engleski

The bivalve Glycymeris pilosa as a multidecadal environmental archive for the Adriatic and Mediterranean Seas

We evaluated the potential of G. pilosa as an environmental indicator for the Mediterranean region by applying sclerochronological techniques. A sample set of shells (N=50) was live-collected from Pašman Channel in the middle Adriatic Sea with individuals ranging in age from 24 to 69 years (N=44, x=45.6±11.4 years), 5 of which were older than 60. There was strongly synchronous growth among individuals, though increments in 18 samples were not clear enough for crossdating and were discarded from further analysis. Once visual crossdating was completed, growth-increment widths in the remaining 26 individuals were measured. Mean sensitivity was 0.178, mean segment series length was 37.3 years, and interseries correlation, representing the mean correlation between each sample and the average of all others, was 0.592. A master chronology was developed by detrending each measurement time series with a negative exponential function (N=23) or 50-year 50% frequency cutoff cubic spline (N=3). A running EPS calculated over a 30-year window indicated the chronology was robust from 1969 - 2013, though the oldest G. pilosa was measured back to 1948. The chronology significantly and negatively correlated with local summer sea temperatures (ST), especially between August (r=-0.464, p=0.017) and September (r=-0.442, p=0.024). There was also a correlation with a multivariate index of circulation (cyclonic vs. anticyclonic patterns) in the northern Ionian Sea (r=-0.536, p=0.012). In summary, reduced growth tends to occur under warm, saline, periods typical of cyclonic regimes. There was also an apparent terrestrial influence in which growth significantly and positively correlated with November precipitation (r=0.410, p=0.020). This is typically the wettest period of the year during which terrestrial inputs would be at a maximum and most likely to influence nearshore processes. Live and dead G. pilosa shells were also collected from the northern Adriatic Sea, and preliminary analysis indicates the longevity of dead-collected individuals is > 100 yr. Given this longevity, clarity of annual increments, and broad geographic distribution, G. pilosa has considerable potential to test hypotheses relating to environmental variability and biological response in the Mediterranean. Indeed, the power of such analysis could be further expanded if chronologies from the closely related Glycymeris bimaculata and Callista chione, for which preliminary data are promising, can be incorporated.

bivalve ; sclerochronology ; Glycymeris ; Adriatic ; chronology ; growth

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