The aim of this brief research report was to define the consequential shifts in biomass and trophic structure of an ecosystem surrounding an offshore monoculture fish farm in Israel. It attempts to clarify the impact of the industry expansion and input of artificial fish pellets on functional group biomasses. We account for the direct addition of artificial food pellets, the metabolic wastes from the caged fish in a mass-balance food web model (Ecopath), as well as the temporal expansion of the farm's production capacity to 21,000 t over a 30-year period (Ecosim). In the static mass-balance model of the food web, the addition of the fish cages at its current production size of 1000 t does not adversely affect the system, and trophic energy transfer is still dependent on primary production versus the detrital pathway. The model suggests a semi-stable ecosystem with low trophic interactions. With time, the increase in fish farming at the site is characterized by an increase of all functional group biomasses at the site over the 30year period. The accumulation in detritus most notably correlates to greater biomass for all benthic functional niches and their secondary consumers. It is, therefore, apt to develop an indicator species list to indicate negative site disturbance. In summary, the sediment column condition will be the main indicator for ecosystem stability, as well as the increase in apex predators that are attracted to the site from the accumulation of discards at the cage bottom.

Sharks, as apex predators, play an essential ecological role in shaping the marine food web and maintaining healthy and balanced marine ecosystems. Sharks are sensitive to environmental changes and anthropogenic pressure and demonstrate a clear and rapid response. This designates them a “keystone” or “sentinel” group that may describe the structure and function of the ecosystem. As a meta-organism, sharks offer selective niches (organs) for microorganisms that can provide benefits for their hosts. However, changes in the microbiota (due to physiological or environmental changes) can turn the symbiosis into a dysbiosis and may affect the physiology, immunity and ecology of the host. Although the importance of sharks within the ecosystem is well known, relatively few studies have focused on the microbiome aspect, especially with long-term sampling. Our study was conducted at a site of coastal development in Israel where a mixed-species shark aggregation (November–May) is observed. The aggregation includes two shark species, the dusky (Carcharhinus obscurus) and sandbar (Carcharhinus plumbeus) which segregate by sex (females and males, respectively). In order to characterize the bacterial profile and examine the physiological and ecological aspects, microbiome samples were collected from different organs (gills, skin, and cloaca) from both shark species over 3 years (sampling seasons: 2019, 2020, and 2021). The bacterial composition was significantly different between the shark individuals and the surrounding seawater and between the shark species. Additionally, differences were apparent between all the organs and the seawater, and between the skin and gills. The most dominant groups for both shark species were Flavobacteriaceae, Moraxellaceae, and Rhodobacteraceae. However, specific microbial biomarkers were also identified for each shark. An unexpected difference in the microbiome profile and diversity between the 2019–2020 and 2021 sampling seasons, revealed an increase in the potential pathogen Streptococcus. The fluctuations in the relative abundance of Streptococcus between the months of the third sampling season were also reflected in the seawater. Our study provides initial information on shark microbiome in the Eastern Mediterranean Sea. In addition, we demonstrated that these methods were also able to describe environmental episodes and the microbiome is a robust measure for long-term ecological research.

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