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Capital of several empires through centuries, Istanbul has been a populated city in history. However, the population has increased by a factor of 13.3 over the last seven decades, which in turn has made this megacity a hotspot of domestic and industrial pollution. Marine biodiversity around Istanbul suffered from the increased pressures due to overfishing, extensive recreational usage, extreme habitat destruction and introduction of alien species via heavy maritime traffic. 70 years before, Muzaffer Demir published a colossal marine biodiversity study in 1952. We used the organization of this publication, and particularly employed it as a methodology, combined with Underwater Visual Census for a later study between 1997–1999 which involved more than 100 scuba dives. Our study investigated the abundance status of benthic species living mainly on rocky reefs as deep as 50 meters. The investigated species represented four phyla: Cnidaria, Echinodermata, Mollusca and Porifera. Approximately 40% of cnidarians, 40% of echinoderms, 65% of molluscs, and 80% of sponges recorded in the 1950s, were not recorded during our study, particularly due to methodological differences and population collapses or local extinctions. This paper aims to analyze and compare the temporal aspects of marine biodiversity in the Prince’s Islands and Bosphorus region using several time domains; historical records, Demir’s compendium in 1952, our field study in the closing of the previous millennium, combined efforts of the Turkish Journal of Zoology in 2014 of Turkey biodiversity checklists, and the most recent literature after that.

The invasive alien lionfish, Pterois miles is a ray-finned fish from the Scorpaenidae family, which has twelve accepted species from the genus Pterois. It was recorded in May 2014 at the Pina Reef, 2.28 miles off Kas harbour (southwestern coasts of Turkey) for the first time, and showed a very rapid establishment in the rocky habitats throughout Kas-Kekova Special Environmental Protected Area (SEPA). During the summer of 2014 only three individuals were recorded at two different locations, however as of 2017, regular observations could be made at each diving spot, which is indicative of an increasing trend. The temporal perspective of this study increases the understanding on the progression of expected range expansion of P. miles within a relatively small region, covering the period of 2014–2019. Fish count observations from underwater visual census surveys in addition to records from citizen science approach were evaluated based on spatio-temporal analysis. Resulting visualizations were prepared to present annual dynamics of spatio-temporal distribution within and outside the SEPA. Rapid expansion, up to 22 individuals per 500 m linear transects of an estimated area of 15.000 m2 each, and the increases in the numbers of fish are quantified in this study, which can be used as a baseline to develop conservation strategy for native species. Efforts to cull and create consumption demand to decrease the population trend of the lionfish have already started in the region.