Scenarios of nonlinear wave transformation in the coastal zone

On the basis of field experiments and numerical modeling, we show that coastal zones are classifiable according to manifestations of wind wave nonlinearity, which herein is recognized as periodic energy exchange between the first and second nonlinear wave harmonics depending on the average bottom slope and the Iribarren and Ursell numbers. The results offer a basis for developing vulnerability criteria for the coastal zone taking into account its nonlinear dynamics.     

Space-time variability of the field of mechanical energy transfer from the atmosphere to the Indian Ocean

An analysis of the spatial and temporal variability of the field of mechanical energy transfer (MET) from the atmosphere into the ocean is based on a separate numerical simulation of evolution for the terms of source function for a wind-wave model conducted in the Indian Ocean area for the period 1998 to 2009. The MET field is described by two integral values calculated per unit area: the total rate of energy flux from the wind to waves, I _E (x, t), and the rate of energy-loss flux for the wind waves, D _E (x, t). To solve this problem, the wind field W(x, t) is used, downloaded from the NCEP/NOAA archive [1], and the fields I _E (x, t) and D _E (x, t) were calculated using the numerical model WAM [2] with the modified source function proposed in [3]. Maps for the fields I _E (x, t) and D _E (x, t) were obtained by calculations with different scales of the space-time averaging, extreme and average values of the MET were found, seasonal and interannual variability was estimated, and the 12-year trend for several mean quantities was obtained.     

A tool for site prioritisation of marine protected areas under data poor conditions

A challenge of managing data poor fisheries lies in overcoming uncertainties associated with a lack of information on biological and socio-economic conditions. This paper focuses on site prioritisation for marine protected areas, a process that usually imposes moderate to heavy demands on data, time, local expertise, and funds. A fuzzy logic decision support tool for zoning marine areas that is suitable for use in data poor conditions is developed. This tool, the Protected Area Suitability Index (PASI), assesses the suitability of sites for protection based on fishers’ preferences for that site and the site’s conservation value. Only eight input attributes are required to run the PASI, which operates on a series of heuristic rules to estimate a site suitability score that ranges from 0 to 10, where 10 indicates that a site is highly suitable for being protected from fishing. Sensitivity analysis reveals that the PASI is relatively robust, and produces reliable results even as the system is degraded by the loss of data. Eighteen actively fished sites and 11 sites that are closed to fishing are assessed to evaluate how well the PASI is able to distinguish differences between sites. The estimated scores are significantly different (p<0.05), whereby non-fished sites are scored as being more suitable for protection than fished sites. The PASI can be used as a decision support tool to facilitate systematic marine spatial management under data poor conditions, especially in the task of identifying suitable sites for protection.     

Deep-water geomorphology of the glaciated Irish margin from high-resolution marine geophysical data

The continental margin offshore of western Ireland offers an opportunity to study the effects of glacial forcing on the morphology and sediment architecture of a mid-latitude margin. High resolution multibeam bathymetry and backscatter data, combined with shallow seismic and TOBI deep-towed side-scan sonar profiles, provide the basis for this study and allow a detailed geomorphological interpretation of the northwest Irish continental margin. Several features, including submarine mass failures, canyon systems and escarpments, are identified in the Rockall Trough for the first time. A new physiographic classification of the Irish margin is proposed and linked to the impact of glaciations along the margin. Correlation of the position and dimensions of moraines on the continental shelf with the level of canyon evolution suggests that the sediment and meltwater delivered by the British–Irish Ice Sheet played a fundamental role in shaping the margin including the upslope development of some of the canyon systems. The glacial influence is also suggested by the variable extent and backscatter signal of sedimentary lobes associated with the canyons. These lobes provide an indirect measurement of the amount of glaciogenic sediment delivered by the ice sheet into the Rockall Trough during the last glacial maximum. None of the sedimentary lobes demonstrates notable relief, indicating that the amount of glaciogenic sediment delivered by the British–Irish Ice Sheet into the Rockall Trough was limited. Their southward disappearance suggests a more restricted BIIS, which did not reach the shelf edge south of 54°23′ N. The various slope styles observed on the Irish margin represent snapshots of the progressive stages of slope development for a glacially-influenced passive margin and may provide a predictive model for the evolution of other such margins.     

Sedimentology and evolution of Omaro Spit,Coromandel Peninsula

The sedimentary structures, composition, and texture of sediments from the barrier coast complex (Matarangi Beach—Omaro Spit—Whangapoua Harbour) at Whangapoua, Coromandel Peninsula, are described. Sediments are mainly fine sands, rarely muddy or silty, and most are plagioclase feldsarenites, reflecting derivation from a predominantly Tertiary volcanic hinterland. Sediments from each of the modern environments, namely nearshore, foreshore, back‐shore, frontal dunes, tidal flats, and tidal channels, are characterised by a particular combination of sedimentary structures and subtle textural parameters. Dune ridge and barrier flat paleoenvironments on Omaro Spit were successfully identified by comparing their lithologic properties with the modern sediments. ‘Surficial’ sediments of the well‐preserved dune ridge system developed immediately inland from Matarangi Beach closely resemble those in the modern frontal dunes, and the ‘in depth’ dune ridge sediments are more analogous to the present foreshore sands. The barrier flat deposits separating the dune ridge system from Whangapoua Harbour have similar characteristics to the modern tidal flat sediments in the harbour.

Omaro Spit probably began as an offshore bar across the mouth of Whangapoua Harbour, an embayment formed by the post‐glacial drowning of a Late Tertiary dislocated fault‐block. Tidal flat sedimentation within the harbour formed the ancient barrier flat deposits which rise to at least 2 m above the modern harbour flats, suggesting local sea level at the time was higher than at present. During a subsequent cyclic fall in sea level, supratidal aeolian deposition led to a succession of 15 to 18 parallel dune ridges developed on high‐tide berms. Linear regression analyses of dune ridge and swale heights and the height distribution of positive (aeolian) and negative (beach foreshore) skewness values and of contrasting sedimentary structures in dune ridgL paleosediments, together with the stages in dune soil development across the barrier, suggest initial sedimentation occurred from 4000–5000 years ago when local sea level was 2–3 m above present mean high water level. Barrier progradation was interrupted by an important period of coastal erosion during a temporary rise in sea level immediately before deposition in the dune ridge system of a layer of 2000‐year‐old sea‐rafted Leigh Pumice. Sea level probably reached its modern position at Whangapoua about 1000 years ago, since when some evidence suggests the barrier spit may have experienced minor uplift.     

Oxygen consumption in the epilimnia and hypolimnia of two eutrophic,warm‐monomictic lakes

Oxygen consumption was estimated for two eutrophic New Zealand lakes using a simple 2‐layer model, from estimates of net changes in oxygen, phytoplankton photosynthesis, inflow and outflow, diffusion, eddy diffusion, and changes in the depth of the thermocline. Of the total oxygen consumption, 75–85% occurred in the epilimnia. Epilimetic oxygen consumption per m³ and per m² in Lake Johnson were higher than in Lake Hayes, reflecting known differences in the trophic status of the lakes, but estimates for the hypolimnia of the two lakes were similar. Daily hypolimnetic areal deficits were sensitive to both the depths and time intervals chosen.

In the epilimnia, monthly oxygen production by photosynthesis averaged 1.1 and 1.8 times the initial oxygen content in Lakes Hayes and Johnson respectively. Diffusion appeared to be of similar magnitude to photosynthesis in the isothermal period, but was less important during stratification. Losses to the hypolimnia by eddy diffusion were less than 10% of photosynthesis. Photosynthesis in the hypolimnia contributed 30–40% of the oxygen consumed there and eddy diffusion supplied a further 20%.

In Lake Johnson a 3–5 m stratum of water in the metalimnion became anoxic for 2–3 months each summer while there were still up to 5.2 g.rer³ of oxygen remaining in the hypolimnion. Metalimnetic anoxia is attributed largely to oxygen consumption in situ, resulting from the highly eutrophic state of the lake and intense thermal stratification. Zooplankton respiration accounted for less than 10% of the maximum net decline in metalimnetic oxygen in 1970–71, but was more important in the other 2 years.

Changes in the oxygen content of the hypolimnion indicate that Lake Hayes has become more eutrophic since 1954–55. In Lake Johnson low oxygen concentrations at the autumn overturn (<5 g.m^‐3) represent a threat to the trout population.     

Effects of protandric sex change on radula,pedal morphology,and mobility in Crepidula fecunda (Gastropoda: Calyptraeidae)

Protandrism was confirmed in Crepidula fecunda Gallardo 1979 by histological analysis of the gonad. Individuals were classified as immature (12 mm or less in shell length), male (13–26 mm), intersex (25–28 mm), and female (over 26 mm). There was an evident loss of mobility with growth— large females became completely sessile. The presence of epithelial glands in mobile individuals was associated with the need for lubrication during crawling, whereas the proliferation of subepithelial glands in sessile females was associated with adhesion. Mobility of immature and male individuals was related to grazing activities on biofilms, and in males was also associated with copulation. Grazing activity of motile individuals was carried out so that the radula teeth did not come into direct contact with the substratum, but rather harvested the biofilm surface. Sessile females used the radula to rasp the area under their shells, thus cleaning the substratum in preparation for oviposition. Since this process required that the radula enter into direct contact with the substratum, it suffered abrasion of radular teeth and loss of radular denticles, producing important alterations in its appearance in mature females. A complex interaction was observed between size, mobility, histological changes in the foot, activity, and tooth‐wear of the radula, which have been related to the sessile habit, sex change, and the oviposition process in this species.     

Macrobenthic polychaete assemblages of the continental shelf and upper slope off the west coast of the South Island,New Zealand

Polychaete assemblages are described from replicate box‐core samples collected in summer 1983 at 18 stations on the continental shelf and upper slope (28–943 m) off the west coast of the South Island, New Zealand, south‐eastern Tasman Sea (c. 41–43°S, 169–172°E). Three main station groupings were identified by multivariate analysis: (1) inner shelf sandy stations characterised by Prionospio australiensis, Aricidea (Acesta) sp., Magelona cf. dakini, Paraprionospio aff. pinnata, Aglaophamus sp., Heteromastus filiformis, and Magelona sp.; (2) middle to outer shelf muddy stations characterised by Levinsenia cf. gracilis, Prionospio australiensis, Paraprionospio coora, Aglaophamus verrilli, and Auchenoplax mesos; and (3) upper slope sandy mud or mud stations characterised by Prionospio ehlersi. A combination of water depth and sediment clay content provided the best correlation with the biotic pattern. Spionidae was the most abundant family (49% of polychaete individuals), which may reflect the scope for opportunistic species in a shelf environment characterised by a high input of terrigenous sediment and episodic upwelling.     

Fish effects on charophyte establishment in a shallow,eutrophic New Zealand lake

Fish exclosures were deployed within shallow, eutrophic Lake Rotoroa, Hamilton, New Zealand to assess the influence of an alien‐dominated fish population on establishment by charophytes. Replicated mesh exclosures were placed at sites differing in wave exposure and received transplanted charophyte oospores and plants, with identical material placed outside. Charophyte establishment from oospores and plant biomass were greater inside exclosures compared with outside. Wave exposure did not depress germling response and the effect of fish exclosures on charophyte establishment was least apparent at the most exposed site. Exclosures did not have a statistically significant influence on the light climate, and epiphytic algal development was similar or higher inside the exclosures. However, sediment mobilisation was lower inside the exclosures. Results suggest that fish were primarily responsible for the poor performance of unprotected charophytes in Lake Rotoroa, with fish effects on plants operating via direct disturbance or grazing.