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Organic matter input and processing was studied in 2 contrasting sediments (Stn 115FINE and Stn 330COARSE) in the southern North Sea. The sediments are subjected to similar hydrodynamic conditions, but Stn 115FINE underlies a high turbidity zone, making it a fine, low-permeability sediment. Monthly data on chlorophyll a (chl a), d13C and d15N of particulate organic matter in the water column and sediment showed that the algal spring bloom deposition created a strong vertical gradient of sedimentary chl a at Stn 115FINE. Macrobenthic biomass (78 ± 60 g Cm-2, mean ± SD) was dominated by suspension feeders, suggesting biological mediation of the organic matter input. In contrast, the offshore Stn 330COARSE is a coarse, high-permeability sediment in which chl a penetrated centimeters deep due to physically mediated input. The macrobenthic community, low in biomass (3.8 ± 2.4 g Cm-2), was dominated by mobile polychaetes and epibenthic amphipods, which is characteristic of physically disturbed sediments. Overall, sediment characteristics played an important but indirect role in the organic matter input and processing. At Stn 115FINE, a large macrobenthic community developed that mediated the input of organic matter to the sediment through herbivore and predatory pathways. At Stn 330COARSE, in contrast, organic matter input seemed to be dominated by physical processes. Overall, the fraction of algal carbon degraded in the sediment was higher at Stn 115FINE than at Stn 330COARSE, indicating that the physical input at Stn 330COARSE was less efficient than the biological input at Stn 115FINE.

Climate change is affecting large-scale oceanic processes. How and when these changes will impact those reliant on marine resources is not yet clear. Here we use end-to-end modeling to track the impacts of expected changes through the marine ecosystem on a specific, small community: Cochamó, in the Gulf of Ancud wider area, Chile. This area is important for Chilean fisheries and aquaculture, with Cochamó reliant on both lower and upper trophic level marine resources. We applied the GOTM-ERSEM-BFM coupled hydro-biogeochemical water-column model to gauge lower-trophic level marine ecological community response to bottom-up stressors (climate change, ocean acidification), coupled to an existing Ecopath with Ecosim model for the area, which included top-down stressors (fishing). Social scientists also used participatory modeling (Systems Thinking and Bayesian Belief Networking) to identify key resources for Cochamó residents and to assess the community’s vulnerability to possible changes in key resources. Modeling results suggest that flagellate phytoplankton abundance will increase at the cost of other species (particularly diatoms), resulting in a greater risk of harmful algae blooms. Both climate change and acidification slightly increased primary production in the model. Higher trophic level results indicate that some targeted pelagic resources will decline (while benthic ones may benefit), but that these effects might be mitigated by strong fisheries management efforts. Participatory modeling suggests that Cochamó inhabitants anticipate marine ecosystem changes but are divided about possible adaptation strategies. For climate change impact quantification, detailed experimental studies are recommended based on the dominant threats identified here, with specific local species.

The net growth rate of marine zooplankton entering the Westerschelde estuary was investigated using an advective-dispersive transport model that simulates zooplankton biomass behaving conservatively in the estuary. Total biomass of marine zooplankters in the Westerschelde was much lower than what would be expected based on transport alone, indicating negative growth rates in the estuary. Including a net consumption term in the transport model allowed the estimation of total net mortality. About 3% of all marine zooplankters that enter the Westerschelde with the flood currents are retained in the estuary, where they die. On average, 5% of the total marine zooplankton biomass in the estuary died per day. Each year a net amount of about 1500 t of zooplankton dry weight (DW) is imported from the sea to the estuary. Thus in the Westerschelde the marine zooplankton persists mainly due to continuous replenishment from the sea. Average net production/biomass rates of the major marine zooplankton species varied from -0.02 g DW (gDW)-1 d-1 (Temora longicornis) to -0.39 g DW (gDW)-1 d-1 (Pseudocalanus elongatus). In the estuary, the differential mortality of these species resulted in shifts in dominance within the zooplankton community relative to that in the sea. Possible causes of this zooplankton mortality are discussed.

Within the European Network of Excellence (NoE) on Marine Biodiversity and Ecosystem Functioning (MarBEF), marine biodiversity scientists from across Europe have been brought together to focus on 3 broad themes. Theme 1 describes large-scale (and long-term) distribution patterns of marine biodiversity, Theme 2 examines the consequences of changes in marine biodiversity for the functioning of marine ecosystems, and Theme 3 explores and disseminates the socio-economic consequences of changes in marine biodiversity and biodiversity-mediated processes. Within MarBEF Theme 1, a large collaborative effort has produced an integrated database of species occurrence information (MacroBen), which contains data of quantitative samples of soft-sediment benthic infauna collected in European continental waters, from the Arctic to the Black Sea. Papers in this Theme Section describe initial studies based on the database. The late Prof. John S. Gray led activities within MarBEF Theme 1 for the first 2.5 yr, during which time the majority of the work described in this Theme Section was set in motion, and he continued to be involved in the work until his untimely death. We dedicate this body of work to his memory.

The blue mussel (Mytilus species complex) is an important ecosystem engineer, and salinity can be a major abiotic driver of mussel functioning in coastal ecosystems. However, little is known about the interactive effects of abiotic drivers and trematode infection. This study investigated the combined effects of salinity and Himasthla elongata and Renicola roscovita metacercarial infections on the filtration capacity, growth, and condition of M. edulis from the Baltic Sea. In a laboratory experiment, groups of infected and uninfected mussels were exposed to a wide range of salinities (6-30, in steps of 3) for 1 mo. Shell growth was found to be positively correlated with salinity and optimal at 18-24 at the end of the experiment, imposed by constraints in shell calcification under lower salinities. Mussel shell growth was not affected by H. elongata infection. While salinity had only a minor effect on tissue dry weight, infected mussels had a significantly lower tissue dry weight than uninfected mussels. Most interestingly, the combination of salinity and trematode infections negatively affected the mussels’ condition indices at lower salinity levels (6 and 9), suggesting that trematode infections are more detrimental to mussels when combined with freshening. A significant positive effect of salinity on mussel filtration was found, with an initial optimum at salinity 18 shifting to 18-24 by the end of the experiment. These findings indicate that salinity and parasite infections act as synergistic stressors for mussels, and enhance the understanding of potential future ecosystem shifts under climate change-induced freshening in coastal waters.

Oyster transports are among the leading anthropogenic vectors of coastwise introduction of non- indigenous species. Using the oyster industry of the Netherlands as a model system, we investigated the rela- tionship between vector strength (number of invasions) and vector tempo (magnitude and frequency of transport) in analyzing and predicting invasion patterns. We re- viewed literature on oyster-associated species introduc- tions, analyzed the scale of commercial oyster imports, and collected and identified epiflora from Pacific oyster shells. A total of 35 protist, algal, and invertebrate species have been introduced to the Netherlands with oysters, and we found 41 species of macroalgae on transported oysters. However, the number of introductions and quan- tity of oysters imported are not necessarily positively cor- related, particularly in the past 20 yr, when oyster imports decreased but the rate of introductions increased. The discrepancy between vector tempo and strength can be explained by unreported imports and vector characteris- tics: a single oyster may harbor a large number of species which are introduced with their substrate, thus facilitat- ing establishment. Further, the recently developed exten- sive Pacific oyster reefs in Dutch waters provide a suit- able substrate, enabling establishment even after low propagule pressure introduction events. Assumptions that are made about crucial parameters need to be recon- sidered: reported propagule pressure is not the same as actual propagule pressure; per-episode diversity of po- tential inoculants is not at a fixed level without episodic unpredictable spikes, and the recipient environment is not static. With increasing interest in predicting invasion patterns, caution must be taken in assuming that reduced propagule pressure will lead to reduced invasions.

The vertical distribution patterns of the nematode community and of the 10 most dominant nematode species on an intertidal flat in the Schelde Estuary (the Molenplaat, The Netherlands) are described at specific time intervals over a tidal cycle. The observed distribution profiles indicate that vertical migrations occur and are species-specific. The predatory Enoploides longispiculosus and the deposit-feeding Daptonema normandicum migrated upwards at incoming tide and downwards when the flat became exposed, while another deposit feeder,Daptonema setosum, did the opposite. Several abiotic and biotic factors may contribute to the observed patterns. Hydrodynamics, pore water drainage and episodic steep increases in temperature upon low tide exposure as well as vertical movements of prey organisms may have been of particular relevance at the time and site of sampling. However, the impact of each of these factors needs further investigation. The present study corroborates the dynamic nature of vertical distribution profiles of nematodes in intertidal sediments, highlighting the importance of sampling time with respect to the tide, as well as a species approach.