Localization of infaunal prey by the sea star<Emphasis Type="Italic"> Leptasterias polaris</Emphasis>

We performed field and laboratory studies to investigate how large adult Leptasterias polaris detect and locate their major prey, large infaunal bivalves, in the sediment bottom community. A field survey using SCUBA diving showed that 95% of the locations where L. polaris dug into the sediment bottom were over bivalves and this success rate was much greater than if digging was done at random (22%). Furthermore, when sea stars were provided with a low density of randomly distributed prey in a laboratory arena, they dug exclusively in locations where a clam had been buried. These observations indicated that L. polaris locates infaunal prey prior to investing energy into digging. Studies in a laboratory flow tank showed that L. polaris readily detected and moved towards its preferred prey Ensis directus whereas its responses to less preferred prey Mya truncata and Spisula polynyma were much weaker. The degree to which it oriented towards these three common prey seemed to reflect potential energy intake relative to foraging costs (which likely increase with the depth of the different prey) and risks from interactions with other carnivores (which are greatest when feeding on large prey). This is the first study to clearly demonstrate that sea stars use prey odours to locate infaunal prey.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-004-1497-1Communicated by R.J. Thompson, St. Johns     

Interspecific territoriality and competition for food between the reef fishes Forsterygion varium and Pseudolabrus celidotus

Long-term behavioural studies were made of the blennioid fish Forsterygion varium and the wrasse Pseudolabrus celidotus in the Cape Rodney-Okakari Point Marine Reserve in New Zealand. Both male and female F. varium defended small 1 to 2 m² territories from the wrasse all year round, althoughl aggressive encounters were most frequent from December to April. Only Large P. celidotus (≧180 mm standard length) were observed to dominate the blenny in interactions. Defence of nests, which were found only on the territories of males between May and October, did not explain the distribution of F. varium aggression between the sexes and seasons. An extensive overlap in the categories and size of prey eaten suggested that protection of food was a major function of F. varium territoriality. F. varium was most frequently aggressive toward P. celidotus of an intermediate size (110 to 160 mm SL) and exhibited greatest overlap in diet with wrasses in this size lange. This dnected the study toward examining the effect of F. varium on the feeding activity of P. celidotus. Within a shallow, Leterogeneous reef habitat, feeding pressure by P. celidotus (bites/are/time) was inversely related to the density of F. varium. Removal of F. varium from small 5x5 m quadrats resulted in large increases in wrasse feeding pressure, suggesting that the blenny influences the foraging of wrasses within their home ranges. When F. varium were removed from the entire home ranges of five 1+yr (110 to 130 mm SL) P. celidotus, these fish exhibited relative increases in both feeding rate and foraging time. The results suggest that P. celidotus grow through a period during which individuals compete with F. varium for food, adding support to the contention that territoriality in F. varium functions to preserve its food supply.     

Echolocation by cave swiftlets

Summary The ability of cave dwelling swiftlets (Collocalia spodiopygius) to detect small cylindrical obstacles by echolocation was tested in a 3x9 m flight chamber. Although there was great individual variability, 6.3 mm obstacles were avoided much more often in total darkness than 1.5 wires (P<0.001). Flash photographs showed that the latter were avoided only by chance (about 50% misses). Obstacles 3.0 mm in diameter were avoided only slightly more often than 1.5 mm wires.Even in the light these swiftlets avoided the obstacles in only about 75% of the trials, probably because gentle touches with the primary feathers caused little discomfort.The 3.0 and 6.3 mm obstacles tended to be avoided more often on first encounters after they had been shifted horizontally by 10–30 cm, probably because the birds became more attentive.     

Social inhibition of maturation in females of the temperate wrasse Pseudolabrus celidotus and a comparison with the blennioid Tripterygion varium

In two temperate reef fish, Pseudolabrus celidotus (Bloch and Schneider) and Tripterygion varium (Bloch and Schneider) studied near Leigh, New Zealand, most spawning activity was concentrated during the first 2 months of spawning seasons which lasted about 5 months. In P. celidotus, maturation and spawning of first-year females (0+) was delayed with respect to older (1+yr) females. Within the 0+ age class, the minimum size of maturation declined as the spawning season proceeded. However, in all females of T. varium, ripening and spawning took place over the same time ranges. Observations on the seasonal patterns of female aggression suggested that larger female P. celidotus were socially inhibiting the maturation of small females. The level of interaction was high compared to that in T. varium, and reached a peak over the onset of the spawning season. This hypothesis was tested by the removal of larger (1+yr) female P. celidotus from a field population. The remaining 0+ females increased in ovary weight and matured earlier than those in an undisturbed area. We argue from this experiment that it is of advantage for P. celidotus females to spawn early in the season and of advantage to inhibit other females from doing so. Two possible reasons are suggested, the first applying to sexchanging species such as P. celidotus, the second to temperate-water fishes in general.     

Linear regression with Type I interval- and left-censored response data

Laboratory analyses in a variety of contexts may result in left- and interval-censored measurements. We develop and evaluate a maximum likelihood approach to linear regression analysis in this setting and compare this approach to commonly used simple substitution methods. We explore via simulation the impact on bias and power of censoring fraction and sample size in a range of settings. The maximum likelihood approach represents only a moderate increase in power, but we show that the bias in substitution estimates may be substantial.     

Reproductive isolation and reproductive output in two sympatric mussel species (Mytilus edulis, M. trossulus) and their hybrids from Newfoundland

The mussels Mytilus edulis L. and M. trossulus Gould are found sympatrically in most areas of Newfoundland, with a low frequency of hybrids. To assess the potential for reproductive isolation, we sampled mussels from three sites in an eastern Newfoundland Bay from May–October 1996 to determine if there were differences in the reproductive cycles of the two species and their natural hybrids. In mussels with sheil lengths of 38–42 mm, males and females with mature gametes were dominant in June for M. edulis and hybrids, while M. trossulus showed a lower frequency of individuals with mature gametes. M. trossulus and hybrids spawned over a prolonged period (from late spring to early autumn) compared with most M. edulis individuals that spawned over a period of 2–3 weeks in July. This asynchrony in spawning activity between the two species may partially explain the low frequency of hybrids found in previous studies of these mussel populations. Female and male hybrids between M. edulis and M. trossulus showed normal gonad development, ripening and spawning, providing an opportunity for the introgression of genes between the two species. M. trossulus had a higher reproductive output than M. edulis of similar shell length, while hybrids showed intermediate values of reproductive output. M. trossulus females produced smaller eggs than either M. edulis or hybrids. Differences in reproductive traits may partially explain the maintenance of the mussel hybrid zone in Newfoundland. Published online: 13 August 2002     

The fate and removal of triclosan during wastewater treatment.

This work examines the variation in removal efficiency of triclosan in wastewater treatment works in the United Kingdom between November 2003 and April 2004. Concentrations of triclosan were measured at set points within three different types of wastewater treatment works: rotating biological contactors, trickling filters, and activated sludge. Overall removal of triclosan through these plants ranged from 58 to 96% (rotating biological contactors), 86 to 97% (trickling filter), and 95 to 98% (activated sludge).