Effect of detrital nutritional quality on population dynamics of a marine nematode (Diplolaimella chitwoodi)

The quantity and nutritional quality of detritus significantly affected the population growth rate (r) and carrying capacity (K) of Diplolaimella chitwoodi (Nematoda) in laboratory cultures. The rate of increase (r) was roughly constant for cultures fed Ulva fasciata, Pablum, Gracilaria foliifera and one Spartina alterniflora detritus, but was lower for Thalassia testudinum detritus and another S. alterniflora detritus. Rate of increase was unaffected by amount of food supplied except for seaweed detritus where r was lower for lower ratios. Carrying capacity (K) was strongly affected by both detrital type and rate of food supply. The best predictor of K was the rate of nitrogen supply to these cultures implying that natural populations may be N-limited. The nitrogen content of detritus appears to be the best measure of its nutritional quality.     

Spatial distribution of the infaunal benthic communities of the Ría de Muros,north-west Spain

Benthic samples were collected at 13 stations in the Ría de Muros, north-west Spain. There are three major communities: (1) in the southern and outer part of the ría, an Amphiura filiformis—Thyone fusus community, inhabiting sandy sediments with low organic content; (2) in the middle part of the ría, and Amphiura chiajei—Maldane glebifex community, inhabiting muddy sediments that are not anoxic (sulphide not detected); (3) in Muros Bay and the inner part of the ría, a Spiochaetopterus costarum community, inhabiting anoxic sediments with high organic content. Biomass is very high (up to 46.2 g ash-free dry wt) in the first two communities. In the Spiochaetopterus costarum community, biomass and diversity are much lower, probably because of oxygen deficiency.     

A new method for estimating phytoplankton growth rates and carbon biomass

A new method is described for the determination of phytoplankton growth rates and carbon biomass. This procedure is easy to apply and utilizes the labeling of chlorophyll a (chl a) with ¹⁴C. Pure chl a is isolated using two-way thin-layer chromatography, and the specific activity of chl a carbon is determined. Data from laboratory cultures indicate that the specific activity of chl a carbon becomes nearly equal to that of total phytoplankton carbon in incubations lasting 6 to 12 h and can be used to calculate phytoplankton growth rates and carbon biomass. Application of the method to the phytoplankton community in an eutrophic estuary in Hawaii indicates that the cells are growing with a doubling time of about 2 d and that about 85% of the particulate carbon consists of phytoplankton carbon.     

Range extensions of teredinids (shipworms) and polychaetes in the vicinity of a temperate-zone nuclear generating station

A study of marine boring and fouling organisms in the vicinity of the thermal effluent from the Oyster Creek Nuclear Generating Station, Barnegat Bay, New Jersey, USA has been conducted since 1971. Two subtropical species of shipworms have been found in significant numbers in the effluent. These are Teredo bartschi Clapp and Teredo furcifera von Martens. The shipworm Lyrodus sp. and the flatworm Taenioplana teredini Hyman, which is predatory on teredinids, were also found, but on only one occasion. The polychaete Ficopomatus enigmaticus (Fauvel) has been found for the first time on the Atlantic Coast of North America. Three other polychaetes, Potamilla (Potamethus) spathiferus (Ehlers), Loimia medusa (Savigny), and Sphaerosyllis sp., have been newly identified from Barnegat Bay, but probably are not recent range extensions. Only T. bartschi, T. furcifera, and F. enigmaticus have established breeding populations. Their distributions and abundances are probably related to the thermal effluent; this is most clear in the case of T. bartschi and least clear in the case of F. enigmaticus. T. bartschi was confined at first to the heated effluent in Oyster Creek, but has spread to Forked River. It has become a major faunal element in Oyster Creek. The impact of the other exotic species has been negligible. The primary mechanism of the range extensions is by boat transport.     

Predator-prey relationships between the rock lobster Jasus lalandii and the mussel Aulacomya ater at Robben Island on the Cape West Coast of Africa

The natural diet and mode of feeding of the rock lobster Jasus lalandii (H. Milne Edwards) was determined in a rock-lobster sanctuary near Cape Town, South Africa. Field observations were tested and confirmed by means of aquarium studies. Rock lobsters feed mainly upon ribbed mussels Aulacomya ater (Molina), which comprise the largest component of the sessile benthic fauna. Mussel remains were found as the major constituent in 97% of the rock-lobster stomachs examined. The density of rock lobsters averaged 8,100 per hectare (0.81 m^-2), while mussel biomass averaged more than 5 kg (wet whole weight) m^-2 within the same depth range (12 to 30 m). More than 80% of the mussel biomass comprised large individuals between 60 and 90 mm in length. Large rock lobsters (mainly males) were capable of feeding on all sizes of mussels, although many of these were inaccessible to predation. Smaller rock lobsters became progressively more limited in the size range of mussels which they could crack open and consume. Competition between rock lobsters for small mussels appeared to be intense, as mussels of suitable size for feeding were generally in short supply to most of the rock-lobster population. Hence, feeding and growth rates of rock lobsters are likely to be affected by the relative population densities of predator and prey. Growth rates of rock lobsters could be limited by food supplies even in areas where mussel biomass is comparatively large.     

Algal chloroplasts in the protoplasm of three species of benthic foraminifera: taxonomic affinity,viability and persistence

The ultrastructure and pigment content of algal chloroplasts (derived from Bacillariophyceae or Chrysophyceae) are described from 3 benthic species of brackish-water foraminiferans.Elphidium williamsoni Haynes contains 4×10⁶ chloroplasts mg^-1, whereas the contents ofNonion germanicum (Ehrenberg) andE. excavatum (Terquem) are about 10% of this value. The two former contain chlorophyllsa andc and fucoxanthin, but these pigments were not detectable in the latter.E. williamsoni andN. germanicum had a net uptake of¹⁴C–HCO ₃ ^- , proportional to their content of chlorophyll and number of chloroplasts, increasing linearly up to approximately 10 Klux. At light saturation the former assimilates 2.3x10^-3 mg C mg^-1 h^-1 and the latter only about 20% of this value. Dark uptake was insignificant in all cases. Uptake could not be demonstrated inE. excavatum. The photosynthesis effected by these species is trivial in terms of the total benthic carbon fixation effected by the microflora. The chloroplasts survived longer in forminiferans kept in the dark than in light/dark adapted individuals. To keep a steady state population of chloroplasts under light/dark conditions,E. williamsoni must eat at least 65 chloroplasts individual^-1 h^-1, whereas the minimum consuption rate inN. germanicum is 20.     

Eyes and extraocular photoreceptors in midwater cephalopods and fishes: Their roles in detecting downwelling light for counterillumination

The means of detecting downwelling light for counterillumination in several midwater animals has been examined. Eyes and extraocular photoreceptors (drosal photosensitive vesicles in the enoploteuthid squid Abraliopsis sp. B and pineal organs in the myctophid fish Myctophum spinosum) were alternately exposed to overhead light or covered by a small opaque shield above the animal and the bioluminescent response of the animal was monitored. Covering either the eyes or the extraocular photoreceptors resulted in a reduction in the intensity of counterillumination. Preliminary experiments examining the bioluminescent feedback mechanism for monitoring intensity of bioluminescence during counterillumination in the midwater squid Abralia trigonura indicated that the ventral photosensitive vesicles are responsible for bioluminescent feedback.     

Lysosomal responses to experimentally injected anthracene in the digestive cells of Mytilus edulis

Experimentally injected anthracene (10 to 100 g mussel^-1) has been shown to induce dose-dependent lysosomal destabilisation and release of hexosaminidase in the digestive cells of Mytilus edulis after 24 h. This destabilisation was accompanied by cytological evidence of cytolysis of the digestive cells. The destabilising effect of 100 g of injected anthracene persisted for 96 h with a return to the control condition by 168 h. These results are discussed in the context of environmental contamination by polycyclic aromatic hydrocarbons.     

Long-distance dispersal and the reef-building corals of the Eastern Pacific

It is currently widely accepted that the hermatypic coral fauna in the Eastern Pacific Ocean underwent massive extinction during the mid-Tertiary, with subsequent transoceanic colonizatiion by planulae from the Indo-West Pacific region during periods of favorable conditions. We suggest that the available evidence does not strongly support this biogeographic hypothesis; moreover, we contend that it is untestable in its present form. In its place we propose an alternative hypothesis based upon modification of a previously widespread, pan-Tethyan coral biota which has since been modified by tectonic events, speciations, and extinctions.Order of authorship was determined by the toss of a coin.     

Dispersal,population structure and burrow shape of Ocypode cursor

The distribution of the sand crab Ocypode cursor (L.), as indicated by the number of burrows, was studied for 2 years in a 50×50 m sand beach area in northern Israel. A definite relationship was established between the distribution pattern from the seashore inwards towards the sand dunes, and the degree of sand moisture as it changed seasonally. During autumn, more crabs were found at a distance of 15 to 25 m from the sea where sand moisture was about 14%. At the beginning of winter crabs dispersed evely, disappearing with advancing winter. Crabs reappeared in spring, although in smaller numbers, dispersing in a pattern similar to that in autumn. At the beginning of summer and later on, more crabs appeared and concentrated closer to the sea (5 to 10 m). The population structure was analysed directly by measuring the crab's dimensions, and indirectly by counting burrows and measuring the diameter of their openings. Direct analysis revealed two distinct sizeage groups: smaller crabs 0.5 to 3 cm long, and larger ones over 4 cm long. The smaller burrows were inhabited by the first group and were mostly found closer to the sea; the second group was found more landwards. Three main types of burrow shapes are described.