long-term-video-tracking-cohoused-aquatic-animals-case-study-daily

Long-term Video Tracking of Cohoused Aquatic Animals: A Case Study of the Daily Locomotor Activity of the Norway Lobster (<em>Nephrops norvegicus</em>)

We present a protocol related to a video-tracking technique based on the background subtraction and image thresholding that makes it possible to ...

Institute for Environmental Protection and Research (ISPRA)

Leibniz-Institute of Freshwater Ecology and Inland Fisheries

Animals fight over resources such as mating partners, territory, food or shelter and repeated contests lead to stable social hierarchies in different phyla. The group dynamics of hierarchy formation are not characterized in the Norway lobster (). Lobsters spend most of the day in burrows and forage outside of them according to a diel (i.e. 24 h-based) activity rhythm. Here, we use a linear and generalized mixed model approach to analyse, in seven groups of four male lobsters, the formation of dominance hierarchies and rank-related changes in burrowing behaviour. We show that hierarchies emerge within 1-3 days and increase in steepness over a period of 5 days, while rank changes and number of fights gradually decrease over a 5-day period. The rank position determined by open area fights predicts the outcome of fights over burrows, the time spent in burrows, and the locomotor activity levels. Dominant lobsters are more likely to evict subordinate lobsters from their burrows and are more successful in defending their own burrows. They spend more time in burrows and display lower levels of locomotor activity outside the burrow. Lobsters do not change their diel activity rhythms as a result of a change in rank, and all tested individuals showed higher activity at night and dusk compared with dawn and daytime. We discuss how behavioural changes in burrowing behaviour could lead to rank-related benefits such as reduced exposure to predators and energy savings.

Fighting over burrows: the emergence of dominance hierarchies in the Norway lobster ().

The seasonal timing of recurring biological processes is essential for organisms living in temperate regions. While ample knowledge of these processes exists for terrestrial environments, seasonal timing in the marine environment is relatively understudied. Here, we characterized the annual rhythm of habitat use in six fish species belonging to the Sparidae family, highlighting the main environmental variables that correlate to such rhythms. The study was conducted at a coastal artificial reef through a cabled observatory system, which allowed gathering underwater time-lapse images every 30 minutes consecutively over 3 years. Rhythms of fish counts had a significant annual periodicity in four out of the six studied species. Species-specific temporal patterns were found, demonstrating a clear annual temporal niche partitioning within the studied family. Temperature was the most important environmental variable correlated with fish counts in the proximity of the artificial reef, while daily photoperiod and salinity were not important. In a scenario of human-induced rapid environmental change, tracking phenological shifts may provide key indications about the effects of climate change at both species and ecosystem level. Our study reinforces the efficacy of underwater cabled video-observatories as a reliable tool for long-term monitoring of phenological events.

Valerio Sbragaglia

Institute for Environmental Protection and Research (ISPRA)

Long-term Video Tracking of Cohoused Aquatic Animals: A Case Study of the Daily Locomotor Activity of the Norway Lobster (Nephrops norvegicus)