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Metal concentrations (Cu, Cr, Ni, Zn, Fe, Mn, Cd, and Pb) in marine indicator species were assessed for the study of metal pollution in the Eastern Ionian Sea during the cold period of the year (December 2018 to February 2019). Limpets and sea urchins were collected from natural populations at seven coastal stations while mussels were transplanted at three near-shore stations in the study area. Mixed mesozooplankton samples were selected from a twelve-station offshore network. Additionally, fish, shrimp, and shortfin squid samples were collected by trawling. For the first time, metal concentrations in marine animals were measured in an extended variety of organisms in the area. Higher metal concentrations in limpets, sea urchins, and mussels were observed in the wider area of the two ports located at the sampling area's eastern and southern geographical borders. Levels in zooplankton also followed the same spatial variation. In general, metal concentrations in the investigated organisms were within the same range as those in other non-impacted Mediterranean areas. Accordingly, metal levels in the flesh of the fish, shrimps, and the mantle of shortfin squids did not reveal any risk for human consumption. Metal levels from the present study are proposed as a reference state for the area, while future deviations should be evaluated taking into account potential changes in the natural and anthropogenic pressures on the specific coastal marine ecosystem., Competing Interests: Declarations. Ethics approval: Not applicable. Consent to participate: Not applicable. Consent for publication: Not applicable. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Plankton are key ecological indicators for assessing the impacts of human-induced pressures like climate change and waste-water discharge. Here, 26 years (1988-2015) of biweekly in-situ chlorophyll-a concentration, mesozooplankton biomass and remotely-sensed sea surface temperature (SST) data are utilized to investigate long-term changes of plankton biomass and timing of growth (phenology) in relation to warming, in a coastal region of the Saronikos Gulf (Aegean Sea). A Waste-Water Treatment Plant (WWTP) was established in 1995, leading to decreased nutrient concentrations circa 2004. Overall, the results indicate an interplay between warming and changes in ecological status. During higher nutrient input (1989-2004), a temporal mismatch between zooplankton and phytoplankton, and a positive zooplankton growth-SST association, are evident. Conversely, in the warmer, less mesotrophic period 2005-2015, an earlier timing of zooplankton growth (related to copepod abundance) synchronizes with phytoplankton growth, including a secondary autumn growth period. Concurrently, an abrupt negative interannual relationship between SST and mesozooplankton, and a summer biomass decrease (linked with cladoceran abundance) are observed. This work provides evidence that current warming could alter plankton abundance and phenology in nearshore Eastern Mediterranean ecosystems, suggesting shifts in plankton community composition that could trigger potential cascading effects on higher trophic levels., (© 2023. The Author(s).)

Spatial variability of Cd, Cu, Cr, Ni, Zn, Fe, Mn, Pb and metallothionein (MT) concentrations were determined in mesozooplankton samples along the west-east axis of the Cretan Passage in the western Levantine Sea (Eastern Mediterranean). Metal and MT values from the present study are proposed as background levels, due to the lack of substantial anthropogenic activities in the area, where only maritime traffic and atmospheric deposition could be potential sources. Higher concentrations, of both metals and MTs, were recorded mainly at the western stations indicating higher metal bioavailability than in the eastern part. An inverse relationship of the metal zooplankton levels with zooplankton biomass, abundance and vital rates (production, respiration and ingestion rates), as well as salinity, was evident. We discuss the hypothesis that physical and biological characteristics of the marine environment, affecting growth dynamics of phytoplankton and zooplankton communities, may also act on metal uptake in oligotrophic marine systems., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

HABs pose a threat to coastal ecosystems, the economic sector and human health, and are expanding globally. However, their influence on copepods, a major connector between primary producers and upper trophic levels, remains essentially unknown. Microalgal toxins can eventually control copepod survival and reproduction by deterring grazing and hence reducing food availability. We present several 24-h experiments in which the globally distributed marine copepod, Acartia tonsa , was exposed to different concentrations of the toxic dinoflagellate, Alexandrium minutum , grown under three N:P ratios (4:1, 16:1 and 80:1), with the simultaneous presence of non-toxic food (the dinoflagellate Prorocentrum micans ). The different N:P ratios did not affect the toxicity of A. minutum , probably due to the low toxicity of the tested strain. Production of eggs and pellets as well as ingested carbon appeared to be affected by food toxicity. Toxicity levels in A. minutum also had an effect on hatching success and on the toxin excreted in pellets. Overall, A. minutum toxicity affected the reproduction, toxin excretion and, to an extent, the feeding behavior of A. tonsa. This work indicates that even short-term exposure to toxic A. minutum can impact the vital functions of A. tonsa and might ultimately pose serious threats to copepod recruitment and survival. Still, further investigation is required for identifying and understanding, in particular, the long-term effects of harmful microalgae on marine copepods.

We compare the nature of copepod outfluxes of nonliving matter, the factors controlling their rate and their fate, and finally their role, particularly their relative importance in the carbon and nitrogen cycle. Copepods release dissolved matter through excretion and respiration and particulate matter through production of faecal pellets, carcasses, moults, and dead eggs. Excretion liberates several organic C, N, and P compounds and inorganic N and P compounds, with inorganic compounds constituting the larger part. The faecal pellets of copepods are covered by a peritrophic membrane and have a highly variable size and content. There is less information on the nature of other copepod particulate products. The weight-specific rates of posthatch mortality, respiration, excretion, and faecal pellet production have similar C or N levels and are higher than those of moulting and egg mortality. In general, most important factors controlling these rates are temperature, body mass, food concentration, food quality, and faunistic composition. Physical and biological factors govern the vertical fate of copepod products by affecting their sedimentation speed and concentration gradient. The physical factors are sinking speed, advection, stratification, turbulent diffusion, and molecular diffusion. They influence the sedimentation speed and degradation of the copepod products. The biological factors are production, biodegradation (by zooplankton, nekton, and microorganisms) and vertical migration of copepods (diel or seasonal). Physical degradation and biodegradation by zooplankton and nekton are faster than biodegradation by microorganisms. The most important copepod outfluxes are excretion and faecal pellet production. Excretion offers inorganic nutrients that can be directly used by primary producers. Faecal pellets have a more important role in the vertical transport of elements than the other particulate products. Most investigation has focused on carbon burial in the form of copepod faecal pellets, measured by sediment traps, and on the role of ammonia excretion in nutrient recycling. Full evaluation of the role of copepod products in the transport and recycling of elements and compounds requires a quantification of all copepod products and their different fates, particularly detritiphagy, remineralization, and integration as marine snow.