The distribution of sea urchins (Echinodermata, Echinoidea), and changes therein over the course of a decade, were investigated around Cape Bansho, which marks the southern limit of Tanabe Bay, Japan (33°42′N, 135°20′E). Censuses were carried out once each in 2000 and 2011, using a semi-quantitative timed search technique on both occasions. Fourteen species of sea urchin were recorded in the two survey years, of which 64% were tropical Indo-Pacific species. Echinostrephus aciculatus, Anthocidaris crassispina, and Stomopneustes variolaris were more abundant in the intertidal than subtidal zone. In contrast, Echinometra sp. A, Toxopneustes pileolus, and Diadema setosum were more abundant in the subtidal zone than intertidally. The densities of Echinometra mathaei, Echinometra oblonga, and Stomopneustes variolaris were higher on more exposed shores whereas those of Echinometra sp. A and Mespilia globulus were higher on more sheltered shores. The present results concerning Echinometra species and wave exposure are consistent with previous reports from Okinawa. From 2000 to 2011 there was a contraction in the ranges of Mespilia globulus, Diadema setosum, and Stomopneustes variolaris, all of which are tropical species, but the range of the warm-temperate species Anthocidaris crassispina remained constant. Environmental and biological evidence around Tanabe Bay suggests that climatic events such as a severe winter and typhoons were responsible for the decline of the three tropical species between 2000 and 2011.
Stomach contents of the macrourid fish Caelorinchus anatirostris Jordan and Gilbert, 1904, collected by a series of beam trawl surveys southwest of Nagasaki, Japan, were analyzed to obtain ecological information on these slope-dwelling fish. The index of relative importance(%IRI)of polychaetes was, on the whole, high for all specimens. The %IRI of crustaceans(copepods and amphipods)was high for small specimens(under 69 mm in pre-anal length), while that for fish(Myctophidae gen. sp., Bregmaceros spp., and others)was highest for large specimens(over 112 mm in pre-anal length). Both crustaceans and fish were found in the stomachs of middle specimens(69–112 mm in pre-anal length). These results indicate ontogenetic changes in the diet of C. anatirostris. No significant difference in stomach contents according to sex or day-night timing of capture was detected.
Males of the hermit crab Pagurus filholi guard females until spawning, and male-male contest often occur when guarding males encounter other males. A contest comprises two phases, initial contact and physical combat, and larger males typically win. We conducted male-male contest experiments to examine whether body sizes of both sexes of P. filholi and female receptivity affect whether and when a contest escalates to physical combat, as well as contest duration and outcome. For each experimental trial, a pair, comprising a “pairing male” and a “pairing female”, and a second male (“intruder”) were placed into a small container, and their behaviors were observed for 15 minutes. Each intruder had been guarding a female in the field but we removed this female (“removed female”) just before the trial. All pairs in the field were reconstructed each after trial to quantify female receptivity. This was done by checking each female for spawning every day. As an index of size, we measured shield length (length of calcified anterior portion of cephalothorax) of all crabs. In the trials, large size of the intruder and high receptivity of the removed female significantly shortened the time until the onset of physical combat. Intruders needed more time to take over the pairing females and were less likely to win the contests when the intruders were small, the pairing males were large, and the removed females were large. Body size and receptivity of the pairing female had no effect on the process and the outcome of male-male contest. These results suggest that a male P. filholi can assess the quality of female it is guarding and remember its assessment for at least a short period. Asymmetry between contestants in this memory store for female quality could affect the process and the outcome of male-male contests in P. filholi. Contents of supplementary materials: Appendix 1: Explanation of movie files, Mov 1: Male-male contest, Mov 2: Cessation of male contest, Mov 3: No guarding after takeover.
Gamo Lagoon (Sendai, Miyagi Prefecture, Japan), a shallow brackish lagoon, was struck by a 7.2-m-high tsunami on 11 March 2011. In order to assess the tsunami-induced changes in the ecosystem of Gamo Lagoon, we examined the topography and distribution of plants and macrobenthos between April and August, 2011, and compared them with available pre-tsunami data. The submerged area decreased from 17.3 to 11.8 ha, sand dune vegetation from 8.6 to 0.1 ha, pine forest from 4.2 to 2.0 ha, and macroalgal patches from 7.8 to 1.8 ha. Conversely, the area of bare intertidal flats increased from 4.7 to 5.3 ha, mainly owing to the near disappearance of reed marshes (7.8 to 1.2 ha). Muddy sediment was flushed out and the sediment became sandier. The population of the marsh-associated gastropod Cerithidea rhizophorarum in the lagoon declined sharply from about 40,000 (estimated from mean density and habitat area) to just 26 individuals. Of 79 species of macrobenthos found before the tsunami, 47 species (especially bivalves) were absent or nearly extirpated after the tsunami. The temporary immigration of 12 marine species was noted shortly after the tsunami, but most disappeared within 5 months. The populations of dotillid crabs (i.e., Scopimera globosa and Ilyoplax pusilla), the nereidid polychaete Hediste diadroma, and opportunistic species including polychaetes (e.g., Pseudopolydora cf. kempi, Heteromastus cf. similis, and Capitella sp.) and amphipods (Grandidierella japonica and Corophiidae sp.) recovered rapidly within the same 5-month period.