Digestion in pycnogonids: a study of some polar forms

The process of digestion was studied in some polar pycnogonids, mainly the Antarctic forms Nymphon australe and Nymphon orcadense. Our findings did not support the theory of the digestive process proposed by Schlottke (1933) and this led to a re-examination of his ideas. We propose a new scheme for digestion in pycnogonids and fit Schlottke's observations into this framework. It is suggested that Antarctic pycnogonids may possess behavioural adaptations peculiar to their supply of food. Some directions for further study are indicated.     

Locomotory activity and exploration behaviour of juvenile European lobsters (Homarus gammarus) in the laboratory

The behaviour of juvenile European lobsters (Homarus gammarus) in the wild is little understood. A laboratory system was designed with a maze-like environment as an alternative to the large technological expenditure of a field study. It provided an apparently endless runway with uniform thigmotactical cues. Juvenile lobsters having a total length of 68 to 115 mm were studied. The lobsters showed an extensive nocturnal locomotory activity. They established home shelters in which they spent the day and covered distances of 1200 to 1600 m during the night. On average, the lobsters performed 136 excursions from their shelters, of which 10% led only to the immediate surroundings of the shelters. Of all the excursions 90% were shorter than 16 m. In some exceptional cases distances of several hundred meters were covered in the maze between shelter visits. Excursions of less than 16 m lasted on average less than 5 min. The frequencies of shelter visits during the dark phase were highest in small lobsters (300 visits) and lowest in larger lobsters (50 visits). The time spent within shelters decreased from 10% to less than 2% with lobster size. A distinct change in behaviour was obvious at a body length of 75 to 80 mm. Smaller lobsters behaved defensively and relied on shelter protection. Larger lobsters were less dependent on shelter protection and thus were able to explore and utilize their environment more intensively.     

Predatory behavior of giant Antarctic sea spiders (Colossendeis) in nearshore environments

Pycnogonids in the genus Colossendeis are found in the deep sea and Southern Ocean. Although the genus contains the largest and most conspicuous species of sea spiders, little is known about their ecology or behavior. We documented two species feeding on a variety of benthic and pelagic invertebrates during three diving field seasons at McMurdo Station, Antarctica. Individuals of one species, Colossendeis megalonyx, fed on a variety of pelagic organisms, particularly the pteropod Clione antarctica. We used video to document rapid capture of individuals of C. antarctica by captive specimens of C. megalonyx in the laboratory, and we suggest that, at least in the nearshore environment, pelagic invertebrates are an important food source for this and potentially other pycnogonid species.     

南极半岛北部南极磷虾渔业空间点格局特征

南极磷虾作为南极生态系统中的关键物种,在空间分布上常表现出集群特征.这也反映到磷虾渔业生产的空间格局特征上.为了探讨捕捞能力有明显差异的船队在高/低单位捕捞努力量渔获量(CPUE)的情况下空间点分布格局特征及其生态学效应,基于南极半岛北部海域的两艘中国南极磷虾渔船(船A为专业南极磷虾渔船,船B为在智利竹筴鱼渔场与南极磷虾渔场转换的兼作渔船)的磷虾渔业数据,从空间点格局的角度出发,分别从两船的高、低CPUE的空间点格局在不同尺度上聚集特征,高、低CPUE在不同尺度上的二元点格局相关关系,以及CPUE点标记格局下的相关性关系等3个方面进行了分析.Ripley的L函数和标记相关函数分析结果表明: 研究对象在空间窗口所有尺度上的空间格局均表现为聚集性,高、低CPUE下均有聚集发生;在15 km尺度上,聚集强度近最大,在15~50 km尺度下,聚集程度稳定;总体上点格局分布的聚集强度依次为:船A高CPUE>船B低CPUE>船B高CPUE>船A低CPUE.船A高、低CPUE在0~75 km尺度上为正相关关系,在大于75 km尺度上为随机关系;船B在所有尺度上的高、低CPUE均为正相关,说明了低CPUE点事件伴随高CPUE的点事件同步发生,两者在大部分尺度下均显著相关.这是磷虾集群模式的动态性和复杂性造成.船A各点的CPUE值在0~44 km尺度上呈正相关,在44~80 km尺度上呈负相关;船B各点的CPUE值在50~70 km尺度上呈负相关,在其他尺度上无显著相关性;正相关反映了磷虾密集集群的种群分布特性,而负相关表明了磷虾群间由于食物和空间原因存在一定的竞争关系.捕捞能力强的船A和捕捞能力较弱的船B在点格局分布上存在较大差异.专业南极磷虾渔船更适于开展磷虾作业空间点格局分析及相关科学调查工作.     

Novel locomotory mechanisms in caterpillars: life-line climbing in Epinotia abbreviana (Tortricidae) and Yponomeuta padella (Yponomeutidae)

Abstract. When alarmed, caterpillars of the tortricid Epinotia abbreviana (Fabricius) and the yponomeutid Yponomeuta padella (Linnaeus) parachute at the end of a single life-line spun out by the head spinnerets.Two methods are employed to climb back up the line.The first makes use of alternate movements of the left and right set of thoracic legs, aided by side-to-side movements of the body.This results in the life-line being wound in around the third pair of thoracic legs.The second method is based on the normal peristaltic rhythm used when walking on a solid substrate.Dorsoventral curling movements gradually transfer life-line from the thorax along the succession of abdominal pro-legs to the claspers at the end of the body.The life-line has similar physical characteristics to spider orb-web silk, and a breaking force equivalent to 5–8 times body weight.The holding force of the claspers when in contact with the ground exceeds the breaking force of the life-line.These studies demonstrate the flexibility of caterpillar locomotion, when confronted with a novel situation.     

Oxygen hypothesis of polar gigantism not supported by performance of Antarctic pycnogonids in hypoxia

Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (−1.8–0°C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for size×DO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.     

Biodiversity of yeasts and filamentous microfungi in terrestrial Antarctic ecosystems

Fungal biodiversity in Antarctic terrestrial ecosystems increases with the availability of water and energy, but cannot now be precisely described because of problems with identification and questions us to what organisms are truly indigenous. Yeasts probably predominate on continental Antarctica, while other microfungi usually do so in maritime and sub-Antarctica. Lists of nematophagous species and of microfungal species reported from maritime and sub-Antarctica are given. The ecological roles of these fungi are worthy of further research. The ability of common airspora and pathogens to survive and colonize should be investigated.     

南极菲尔德斯半岛水生植物的生物地球化学特征研究

利用中子活化分析技术,得到南极西湖沉积岩芯中水生植物（镰刀藓）的22种化学元素含量,发现南极水生植物的地球化学元素含量范围变化较大,而且在沉积层次上,各个元素的变异系数也较大,水生植物吸收和累积元素的特征为：稀土元素,U,As极容易为植物吸收同化,Ca,Co,Sc为水生植物容易吸收的元素,Th,Hf,Na为水生植物难以同化的元素。同时,研究发现水生植物的直接营养物源为湖水中的可溶性离子;对水生植物的22种化学元素进行聚类分析,发现稀土元素,Ca,Zn,U之间,As,Fe,Co之间共生关系密切,对水生植物具有相似的生理作用。     

Rafting in Antarctic Collembola

Darwin was an early exponent of the importance of 'occasional means of dispersal' in accounting for the present-day distribution of plants and animals. This study examined the implications of capture on the water surface of meltwater and seawater for the local and long-range dispersal of Antarctic springtails. Individuals of the maritime Antarctic collembolan Cryptopygus antarcticus , were floated on tap water and seawater at 0, 5 and 10°C. LT₅₀s on seawater were 34 (10°C), 65 (5°C) and 75 (0°C) days. On tap water, LT₅₀s were 69 (10°C), 126 (5°C) and 239 (0°C) days. Less than 20% escaped from the water surface. A significantly greater proportion of springtails moulted on tap water and viable offspring were produced on both tap water and seawater. Comparison across treatments of survival of moulting and non-moulting individuals found significantly greater survival in moulting animals for three of the treatment combinations. It is suggested that moult exuviae facilitate survival on the water film through the simultaneous provision of a flotation aid and a source of nourishment – that is, an 'edible raft'. A separate experiment measuring changes in haemolymph osmolality over time on tap water and seawater at 2 and 5°C found significant differences in all treatments. Causes of mortality are discussed in relation to osmoregulatory failure and starvation.     

Light climate and phytoplankton photosynthesis in maritime Antarctic lakes

The responses of phytoplankton populations to seasonal changes in radiation flux in two Antarctic lakes with extensive winter ice-cover are described. A phytoplankton capable of photosynthesis was found throughout the year in both systems. During winter, low incident radiation combined with thick layers of snow and ice prevented in situ photosynthesis becoming detectable. The beginning of spring was marked by a reduction in snow cover which resulted in a considerable increase in surface penetrating radiation. Planktonic algae rapidly adapted to utilise these increased levels efficiently, though they still showed characteristics of strong shade adaptation.Loss of ice cover at the start of the short open water period further increased the radiation levels and a summer population developed which was much less shade adapted. Saturation and photoinhibition effects were widespread during this period as the algae proved unable to utilise high radiation levels efficiently. They were however effective at the radiation fluxes prevalent in the lower part of the rapidly circulating water columns.     

Nitrogenous excretion in the Antarctic plunderfish

The nitrogenous excretion rates (total ammonia nitrogen, urea, and primary amines) of plunderfish Harpagifer antarcticus were related significantly to length and to wet mass (mass exponents of 0·94, 1·01, 1·07 and 0·93 for total ammonia nitrogen, urea, primary amines, and total nitrogen, respectively). The routine total ammonia excretion rates [22·23 & 2·0 mg N kg⁻¹ day⁻¹ (mean±S.E.)] of plunderfish measured in Antarctica are 10–69% lower than those of comparable non-polar species. Plunderfish are ammonotelic, but the proportion of the total nitrogenous waste attributable to each category was variable between individuals. On average (ranges in parentheses), total ammonia nitrogen, urea, and primary amines accounted for c .82 (57–97), 13 (2–28), and 5 (0·6–22)%, respectively, of the total nitrogen excreted. Polar fish differ from their non-polar relatives only in the rate, and not the nature, of their nitrogenous waste excretion processes.     

Ovarian development associated with first maturity in three Antarctic channichthyid species

It has been known for some time that yolk deposition and final ovarian maturation were prolonged processes for many Antarctic fish. The adolescent phase in three species of channichthyid has been studied, based on an extensive series of samples over five seasons. Samples were obtained during a series of abundance estimation surveys on the shelf around South Georgia. Fish were measured, and sex and maturity stage determined from macroscopic examination of the gonads. It was found that for female Champsocephalus gunnari and Pseudochaenichthys georgianus the adolescent phase lasts <1 year but in Chaenocephalus aceratus it lasts for nearly 4 years.     

Composition and significance of picophytoplankton in Antarctic waters

Filter fractionated picophytoplankton from Antarctic coastal waters (summer 2001) represented only 7–33% of total phytoplankton, even though total stocks were low (average Chl a = 0.32 μg l⁻¹, range = 0.13–1.03 μg l⁻¹). Though all cells passed a 2 μm filter, electron microscopy revealed most cells were over 2 μm, principally Parmales, Phaeocystis sp., and small diatoms. CHEMTAX analysis of HPLC pigment data suggested type 8 haptophytes (e.g. Phaeocystis sp. plus Parmales and pelagophytes) contributed 7–58% of picoplanktonic chlorophyll a, type 6 haptophytes (e.g. coccolithophorids) 18–59%, diatoms 0–18% (mostly type 2 diatoms, e.g. Pseudonitzschia sp., 0–15%), prasinophytes 0–17%, with cell fragments of cryptophytes 0–40%, and dinoflagellates 0–11%. Only stocks of type 8 haptophytes and prasinophytes differed significantly due to successional changes. Zeaxanthin concentrations exceeded estimates from previous cyanobacterial counts and may derive from non-photosynthetic bacteria.     

Iron-Rich Diagenetic Minerals are Biomarkers of Microbial Activity in Antarctic Rocks

The cold, dry ecosystems of Antarctica have been shown to harbor traces left behind by microbial activity within certain types of rocks, but only two indirect biomarkers of cryptoendolithic activity in the Antarctic cold desert zone have been described to date. These are the geophysical and geochemical bioweathering patterns macroscopically observed in sandstone rock. Here we show that in this extreme environment, minerals are biologically transformed, and as a result, Fe-rich diagenetic minerals in the form of iron hydroxide nanocrystals and biogenic clays are deposited around chasmoendolithic hyphae and bacterial cells. Thus, when microbial life decays, these characteristic neocrystalized minerals act as distinct biomarkers of previous endolithic activity. The ability to recognize these traces may have potential astrobiological implications because the Antarctic Ross Desert is considered a terrestrial analogue of a possible ecosystem on early Mars.     

British biological research in the Antarctic

A tradition of biological research in the Antarctic was established by Cook 200 years ago. This tradition has been built on by other British expeditions, notably the 'Discovery' Investigations. The British Antarctic Survey, which arose from Operation Tabarin and the Falkland Islands Dependencies Survey, now carries out a programme of coordinated and continuous biological research. The Atlantic sector of the Antarctic, in which the Survey operates, is of key importance biologically. The Antarctic provides a striking biological contrast between a species-poor and very barren terrestrial ecosystem and the species-rich and productive ocean which surrounds it. Severe climatic conditions and great isolation (a contrast to the Arctic) characterize the Antarctic environment. Work at the Survey's biological research stations is designed to study the distribution and interactions of organisms and communities, how they have adapted to Antarctic conditions, and which by their abundance may be deemed successful. Research is done into terrestrial, fresh-water and marine systems. Additionally, there is a major research programme into the biologv, environment and principal predators of krill, Euphausia superba. The Antarctic is a laboratory where opportunities exist for natural experiments to test theories and elucidate basic biological problems.     

Freezing in the Antarctic limpet, Nacella concinna

The process of organismal freezing in the Antarctic limpet, Nacella concinna, is complicated by molluscan biology. Internal ice formation is, in particular, mediated by two factors: (a) the provision of an inoculative target for ice formation in the exposed mucus-secreting foot; and (b) osmoconformity to the marine environment. With regard to the first, direct observations of the independent freezing of pedal mucus support the hypothesis that internal ice formation is delayed by the mucal film. As to the second, ice nucleation parametrics of organismal tissue (head, midgut, gonad, foot) and mucus in both inter- and subtidal populations were characterized by high melting points (range = −4.61 to −6.29 °C), with only c.50% of a given sample osmotically active. At this stage it would be premature to ascribe a cryo-adaptive function to the mucus as the protective effects are more readily attributed to the physical properties of the secretion (i.e. viscosity) and their corresponding effects on the rate of heat transfer. As it is difficult to thermally distinguish between the freezing of mucus and the rest of the animal, the question as to whether it is tolerant of internal as well as external ice formation remains problematic, although it may be well suited to the osmotic stresses of organismal freezing.