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This volume comprises invited contributions on important aspects of plant-animal interactions in Mediterranean-type ecosystems, which was the subject of the Sixth International Conference on Mediterranean Climate Ecosystems, held in Crete (Greece), from September 23 to 27, 1991. The subject of plant-animal interactions is fundamental to an understanding of the structure and the function of the Mediterranean-type ecosystems and their rational management.

Understanding the energy flux through food webs is important for estimating the capacity of marine ecosystems to support stocks of living resources. The energy density of species involved in trophic energy transfer has been measured in a large number of small studies, scattered over a 40-year publication record. Here, we reviewed energy density records of Southern Ocean zooplankton, nekton and several benthic taxa, including previously unpublished data. Comparing measured taxa, energy densities were highest in myctophid fishes (ranging from 17.1 to 39.3 kJ g−1 DW), intermediate in crustaceans (7.1 to 25.3 kJ g−1 DW), squid (16.2 to 24.0 kJ g−1 DW) and other fish families (14.8 to 29.9 kJ g−1 DW), and lowest in jelly fish (10.8 to 18.0 kJ g−1 DW), polychaetes (9.2 to 14.2 kJ g−1 DW) and chaetognaths (5.0–11.7 kJ g−1 DW). Data reveals differences in energy density within and between species related to size, age and other life cycle parameters. Important taxa in Antarctic food webs, such as copepods, squid and small euphausiids, remain under-sampled. The variability in energy density of Electrona antarctica was likely regional rather than seasonal, although for many species with limited data it remains difficult to disentangle regional and seasonal variability. Models are provided to estimate energy density more quickly using a species’ physical parameters. It will become increasingly important to close knowledge gaps to improve the ability of bioenergetic and food web models to predict changes in the capacity of Antarctic ecosystems to support marine life.

Offshore platforms are known to act as artificial reefs, though there is on-going debate on whether this effect is beneficial or harmful for the life in the surrounding marine environment. Knowing what species exist on and around the offshore platforms and what environmental variables influence this species assemblage is crucial for a better understanding of the impact of offshore platforms on marine life. Information on this is limited for offshore platforms in the southern North Sea. This study aims to fill this gap in our knowledge and to determine how the composition and the abundance of species assemblages changes with depth and along a distance-from-shore gradient. The species assemblages on five offshore gas platforms in the southern North Sea have been inventoried using Remotely Operated Vehicles inspection footage. A total of 30 taxa were identified. A Generalised Additive Model of the species richness showed a significant non-linear relation with water depth (p = 0.001): from a low richness in shallow waters it increases with depth until 15-20 m, after which richness decreases again. Using PERMANOVA, water depth (p≤0.001), community age (p≤0.001) and the interaction between distance from shore and community age (p≤0.001) showed a significant effect on the species assemblages. Future research should focus on the effect additional environmental variables have on the species assemblages.

Effective ecosystem-based management requires estimates of abundance and population trends of species of interest. Trend analyses are often limited due to sparse or short-term abundance estimates for populations that can be logistically difficult to monitor over time. Therefore it is critical to assess regularly the quality of the metrics in long-term monitoring programs. For a monitoring program to provide meaningful data and remain relevant, it needs to incorporate technological improvements and the changing requirements of stakeholders, while maintaining the integrity of the data. In this paper we critically examine the monitoring program for the Australian fur seal (AFS) Arctocephalus pusillus doriferus as an example of an ad-hoc monitoring program that was co-ordinated across multiple stakeholders as a range-wide census of live pups in the Austral summers of 2002, 2007 and 2013. This 5-yearly census, combined with historic counts at individual sites, successfully tracked increasing population trends as signs of population recovery up to 2007. The 2013 census identified the first reduction in AFS pup numbers (14,248 live pups, -4.2% change per annum since 2007), however we have limited information to understand this change. We analyse the trends at breeding colonies and perform a power analysis to critically examine the reliability of those trends. We then assess the gaps in the monitoring program and discuss how we may transition this surveillance style program to an adaptive monitoring program than can evolve over time and achieve its goals. The census results are used for ecosystem-based modelling for fisheries management and emergency response planning. The ultimate goal for this program is to obtain the data we need with minimal cost, effort and impact on the fur seals. In conclusion we identify the importance of power analyses for interpreting trends, the value of regularly assessing long-term monitoring programs and proper design so that adaptive monitoring principles can be applied.

In the Arctic Ocean, sea-ice habitats are undergoing rapid environmental change. Polar cod ( Boreogadus saida ) is the most abundant fish known to reside under the pack-ice. The under-ice distribution, association with sea-ice habitat properties and origins of polar cod in the central Arctic Ocean, however, are largely unknown. During the RV Polarstern expedition ARK XXVII/3 in the Eurasian Basin in 2012, we used for the first time in Arctic waters a Surface and Under Ice Trawl with an integrated bio-environmental sensor array. Polar cod was ubiquitous throughout the Eurasian Basin with a median abundance of 5000 ind. km −2 . The under-ice population consisted of young specimens with a total length between 52 and 140 mm, dominated by 1-year-old fish. Higher fish abundance was associated with thicker ice, higher ice coverage and lower surface salinity, or with higher densities of the ice-amphipod Apherusa glacialis . The fish were in good condition and well fed according to various indices. Back-tracking of the sea-ice indicated that sea-ice sampled in the Amundsen Basin originated from the Laptev Sea coast, while sea-ice sampled in the Nansen Basin originated from the Kara Sea. Assuming that fish were following the ice drift, this suggests that under-ice polar cod distribution in the Eurasian Basin is dependent on the coastal populations where the sea-ice originates. The omnipresence of polar cod in the Eurasian Basin, in a good body condition, suggests that the central Arctic under-ice habitats may constitute a favourable environment for this species survival, a potential vector of genetic exchange and a recruitment source for coastal populations around the Arctic Ocean.

Terrestrial and marine wildlife populations have been severely reduced by hunting, fishing and habitat destruction, especially in the last centuries. Although management regulations have led to the recovery of some populations, the underlying processes are not always well understood. This study uses a 40-year time series of counts of harbour seals (Phoca vitulina) in the Wadden Sea to study these processes, and demonstrates the influence of historical regional differences in management regimes on the recovery of this population. While the Wadden Sea is considered one ecologically coupled zone, with a distinct harbour seal population, the area is divided into four geo-political regions i.e. the Netherlands, Lower Saxony including Hamburg, Schleswig-Holstein and Denmark. Gradually, seal hunting was banned between 1962 and 1977 in the different regions. Counts of moulting harbour seals and pup counts, obtained during aerial surveys between 1974 and 2014, show a population growth from approximately 4500 to 39,000 individuals. Population growth models were developed to assess if population growth differed between regions, taking into account two Phocine Distemper Virus (PDV) epizootics, in 1988 and 2002 which seriously affected the population. After a slow start prior to the first epizootic, the overall population grew exponentially at rates close to assumed maximum rates of increase in a harbour seal population. Recently, growth slowed down, potentially indicative of approaching carrying capacity. Regional differences in growth rates were demonstrated, with the highest recovery in Netherlands after the first PDV epizootic (i.e. 17.9%), suggesting that growth was fuelled by migration from the other regions, where growth remained at or below the intrinsic growth rate (13%). The seals' distribution changed, and although the proportion of seals counted in the German regions declined, they remained by far the most important pupping region, with approximately 70% of all pups being born there. It is hypothesised that differences in hunting regime, preceding the protection in the 1960's and 1970's, created unbalance in the distribution of breeding females throughout the Wadden Sea, which prevailed for decades. Breeding site fidelity promoted the growth in pup numbers at less affected breeding sites, while recolonisation of new breeding areas would be suppressed by the philopatry displayed by the animals born there. This study shows that for long-lived species, variable management regimes in this case hunting regulations, across a species' range can drive population dynamics for several generations.

Intertidal blue mussel beds are important for the functioning and community composition of coastal ecosystems. Modeling spatial dynamics of intertidal mussel beds is complicated because suitable habitat is spatially heterogeneously distributed and recruitment and loss are hard to predict. To get insight into the main determinants of dispersion, growth and loss of intertidal mussel beds, we analyzed spatial distributions and growth patterns in the German and Dutch Wadden Sea. We considered yearly distributions of adult intertidal mussel beds from 36 connected tidal basins between 1999 and 2010 and for the period 1968–1976. We found that in both periods the highest coverage of tidal flats by mussel beds occurs in the sheltered basins in the southern Wadden Sea. We used a stochastic growth model to investigate the effects of density dependence, winter temperature and storminess on changes in mussel bed coverage between 1999 and 2010. In contrast to expectation, we found no evidence that cold winters consistently induced events of synchronous population growth, nor did we find strong evidence for increased removal of adult mussel beds after stormy winter seasons. However, we did find synchronic growth within groups of proximate tidal basins and that synchrony between distant groups is mainly low or negative. Because the boundaries between synchronic groups are located near river mouths and in areas lacking suitable mussel bed habitat, we suggest that the metapopulation is under the control of larval dispersal conditions. Our study demonstrates the importance of moving from simple habitat suitability models to models that incorporate metapopulation processes to understand spatial dynamics of mussel beds. The spatio-dynamic structure revealed in this paper will be instrumental for that purpose.

In the spring and summer 2014, an outbreak of seal influenza A(H10N7) virus infection occurred among harbor seals (Phoca vitulina) off the coasts of Sweden and Denmark. This virus subsequently spread to harbor seals off the coasts of Germany and the Netherlands. While thousands of seals were reported dead in Sweden, Denmark and Germany, only a limited number of seals were found dead in the Netherlands. To determine the extent of exposure of seals in the Netherlands to influenza A/H10N7 virus, we measured specific antibody titers in serum samples from live-captured seals and seals admitted for rehabilitation in the Netherlands by use of a hemagglutination inhibition assay and an ELISA. In harbor seals in 2015, antibodies against seal influenza A(H10N7) virus were detected in 41% (32 out of 78) pups, 10% (5 out of 52) weaners, and 58% (7 out of 12) subadults or adults. In gray seals (Halichoerus grypus) in 2015, specific antibodies were not found in the pups (n = 26), but in 26% (5 out of 19) of the older animals. These findings indicate that, despite apparent low mortality, infection with seal influenza A(H10N7) virus was geographically widespread and also occurred in grey seals.

Foraging distributions are thought to be density-dependent, because animals not only select for a high availability and quality of resources, but also avoid conspecific interference. Since these processes are confounded, their relative importance in shaping foraging distributions remains poorly understood. Here we aimed to rank the contribution of density-dependent and density-independent effects on the spatio-temporal foraging patterns of eurasian oystercatchers. In our intertidal study area, tides caused continuous variation in oystercatcher density, providing an opportunity to disentangle conspecific interference and density-independent interactions with the food landscape. Spatial distributions were quantified using high-resolution individual tracking of foraging activity and location. In a model environment that included a realistic reconstruction of both the tides and the benthic food, we tested a family of behaviour-based optimality models against these tracking data. Density-independent interactions affected spatial distributions much more strongly than conspecific interference, even in an interference-prone species like oystercatchers. Spatial distributions were governed by avoidance of bill injury costs, selection for high interference-free intake rates and a decreasing availability of benthic bivalve prey after their exposure. These density-independent interactions outweighed interference competition in terms of effect size. We suggest that the bottleneck in our mechanistic understanding of foraging distributions may be primarily the role of density-independent prey attributes unrelated to intake rates, like damage costs in the case of oystercatchers foraging on perilous prey. At a landscape scale, above the finest inter-individual distances, effects of conspecific interaction on spatial distributions may have been overemphasised.