Plankton Response to Salinity Changes in the WAP: Application of a 1D physical-biological model

MARINA, TOMÁS IGNACIO; SCHLOSS, IRENE R.; DUMONT, DANY; MOMO, FERNANDO R.

Congreso; XII SCAR Biology Symposium; 2017

Glacier melting rate in the Western Antarctic Peninsula (WAP) has increased over the past 50 years, promoting freshwater input into the water column, especially in shallow coastal environments. Freshwater is likely impacting on the structure and function of coastal food webs. Experimental studies in the WAP have demonstrated an association between salinity changes and the dominance of certain phytoplankton groups in coastal ecosystems of the WAP: a microcosm study performed in Potter Cove (Isla 25 de Mayo/King George Is.) with a natural marine phytoplankton assemblage exposed to low salinity conditions (30 psu) showed a replacement of big centric diatoms by small pennate ones. Here we study phytoplankton and zooplankton responses to salinity fluctuations in a turbulent environment applying a coupled physical-biological model. We used a one-dimensional water column model (General Ocean Turbulence Model) coupled to a simple biological model with two phytoplankton groups (large and small) and two zooplankton groups (microzooplankton and mesozooplankton) simulating plankton dynamics. The model was modified to take into account the osmotic stress: classes of phytoplankton had different optimum salinity habitat. Forcing of the model was done with local meteorological data, and temperature and salinity profiles of 2009-10 and 2010-11 summer seasons from Potter Cove. Outcomes of the model show distinct phytoplankton responses between seasons, where dominance in the phytoplankton community differs due to salinity variation. In 2009-10, when salinity presented a relatively constant value of 34 psu, simulations resulted in lower concentrations of small phytoplankton and higher concentrations of large phytoplankton. On the other hand, in season 2010-11 when surface salinity fluctuated between 30 and 34 psu, small cells were the dominant group. Interestingly, if both phytoplankton groups are considered, the dynamics of the phytoplankton community is similar, with low concentrations in spring (Oct-Nov) and high concentrations in summer (Dec-Feb). Microzooplankton dynamics was tightly coupled with phytoplankton behavior, showing a strong prey-predator relationship. Our results of plankton response to salinity variation in Potter Cove suggest that phytoplankton responds to a threshold in salinity, upon which the community structure varies between two dominant groups. Ongoing changes in environmental conditions, such as larger freshwater inputs, might lead to a marked and irreversible shift in the plankton assemblage of coastal areas in the WAP.