Maria Eugenia Manjón-Cabeza

Diel and seasonal changes in the structure of a Decapod (Crustacea: Decapoda) community of Cymodocea nodosa from Southeastern Spain (West Mediterranean Sea)

The study of a decapod community in a Cymodocea nodosa meadow from Southeastern Spain (Western Mediterranean Sea) showed a stable structure, in which the families Hippolytidae, Processidae, Majidae and Portunidae were the most abundant and the species Hippolyte niezabitowskii dominated. The animal community was more numerous and diverse during the night, showing the existence of nychthemeral movements, which are essentially related to the trophic behaviour and shelter. In this way, many species increased their abundance as a result of an increasing activity and, also, of an influx of other species and specimens from adjacent sandy bottoms, such as Processa spp. (mainly P. modica) Sicyonia carinata, Liocarcinus spp. (mainly juveniles) and several species of hermit crabs, which were rare or absent during the day. All these changes produced modifications in the dominance curves and in the values of all ecological indices (richness, diversity and evenness). Monthly samples were grouped and ordered (MDS) by the factor “day-night”, which showed slight qualitative and quantitative differences (SIMPER, dissimilarity average of the factor day-night = 61.67). On the other hand, no global seasonal differences have been found (one way ANOSIM), but there was a significant level of similarity between winter and spring, while the summer samples were the most different. The differentiation of the summer 1999 can be attributed to a decrease in species abundance and richness, probably due to the dynamics of the decapod populations and the balance with predators (fishes), while that of the summer 2000, to an anomalous event: the massive proliferation of filamentous algae, mainly Ectocarpus s.l., which modified the environmental conditions.

Structure and evolution of a decapod crustacean community from the coastal detritic bottoms of Barbate (Cadiz, Southern Spain)

During 1993–1994 the decapod crustacean community of littoral detritic bottoms (15–24 m deep) from Southern Spain (Barbate Bay, near the Straits of Gibraltar) were studied. The substrata include coarse sand, fine gravel, Amphioxus sand, and contain abundant bioclastic remains (bivalve and gastropod shells), which are under the influence of bottom currents. The taxocoenosis shows a clear dominance of the Anomura, 87% of those being hermit crabs; among them, Diogenes pugilator (Roux, 1829) is the dominant species (76.6%). The structure and development of the taxocoenosis during an annual cycle (number of specimens, richness, diversity, evenness and heterogeneity) is controlled by the cycle of D. pugilator, a characteristic species of shallow fine sand bottoms, and by the appearance of, or increase in, seaweed in the late summer and autumn; this produces a notable seasonal variation and modifies the dominance and composition of species.

Sublethal foot-predation on Donacidae (Mollusca: Bivalvia)

Abstract The incidence of foot nipping was studied on the Donax spp. of the littoral of Malaga (Southern Spain, 2875 specimens collected from February 1990 to January 1991) and of Re island (French Atlantic coast, 262 specimens of Donax vittatus (Da Costa, 1778) collected in May 1996). In Malaga, Donax trunculus L., 1758 was the species most regularly nipped (18% of individuals), with peaks in summer (25% in August and 48% in September) and winter (34% in December). In Re island, 27% of the specimens showed a nipped foot. Logistic regression shows that in D. trunculus length is the variable that most influences the probability of foot nipping, followed by weight and chlorophyll a. However, the difference in length between damaged and undamaged individuals was not significant (U-Mann–Whitney test). The size class frequency and the values of Ivlevs index show that the small size classes were avoided, while for the other size classes predation remained balanced throughout the year. Therefore, the avoidance of the small size classes makes length the most influential variable. The logistic regression indicated a coefficient B=−0.03 for weight. This implies a slightly negative influence on the probability of foot nipping. However, without the data of September, there is a positive correlation (r=0.76, p The biomass (as flesh dry weight) of D. trunculus lost by foot nipping amounts to more than 20% in most of the size classes. There was an increase from the small sizes to the largest ones, in which it reaches 37%, with a positive correlation (r=0.84; p

Reproductive aspects of females of the hermit crab Diogenes pugilator (Crustacea: Decapoda: Anomura) from southern Spain

The ovary structure of the hermit crab Diogenes pugilator (Crustacea: Decapoda), is described in the diierent phases using electron microscopy. Sexual maturity was reached at a very small size; females from 0.74mm shield length (SL) could be found in vitellogenesis stage and even 0.6mm SL ovigerous females exist. The biometric study of the ovigerous females by independent size-class (non-accumulative) shows that 1.3mm SL is the size at which 50% of females are ovigerous; this value is increased a little (1.7^1.8mm) if the population of females, or ovigerous females, is analysed from an accumulative point of view. In addition, an optimal reproductive size (between 2.1and 2.3mm SL) and a reproductive decrease in the maximum size-classes have been detected. The relation between brood size (measured through egg number) and the hermit crab size follows a potential function. The number of eggs by brood varies in a wide range (9^2838), with a mean diameter of 0.350.03mm. No relationship between egg size and shield length has been found.

Considerations On Some Species of Hippolyte (Decapoda, Caridea) From Southern European Waters, H. Niezabitowskii, H. Holthuisi, and H. Varians

[Preliminary samples taken from Zostera marina beds on the Mediterranean coast of southern Spain, have allowed us to obtain three species of Hippolyte. One of them, Hippolyte niezabitowskii, represents the first record for Spain and the western Mediterranean. Also, the morphology of the present material shows clear differences with that of specimens from the Adriatic and Ionian seas. A complementary description and some considerations on a presumably subspecific status are given. The capture of many specimens belonging to the complex H. varians-H. holthuisi (H. holthuisi represents a new record for the area) has allowed us to make a comparative analysis between populations from the Alboran Sea and from the Gulf of Cadiz, which has established the existence of consistent differences between these., Preliminary samples taken from Zostera marina beds on the Mediterranean coast of southern Spain, have allowed us to obtain three species of Hippolyte. One of them, Hippolyte niezabitowskii, represents the first record for Spain and the western Mediterranean. Also, the morphology of the present material shows clear differences with that of specimens from the Adriatic and Ionian seas. A complementary description and some considerations on a presumably subspecific status are given. The capture of many specimens belonging to the complex H. varians-H. holthuisi (H. holthuisi represents a new record for the area) has allowed us to make a comparative analysis between populations from the Alboran Sea and from the Gulf of Cadiz, which has established the existence of consistent differences between these.]