagiosus etc. As Ptolemy says, plague is a contagious sickness that people take one from the other. And Galen says also that plague is the aerial element turning from its proper moderation to corruption and putrefaction. For this is the cause of it: the evil-smelling putrescent air that rises from gross earthy vapours mixing with the thin parts of the air, or gross mist that rises from stagnant water such as ditches of the city and places p.149
It is asked here why pure thin air is best, for Galen says thin bright air is good for the maintenance of health, and that the blood and the spirits are purified by it; therefore pure air is good at this season. Item, everything that lessens and evacuates the corruption of the humours in general is to be recommended, therefore since pure transparent(?) air does these things, it is best. Item, Almansor says whenever the beasts of the earth leave their lairs and the places where they dwell underground, such as mice and weasels, stoats(?) badgers and rabbits; and the birds that are under the ground, such as bitterns and stonechats(?) leave their eggs and nests and flee from the corrupt vapours of the earth to the pure bright air, as Nature teaches them; hence since the nature of brutish beasts understands that pure air is the best, so human nature understands that it is best, and therefore pure air is best at this season. Item, Gilbert says if the spring be cold and wet, along with dark air and often with heavy, dark, black clouds, this signifies plague that year, therefore the contrary is best. Item, Hippocrates says everything that comforts the heart and expels its diseases such as syncope, cardiaca passio and the like is good; therefore since pure air exerts these powers it is best at this season. Item, Galen says the bodies that are purging themselves from their gross superfluities, such as phlegmatic people and melancholics, will be well at this season, therefore as it is pure air from which these powers are derived, it is best. Item, Galen says in the same place, everyone who has a complexion contrary to the complexion of the p.150
Item, Magister Ricardus says everything that increases the sperm increases the humours in the body, such as cold foods like lettuce, melons, pomegranates, vinegar, ripe grapes, carrots(?) beet root, borrage, almond milk and the like, is good. Therefore since gross air fattens and increases these things, it is best. Item, the doctors say it behoves in time of plague to fly to glens and dark woods and other damp places, so according to this it is gross air that is best. Item, everything by which the body is purged, such as coition, hard labour, work at a forge, a dry bath or dry feeding (?) is bad at this season; according to this gross air is best. Item, everything that increases the spirits and prevents sleep, such as the smell of fragrant apples, ambergris, quinces, and lily flowers, the smell of mullen, and musk, nenufar flowers, violets, and sally-leaves, white rose flowers, and elder-blossoms, is good at this season; therefore since gross air does these things, it is best, as Johannes Mesue says.
Avicenna says in the first book, in the eighth chapter of perverse seasons that there are twelve rules that should be regarded in time of plague, concerning the seasons of the weather. The first rule: if the winter be cold and wet, and the wind frequently north, and the summer wet and windy, there will be a great plague amongst children the following autumn, and moreover flux of the belly, tertian fever, and ulceration of the guts i. e. dysentry, and the like. The second rule: if the winter be windy and wet, and the wind south, the spring dry and the wind NE there will frequently be abortions and many other diseases among pregnant women that year; and there will also be disease of the eyes, bloody flux i. e. dysentery, and ague, scrofula, constriction of the nose and every sickness that comes from rheum particularly. The third rule: if the winter be dry and the wind NW, the spring wet and the wind frequently south, there will be acute fevers, disease of the p.151
It is clear here that every star and every other heavenly body has three risings i. e. (C)osmicus and (A)cronicus and (H)eliacus. This is Cosmicus: when a star or heavenly body rises under the sun to the east, and goes with it (the sun) until it sets on the west of the world. Acronicus moreover is when it rises to the west, and proceeds in company with the sun to walk the natural sphere which encircles the universe both land and sea, so that it sets to the east. And it is called acronicus from the word cronon, for ‘cronon’ in Greek is the same as ‘contrary’ in Gaelic, that is to say it rises in the west and finishes in the east. Heliacus moreover is when a star or heavenly body rises in the circle of the natural or material sphere on the horizon(?) and proceeds with the sun in the circle which is called Zodiac. And know, that this is Zodiac: the place where the sun is throughout the year, and it is divided into thirty degrees, and the sun is in each degree for thirty days and ten hours and a halfhour. 152ee80cbc
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