{"id":19,"date":"2017-11-16T17:05:38","date_gmt":"2017-11-16T21:05:38","guid":{"rendered":"https:\/\/www2.whoi.edu\/staff\/template-blue-prepop\/?page_id=19"},"modified":"2022-12-20T09:42:41","modified_gmt":"2022-12-20T13:42:41","slug":"physical-biological-interactions","status":"publish","type":"page","link":"https:\/\/www2.whoi.edu\/staff\/dralston\/areas-of-research\/physical-biological-interactions\/","title":{"rendered":"Physical-biological interactions"},"content":{"rendered":"\n\n\t

Physical-biological interactions<\/h1>\n

For many organisms in estuaries and coastal that are sessile or swim relatively slowly, environmental conditions such as stratification, turbulence, or other water properties present primary controls on their viability. Working closely with biologists, we are interested in exploring how the physical framework affects biological response. The harmful algae Alexandrium fundyense<\/em> can cause paralytic shellfish poisoning and has major economic impacts through shellfishing closures. We have been examining how physical processes enhance a recurring estuarine bloom in Nauset estuary<\/a> on Cape Cod, and used a simple model to show how vertical migration<\/a> can explain observed distributions in the Gulf of Maine.\u00a0 Other biophysical collaborations have looked at how oyster survival in the Hudson<\/a> depends on river discharge and may shift with future climate conditions, and on how beach contamination<\/a> depends on tidally modulated fluxes of groundwater through the sand.<\/p>\n

Selected publications<\/h2>\n\t\t\t\t\n\t\t\t\t\"RalstonEtal_Estuaries_2015_NausetHabModel8_396633\"\n\t\t\t\t<\/a>\n\t

Stratification increases residence time and growth of harmful algal bloom<\/h3>\n

Ralston, DK, ML Brosnahan, SE Fox, KD Lee, and DM Anderson, 2015.\u00a0Temperature and residence time controls on an estuarine harmful algal bloom: Modeling hydrodynamics and\u00a0Alexandrium fundyense<\/em>\u00a0in Nauset estuary<\/a>.\u00a0Estuaries and Coasts<\/em>, doi:10.1007\/s12237-015-9949-z.<\/p>\n

We use a highly resolved, 3-d model to simulate the hydrodynamics and A. fundyense<\/em>\u00a0bloom in\u00a0Nauset estuary on Cape Cod over multiple years. The physical and biological properties in the model were evaluated with quantitative skill metrics by comparison with moored and survey data over a four year period. While the\u00a0A. fundyense<\/em> model is based on existing models for the Gulf of Maine bloom, we found that significant modifications were required to represent the Nauset bloom, including earlier cyst germination, greater maximum growth rates, and a different functional form of the mortality term driving bloom termination. \u00a0Using the model we found that residence times of cells in the three salt ponds of Nauset were long compared with the cell doubling time, allowing the blooms to grow rapidly rather than being flushed to the coastal ocean. Retention in the ponds depended on the vertical migration pattern (cells avoid the surface layer where most of the tidal exchange occurs) and stratification (reduces vertical mixing of cells into the surface layer). \u00a0The bloom was relatively insensitive to nutrient concentrations due to the eutrophic conditions of the estuary.<\/p>\n\t\t\t\t\n\t\t\t\t\"RalstonEtal_LO_2014_NausetDegreeDay_fig10_365713\"\n\t\t\t\t<\/a>\n\t

Using degree days to predict a harmful algal bloom<\/h3>\n

Ralston, DK, BA Keafer, ML Brosnahan, and DM Anderson, 2014.\u00a0Temperature dependence of an estuarine harmful algal bloom: Resolving interannual variability in bloom dynamics using a degree day approach<\/a>.\u00a0Limnol. Oceanogr.<\/em>, 59(4):1112-1126, doi:10.4319\/lo.2014.59.4.1112.<\/p>\n

Nauset Estuary on Cape Cod\u00a0has a recurrent\u00a0harmful algal bloom of the dinoflagellate Alexandrium fundyense that\u00a0leads to nearly annual closure to shellfishing. Major A. fundyense blooms were\u00a0observed in 4 consecutive years. Max concentrations exceeded 1 million cells\/L, and were greatest in three salt ponds\u00a0at the edges of the estuary. Bloom timing varied among the ponds and among years, and was associated with\u00a0differences in water temperature.\u00a0A growing degree-day calculation was used to account interannual variability and\u00a0spatial gradients in temperature on growth rate and population development, and it collapsed variability in the\u00a0timing of bloom onset, development, and termination. This\u00a0relatively simple metric may be useful as an early-warning indicator for HABs in Nauset and similar systems with\u00a0localized, self-seeding blooms.<\/p>\n\t\t\t\t\n\t\t\t\t\"RalstonEtal_JPR_2007_verticalMigration_fig3_365694\"\n\t\t\t\t<\/a>\n

Asynchronous vertical migration of dinoflagellates<\/h3>\n

Ralston, DK, DJ McGillicuddy, and DW Townsend, 2007.\u00a0Asynchronous vertical migration and bimodal distribution of motile phytoplankton<\/a>.\u00a0J. Plankton Res<\/em>., 29(9), 803-821, doi:10.1093\/plankt\/fbm061.<\/p>\n

Some phytoplankton can exploit deep sources of nutrients with vertical\u00a0migration: photosynthesis near the surface, transit to depth, nutrient uptake,\u00a0and back to the surface. If the cycle takes less than 24 h, then\u00a0it can be synchronized to the day\/night cycle.\u00a0If it takes longer than\u00a024 h, then migration may be asynchronous.\u00a0Many observations have found bimodal vertical distributions of phytoplankton, with maxima near the surface and the nutricline.\u00a0We show how bimodal distributions may result from asynchronous\u00a0vertical migration, modeling the\u00a0dinoflagellate Alexandrium fundyense<\/em> in conditions similar to those in the Gulf of\u00a0Maine. Migration is regulated by\u00a0internal nutritional state-organisms swim down when depleted of nitrogen,\u00a0and return to the surface after nutrient uptake. Depending on growth rate,\u00a0uptake rate and swimming speed, phytoplankton distributions can be bimodal or\u00a0unimodal.<\/p>\n\n","protected":false},"excerpt":{"rendered":"

Physical-biological interactions For many organisms in estuaries and coastal that are sessile or swim relatively slowly, environmental conditions such as stratification, turbulence, or other water properties present primary controls on their viability. Working closely with biologists, we are interested in exploring how the physical framework affects biological response. The harmful algae Alexandrium fundyense can cause…<\/p>\n","protected":false},"author":147,"featured_media":0,"parent":13,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/pages\/19"}],"collection":[{"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/users\/147"}],"replies":[{"embeddable":true,"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/comments?post=19"}],"version-history":[{"count":3,"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/pages\/19\/revisions"}],"predecessor-version":[{"id":346,"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/pages\/19\/revisions\/346"}],"up":[{"embeddable":true,"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/pages\/13"}],"wp:attachment":[{"href":"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-json\/wp\/v2\/media?parent=19"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}