The body condition of the shore crab Carcinus maenas in a temperate coastal system (western Dutch Wadden Sea) was followed over 14 mo. Fulton’s condition factor K, dry weight condition and the percentage of dry weight were determined as indirect indices, while bomb calorimetry was applied to obtain the energy density and total energy, as direct biochemical measures of condition. General linear models identified sex, size and season as relevant regressors explaining observed variance in crab condition, whereas colour morphotype effect was negligible. The seasonal pattern was consistent with the natural cycling in temperature and expected food availability, but the peak in body condition differed depending on the type of measure used: energy peaked in autumn, while morphometric condition was at its highest in winter, uncovering different latencies in the response of direct and indirect indices. Concordant with higher energy investment in reproduction, body condition and energy content of non-ovigerous females were higher than those of males, and egg-bearing females always had the lowest condition values. Energy content of adult females ranged from 16.37 ± 1.30 (winter 2013) to 19.83 ± 0.54 kJ g-1 ash-free dry weight (AFDW) (autumn 2013), attaining 18.77 ± 1.22 kJ g-1AFDW prior to the onset of reproduction in 2012, while maximum energy density of ovigerous females (eggs excluded) was 16.49 ± 0.64 kJ g-1AFDW. Besides low correlation between indirect and direct indices, fluctuations were more pronounced in the energetic data. Therefore, the morphometric measures seem weak surrogates to estimate energy density of these crabs.

No abstract

Intraspecific agonistic interactions are widespread across the animal kingdom, with many individual morphological and physiological characteristics playing important roles in the fate of disputes. Additionally, changes to environmental conditions can influence the outcomes of animal contests. The shore crab (Carcinus maenas) is a globally distributed species, present in numerous coastal and estuarine temperate systems around the world. Although shore crabs are highly tolerant to changes in temperature, this parameter has important physiological effects on the species’ ecology, while its effects on behavior are not fully understood. Our study aims to investigate how different individual characteristics (such as sex, color morphotype, carapace and chela morphology) and temperature conditions affect the dyadic interactions between shore crabs when disputing food resources. In general, the differences in carapace width between opponents, their sexes, color morphotypes and the temperature conditions interacted and were important predictors of the contest fate. We found that the body size and color morphotype of C. maenas determined the fate of dyadic disputes. However, the higher temperatures disrupted the well-established dominance of the larger red color morphotype individuals. Overall, the agonistic contest results suggest higher plasticity than previously acknowledged.

The impact of barnacle epibionts on the condition of the shore crab Carcinus maenas was studied for the western Wadden Sea population. Approximately 39% of the crabs were fouled with the barnacle Balanus crenatus. Although the morphological Fulton's K condition decreased by 5.8% in fouled crabs, Linear Mixed-Effects Models (LMM) showed that only the energetic condition of the crabs was significantly affected by fouling. The energy density of fouled crabs was consistently poorer (4.1% in AFDW; 8.7% in dry weight) than that of non-fouled crabs, especially in females and green forms in dry weight (12.8 and 11.4% reduction, respectively). Cumulative infection with Sacculina carcini, detected in 4.5% of the fouled crabs, additionally reduced by 14.3% the energy density in dry weight and almost to half of the total energy of the fouled crabs. Impacts of energy density reduction on crabs' growth and reproduction are discussed.

The impact of Sacculina carcini infection on the nutritional status of the shore crab Carcinus maenas was investigated in the western Dutch Wadden Sea for a period of 20 months. About 3.3% of the population was sacculinized, i.e. externally infected with S. carcini and only 0.7% presented scars of previous infection. The results of mixed linear models showed that sacculinized and non-sacculinized crabs had similar morphometric condition, while the energy density of parasitized crabs (externa excluded) was significantly reduced by about 4.3% overall, and by up to 5.8% in crabs under 40 mm carapace width. However, when Sacculina externa was included in the energy determinations, the difference in energy density decreased to 1.2%, while total energy content of the pair infected crab-parasite including externa was 30.8% higher than non-sacculinized crabs of similar size. The total energy content of ovigerous females (eggs included) was even higher, near doubling the energy of similar-sized crabs. The same way, total energy content of Sacculina externa was about 4 times lower than total energy of egg mass. The results suggest that the rhizocephalan parasite is efficient in consuming the energy that the host may allocate for growth and maintenance, but require future studies to disentangle the impact of the degree of internal infection and the implications for the dynamics of the population.