Population structure, growth and reproductive activities were investigated over one year for the boring isopod Sphaeroma sieboldii Dollfus, 1889 for a population burrowing in sand-stone. The occurrence of heterosexual pairs peaked in spring, followed by the peak occurrence of ovigerous females and females cohabiting with early juveniles in the summer. This suggests the reproductive season is from spring to summer. For adult males that had penes, three reproductive stages were recognized: large-sized males with mature appendices masculinae, intermediate-sized males with immature appendices masculinae, and small-sized male without appendices masculinae. Most of the males pairing with females were large-sized males with mature appendices masculinae, while most of the pairing females were smaller than the partners, carrying small, non-functional oostegites. Males with mature appendices masculinae were frequent from winter to summer, covering the reproductive season. Size-assortative pairing was found in the peak season of heterosexual coupling. Sex ratios were female-biased in all months. Observation of the interior reproductive organs confirmed that adult females had ovaries, while most males had both ovaries and male reproductive tracts. Some males with mature appendices masculinae were found to have degenerated ovaries. These findings suggest that protogynous sex change occurs in S. sieboldii.
The blue crab, Callinectes sapidus Rathbun, 1896, is native to the Atlantic coasts of the Americas and globally one of the most highly invasive marine species. In the present study, the species’ diet and the foraging behaviour was studied in the Thermaikos Gulf and Papapouli Lagoon for the first time. Surveys were undertaken using fyke nets, shore surveys, scuba and snorkelling. Additional data were compiled from systematic interviews with mussel farmers, shellfish traders and fishermen. In both Thermaikos Gulf and Papapouli Lagoon C. sapidus was found to prey on a wide variety of species including economically important molluscs, fishes, and crustaceans, indicating a substantial potential impact on fisheries and aquaculture in the region. Observation showed that over 6 (2009–2014) years, the blue crabs became dominant in Papapouli Lagoon at the expense of the native commercially fished crab Carcinus aestuarii Nardo, 1847 according to fisheries data. Potential management implications are discussed.
A new species of the alpheid shrimp genus Potamalpheops Powell, 1979 is described from an anchialine cave on Nggela Pile Island, Solomon Islands. Potamalpheops nazgul sp. nov. belongs to the P. monodi (Sollaud, 1932) species group, defined by the presence of two pairs of cuspidate setae on the distal margin of the telson and feebly or non-enlarged chelipeds. The new species is morphologically closer to P. pininsulae Bruce & Iliffe, 1992 and it is characterised among others by the presence of a well-developed antero-mesial tubercle on the eyestalk, a short rostrum with a dentate ventral carina, a toothed distal margin of first antennular segment and a non-strongly inflated carapace. The description of this new species raises the number of known species of Potamalpheops to fifteen.
Egg loss from ovigerous females has hampered larval culture experiments for life history studies of the coconut crab Birgus latro. We conducted two preliminary experiments to develop a method to artificially incubate and hatch embryos separated from the mother: 1) manipulation of incubation duration in a pseudo-terrestrial environment and 2) manipulation of incubation temperature. In experiment 1, we incubated embryos on medical gauze moistened with seawater for 7 or 17 days at 27–28°C before incubation by immersion in seawater (27–28°C), or we continuously incubated them in seawater only. In experiment 2, we similarly incubated embryos on medical gauze until 1–2 days before hatching at 21–22°C, 24.5–25.5°C, or 27–28°C before incubation in seawater (27–28°C). Successful hatching occurred, but embryos did not hatch synchronously, and hatching continued for approximately a week. Incubating embryos in seawater continuously led to the highest hatching rates of morphologically normal zoeae; however, hatching rates of normal zoeae did not exceed 50%. Increased incubation temperature reduced the incubation duration until hatching. Zoeae could metamorphose into megalopae, but survival rates were generally low. Further studies are required to improve the hatching rate of viable larvae under artificial conditions.