Demographic Characteristics of Lytechinus variegatus (Echinoidea: Echinodermata) from Three Habitats in a North Florida Bay, Gulf of Mexico

Abstract. The population densities, spatial distributions, size frequencies, growth rates, longevity and reproductive activities of sub‐populations of the sea urchin Lytechinus variegatus were investigated over a two‐year period. Sea urchins were examined in three habitats in Saint Joseph Bay, Florida, which is within the northern limits of their distribution. Densities of sea urchins, which ranged as high as 35 individuals ·^?2, fluctuated seasonally at all sites and were higher in seagrass beds comprised of Thalassia testudinum than Syringodium filiforme or on a sand flat. A cold front caused large‐scale, catastrophic mortality among adult, and especially juvenile, sea urchins in nearshore habitats of the Bay in the spring of 1993, leading to a dramatic decline in sea urchin densities at the Thalassia seagrass site. The population recovered over 6 months at this site and was attributable to immigration of new adults. Juvenile recruitment displayed both interannual and site‐specific variability, with recruitment being highest in seagrass habitats in fall and spring. The most pronounced recruitment event occurred in fall 1993 at the Thalassia site. Spatial distributions of adult individuals ascertained monthly never varied from random in the seagrass beds (T. testudinum and S. filiforme) or during spring, summer or fall months on the sand flat. Nonetheless, aggregations of adult sea urchins were observed on the sand flat in the winter months and were associated with patchy distributions of plant food resources. Juvenile sea urchins (< 25 mm test diameter) exhibited aggregations at all sites and 67 % of all juveniles under 10 mm test diameter (91 of 165 individuals observed) were found under the spine canopies of adults. Measurements of the inducibility of spawning indicated peak gametic maturity in all three sub‐populations in spring and summer. Gonad indices varied between habitats and years, but distinct maxima were detected, particularly in spring 1993 and late summer 1994. The mean gonad index of individuals at the Syringodium seagrass site was 2‐ to 4‐fold higher than the other sites in spring 1993 and gonad indices were much higher at all sites in spring of 1993 than 1994. Estimates of growth based on changes in size frequency cohorts coupled with measurements of growth bands on lantern demipyramids indicated that L. variegatus in three habitats of Saint Joseph Bay have similar growth rates and attain a mean test diameter of approximately 35 mm in one year. In contrast to populations within the central biogeographical range of the species, which may attain test diameters up to 90 mm, the largest individuals recorded in Saint Joseph Bay were 60 mm in test diameter, and almost all individuals were no more than 45 mm in test diameter or two years of age. The demographics of L. variegatus in the northern limits of their distribution appear to be strongly influenced by latitudinally driven, low‐temperature events and secondarily by local abiotic factors, especially springtime low salinities, which may negatively impact larval development and recruitment.     

Fitness‐related consequences shed light on the mechanisms of covering and sheltering behaviors in the sea urchin Glyptocidaris crenularis

We know of no comparative assessment on the benefits and costs of long‐term covering and sheltering behaviors in sea urchins. The present study investigated the long‐term effects of conditions suitable for sheltering and covering behaviors on fitness‐related traits of sea urchins Glyptocidaris crenularis. In general, conditions suitable for covering and sheltering behaviors significantly affected the fitness‐related traits of G. crenularis in a long‐term laboratory study of 31 months. Glyptocidaris crenularis kept in conditions suitable for sheltering behavior (bricks with openings) showed significantly lower test size, body weight, organ (test, lantern, gonad and gut) weights, gonad index and slower gonad development than those kept in conditions suitable for covering behavior (presence of shells) and the control conditions (without conditions for covering and sheltering). However, the index of maximum pressure resistance of the test was significantly higher in G. crenularis kept in the sheltering conditions than those in the covering and control conditions. The present study provides new insight into the mechanisms of covering and sheltering behaviors and has implications for the conservation and aquaculture of sea urchins.     

Offshore sand sources for beach replenishment: Potential borrows on the continental shelf of the Eastern Gulf of Mexico

Erosion of sandy beaches is a worldwide problem that elicits innovative geoengineer‐ing techniques to reduce adverse impacts of shoreline retreat. Beach replenishment has emerged as the “soft”; shore‐stabilization technique of choice for mitigating beach erosion. This method of shore protection involves the addition of sand to the littoral sediment budget for sacrificial purposes. Because inland sand sources are often uneconomical or impractical to use, and known nearshore sources are limited, finding adequate quantities of suitable sand on the inner continental shelf is often vital to beach replenishment projects. The technical studies of survey and materials analysis that identify and delineate usable sand sources are sometimes almost as expensive as small‐project dredging, pumping, and placing the sand on the beach as fill. Inadequate quantity or substandard quality of shelf sand, as well as often‐prohibitive overhead expenses, thus compel shoreline managers to seek suitable sand sources offshore.

In the study area off the central‐west coast of Florida, offshore potential borrow areas (PBAs) were identified on the basis of studies conducted in reconnoitory and detailed phases. Sophisticated state‐of‐the‐art equipment used in this investigation provided more detailed subbottom mapping information than is normally obtained with conventional seismic equipment. An example of sand exploration studies was incorporated in a 215‐km² survey of offshore areas by conducting bathymetric surveys and subbottom seismic profiling, collecting jet probes, grab samples, and vibrocores, and analyzing sediment grading in subsamples from vibrocores. These combined analyses indicated that at least 8.8 ×10⁶ m³ of sand is available in potential borrow areas from 7.0 to 12 km offshore in water depths of 8.0 to 11.5 m. In the PBAs, mean grain size of sand falls into the range 0.13–0.53 mm, sorting averages 0.65–1.31ø, and the overall silt content varies from 3.9–8.5%. High silt contents (13–19%) mapped in some areas make these sedimentary deposits unsuitable as fill for artificial beach renourishment.     

Distribution, abundance, and growth of larval tautog, Tautoga onitis, in Buzzards Bay, Massachusetts, USA

Tautog, Tautoga onitis, is an abundant species of fish in estuaries of the northeastern United States. Planktonic tautog larvae are abundant in summer in these estuaries, but there is little information on rates of growth of tautog larvae feeding on natural assemblages of food in the plankton. We examined abundance and growth of larval tautog and environmental factors during weekly sampling at three sites along a nearshore‐to‐offshore transect in Buzzards Bay, Massachusetts, USA during summer 1994. This is the first study of a robust sample size (336 larvae) to estimate growth rates of field‐caught planktonic tautog larvae feeding on natural diets, using the otolith daily‐growth‐increment method. The study was over the entire summer period when tautog larvae were in the plankton. The sampling sites contrasted in several environmental variables including temperature, dissolved oxygen (DO), and chlorophyll a concentration. There was a temporal progression in the abundance of tautog larvae over the summer, in relation to location and temperature. Tautog larvae were first present nearshore, with a pronounced peak in abundance occurring at the nearshore sites during the last 2 weeks in June. Larvae were absent at this time further offshore. From late June through August, larval abundance progressively decreased nearshore, but increased offshore although never approaching the abundance levels observed at the nearshore sites. The distribution and abundance of tautog larvae appeared to be related to a nearshore‐to‐offshore seasonal warming trend and a nearshore decrease in DO. Otoliths from 336 larvae ranging from 2.3 to 7.7 mm standard length had otolith increment counts ranging from 0 to 19 increments. Growth of larval tautog was estimated at 0.23 mm·day^?1, and length of larvae prior to first increment formation was estimated at 2.8 mm indicating that first increment formation occurs 3–4 days after hatching at 2.2 mm. Despite spatial and temporal differences in environmental factors, there were no significant differences in growth rates at any of three given sites over time, or between sites. Because larval presence only occurred at a narrow range of temperature (17–23.5 °C) and DO (6.5–9.3 mg·l^?1), in situ differences in growth did not appear to be because of differences in larval distribution and abundance patterns relative to these parameters.     

Responses to Predation Cues and Food in Two Species of Sympatric, Tropical Sea Urchins

Abstract. We examined the responses of two tropical sea urchins, Lytechinus variegatus and Tripneustes ventricosus, to cues from predators, simulated predation events and food. Cues released from damaged conspecifics, heterospecifics and heteroclassics (holothurian) were used to simulate predation events in field experiments. Responses to the presence of seagrass, spiny lobster or both were tested in tanks. Findings were supplemented by natural history observations of dispersion patterns off Bermuda. In field experiments, neither species formed groupings in the presence of conspecific, heterospecific or heteroclassic cues. Flight responses were greatest in conspecific treatments; responses to heterospecific cues were intermediate to control and conspecific cues. Urchins in pre‐assembled associations remained in groups in control trials but dispersed when exposed to predation cues. Lytechinus exhibited greater sensitivity to predation cues than Tripneustes. Cues from a damaged sea cucumber invoked a response from Lytechinus but not Tripneustes. Both species employed a two phased response to cues from damaged conspecifics: initially a rapid, but ephemeral (2 min), alarm response followed by a slower (≈ 35 % lower) sustained flight phase for 6+ min, which in nature would disperse urchins downstream and away from a predator. In tank experiments, Lytechinus formed groupings only around food or food + predators. The presence of a predator reduced the aggregation response to food, suggesting that Lytechinus employed a risk aversion strategy. Tripneustes exhibited escape or refractory behavior in both control and experimental treatments in laboratory tanks.     

Seasonal and spatial variation in abundance and egg production of Paracalanus parvus (Copepoda: Calanoida) in/out Jiaozhou Bay, China

The spatial distribution of stage-specific abundance and reproduction of the copepod Paracalanus parvus were studied from October 2005 to September 2006 in the Jiaozhou Bay. This copepod occurred continuously in this bay throughout the year. The species reached the lowest abundance in April and peaked in June. From October to December, distribution center mainly occurred in offshore water and at the mouth of the bay. In winter, early copepodites and adults gradually decreased and till February, most of the population was only comprised of CIV–CV stages. Overwintering copepodites matured in March and males tended to mature before female. From May to September, each stage occurred in the population and gradually reached high abundance. Temperature and chlorophyll a (Chl-a) concentration in the three stations can't clearly explain the seasonal variation in stage-specific abundance, so we surmised the important effect of the Yellow Sea. Egg production rate (EPR) reached its lowest in winter and peaked in June at 60.8 eggs female⁻¹ day⁻¹ in nearshore water. In the warming period, EPR in nearshore water was statistically higher and EPR > 10 eggs female⁻¹ day⁻¹ lasted longer than that in offshore water, showing the importance of nearshore water for recruitment of P. parvus. Our study showed that EPR was positively related to temperature and total chlorophyll a in offshore water and mouth of the bay. In nearshore water, the relationships between EPR and temperature and Chl-a in three size fractions were not the same as those in offshore water, suggesting complicated ecosystem in such a eutrophic area in warming period.     

Zonation and species diversity of smaller macrobenthos in the westernmost part of Wakasa Bay (the Sea of Tango)

Grab samples of the smaller macrobenthos (>1 mm, <1g wet weight) were obtained seasonally at fourteen stations along two transects in the shallow coastal waters of the westernmost part of Wakasa Bay. According to Morisita's similarity index (C _i , two faunal groups were recognized to be present throughout the year. The boundary between them was found to lie between depths of 10 and 20 m where the silt-clay fraction increased abruptly in the sediment, although the boundary was less obvious in summer. Statistics on community structure (species diversity, species richness, and evenness) also showed marked differences between the two assemblages. The change in faunal features was found to be roughly parallel to changes in sediment characteristics. On the nearshore sandy bottom, the influence of wave action is considered to be the major factor affecting the fauna as it results in a decrease in evenness and species richness. On the other hand, on the offshore muddy bottom, stagnant conditions cause the benthic fauna to decrease in density and to bear some resemblance to those of enclosed bays. The highest species diversity was found on the silty sand bottom (20 m deep). This can be understood as an edge effect of an ecotone.     

The impact of rising sea temperature on innate immune parameters in the tropical subtidal sea urchin Lytechinus variegatus and the intertidal sea urchin Echinometra lucunter

Ocean temperatures are rising throughout the world, making it necessary to evaluate the impact of these temperature changes on sea urchins, which are well-known bioindicators. This study evaluated the effect of an increase in temperature on the immune response of the subtidal Lytechinus variegatus and the intertidal Echinometra lucunter sea urchins. Both species were exposed to 20 (control), 25 and 30 °C temperatures for 24 h, 2, 7 and 14 days. Counting of coelomocytes and assays on the phagocytic response, adhesion and spreading of coelomocytes were performed. Red and colorless sphere cells were considered biomarkers for heat stress. Moreover, a significant decrease in the phagocytic indices and a decrease in both cell adhesion and cell spreading were observed at 25 and 30 °C for L. variegatus. For E. lucunter, the only alteration observed was for the cell proportions. This report shows how different species of sea urchins respond immunologically to rising temperatures.     

Influence of buoyancy and vertical distribution of sardine Sardinops sagax eggs and larvae on their transport in the northern Benguela ecosystem

In recent years, sardine Sardinops sagax spawning has been recorded inshore off central Namibia. Field observations on eggs and laboratory measurements show that spawning, demonstrated by the distribution of newly spawned eggs, takes place just below the upper mixed layer. The high positive buoyancy of the eggs causes them to ascend rapidly to the surface layer, where they are moved offshore by upwelling-induced offshore transport. However, increased wind-induced mixing also influences the vertical distribution of eggs, causing them to be partly mixed down below the layer moving offshore and into the layer moving inshore. This mechanism acts to retard the transport and offshore loss of eggs from the spawning areas. The vertical distribution of sardine larvae, with highest concentrations deeper than 20 m, indicates active movement out of the layer moving offshore, and this tendency seems to be more pronounced for older larvae. Hence, vertical migration of larvae is an additional factor mitigating their loss from nearshore. Taken together, these features seem to minimize the offshore loss of offspring, particularly in periods of low stock biomass when spawning close to the shore seems to be common.     

Growth and gonad production of the sea urchin Hemicentrotus pulcherrimus in the fucoid bed and algal turf in northern Japan

To clarify the differences in the growth and gonad size of the sea urchin Hemicentrotus pulcherrimus among algal sere, the study was conducted in June and July, and September 1998 at three fucoid beds in Oga and at three algal turfs in Hachimori, Akita Prefecture in northern Japan. The most rapid growth was observed in a large perennial fucoid bed at the climax stage. Growth in a small perennial Chondrus ocellatus‐dominated bed in algal turfs in the seral stage was then high. The slowest growth was observed in the small perennial Dictyopteris divaricata‐ and Laurencia spp.‐dominated beds which are known to possess chemicals which act as feeding deterrents against the sea urchins. The gonad index (gonad wet weight × 100/body wet weight) at a fucoid bed was high where standing crops exceeded 3 kg·m^?2. The gonad index in the Laurencia bed was lower than those at fucoid beds. These results suggest that growth and gonad production are affected by algal sere and differ among species of small perennial algae in the seral stage with or without chemical defense.     

Fish populations of the Avon‐heathcote estuary

Details are given of gut‐content analyses for nine fish species from the Avon‐Heathcote Estuary, Christchurch, New Zealand: sand flounder, Rhombosolea plebeia (Richardson); yellow‐bellied flounder, R. leporina (Hutton); common sole, Peltorhamphus novaezeelandiae (Gunther); yellow‐eyed mullet, Aldrichetta forsteri (Cuvier & Valenciennes); kahawai, Arripis trutta (Bloch & Schneider); spotty, Pseudolabrus celidotus (Bloch and Schneider); cockabully, Tripterygion nigripenne (Cuvier & Valenciennes); common bully, Gobiomorphus basalis (Gray); and globefish, Spheroides richei (Freminville). The percent occurrences of each food type recorded over Ihe sampling period (April 1965‐April 1966) for each species are compared. Monthly food tables are given for those species of which suitably large samples were obtained (sand flounder, yellow‐bellied flounder, common sole, yellow‐eyed mullet, and globefish). Where possible, the dietary occurrence of different food types is related to environmental and other factors observed or considered likely to influence food selection.     

Fish populations of the Avon‐Heathcote Estuary

Breeding seasons and sizes at first maturity for nine species of fish in the Avon‐Heathcote Estuary, Christchurch, New Zealand, were: sand flounder, Rhombosolea plebeia, mid‐winter to spring at 200 mm+; yellow‐bellied flounder, Rhombosolea leporina, winter and spring at 260 mm+; common sole, Peltorhamphus novaeieelandiae, did not breed in the estuary but reached first maturity at 220 mm +; yellow‐eyed mullet, Aldrichetta forsteri, spawned twice a year, winter and summer, at 220 mm +; kahawai, Arripis trutta, bred outside the estuary at 520–540 mm +; spotty, Pseudolabrus celidotus, spring to autumn at 200 mm for males and 160 mm for females; cockabully, Tripterygion nigripenne, spring and early summer at 52–57 mm +; common bully, Gobiomorphus basalis, spring and early summer at 45–50 mm+; and globefish, Speroides richei, spring to autumn at 147 mm + for males and 120 mm + for females. The successive stages in gonad development are described for these species.

In pelagic species, e.g., flatfish and kahawai, x² analyses showed that for most months females are more numerous than males, and that migration is of major importance. In (littoral species, e.g., common bully and cockabully, there is a 1 : 1 sex ratio in the breeding season, but this ratio subsequently breaks down.

The Avon‐Heathcote estuary was used mainly as a nursery area by juvenile fish, although some species, such as sand flounder, yellow‐bellied flounder, yellow‐eyed mullet, and cockabully spawned in the estuary.     

Sand suction mechanism in artificial beach composed of rubble mound breakwater and reclaimed sand area

An artificial beach has been constructed compensating for losing of the natural one caused by the development of coastal area. In this paper, the hydraulic model tests are carried out to investigate the suction phenomenon on the artificial beach constituted of rubble mound breakwater with gravel and the reclaimed sand area. In addition, the numerical model for waves, structures and seabed interaction as well as the numerical method based on the u–p approximation of the Biot equations is developed for investigation of suction mechanism. After verification of the numerical models by comparing numerical results with experimental data, the numerical models are further used to clarify the detailed suction mechanism of the reclaimed sand. The factors that affect the suction phenomenon are examined experimentally and their critical values are presented. Also, it can be pointed out that the vertical discharge velocity as well as the volumetric strain around the still water level of the boundary between the breakwater and the beach gets up to the critical value, the reclaimed sand starts to flow out to the offshore, and it finally leads to caves and cave-ins in the reclaimed zone.     

Sublethal effects of hydrogen sulfide in sediments on the Urchin Lytechinus pictus

Laboratory exposures of the urchin Lytechinus pictus to sediment dosed with varying concentrations of hydrogen sulfide (H₂S), but without elevated organic material, were conducted. Changes in mortality, behavior, growth and gonad production were measured during 49 days' flow through exposures. Hydrogen sulfide concentrations of 165·8 μ liter⁻¹ in pore water caused significant changes in all parameters measured. Concentrations as low as 32·9 μ liter⁻¹ caused significant decreases in wet weight and male gonad production. A concentration of 91·8 μ liter⁻¹ caused the mortality rate to increase 100-fold over control exposures (0·63 μ liter⁻¹). Sublethal effects on growth and gonad production could have been caused by either direct biochemical inhibition by H₂S or secondarily through behavioral modifications. Hydrogen sulfide concentrations above 165·8 μ liter⁻¹ are common near sewage outfalls and could contribute to changes in species composition and sediment toxicity that occur there.     

北仑河口的表层沉积物类型及其分布特征

北仑河口84个表层沉积物样品的分析结果表明,该河口有含砾砂、砂、粉砂质砂、砂质粉砂、粉砂、砂-粉砂-粘土、粘土质粉砂等7种沉积物类型,并具有自西北往东南逐渐变细的特征;分析结果还表明北仑河口可划分为近口、河口和口外海滨3个沉积区,近口区以河流作用为主,河口区粗颗粒沉积作用主导,而口外海滨区则主要受到两种营力的共同作用．     

Submerged vegetation of the Rotorua and Waikato Lakes

In Lake Rotoiti, North Island, New Zealand, ‘cyclic change’ apparently occurs among mounds of the ‘Low Mixed Community’ of plants; this is the first evidence of cyclic change in a wholly submerged community. The Low Mixed Community grows on gently sloping, sandy substrates ndar the shores of bays sheltered from the prevailing SW winds, and usually extends to depths of about 1.8 m, where dense beds of Lagarosiphon major begin.

The work we report Was done in 1968–70. We sampled ithe community by transects, various types of quadrats, and by monitoring marked mounds, and from these data we analysed the composition, distribution, growth and fate of mounds at various depths.

We observed that one species of five genera (namely Glossostigma spp., Elarine spp., Lilaeopsis lacustris, Elodea canadensis, and Myriophyllum propinquum) colonised bare sand and trapped more sand; as the mound grew, other species appeared. Mounds in deeper water (> 0.9 m) were larger and floristically richer than those in shallower water, and were thus probably older. In calm conditions, mounds sometimes fused to form a polytypic sward. Typically, however, the backwash of waves eroded the shoreward ends and sides of mounds; the mounds thus became elongated parallel to the wind direction. Provided that their growth at the offshore end at least balanced erosion at their shoreward ends, some marked mounds tended to grow downslope into deeper, less often disturbed water.

Although backwash started mound erosion down to 0.6 m depth, it could also erode bare areas in mounds (caused by die‐off of plants, herbicide sprays, and mechanical damage) down to 1.2 m, the depth to which it normally influenced loose substrate. In exceptional easterly storms, backwash might influence plants at greater depths, and perhaps locally destroy the community so that the cycle would have to begin again.

Briefly, we suggest that these characteristic signs of cyclic change in this community result from an interaction between fragile mounds of plants growing on an unstable, sandy substrate which is easily eroded by wave backwash. However, more observations over a longer time will be needed before our prima facie case for the occurrence of cyclic change can be proved.

We also recorded an invasion of Lagarosiphon over mound plants into depths of only 0.9 m, and we proposed for the “Low Mixed Community” the appropriate name Glossostigmatum aquaticae because Glossostigma spp. predominated in all floristic analyses.     

圆斑星鲽(Verasper variegatus)wtl基因的克隆与表达分析

圆斑星鲽（Verasper variegatus）雌鱼生长快,成熟雌鱼个体大小是雄鱼的2倍以上,开展性别相关基因的功能研究,对于探究圆斑星鲽性别决定机制,建立单性培育技术具有重要意义。本研究获得了wt1a及wt1b两个同源基因,wt1a基因全长为3263bp,预测开放阅读框（ORF）长为1245bp,编码415个氨基酸,5''-UTR和3''-UTR分别长372bp和1640bp;wt1b基因全长为2312bp,预测开放阅读框（ORF）长为1281bp,编码427个氨基酸,5''-UTR和3''-UTR分别长369bp和659bp。wt1a基因编码氨基酸分子量为46.2kDa,理论等电点为9.24,无跨膜结构及信号肽,在ORF末端有4个锌指结构,编码KTS三肽;wt1b基因编码氨基酸分子量为46.95kDa,理论等电点为8.99,无跨膜结构及信号肽,在ORF末端有4个锌指结构,并且编码KTS三肽。基因表达结果表明：wt1a和wt1b基因主要在圆斑星鲽性腺中表达,精巢的表达高于卵巢,肾脏的表达量显著高于其他组织,推测wt1a基因和wt1b基因在性腺和肾脏发育过程及功能方面均发挥重要作用;在早期发育阶段,wt1a基因在原肠期之前微弱表达,从原肠早期开始逐渐上升至神经胚期表达量达到最高,之后逐渐下降,直至孵化阶段,推测wt1a基因在圆斑星鲽原始生殖细胞分化过程及性腺发育中发挥重要作用。     

Influence of the Po River runoff on the bacterioplankton community along trophic and salinity gradients in the Northern Adriatic Sea

The Po River runoff strongly affects the oceanographic and ecological characteristics of the Northern Adriatic Sea. Catalysed reported deposition ‐ fluorescence in situ hybridization (CARD‐FISH) analysis was employed to assess how the composition of the coastal bacterioplankton community is influenced by the river runoff in two different seasons (spring and autumn). Samples were collected from the water column along a coastal–offshore transect in the Northern Adriatic Sea at different depths. Four clone libraries were then constructed from coastal (0 m) and offshore waters (?65 m). Higher abundances of bacteria were recorded in coastal waters as compared with the offshore samples. This result was mainly due to the trophic state of the water column, and it was related to salinity. Particularly, Actinobacteria and Gammaproteobacteria were affected by the riverine inputs, whereas Bacteroidetes and Alphaproteobacteria showed only minor responses. This was particularly clear in the autumn sample, in which a clear difference between the coastal and the offshore samples was found due to a strong influence of the less saline river water with high nutrient concentrations. Analysis of 205 partial length 16S rRNA gene sequences indicated a high diversity with the dominance of Alphaproteobacteria, Bacteroidetes and Gammaproteobacteria mainly affiliated to coastal and marine bacterioplankton clades. Actinobacteria were also detected and, together with Gammaproteobacteria, strongly follow the freshwater intrusion. Overall, our results indicate that the seasonal difference in the Po River discharge greatly affects the bacterioplankton community. In spring we observed a smooth transition from coastal to open‐sea conditions owing to the more superficial freshwater plume. In autumn the deeper freshwater intrusion in the coastal site and thermal stratification offshore resulted in a marked difference between the coastal and offshore microbial communities.     

Summer spatial patterns of the fish community in a large,shallow, turbid coastal lake

Several water quality parameters, marginal vegetation, and the fish community in Lake Ellesmere, a large, shallow, turbid lake situated on the east coast of the South Island, New Zealand, were sampled along selected transects in late summer to determine species spatial patterns. Thirteen species offish were caught, with seven of them comprising major populations, although only four of these were adequately sampled by the method used—they included inanga (Galaxias maculatus), common smelt {Retropinna retropinna), shortfinned eel (Anguilla australis), and common bully (Gobiomorphus cotidianus). Inanga were almost exclusively confined to areas on the western side of the lake which has a convoluted shoreline with a variety of small embayments with scattered vegetation along the margins. Common smelt occupied both marginal and offshore areas, but they too were more abundant along the margins particularly on the western side. Both the common bully and shortfinned eel were widespread and abundant in the lake, although their abundance and biomass were higher within the vicinity of the lake outlet, major inflowing tributaries, and other marginal habitats. All three species of flounders of the genus Rhombosolea were poorly represented in our samples. However, in commercial catches they were reasonably abundant, with the sand flounder (R. plebeia) and yellowbelly (R. leporina) being more common in offshore than inshore catches, whereas the black flounder (R. retiaria) showed no difference in the catches between areas. Our overall findings are consistent with the hypothesis that bottom‐dwelling species (eels, bullies, flounders) are more widely distributed than free‐swimming forms (inanga, common smelt), which were largely confined to areas sheltered from prevailing winds. The highly turbid nature of the lake, primarily because of re‐suspension of fine bottom sediments by frequent winds, is considered an important factor in the distribution of the fish fauna.     

Food utilisation by coastal fish assemblages in rocky and soft bottoms on the Swedish west coast: Inference for identification of essential fish habitats

The concept of essential fish habitats (EFHs) is widely accepted for conservational and management purposes. EFHs are often considered as high quality habitats for fisheries species and subsequently of high values for society. In this study, fish and Substrate-Associated Prey (SAP) were sampled during the productive summer season 1998 (fish) and 2003 and 2004 (SAP) in shallow coastal rocky- and soft-bottom habitats on the Swedish west coast. The aim was to study the spatial and monthly variation of SAP as well as abundance and biomass of fish, and to examine if food items found in the diet of the fish assemblage were derived from SAP. We also examined if the diet of Ctenolabrus rupestris, a resident and abundant fish species in the shallow coastal habitats, and the diet of four seasonally abundant and commercially important fish species (Gadus morhua, Pleuronectes platessa, Salmo trutta and Scomber scombrus) were derived from SAP. There were significantly higher mean species number and abundance of the SAP assemblage on rocky compared to soft bottoms and the highest values were found on the rocky bottoms in August and in the shallowest (0–3 m) depth strata. There were no significant differences in number of fish species caught in the two habitats, although mean number of fish and mean biomass were significantly higher on rocky bottoms. Both habitats showed the same seasonal variation and the highest values of number of fish species, abundance and biomass were observed in June. On rocky bottoms, gastropods and amphipods were the most frequent food items in the diet of the entire fish assemblage and these items were also the most abundant SAP in this habitat. The dominant food items of the soft-bottom fish assemblage were decapods and fish, which were not common SAP. However, except for S. scombrus, the diet of the selected fish species showed a strong association to the SAP availability. Gadus morhua displayed the strongest association to SAP on rocky bottoms and P. platessa and C. rupestris to SAP on soft bottoms. Further, for C. rupestris, multivariate statistical analysis showed a significant association to the SAP assemblage on both rocky and soft bottoms. These results provide vital new information for the management and conservation of Essential Fish Habitats on the Swedish west coast.