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Shallow and sheltered marine embayments in urbanized areas are prone to the accumulation of pollutants, but little is known about the historical baselines of such marine ecosystems. Here we study foraminiferal assemblages, geochemical proxies and sedimentological data from 1.6 m long sediment cores to uncover ∼ 500 years of anthropogenic pressure from mining, port and industrial activities in the Gulf of Trieste, Italy. From 1600 to 1900 AD, normalized element concentrations and foraminiferal assemblages point to negligible effects of agricultural activities. The only significant anthropogenic activity during this period was mercury mining in the hinterlands of the gulf, releasing high amounts of mercury into the bay and significantly exceeding the standards on the effects of trace elements on benthic organisms. Nonetheless, the fluctuations in the concentrations of mercury do not correlate with changes in the composition and diversity of foraminiferal assemblages due to its non-bioavailability. Intensified agricultural and maricultural activities in the first half of the 20th century caused slight nutrient enrichment and a minor increase in foraminiferal diversity. Intensified port and industrial activities in the second half of 20th century increased the normalized trace element concentrations and persistent organic pollutants (PAH, PCB) in the topmost part of the core. This increase caused only minor changes in the foraminiferal community because foraminifera in Panzano Bay have a long history of adaptation to elevated trace element concentrations. Our study underlines the importance of using an integrated, multidisciplinary approach in reconstructing the history of environmental and anthropogenic changes in marine systems. Given the prolonged human impacts in coastal areas like the Gulf of Trieste, such long-term baseline data are crucial for interpreting the present state of marine ecosystems.

The ecological consequences of climate change on marine ecosystems remains poorly understood, particularly for ecological communities that reside in enclosed basins, which limit marine species in their ability to migrate. Here we use assemblages of late Quaternary fossils mollusks preserved in nearshore sediments to explore how nearshore marine benthic communities responded to past climate changes in the northern Adriatic. We focus on three time periods: (1) the last interglacial (

The size of the bivalve Corbula gibba increased by a factor of two during the 20 century in the Gulf of Trieste and at Poprodelta in the northern Adriatic Sea. However, it is unclear whether present-day large-sized populations of this species have analogues either in the older Holocene record of the northern Adriatic Sea and/or in earlier pre-Holocene record of the Mediterranean Sea and Paratethys and what mechanisms are responsible for this trend. Here, we assess temporal size variation in Holocene death assemblages of C. gibba in the NW and NE Adriatic, in combination with age dating based on radiocarbon-calibrated amino acid racemisation and taphonomic clock based on conchiolin preservation. We find that, first, C. gibba populations inhabiting locations with high sediment accumulation rates (death assemblages timeaveraged to decades) prior to the late 20th century were not dominated by large-sized individuals (> 10 mm in length). Second, C. gibba increased in size also at locations with slow sediment accumulation rate in the NE Adriatic (off Istria), but the proportion of large-sized individuals in surface death assemblages (time-averaged to millennia) is small. However, the size increase is stronger when shells without conchiolin preservation (that are probably older than 100- 200 years) are omitted from analyses, indicating that C. gibba grew to sizes > 10 mm effectively in the whole northern Adriatic Sea. Death assemblages off Istria, affected by mixing of the late 20th century large-sized shells with much older, small-sized shells, are thus inert to late 20th century changes in size structure of C. gibba populations, in contrast to death assemblages at sites with high sedimentation rate. We conclude that the temporal shift from right-skewed distributions to bimodal distributions (with high abundance of shells > 10 mm) is a unique feature of the late 20th century and correlates with an increase in the frequency of hypoxia and eutrophication and with delayed recovery of hypoxia-sensitive species in the wake of mass mortality events. Analyses of growth increments indicate that the size increase is primarily underlain by an increase in growth rate.