engleski

Association of fish and invertebrates with shallow benthic habitats revealed by DGPS/video-tracked dive transects

A lure assisted visual census method has been developed to identify habitat related differences in fish abundance, diversity and assemblage structure across twelve study sites on Ugljan Island located in the central Croatian Adriatic. Approximately 150 short visual census transects (each 3 m long) were performed per site in fall 2009 and spring 2010. Almost all observed fish were attracted by and interacted with the lure, which substantially increased their chances of being censused. This novel method is especially advantageous for species that are difficult to detect and identify with traditional visual census methods, including hidden, cryptic, or fast-swimming species. Fish were most abundant and diverse in rocky habitats and least abundant in Cymodocea nodosa meadows. Rocky habitat patches with a minor component of unconsolidated sediment and/or vegetation harbored a more diverse and abundant fish assemblage than patches of rock only, and the same applied to habitat patches of unconsolidated sediments as the dominant component. A cluster analysis of the various habitat types and their combinations based on species’ relative abundances resulted in four main clusters: rock dominated habitats, combinations of bare sediment and Cymodocea nodosa, algae dominated habitats, and the seagrass Posidonia oceanica. The lure assisted visual census method is applicable in shallow (snorkel or SCUBA) and deep waters (SCUBA) and allows for the recording of demographic fish descriptors, like size (age) and sex, as well as of fish-lure interaction behaviors (e.g. active vs. passive lure encounter and frequency of lure ingestion) that can be used to identify and quantify the frequencies of various predation modes as well as to compare the predation risks posed by each mode across habitats and study sites.

Seagrass; Habitat structure; Abundance; Diversity; Adriatic

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