Shallow coves in Chesapeake Bay have abundant food and serve as nursery grounds for juvenile blue... more Shallow coves in Chesapeake Bay have abundant food and serve as nursery grounds for juvenile blue crabs. In this study, we examined the relationships between the diet of very small (4–40mm CW) juvenile blue crabs and the benthic infauna in shallow, unvegetated nursery coves. We compared infauna in benthic samples with gut contents of juvenile blue crabs from six shallow coves in each of two sub-estuaries (Rappahannock and York Rivers) in Chesapeake Bay, Virginia, USA. Benthic communities differed depending on river and location, with abundant clams in upriver regions and abundant polychaetes in downriver regions. Juvenile crabs, like adults, appeared to be opportunistic feeders,
with gut contents including clams, amphipods, polychaetes, small crustaceans, plant matter, and detritus. There was a positive relationship between polychaetes in the benthic samples and in crab guts, suggesting that juvenile crabs are opportunistic feeders on polychaetes in the benthos. Moreover, Ivlev’s electivity index and foraging ratio showed that clams and polychaetes were selectively eaten at all locations. Alternatively, crabs selectively rejected amphipods. Crab densities corresponded positively with polychaete densities, which suggests that there may be bottom–up control of crab
distributions and that food resources are important in nursery habitats.
Populations of the eastern oyster, Crassostrea virginica, in Chesapeake Bay have been severely de... more Populations of the eastern oyster, Crassostrea virginica, in Chesapeake Bay have been severely depleted by overfishing, habitat degradation, and disease. Information on age and size structure of these populations is critical for management and restoration decisions. Unfortunately, age structure is often not directly measured but rather derived from size structure, which can be inaccurate and imprecise. In this study, I directly estimated both age and size from a modern oyster population to determine the relationship between shell length and age, and whether shell length is a useful proxy for age. I counted growth bands to estimate age in a cohort of oysters sampled on a restoration reef in Baines Creek, a tributary of the Elizabeth River in Portsmouth, Virginia. I analyzed length-at-age data using the von Bertalanffy growth model, which is commonly applied to fisheries data (Onishi and Akamine, 2006). Additionally, the Baines Creek size-and-age data were compared to the size-and-age structure of a Pleistocene fossil reef from the lower Chesapeake Bay that developed under similar temperature and salinity conditions as Baines Creek. Results suggest the Baines Creek is a healthy restored reef, and that Pleistocene oysters have a larger average maximum size and lifespan, but modern oysters have a faster growth rate. Possible drivers for these patterns include overfishing, an increase in sedimentation rates, and increased nutrient availability in modern oysters as compared to Pleistocene oysters in Chesapeake Bay
File List MbPopModel.m (MD5: fbf47bb585a7f041100da16138dc8ab0) Pop_and_Pred.m (MD5: 435f0942c819b... more File List MbPopModel.m (MD5: fbf47bb585a7f041100da16138dc8ab0) Pop_and_Pred.m (MD5: 435f0942c819b03520e41bea6ec7756e) dA.m (MD5: 67e503d79e2373c3756d7eb322ae4a84) typeIII.m (MD5: 3664dfa10b84d28960b8bd952e66e058) typeIIIH.m (MD5: 7cc47c1e7de06bbf7fb824bcdb03b6e8) typeIII_P.m (MD5: dc445d6b130c070b8f73ffbb9779b08f) typeIIIH_P.m (MD5: f5cf34d4a88340c688394a1be50f9ad7) Description <b>MbPopModel.m-</b> This MATLAB function will model the population of <i>Macoma balthica</i> over a user specified length of time. Required sub-functions that are called within this function are dA.m, which creates a population projection matrix using input parameters and tyepIII.m and typeIIIH.m which are a series of linked ordinary differential equations describing the population dynamics during the summer in normoxic and hypoxic areas of the river. The three inputs to the function are:<br> param- A vector with five parameters: <i>MN</i>, <i>MH</i>, <i>RH</i>, <i>RN</i>, <i>d</i><br> Where <i>M</i> is the proportion of the juvenile population that reproduces in their first year, and <i>R</i> is the number of recruits produced by each female, and d is the areal proportion of the river that remains normoxic. Inits(<i>JN</i>, <i>AN</i>, <i>JH</i>, <i>AH</i>)- A vector with the initial population density of the Juveniles (<i>J</i>), and Adults (<i>A</i>) in the normoxic (subscript <i>N</i>) and hypoxic (subscript <i>H</i>). J- the number of years the model is to be run for. Base parameter estimates used in the paper are: -- TABLE: Please see in attached file. -- <b>Pop_and_Pred.m</b>- This MATLAB function will model the population (output <i>pop</i>) of <i>Macoma balthica</i> and provide an annual estimate of the biomass (output <i>B</i>) and number (output <i>N</i>) of clams consumed by blue [...]
Shallow coves in Chesapeake Bay have abundant food and serve as nursery grounds for juvenile blue... more Shallow coves in Chesapeake Bay have abundant food and serve as nursery grounds for juvenile blue crabs. In this study, we examined the relationships between the diet of very small (4–40mm CW) juvenile blue crabs and the benthic infauna in shallow, unvegetated nursery coves. We compared infauna in benthic samples with gut contents of juvenile blue crabs from six shallow coves in each of two sub-estuaries (Rappahannock and York Rivers) in Chesapeake Bay, Virginia, USA. Benthic communities differed depending on river and location, with abundant clams in upriver regions and abundant polychaetes in downriver regions. Juvenile crabs, like adults, appeared to be opportunistic feeders,
with gut contents including clams, amphipods, polychaetes, small crustaceans, plant matter, and detritus. There was a positive relationship between polychaetes in the benthic samples and in crab guts, suggesting that juvenile crabs are opportunistic feeders on polychaetes in the benthos. Moreover, Ivlev’s electivity index and foraging ratio showed that clams and polychaetes were selectively eaten at all locations. Alternatively, crabs selectively rejected amphipods. Crab densities corresponded positively with polychaete densities, which suggests that there may be bottom–up control of crab
distributions and that food resources are important in nursery habitats.
Populations of the eastern oyster, Crassostrea virginica, in Chesapeake Bay have been severely de... more Populations of the eastern oyster, Crassostrea virginica, in Chesapeake Bay have been severely depleted by overfishing, habitat degradation, and disease. Information on age and size structure of these populations is critical for management and restoration decisions. Unfortunately, age structure is often not directly measured but rather derived from size structure, which can be inaccurate and imprecise. In this study, I directly estimated both age and size from a modern oyster population to determine the relationship between shell length and age, and whether shell length is a useful proxy for age. I counted growth bands to estimate age in a cohort of oysters sampled on a restoration reef in Baines Creek, a tributary of the Elizabeth River in Portsmouth, Virginia. I analyzed length-at-age data using the von Bertalanffy growth model, which is commonly applied to fisheries data (Onishi and Akamine, 2006). Additionally, the Baines Creek size-and-age data were compared to the size-and-age structure of a Pleistocene fossil reef from the lower Chesapeake Bay that developed under similar temperature and salinity conditions as Baines Creek. Results suggest the Baines Creek is a healthy restored reef, and that Pleistocene oysters have a larger average maximum size and lifespan, but modern oysters have a faster growth rate. Possible drivers for these patterns include overfishing, an increase in sedimentation rates, and increased nutrient availability in modern oysters as compared to Pleistocene oysters in Chesapeake Bay
File List MbPopModel.m (MD5: fbf47bb585a7f041100da16138dc8ab0) Pop_and_Pred.m (MD5: 435f0942c819b... more File List MbPopModel.m (MD5: fbf47bb585a7f041100da16138dc8ab0) Pop_and_Pred.m (MD5: 435f0942c819b03520e41bea6ec7756e) dA.m (MD5: 67e503d79e2373c3756d7eb322ae4a84) typeIII.m (MD5: 3664dfa10b84d28960b8bd952e66e058) typeIIIH.m (MD5: 7cc47c1e7de06bbf7fb824bcdb03b6e8) typeIII_P.m (MD5: dc445d6b130c070b8f73ffbb9779b08f) typeIIIH_P.m (MD5: f5cf34d4a88340c688394a1be50f9ad7) Description <b>MbPopModel.m-</b> This MATLAB function will model the population of <i>Macoma balthica</i> over a user specified length of time. Required sub-functions that are called within this function are dA.m, which creates a population projection matrix using input parameters and tyepIII.m and typeIIIH.m which are a series of linked ordinary differential equations describing the population dynamics during the summer in normoxic and hypoxic areas of the river. The three inputs to the function are:<br> param- A vector with five parameters: <i>MN</i>, <i>MH</i>, <i>RH</i>, <i>RN</i>, <i>d</i><br> Where <i>M</i> is the proportion of the juvenile population that reproduces in their first year, and <i>R</i> is the number of recruits produced by each female, and d is the areal proportion of the river that remains normoxic. Inits(<i>JN</i>, <i>AN</i>, <i>JH</i>, <i>AH</i>)- A vector with the initial population density of the Juveniles (<i>J</i>), and Adults (<i>A</i>) in the normoxic (subscript <i>N</i>) and hypoxic (subscript <i>H</i>). J- the number of years the model is to be run for. Base parameter estimates used in the paper are: -- TABLE: Please see in attached file. -- <b>Pop_and_Pred.m</b>- This MATLAB function will model the population (output <i>pop</i>) of <i>Macoma balthica</i> and provide an annual estimate of the biomass (output <i>B</i>) and number (output <i>N</i>) of clams consumed by blue [...]
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with gut contents including clams, amphipods, polychaetes, small crustaceans, plant matter, and detritus. There was a positive relationship between polychaetes in the benthic samples and in crab guts, suggesting that juvenile crabs are opportunistic feeders on polychaetes in the benthos. Moreover, Ivlev’s electivity index and foraging ratio showed that clams and polychaetes were selectively eaten at all locations. Alternatively, crabs selectively rejected amphipods. Crab densities corresponded positively with polychaete densities, which suggests that there may be bottom–up control of crab
distributions and that food resources are important in nursery habitats.
with gut contents including clams, amphipods, polychaetes, small crustaceans, plant matter, and detritus. There was a positive relationship between polychaetes in the benthic samples and in crab guts, suggesting that juvenile crabs are opportunistic feeders on polychaetes in the benthos. Moreover, Ivlev’s electivity index and foraging ratio showed that clams and polychaetes were selectively eaten at all locations. Alternatively, crabs selectively rejected amphipods. Crab densities corresponded positively with polychaete densities, which suggests that there may be bottom–up control of crab
distributions and that food resources are important in nursery habitats.