Data assimilation for a coastal area morphodynamic model: Morecambe Bay

This paper investigates the use of data assimilation in coastal area morphodynamic modelling using Morecambe Bay as a study site. A simple model of the bay has been enhanced with a data assimilation scheme to better predict large-scale changes in bathymetry observed in the bay over a 3-year period. The 2DH decoupled morphodynamic model developed for the work is described, as is the optimal interpolation scheme used to assimilate waterline observations into the model run. Each waterline was acquired from a SAR satellite image and is essentially a contour of the bathymetry at some level within the inter-tidal zone of the bay. For model parameters calibrated against validation observations, model performance is good, even without data assimilation. However the use of data assimilation successfully compensates for a particular failing of the model, and helps to keep the model bathymetry on track. It also improves the ability of the model to predict future bathymetry. Although the benefits of data assimilation are demonstrated using waterline observations, any observations of morphology could potentially be used. These results suggest that data assimilation should be considered for use in future coastal area morphodynamic models.     

Otolith shape as a stock discrimination tool for ling (Genypterus blacodes) in the fjords of Chilean Patagonia

ABSTRACT

Genypterus blacodes, in terms of its fishing history and local economic importance, is an emblematic species harvested in Chilean Patagonia (41°00’–57°00’S). Most of the current fisheries and biological knowledge of this species come from the open ocean, whereas information about the species in fjords and inner channels is fragmentary. In 2018, two research surveys targeting G. blacodes were conducted in the fjords and inner channels of Chilean Patagonia. A total of 253 pairs of sagittal otoliths were sampled at three different localities, and their contours were modelled using wavelet analysis as a tool for stock discrimination. Contours were compared using canonical analysis, and classification was performed using linear discriminant and Random Forest analyses. The results indicated that the wavelet method is efficient in modelling otolith contours, and the discriminant analyses showed differences among fishing grounds across the latitudinal gradient, thus confirming the hypothesis that G. blacodes conform to at least two separate stock units in Chilean Patagonia. Fishing grounds that were closer in space showed higher levels of misclassification. The discussion focuses on how environmental variables and the geography of fjords shape stock differences and how this information can be used for the sustainable management of G. blacodes.     

Carbon stable isotopes in estuarine sediments and their utility as migration markers for nursery studies in the Firth of Forth and Forth Estuary, Scotland

The stable carbon isotope ratios (δ¹³C) of the organic fraction of intertidal sediments in the Forth Estuary and the Firth of Forth, Scotland, were measured to determine if terrestrially derived carbon was present in the estuarine sediments. It was hypothesised that differences in the inputs from marine vs. terrestrial sources to the organic carbon of estuarine and marine sediments, as well as differences in ambient seawater stable oxygen isotope (δ¹⁸O) ratios between the estuary and the Outer Firth, would allow the use of these two stable isotopes as habitat markers for juvenile plaice (Pleuronectes platessa), to allow determination of nursery habitats. Muddy and sandy sediments from the estuary and sandy sediments from the Outer Firth were sampled and δ¹³C measured. Juvenile plaice were caught at two estuarine sites and at two Outer Firth sites and otoliths were removed for δ¹³C and δ¹⁸O analysis. The sandy sediments in the estuary showed a strong gradient of δ¹³C enrichment with distance down the estuary, while the muddy sediments showed a much shallower gradient. δ¹³C and δ¹⁸O measured in the carbonate of juvenile plaice otoliths showed no clear difference between otoliths of fish caught at one of the estuarine sites and at the two Outer Firth sites. However, the isotope ratios of both carbon and oxygen in plaice otoliths from the other estuarine site showed the expected trend of depletion in the heavier isotopes. While the measurements recorded here did not conclusively distinguish between otoliths from juveniles caught in the estuarine site and those caught in the other three sites, they show that stable isotopes have potential to distinguish between estuarine habitats with terrestrial carbon inputs, and coastal marine habitats with predominantly marine carbon inputs.     

Spatial variation of the intertidal sediments and macrozoo-benthic assemblages along Eighty-mile Beach, North-western Australia

The extensive intertidal flats along Eighty-mile Beach in North-western Australia appear to be monotonous and homogeneous and seem ideally suited to study tidal zonation in macrozoo-benthic communities and their possible correlates with characteristics of the sediment. In October 1999, we sampled benthic invertebrates and sediments at a total of 895 sampling stations distributed over six different locations, each location separated by 15 km of unsampled foreshore along Eighty-mile Beach. To test for the presence or absence of patterns of tidal zonation (distinct height-related zones of specific sediment grain sizes or zoobenthic taxonomic groups) or patchiness (distinct patches of specific sediment grain sizes or zoobenthic taxonomic groups not related to tidal height) each location was divided into three along-shore sections and each section (transect) was examined at two or three tidal heights. Zonation was observed for sediment grain sizes. Sediments were coarser at the highest intertidal level and finer towards the low water line. Benthic assemblages also differed among tidal heights, but in terms of species-composition the differences were not consistent among the locations. Each location supported a unique collection of benthic invertebrates. Therefore the hypothesis of the presence of distinct zones of specific species or zoobenthic taxonomic groups was rejected; the presence of benthic patches was confirmed. The distribution of sediments and the composition of benthic assemblages were surprisingly poorly correlated compared to those reported in 12 previous quantitative studies around the world. One possible explanation might be that super-cyclone Vance, which hit the study-area only six months before this study, contributed to this poor correlation. Alternatively, the poor correlation may indicate that biotic interactions are more important than the assumed abiotic structuring.     

Measurement of alkaline and earthy ions in fish otolith and sea water using a high performance ion chromatography

Fish growth and the relation between growth and environmental conditions offer a good opportunity for measuring alkaline and earthy ions in fish otoliths.The analytical method must involve high sensitivity when attempting to discriminate between fish growth and environmental conditions.The aim of this paper is to propose a chromatographic method, with low detection limits, as a new approach in determining some important micronutrients present in sea water and fish otoliths.The work samples are: coastal, off-shore and sediment waters and fish otoliths (Engraulis encrasicholus, Mullus barbatus, Umbrina cirrhosa, Sciaena umbra, Pagellus erythrinus) in the Adriatic Sea and the Canal of Sicily.The analytical method includes an IONPAC CS12A chromatographic column and a 18 mM methanesulfonic acid eluent.The detection limit readings obtained with this method, for one E. encrasicholus fish otolith, weighing 2.6 mg are equal or inferior to 0.1 μg/L for lithium (Li), 59 μg/L for sodium (Na), 46 μg/L for ammonium (NH₄), 23 μg/L for potassium (K), 13 μg/L for magnesium (Mg), 88 μg/L for manganese (Mn), 2.567 μg/L for calcium (Ca) and 13 μg/L for strontium (Sr).The HPIC method minimizes overlaps such as Na on Li, and NH₄ in seawater and Ca on Mg and Sr in fish otolith. These elements are an essential constituent present in otoliths when describing the relation between growth and environmental conditions.Good separation among analytes is achieved within 16 min.     

日本鳗鲡早期阶段耳石日生长轮形成的周期

于1990年4月从江苏太湖搜集日本鳗鲡亲鱼暂养在天津滨海虾场8t玻璃钢水槽中，经人工催熟催产后孵出仔鳗，对孵出仔鳗连续取样；于1989年4月在长江口采集白仔鳗，观察和比较二者的耳石生长轮形成。结果表明，（1）人工繁殖仔鳗耳石第一个生长轮是在孵出后第一天形成的，轮纹形成具有24h周期性；仔鳗孵出后生长天数与生长轮数关系的回归方程以y=0．23＋0．91x表示，其中，x为孵出后的天数，y为生长轮数;在人工繁殖仔鳗耳石上没有观察到“孵化标记”轮。（2）白仔鳗耳石中心核与“孵化标记”轮之间存在日生长轮。（3）人工繁殖仔鳗与白仔鳗耳石中心核同第一个生长轮比较表明，前者小于后者。     

厦门海域鱼类瘤槽科平槽属绦虫一新种

本文报道厦门海域软骨鱼灰星鲨（Mustelus griseus）感染的四叶目瘤槽科绦虫新种——厦门平槽绦虫Platybothrium xiamenensis sp.nov.，对新种形态特征进行了详细描述并与近似种作了比较.     

A phase-resolving cross shore sediment transport model for beach profile evolution

A phase-resolving wave transformation module is combined with an intra-wave sediment transport module to calculate the on-/offshore sediment transport rates. The wave module is based on the Boussinesq equations extended into the surf zone. The vertical variation of the mean undertow and the intra-wave sediment concentrations are calculated. The net sediment transport rates are calculated, and the equation for conservation of sediment is solved to predict the beach profile evolution. The results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone, even for eroding beaches, suggesting that other contributions should not be neglected. The present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded.