Temporal scales of the body size structure and body condition variation in the brackish isopod Lekanesphaera hookeri: is there a role of temperature patterns?

In this research, we analyzed the variation of body-size structure and condition of Lekanesphaera hookeri (Leach, 1814) (Crustacea, Sphaeromatidae) in relation to the variation of temperature over time, using both small and large temporal scales. L. hookeri is an common isopod in detritivore benthic guilds of transitional waters and it is widely distributed from the North-European coasts to the coasts of the Mediterranean Sea and Black Sea. Despite its relatively low individual biomass and secondary production rate, L. hookeri have a key functional role in the lagoon food webs because it is a first consumer of the lagoon detritus, both autochthonous and allocthonous origin. For these reasons, L. hookeri seems to be a model species for analyzing spatial and temporal patterns of population dynamic, size structure and body condition in relation to climatic factors, such as temperature. The climate has been changing over time and temperature variation is one of the main factors. Climatic data, collected in our study site from 1990 to 2010, show two climate trends: the period 1990-2000 shows rising temperatures and, during the period 2000-2010, temperatures were relatively constant. Here, a population of L. hookeri was sampled at the end of these sub-periods, that is at the end of 2001 and at the end of 2010. At each sampling, body-size metrics (total length, dry weight, ash content, AFDW) were recorded for 96 randomly selected individuals. Abiotic data of the site were recorded at each sampling time. Body-size metrics were calculated and compared on small temporal scales (among months) and large temporal scales (among years). Body condition was calculated through statistical analysis, using residuals of length-weight relationship according to the formula: W = aL^b. The main results of this research show: 1. individual biomass decreases significantly with increasing atmospheric temperature, 2. length-weight relationships vary significantly between the two sampling periods.