Kalliopi Pagou

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.

This study presents the impacts of dredge spoil dumping in the pelagic habitat during a 27-month monitoring survey in eastern Mediterranean coastal waters (Saronikos Gulf, Aegean Sea), with a focus on changes in trophic status and eutrophication levels, phytoplankton diversity and bloom dynamics. A number of environmental parameters and phytoplankton metrics were significantly influenced by the dumping operations, specifically phytoplankton diversity indices (number of species, Diatoms:Dinoflagellates ratio) and total abundance, Chlorophyll-a, light transmission, dissolved oxygen and inorganic nutrients, N:P ratio, and the Eutrophication Ιndex (a metric for trophic status assessment). Phosphates started to increase after the first year of dumping operations, shifting the N:P ratio to values lower than 10. A similarity cluster analysis highlighted that the phytoplankton community structure during the pre-dumping and the early-dumping period was clearly discriminated from the period during and after the dumping operations. A clear shift with an increase in the Diatoms:Dinoflagellates ratio was observed immediately after the initiation of dumping operations, which maximized in the dumping site after two years of operations. Diatoms dominated the phytoplankton communities, reaching ~ 95% relative abundance in the dumping site. High biomass producers or potentially toxic diatom species proliferated forming blooms. Pseudo-nitzschia multiseries was the most frequent potentially toxic species. A multivariate analysis (RDA) highlighted that among a suite of phytoplankton metrics plotted against stressors relevant to dumping, the Eutrophication Index, Chlorophyll-a, the diversity index Diatoms:Dinoflagellates ratio and the abundance of the potentially toxic diatom P. multiseries emerged as the most suitable to reflect the responses of phytoplankton communities to dumping. Dredge spoil dumping at sea poses pressures to ecosystem components addressed by the European Marine Strategy Framework Directive (MSFD) monitoring programs. In such a context, this study further supports the role of phytoplankton diversity and blooms as sensitive monitoring elements for the environmental status assessment and dumping management in coastal waters.

Faecal pellet production and content along with egg production of the dominant copepod species Acartia clausi were studied in the Thermaikos Gulf (NW Aegean Sea) during a pre-bloom and a bloom of the toxic dinoflagellate Dinophysis acuminata. Both faecal pellet production (6.8–8.6 ind⁻¹ d⁻¹) and egg production (15.8–47.6 ind⁻¹ d⁻¹) appeared unrelated to the D. acuminata bloom. Less than 11% of the copepod faecal pellets contained one or two D. acuminata cells, almost intact, whereas the other material in the pellets was broken into small pieces or amorphous shapes. The toxin outflux seemed to be insignificant when compared to the mean toxin concentration from the whole D. acuminata population. Finally, the potential grazing impact of A. clausi on D. acuminata during the study period was low.

The estimation of the carrying capacity (CC) is a fundamental process in integrated environmental management, policy making, and decision making. Aquaculture carrying capacity has been studied since the 1960s to allow estimation of the production limits of aquaculture projects and, hence, their maximum economic performance within sustainable limits for the local environment. One major drawback of these approaches is that they can provide CC estimates after a fish farm is installed and operates in a certain location (ex post approaches). This paper approaches the estimation of CC using a Bayesian/CHAID model of profiling information on the environmental quality, geomorphology, and human activities on the adjacent coastal area (land side) using as an indicator the trophic state of the marine area in terms of chlorophyll-a concentration (upper mesotrophic). This way, having the above information for a certain site, it is possible to calculate the maximum annual production of a cage fish farm so that the trophic state of the area will not exceed the environmental goal of the upper mesotrophic level. We examined the effects of 27 different physical, chemical, social and geomorphological parameters on CC (in fish biomass terms). CC was found to be correlated by particulate nitrogen (PN), silicates (Si-SiO₄), salinity, and suspended particulate matter (SPM). The overall relationship found is: Biomass_{at CC level} = +473.762[Chl-a] − 6856.64[PN] + 9.302[Salinity] − 473.5[Si-SiO₄] + 341.864[SPM] − 207.046. The analysis performed allowed us to estimate the maximum levels for each factor to maintain a eutrophication status up to the upper mesotrophic level: particulate nitrogen < 0.018 mg/L, silicates < 0.137 mg/L, salinity > 38 PSU and SPM > 0.815 mg/L. Finally, the current fish farm licensing legislation in Greece concerning the CC estimation algorithm is discussed.