Monitoring spatio-temporal variation in molluscan grazing pressure in seasonal, tropical rock pools

In Hong Kong, low-shore rock pools support a patchy mosaic of different successional stages of crustose coralline algae. Echinoid and molluscan grazers are abundant in these low-shore rock pools and spatial and temporal variation in grazing pressure is thought to play an important role in structuring these assemblages. Direct records of graze marks using a modified wax-disc method were used to monitor spatial (different pools) and temporal (periods, 3 or 4 days each; spring vs. neap tides; summer vs. winter) variations in grazing pressure. Radula marks of Chlorostoma argyrostoma, Lunella coronata and Nerita albicilla were common in all pools. Grazing pressure was highly variable with tidal state and season but also within these two factors. Lunella and Nerita exerted highest grazing pressure at neap tides during summer, whilst Chlorostoma exerted highest grazing pressure in winter. Although overall patterns of temporal variation were similar and consistent in all pools, there was between pool variation in grazing pressure and individual species showed different patterns. Within the seasonal and tidal variations, large period-to-period differences were found for all species, illustrating small-scale temporal variation. Fine-scale spatial and temporal patterns of variation in grazing pressure of different species, therefore, contribute to the highly dynamic nature of these low-shore rock pools.     

Gene flow among giant clam (Tridacna gigas) populations in Pacific does not parallel ocean circulation

Tridacna gigas (L.) populations were sampled from 13 locations throughout the west Pacific in 1990–1991 and screened for allozyme variation at seven polymorphic loci. Significant genetic differences were found between the few large stocks of T. gigas remaining in the world. Cluster analysis identified two major regional groups of populations: a Central Pacific group consisting of Kiribati and the Marshall Islands, and a West Pacific group comprising all other populations. Within the latter group, the Great Barrier Reef populations were significantly differentiated from those in the Solomon Islands. The main routes of gene flow did not run parallel with known major surface currents as might be expected, but crossed them. Gene exchange was limited east-west between the Central and West Pacific groups and the GBR and the Solomon Islands. The lack of correspondence between the major surface currents and the routes of gene flow suggests that the genetic structure of T. gigas reflects historical patterns of migration that no longer occur, rather than presentday dispersal. These findings raise fundamental questions concerning the origin and maintenance of genetic diversity in Pacific faunas, and have important implications for the mariculture and conservation of T. gigas.     

Plankton of the fladen ground during FLEX 76 I. Spring development of the plankton community

Results from plankton sampling in the northern North Sea with the Continuous Plankton Recorder (CPR) and the Undulating Oceanographic Recorder (UOR) during the Fladen Ground Experiment in 1976 (FLEX 76) are summarised. The first evidence of the spring outbreak of phytoplankton was on 19 April, the day after the first signs of vertical stability of the water column were observed. This was followed by spawning of the euphausiid Thysanoessa inermis and rapid increase in the numbers of Calanus finmarchicus. C. finmarchicus was the most abundant species over the FLEX period (19 March to 3 June) and, together with T. inermis, accounted for over 80% of the dry weight of the zooplankton standing stock. By early June the standing crop of phytoplankton had been depleted and nutrients levels were reduced to very low concentrations in the upper 50 m.JONSDAP Contribution No. 49     

Application of function analysis to bathing areas in the Maltese Islands

On a small island such as Malta where many developers and policy makers place a large emphasis on social use and develoment values, which encourages recreational/industrial development, it is often hard to promote the monetary value of coastal conservation due to strong competition with the large tourism industry. An assessment of the ecological (conservation) and economic (use/development) values of four popular Maltese bathing areas (Mellieha, St. George’s, Ramla and Ghajn Tuffieha Bay) was carried out by evaluating their ability to provide a number of functions. This is dependent on the environments’ inherent characteristics within the context of locally applicable time and space functions. Function Analysis is an innovative technique able to provide a means for assessing changes in environmental quality of an area and evaluating the sustainability of applied management regimes. This paper is a first example of an application of the Functional Analysis approach in Malta. Local application of this technique indicates a need for additional refinement in application to coastal areas. Analysis showed that St. George’s, had the lowest conservation value, Ramla and Ghajn Tuffieha bay had the highest conservation values, Mellieha Bay had high conservation value and use/development potential. In this context, conservation value is understood to reflect values of biodiversity, information/knowledge and environmental quality.     

物种灭绝的若干种可能的序

利用集合种群共存动力模式，研究了由于栖息地毁坏而导致物种灭绝的顺序问题．研究结果表明：在群落里各物种种群具有相等的死亡率的假设下，栖息地毁坏而导致物种的灭绝存在3种最基本可能的顺序，既最弱物种与最强物种相伴灭绝，最强物种与最弱物种是强弱交替灭绝，以及由强而弱依次灭绝．参7     

The degradation of plastic litter in rivers: Implications for beaches

Polythene sheeting is a major litter component on estuarine beaches and river banks. Sanitary towel backing strips, which are one of the commonest items of sewage related debris found on beaches, enter the riverine system via combined sewer overflows. Investigations on these items, positioned at natural riverine stranding levels, showed that after an initial rapid breakdown little further loss of tensile strength occurred. Experiments carried out on backing strips, buried in the bank suspended from a tree and tethered to the bank, showed significant change. Buried samples retained the greatest tensile strength retention, dropping no lower than 90 %, the other samples showed similar retention rates at 80%. The difference is probably due to photodegradation as biodegradation effects were minimal. Probably, the longevity of such plastics is a major reason for their abundance and widespread distribution both on river banks and beaches.     

Assessment by Hair analysis of Mercury Exposure Among Mining Impacted Communities of Mindanao and Palawan, The Philippines

Human mercury (Hg) exposure in two contrasting areas of mining and mineral processing activity on the Philippine islands of Mindanao and Palawan was evaluated using hair analysis. On Mindanao, samples were collected from residents of Apokon, a major regional centre for gold beneficiation. On Palawan, a former cinnabar mine and mine-waste disposal site in Honda Bay formed the focus of investigation. Relatively high hair Hg burdens (up to 13mg Hg kg^–1 at Apokon and 18.5mg Hg kg^–1 in Honda Bay) were observed in both populations, with occupational factors apparently constituting a first-order exposure control. At Apokon, hair burdens in excess 2mg Hg kg^–1 were recorded in 90% of Au processing plant workers, compared with 21% of other sectors of the population. In Bay, ex-mineworkers, although possibly subject to occupational Hg exposure in the past, now display no evidence of this influence. Fishermen, however, systematically yielded hair Hg concentrations a factor of 2.5 higher than those of the remaining population. Approximately 7% of the Apokon and Honda Bay residents sampled presented hair Hg concentrations equal to or in excess of the World Health Organisation (WHO) reference dose. There is little evidence to indicate that residential factors significantly influence Hg exposure in either area. Hazard mitigation strategies involving the isolation of resident populations from perceived contaminant sources such as ore processing plant and sites of mine-waste disposal are, therefore, unlikely to prove beneficial.     

Recycling greenhouse gas fossil fuel emissions into low radiocarbon food products to reduce human genetic damage

Radiocarbon from nuclear fallout is a known health risk. However, corresponding risks from natural background radiocarbon incorporated directly into human genetic material have not been fully appreciated. Here we show that the average person will experience between 3.4 × 10¹⁰ and 3.4 × 10¹¹ lifetime chromosomal damage events from natural background radiocarbon incorporated into DNA and histones, potentially leading to cancer, birth defects, or accelerated aging. This human genetic damage can be significantly reduced using low radiocarbon foods produced by growing plants in CO₂ recycled from ordinary industrial greenhouse gas fossil fuel emissions, providing additional incentive for the carbon sequestration.     

Surface-film microbial populations: diel amino acid metabolism,carbon utilization,and growth rates

Microheterotrophic dissolved free amino acid (DFAA) utilization, and microbial community and bacterial community carbon production and growth were studied using ³H-labeled organics as tracers in marine surface-film and subsurface (10 cm) waters off Baja California in November 1983. DFAA utilization was generally more rapid during the day (0.14 to 0.38 nM h^-1) than at night (0.04 to 0.14 nM h^-1) in surface-film and subsurface waters, but the percent of utilized amino acid which was respired was always greater during the night (22 to 57%) compared to the day (14 to 18%). Utilization of DFAA-carbon was estimated to range from 0.3 to 5.3 g C l^-1 d^-1 for all stations studied. In six of the 8 samples examined, the percentage of microbial carbon accounted for by the bacterial component of the population (1.4 to 5.9%) was strikingly similar to the percentage of microbial carbon production accounted for by bacterial carbon production (1.9 to 5.1%). In all of these six samples, total microbial specific-growth rates and bacterial specific-growth rates were approximately equivalent (0.9 to 2.2 d^-1 for the microbial community; 0.7 to 1.9 d^-1 for bacteria). The two exceptions were samples apparently influenced by transient flagellate populations migrating into the surface or subsurface waters at night. These observations support the conclusion that surface films contain unique and highly active microbial populations.     

Mathematical analysis of the effects of particle retention efficiency on determination of filtration rate

Morphological, ecological, and behavioral aspects of filtration of small, inefficiently retained particles by benthic as well as planktonic filter-feeders are of current as well as historical interest. The exponential model applied to determination of filtration rate was originally conceived for filter-feeders clearing suspensions of large, efficiently retained cells. Therefore, applicability of this model and its assumptions to filtration of small, inefficiently retained particles merits critical re-examination. Derivation of the exponential model historically used in calculation of filtration rate is reviewed and shown to be inappropriate when filtration efficiency is less than 100%. Box models are constructed for filter-feeders that act either as sieves or aerosol filters in suspensions of small inefficiently filtered cells. The models predict a complex or double exponential decline in cell concentration that cannot easily be translated into filtering or pumping rates. The models further predict that apparent filtration rate will decline over time because of physical limitations, rather than behavioral changes, with respect to filtration efficiency. Compartmental analysis of filtration of inefficiently retained particles in a turbidostat system predicts a similar artifact in determination of filtration rate.