Food resource partitioning between two sympatric temperate wrasses

The present study analysed two sympatric wrasses, Thalassoma pavo and Coris julis, with similar sizes and morphologies, that are widespread in the reef habitats of the Mediterranean and the eastern Atlantic coast. Ocean warming has induced the northward movement of T. pavo, whereas C. julis has been moving to deeper habitats. In addition, under conditions of high slope of the sea bottom, T. pavo occupies shallow habitats and C. julis is in greater abundance in deeper habitats. By investigating stomach contents and prey availability in the benthos, we assessed whether the two wrasses exploit food resources by choosing different prey within the same habitat both under co-existence and segregation conditions. The results showed that T. pavo mainly feeds on gammarids and sipunculids, whereas C. julis mainly feeds on Alvania spp. and Paguroidea. The two wrasses also showed an intrinsic partitioning of food resources, independently of the condition of co-existence or segregation and benthic prey availability in the environment. The two wrasses fall in the ‘over dispersion of resource use’ model, in which species share numerous niche dimensions in a variable manner. Our findings may contribute to exclude a greater trophic competition between these labrid species in a projected warming scenario.

Density and size of reef fishes in and around a temperate marine reserve

The effects of marine reserve protection on the density, size, biomass, sex-ratio and overall assemblage structure of reef fishes were investigated at Kingston Reef Sanctuary, Rottnest Island, Western Australia. Significant trends in response to reserve protection were found for two species of top predators and several serially protogynous labrid species. The relative density and biomass of the heavily targeted Glaucosoma hebraicum was 10 and five times greater within the sanctuary respectively. Similarly, the biomass of the serranid, Epinephelides armatus, was 3.2 times greater in the sanctuary, although this difference was owing to a greater mean length not relative density. The male : female sex ratio for the labrid, Ophthalmolepis lineolatus, was significantly different between sanctuary and non-sanctuary sites, with the density of male O. lineolatus significantly greater within the sanctuary. Rottnest Island waters are largely restricted to recreational fishing, therefore these results suggest that a range of fish species around Rottnest Island are affected by recreational fishing, and that these effects are found in taxa beyond the primary target species. The patterns in the effects on bycatch species suggest that fishing-related mortality may be exerting a greater control on these populations than that exerted by natural predation.

Embryonic and larval development of the brown wrasse Labrus merula (Pisces: Labridae)

In March 1997 one male and one female brown wrasse Labrus merula spawned spontaneously in aquaria conditions. Eggs were incubated at ambient temperature, salinity, oxygen and pH. The development of the eggs, yolk-sac larvae and larvae is described and illustrated with particular emphasis on features of practical value for identification of specimens from plankton. The ripe egg of brown wrasse is a typical labrid egg with a mean diameter of 0.93±0.05 mm. The incubation period was 106 h 45 min at a mean temperature of 14.3°C. Newly hatched yolk-sac larvae were 3.8±0.02 mm, while the yolk-sac was resorbed when larvae reached 4.68±0.15 mm in total length. Some characteristics which may be useful for identification are described and compared with some other labrid yolk-sac larvae and larvae. The length of newly hatched yolk-sac larvae of brown wrasse was significantly larger (t-test, P<0.05) than those of the other labrid species, but it is similar to that of Labrus bergylta. During the first 16 d (after resorption of yolk-sac) brown wrasse larvae does not possess a double crescent of melanophores on top of the head, but has a few melanophores on the anal fin which is very similar to the pigmentation of Symphodus (Crenilabrus) melops larvae, although there is a difference in length between them. Larvae older than 16 d have a double crescent of melanophores on the top of the head with melanophores on the anal fin-fold identical to L. bergylta larvae, but the difference in larvae length also exists.

Karyotype divergence in Symphodus melops and Symphodus roissali (Labridae, Perciforms): C-banded and Ag-NOR karyotypes

A comparative analysis of conventional C-banded and Ag-NOR karyotypes involving the closely related labrid species Symphodus melops and Symphodus roissali showed conspicuous differences between them, reflected mainly in their 2n and fundamental number values. The chromosome rearrangements apparently involved consisted of three centric fusions, pericentric inversions, and (or) translocations, as well as small heterochromatic additions. In spite of this clear divergence, the two species seem to have one larger metacentric pair, the nucleolar organizer region (NOR) carrier chromosomes, and some smaller unidentified pairs in common. Both karyotypes are fully representative of the described tendency in the labrids towards symmetric morphology. The NOR regions were shown to have C-banding and a heteromorphism between homologous regions was detected by conventional and silver staining, but not by the C-banding technique, which leads us to suggest that the NOR regions' heteromorphism is functional rather than structural in nature.Key words: Labridae, heterochromatin, nucleolus organizers.

Field observations on the reproductive behaviour of the cunner, Tautogolabrus adspersus (Walbaum), in Newfoundland

Courtship behaviour and pair spawning of the cunner, Tautogolabrus adspersus (Walbaum) were observed in Conception Bay, Newfoundland, during midsummer of 1977 and 1978. Courtship displays were recorded between 0600 and 2100 hours and spawns between 1300 and 2100 hours. The frequency of both courtship behaviour and spawns varied with the time of day. Spawning, but not courtship, is correlated with the tidal cycle. Spawns occur most often during the mid flood to high-tide phase of the eye le. Fish of both sexes are capable of multiple spawns per day. Both territorial and non territorial males acquire nuptial colouration between emergence from overwintering torpor and the start of the spawning season. Nonterritorial males are vigorously excluded from territories by the resident males and appear to contribute little to the reproductive effort of the population. Courtship and spawning occur only within male's territories. Group spawning was not observed. Sexual dichromatism and reproductive behaviour in the cunner are discussed with reference to other labrid species.