Population dynamics of the sea urchin Strongylocentrotus purpuratus in a Central California kelp forest: recruitment,mortality, growth,and diet

The population dynamics of Strongylocentrotus purpuratus inhabiting dense mats of geniculate coralline algae in a shallow central California Macrocystis pyrifera forest was examined. Sea otters had occupied the area for over two decades. Sea urchin density and size distribution were sampled during 1984–1986 to determine recruitment and mortality patterns. Growth rates were obtained from tetracycline-labeled individuals and changes in sizefrequency modes. Periodic collections were made to examine gut contents and the relationship of diet to food availability. The interaction of recruitment and mortality resulted in a dynamic population structure. Mean densities ranged from 6.5 to 12.7 urchins 0.25 m^-2. The population consisted primarily of urchins up to 40 mm in test diameter in a size distribution which changed from unimodal to bimodal and back over the 2 yr study. Mortality was temporally variable and related to test diameter. Growth rates were somewhat lower than most previous reports for the species and suggested that most of the population was made up of 1 and 2 yr-old individuals. Diet consisted largely of geniculate coralline algae, with fleshy brown algae becoming important when available as drift. This study showed high densities of small urchins can exist in a California kelp forest inhabited by sea otters, but regular recruitment may be necessary to maintain such populations.     

Fatty acid composition of organs and tissues of the tiger prawn Penaeus esculentus during the moulting cycle and during starvation

The fatty acids (FA) in neutral lipid (NL) and polar lipid (PL) of digestive gland, muscle and integument of Penaeus esculentus Haswell were analysed and compared during the moulting cycle and during starvation. The prawns were collected from Moreton Bay, Queensland, Australia, by trawling during 1985–1987, and were fed with a standard semi-purified diet. Compared with a natural diet, the artificial diet had much higher levels of 18:1n-9 and 18:2n-6, but only trace amounts of 20:4n-6, but there was no evidence of dietary imbalance. The fatty acid composition (percentage of total lipid) of the digestive gland changed markedly during the moulting cycle and during starvation, but the small changes observed in both muscle and integument suggested that these tissues maintained their composition under both conditions. When the fatty acids were calculated as absolute amounts, muscle composition, as well as that of the digestive gland, changed significantly. In the digestive gland, saturated FA (SFA), monounsaturated FA (MUFA), diunsaturated FA (DUFA) and polyunsaturated FA (PUFA) all increased up to the middle of the moulting cycle and then declined; with starvation all groups decreased. In muscle, SFA, MUFA and DUFA all increased during the moulting cycle; starvation caused SFA, MUFA and PUFA to decrease, whereas DUFA did not vary. Starvation caused both 18:2n-6 (linoleic) and 18:3n-3 (linolenic) in the digestive gland to reach or almost reach zero. The other essential PUFA, 20:4n-6 (arachidonic), 20:5n-3 (eicosapentaenoic) and 22:6n-3 (docosahexaenoic), decreased during the moulting cycle, but during starvation 20:4n-6 did not decrease as much. In muscle, the levels of 18:2n-6 and 18:3n-3 increased, while 20:4n-6, 20:5n-3 and 22:6n-3 remained approximately constant during the moulting cycle. Starvation reduced 20:5n-3 and 22:6n-3 to about 60%. The data suggest that levels of 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3 are regulated, and that 20:4n-6 can be synthesised from 18:2n-6. There is no clear evidence that 20:5n-3 and 22:6n-3 are essential in P. esculentus, but tissue catabolism of cell membranes during starvation may have provided sufficient amounts for maintenance.     

Comparative study of the structure of some tropical and temperate marine soft-bottom macrobenthic communities

Macrobenthic sampling of a transect of six stations on the North coast of Central Java in October 1985 revealed three distinct communities which can be regarded as paraliels of those from north temperate waters: (i) An Amphioplus (Lymanella) laevis/Lovenia sp. community parallel with the Amphiura chiajei/Brissopsis lyrifera community. (ii) A Tellinides timorensis community parallel with Tellina spp. communities. (iii) A Laciolina philippinarum community parallel with Macoma spp. communities. A strict comparison of the structure of the first two of these communities with their counterparts in England shows that within-habitat diversity is similar in both regions. Diversity at two shallower subtidal stations is higher than at two deeper stations: this is attributed to the effects of natural, low-level, physical disturbance which maintains the communities in a sub-climax stage. Total abundance and biomass of the macrobenthic fauna was lower at the Javanese stations than in their temperate counterparts.     

Ultrastructure and behavior of the larva of Phragmatopoma californica (Polychaeta: Sabellariidae): identification of sensory organs potentially involved in substrate selection

The tentacles of the larvae of Phragmatopoma californica (Fewkes) a tubicolous, reef-building polychaete, were examined by video-equipped light microscopy and transmission and scanning electron microscopy. The surface of the tentacles has a unique ciliation pattern, consisting of dorsal tufts of short immotile cilia, ventrolateral tufts of short and long immotile cilia, and ventral motile cilia. Cells bearing immotile cilia are primary sensory cells with long basal processes that form synapses with basiepithelial nerve fibers. The sensory cell cytoplasm is similar to that of nervous tissue, and contains microtubules, neurofilaments, and synaptic vesicles. Sensory cell synapses with basiepithelial nerves appear to be both axodendritic and axoaxonic. The structure of the immotile cilia is compared to that of motile cilia. Unlike motile cilia, immotile cilia are short, rigid, end in a blunt tip and possess and axoneme with typically arranged mictotubules that terminate in an electron-dense end plate. The basal feet of immotile cilia do not anastomose with adjacent basal bodies, and the ciliary membrane is loosely applied to the axoneme and is covered by a surface coat of filamentous material. The use of the larval tentacles during substrate exploration, and the location and ultrastructure of sensory cilia, indicate that they may be involved in the perception of substrateassociated chemical signals and/or mechanical cues of significance in substrate selection.     

An unusual blue mesogleal protein from the mangrove jellyfish Cassiopea xamachana

The jellyfish Cassiopea xamachana often contains a blue pigment diffused within the acellular portion of its masoglea. In the bell, both the pigment and endosymbiotic zooxanthellae are concentrated immediately beneath the ex-and subumbrellar epithelia. Chromatographic and polyacrylamide gel electrophoretic techniques demonstrate that the pigment is a highly polymeric glycoprotein (mol. wt>10⁶ daltons) comprised of two subunits with molecular weights of 34 500 and 30 300 daltons and characterized by multiple charged species. The blue native protein exhibits light absorption maxima at 620, 587, 555 and 415 nm, while SDS denatured protein is pink with a single absorption maximum at 507 nm. No prosthetic chromophore or heavy metal component was detected. The pigment is proposed to act as a light attenuator protecting the jellyfish from injurious solar irradiation while allowing photosynthetically active wavelengths to reach the zooxanthellae.     

Polonium-210 and lead-210 in Antarctic marine biota and sea water

Concentrations of the naturally-ocurring radionuclides ²¹⁰Po and ²¹⁰Pb were measured in krill (Euphausia superba), mesozooplankton, phytoplankton and sea water collected during the South African SIBEX cruise to the Antarctic in autumn 1984. The data reported constitute the first substantial measurements on ²¹⁰Po and ²¹⁰Pb in such samples in the Antarctic Ocean. The concentrations of ²¹⁰Po in mesozooplankton and phytoplankton are unexceptional in comparison with those from other oceans. The SIBEX E. superba, however, have higher levels of ²¹⁰Po than usually found in euphausiids. The ²¹⁰Po data, combined with reasonable estimates of biological quantitites such as the fractional assimilation, are used to obtain information about the diet of E. superba. It is suggested that the higher ²¹⁰Po in the SIBEX E. superba reflects a change from an almost entirely phytoplanktonic diet in summer to a more omnivorous diet as winter approaches. The data show that there are allometric relationships between the ²¹⁰Po content of euphausiids and animal size; these are discussed briefly. The limited sea-water data presented are characterized by unusually high ²¹⁰Po:²¹⁰Pb activity ratios and need further investigation.     

Developmental change in aggregation,defense and escape behavior of buckmoth caterpillars,Hemileuca lucina (Saturniidae)

Summary Changes in response to attack and the tendency to aggregate were examined in the six larval instars of the buckmoth, Hemileuca lucina (Saturniidae). In response to simulation of attack by a parasitoid and of biting by a predator, early instars (I, II, and III) exhibited defensive behavior much more often than escape behaviors, whereas late instar larvae (IV, V, and VI) usually resorted to escape rather than defend themselves. The situations in which attacked larvae were most likely to stimulate other group members to respond were: second and third instar larvae thrashing in response to simulation of a parasitoid or headrearing in response to simulation of a biting predator; and fourth, fifth and sixth instar larvae dropping in response to either stimulus. An index of reaggregation indicated that first instar larvae had difficulty reaggregating; second, third and fourth instar larvae reaggregated quickly; and fifth and sixth larvae dispersed. As larvae developed, the change from predominantly defense to escape behaviors paralleled the decline in tendency to aggregate.