Weak Swimmers Research Articles

Quantifying Vegetation on a Rock-Ramp Fishway for Fish Run-Up and Habitat Enhancement: The Case of the Miyanaka Intake Dam in Japan

The Miyanaka Intake Dam fishway underwent improvements in 2012, and we established a new rock-ramp fishway called the Seseragi Fishway, cognizant of its utility as a passage and a habitat for bottom-dwelling and small fish with weak swimming ability. However, the fishway is occasionally submerged by floods, causing sediment accumulation that leads to changes in the vegetation composition. In addition, the arrival and inflow of seeds from upstream and the surrounding areas result in vegetation changes. In this study, the inside and outside of the rock-ramp fishway were divided into eight areas, and the vegetation succession after 2012 was determined. A correlation was observed between the results of fish catch surveys during the same period and the vegetation. Based on these results, we reported on the process of steadily operating the rock-ramp fishway while devising and improving specific management methods. Changes in vegetation, such as an increase in upright vegetation and a decrease in flow-obstructing vegetation, contributed to an increase in the population of bottom-dwellers, weak swimmers, and juvenile fish. The existence and management of appropriate vegetation are important for maintaining fishways inhabited by a variety of fish species.

"I never had a thought about drowning". Exploring water safety attitudes and practices among older adults in WesternAustralia.

The aim of this study was to explore factors associated with drowning among older adults aged 65years and over in Western Australia. This paper was concerned with illuminating older adults experience and perspectives of water safety and drowning prevention. The study used in-depth, semi-structured interviews (n=15) to examine knowledge, attitudes, beliefs and behaviours. The interviews were analysed using a phenomenological hermeneutical interpretation whereby three steps were taken to identify common patterns of meaning from individual's lifeworld. Interviews captured the voices of those who identified as swimmers and those who identified as nonswimmers and revealed nine constitutive patterns which support a central theme of life around water. This study provides insights into perceptions and experiences of water safety as individuals' age. The findings suggest individuals who perceived themselves as strong swimmers had a decreased perception of risk, while participants who self-identified as weak swimmers were more likely to avoid risks and modified their behaviour accordingly. Findings highlighted low water safety literacy and suggest that older people not only underestimate their drowning risk, but also lack an understanding of the risk factors for drowning. SO WHAT?: The findings from this study will have a direct impact on the development of a WA health promotion program to prevent drowning among older adults.

Editorial: Green or red: Challenges for fish and freshwater biodiversity conservation related to hydropower

Editorial: Green or red: Challenges for fish and freshwater biodiversity conservation related to hydropower

Fish passage hydrodynamics: insights into overcoming migration challenges for small-bodied fish

The modification and utilization of rivers in regions where small-bodied diadromous fish are prevalent has largely occurred without fully understanding the migration behaviour of these species. As a result, existing in-stream structures often prevent or restrict migration. Current fish passage design guidance generally focuses on providing average hydrodynamic conditions within the range of known critical swimming velocities for target fish species. Considerable portions of discharge capacity must be sacrificed to achieve average cross-sectional water velocities that will allow passage of weak swimmers. Furthermore, because the hydrodynamic requirements for small-bodied species are poorly understood, successful passage is still not guaranteed even when average hydrodynamic design criteria are met. Ethohydraulic research is focused on how water flow influences fish behaviour and vice versa, by studying the interaction of fish with small-scale in-flow characteristics. We discuss how an ethohydraulic approach may improve fish passage design for small-bodied fish, such as țnanga/common galaxias (Galaxias maculatus), a widespread diadromous Southern Hemisphere species. The ethohydraulic approach is discussed in detail for culverts, a commonly found structure known to impede fish passage for many small-bodied species.

Caraş River Gorge Aspects of Salmonids’ Communities Management – Technical Solutions

Abstract There are many obstacles in rivers that prevent or hinder passage of fish past barriers. Here, we present a specially designed solution for juvenile and adult brown trout so that they may to swim past discharge-regulating weirs in the upper Caraş River in both the upstream and downstream directions. The proposed solution relies on gravity flow and will have current velocities that will not inhibit weak swimmers swimming upstream to pass the weirs. Corrosion-resistant materials and the absence of components that could potentially injure the fish will be used in the construction of these technical solutions. Although testing of the functionality of this solutions for upstream - downstream and downstream - upstream passage of weirs is needed, we believe that if implemented, it should improve connectivity especially for brown trout and consequently conserve within-stream genetic diversity in the Caraş River and where appropriate in alike other Carpathian lotic systems with similar types of weirs.

Three‐dimensional numerical simulations of smooth, asymmetrically roughened, and baffled culverts for upstream passage of small‐bodied fish

AbstractTraditional box culvert designs lead to development of high velocity zones in the culvert barrel that often impede upstream migration of fish. Herein, three‐dimensional Reynolds‐averaged Navier‐Stokes (RANS)‐ and Large eddy simulation (LES)‐based computational fluid dynamics (CFDs) simulations were performed to compare the effectiveness of smooth, asymmetrically roughened, and corner‐baffled barrels, in creating low‐velocity zones (LVZs) and providing opportunity for upstream passage of small‐bodied fish. The results revealed distinctive benefits provided by the asymmetrically roughened and corner‐baffled barrels relative to the smooth barrel. Cross‐sectional asymmetry, corners, and obstructions are important factors that contribute to the generation of LVZs conducive to fish passage, albeit contiguity of LVZs is required, particularly for weak swimmers. The study demonstrates the adequacy and effectiveness of CFD models to complement traditional laboratory studies in understanding basic mechanisms beneficial to fish passage and to provide insights into future designs.

Fish behavior and fish guidance at hydropower intake screens for fish downstream passage

Fish behaviour investigations under controlled laboratory conditions but nature like environment were conducted to clarify the efficiency of inclined and horizontal screen planes for fish protection and fish downstream passage at hydropower plants concerning different potamodromous species and various sizes. The dependency on the underlying geometric and hydraulic parameters was investigated and comprehensive models were deduced to describe these relations. Adequate geometric and hydraulic design could achieve high levels of fish protection and downstream passage efficiency, even for small fish, weak swimmers and riverbed/bottom oriented species. The results imply good transferability and accordance with field observations at large scale facilities and can provide valuable information for facility design.

Ecology of the Critically Endangered Kandian Torrent Toad (Adenomus kandianus) in Pidurutalagala, Sri Lanka

The stream-dwelling Sri Lankan endemic toad genus Adenomus represents two species: A. kelaartii and A. kandianus. The Kandian torrent toad, A. kandianus, was considered extinct until its rediscovery at Peak Wilderness sanctuary after 136 years in 2012. Currently, this species is recorded from two distinct localities in the Central highlands (1400 m above sea level). Red List conservation status has been re-evaluated as Critically Endangered of IUCN. Based on transect surveys and opportunistic excursions, we conducted a 4 year study (1-week-long survey per year during 2011–2013 and two, one-week-long surveys in 2014) to assess habitat associations, abundance, and behavior of A. kandianus in its second locality, near Pidurutalagala Conservation Forest. Surveys were conducted in the morning (07.00–14.00 hrs) and evening (18.00–20.00 hrs). Several environmental parameters were also measured to characterize the habitat preferences of the toads. Our survey revealed that the toads were associated with five microhabitats: on moss-covered in-stream boulders (most of the time, underneath leaf litter on the boulders), in-stream pools with decaying organic-matter substrate, in-stream pools with sandy substrates, riffles with rocky-cobble-pebble substrate, and within undercut banks with leaf litter and complex root structure of riparian vegetation. We recorded a total of 169 individuals which related to an average of 24.5 males, 13 females, and 6.75 juveniles per year. Presence of toads were limited to the stream channel, including undercut banks, and absent in the woodlands. Perching was the most observed behavior among males followed by mating. Among females, mating was the most dominant behavior. Juveniles were mostly observed in their under bank refugee while on limited instances, they emerged onto the river banks. The juveniles had partially-developed webbing in their feet, thus were weak swimmers. Adults had complete webbing, thus were strong swimmers and swam perpendicular to the flow. Anthropogenic activities, such as intensive crop-farming deterred these species; proximity to croplands was a strong negative impact on species abundance. We recommend re-delineation of both the core habitat and the buffer zone of Pidurutalagala Conservation Forest so that the toad habitat can be incorporated into the reserve to limit the impacts of human activities on this population. Keywords: Amphibian, Behavior, Conservation, Extinct, Montane forest, Threats

Evaluating the effectiveness of restoring longitudinal connectivity for stream fish communities: towards a more holistic approach

A more holistic approach towards testing longitudinal connectivity restoration is needed in order to establish that intended ecological functions of such restoration are achieved. We illustrate the use of a multi-method scheme to evaluate the effectiveness of ‘nature-like’ connectivity restoration for stream fish communities in the River Deerness, NE England. Electric-fishing, capture-mark-recapture, PIT telemetry and radio-telemetry were used to measure fish community composition, dispersal, fishway efficiency and upstream migration respectively. For measuring passage and dispersal, our rationale was to evaluate a wide size range of strong swimmers (exemplified by brown trout Salmo trutta) and weak swimmers (exemplified by bullhead Cottus perifretum) in situ in the stream ecosystem. Radio-tracking of adult trout during the spawning migration showed that passage efficiency at each of five connectivity-restored sites was 81.3–100%. Unaltered (experimental control) structures on the migration route had a bottle-neck effect on upstream migration, especially during low flows. However, even during low flows, displaced PIT tagged juvenile trout (total n=153) exhibited a passage efficiency of 70.1–93.1% at two nature-like passes. In mark-recapture experiments juvenile brown trout and bullhead tagged (total n=5303) succeeded in dispersing upstream more often at most structures following obstacle modification, but not at the two control sites, based on a Laplace kernel modelling approach of observed dispersal distance and barrier traverses. Medium-term post-restoration data (2–3years) showed that the fish assemblage remained similar at five of six connectivity-restored sites and two control sites, but at one connectivity-restored headwater site previously inhabited by trout only, three native non-salmonid species colonized. We conclude that stream habitat reconnection should support free movement of a wide range of species and life stages, wherever retention of such obstacles is not needed to manage non-native invasive species. Evaluation of the effectiveness of fish community restoration in degraded streams benefits from a similarly holistic approach.

Unravelling the joint effects of flow regime, climatic variability and dispersal mode on beta diversity of riverine communities

Summary Differences in the composition of ecological communities among rivers with contrasting flow regimes have been detected in many regions worldwide. However, we know little of how climatic variation alters these spatial patterns for constituent species with varying dispersal modes and strengths. We predicted that beta diversity (spatial variation in composition) of macroinvertebrate and fish assemblages among streams with near‐perennial, mildly intermittent and highly intermittent flow regimes would be greater during prolonged drought than under wetter climate conditions. We hypothesised that changes in beta diversity between these climate phases would be greater for taxa with stronger dispersal ability. We tested these predictions with biomonitoring data from Australian subtropical rivers. Differences in average community composition among flow regimes were statistically significant for six groups of macroinvertebrates with differing dispersal (non‐swimmers, weak swimmers, strong swimmers, non‐fliers, weak fliers and strong fliers) and two groups of fish (potamodromous and diadromous), but not for locally dispersing fish. For each of these biotic groups, shifts in assemblage composition between supra‐seasonal drought and a subsequent non‐drought period were either statistically non‐significant or of similar magnitude among flow regimes. Therefore, beta diversity among flow regimes did not change significantly with climate phase. Beta diversity within flow‐regime classes was greater during the drought than afterwards or not significantly different between climate phases, depending on the flow regime and biotic group. Stronger powers of flight were associated with greater change in beta diversity between climate phases in near‐perennial streams, but stronger powers of swimming were not. Within‐regime beta diversity was driven more by replacement of taxa among samples than by nestedness, except for diadromous fish in near‐perennial streams. Our findings are consistent with the hypothesis that decreasing hydrological connectivity and greater environmental heterogeneity during prolonged drought increase beta diversity of stream communities. However, changes in beta diversity between climate phases were not as pronounced as we expected. The communities may have been somewhat drought resistant because the magnitude and duration of the drought were within the range of historical variability and because surface water persisted at study sites during drought‐imposed flow cessations. Our findings suggest that maintenance of refuge pools will be critical to lessening drought impacts on river biodiversity at landscape scales, particularly if drought duration and intensity increase in the future.

Human instability related to drowning risk in surf zones for novice beachgoers or weak swimmers

This paper provides qualitative descriptions of the physical mechanisms that can cause human instability in surf zones, where human instability is considered the loss of solid contact between an individual’s feet and the seabed. The forces resulting from the combination of waves and currents typical in surf zones present a hazard to novice beachgoers and weak swimmers that is often not recognized by those individuals. A conservative “rule of thumb” is that the deepest water a novice beachgoer should reach, even during the passage of wave crests, is a depth that only reaches the persons thigh, that is, between the knee and the waste.

Species-Specific Adaptations of Trypanosome Morphology and Motility to the Mammalian Host.

African trypanosomes thrive in the bloodstream and tissue spaces of a wide range of mammalian hosts. Infections of cattle cause an enormous socio-economic burden in sub-Saharan Africa. A hallmark of the trypanosome lifestyle is the flagellate’s incessant motion. This work details the cell motility behavior of the four livestock-parasites Trypanosoma vivax, T. brucei, T. evansi and T. congolense. The trypanosomes feature distinct swimming patterns, speeds and flagellar wave frequencies, although the basic mechanism of flagellar propulsion is conserved, as is shown by extended single flagellar beat analyses. Three-dimensional analyses of the trypanosomes expose a high degree of dynamic pleomorphism, typified by the ‘cellular waveform’. This is a product of the flagellar oscillation, the chirality of the flagellum attachment and the stiffness of the trypanosome cell body. The waveforms are characteristic for each trypanosome species and are influenced by changes of the microenvironment, such as differences in viscosity and the presence of confining obstacles. The distinct cellular waveforms may be reflective of the actual anatomical niches the parasites populate within their mammalian host. T. vivax displays waveforms optimally aligned to the topology of the bloodstream, while the two subspecies T. brucei and T. evansi feature distinct cellular waveforms, both additionally adapted to motion in more confined environments such as tissue spaces. T. congolense reveals a small and stiff waveform, which makes these parasites weak swimmers and destined for cell adherence in low flow areas of the circulation. Thus, our experiments show that the differential dissemination and annidation of trypanosomes in their mammalian hosts may depend on the distinct swimming capabilities of the parasites.

Past and present drivers of population structure in a small coastal fish, the European long snouted seahorse Hippocampus guttulatus

The effective design of species conservation programs is reliant on information such as extant geographic distribution, taxon-specific life-history characteristics, and the relative influence of historic processes and contemporary environmental parameters in shaping population genetic diversity. Seahorses are weak swimmers and have a brooded young, limiting their dispersal potential. They live in sheltered locations, which are physically isolated from each other. Therefore panmixia across their geographic range is unlikely. Hippocampus guttulatus, a seahorse inhabiting European waters, has a geographic range spanning a number of contemporary oceanographic features that are proposed barriers to gene flow. Thus this fish is well-placed to test the contributions of environment and life-history factors in shaping population structuring. This study found that mitochondrial DNA and nuclear DNA (microsatellite) genotype data are concordant in suggesting that, like many other small fishes in European waters, H. guttulatus extant populations expanded from at least one southern European refugial population. Subsequent population differentiation of four geographic lineages reflects contemporary oceanographic barriers to gene flow. Demographic analyses suggest a northward, and long-term isolation between Black Sea and Mediterranean Sea populations. Moreover H. guttulatus contemporary population distribution and population structure are predominately explained by historic and oceanographic influences. These findings suggest that conservation of genetic diversity in H. guttulatus may be aided by a network of marine protected areas (MPAs), implemented to conserve coastal habitats, but the species’ unusual life history and gamete retaining behaviours should be considered as part of management decisions including MPA design and fisheries management plans.

长江口及邻近海域浮游水螅水母、管水母和栉水母的丰度分布与季节变化

PDF HTML阅读 XML下载 导出引用 引用提醒 长江口及邻近海域浮游水螅水母、管水母和栉水母的丰度分布与季节变化 DOI: 10.5846/stxb201403210505 作者: 作者单位: 中国水产科学研究院东海水产研究所,中国水产科学研究院东海水产研究所,中国水产科学研究院东海水产研究所,国家海洋局第二海洋研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划(973计划)(2010CB428705);海洋公益性行业科研专项经费项目(201305027-8) Abundance distribution and seasonal variation of medusae, siphonophores, and ctenophores in the Changjiang (Yangtze River) Estuary and the adjacent East China Sea Author: Affiliation: East China Sea Fisheries Research Institute,East China Sea Fisheries Research Institute,East China Sea Fisheries Research Institute,Second Institute of Oceanography, SOA Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:依据2002-2003年长江口及邻近海域(29°00'-32° 00' N、122° 00 -123° 30' E)4个季节的海洋调查资料,探讨了该水域小型水母(含水螅水母、管水母和栉水母)总丰度的空间分布特征及季节差异.结果显示,该海域共出现小型水母41种,其中水螅水母28种,管水螅11种,栉水母2种.主要优势种包括管水母大西洋五角水母(Muggiaea atlantica)、双生水母(Diphyes chamissonis)和气囊水母(Physophora hydrostatica)以及水螅水母四叶小舌水母(Liriope tetraphylla)、两手筐水母(Solmundella bitentaculata)和短柄和平水母(Eirene brevistylus),其中大西洋五角水母为冬、春季第一优势种,双生水母则为夏、秋季第一优势种.该水域小型水母总丰度呈明显季节差异,夏季丰度最高((337.33±55.68) 个/m2),春、秋季次之(分别为(142.09±67.71) 个/m2和(132.84±35.17) 个/m2),冬季最低((113.69±32.72)个/m2).水温是影响调查区小型水母总丰度季节变化的主要环境因子,小型水母丰度与表层温度显著正相关(P < 0.01).盐度是影响小型水母平面分布格局的主要环境因子,春季小型水母丰度与底层盐度正相关(P < 0.05),夏季与10 m层盐度正相关(P < 0.01),全年则是与10 m层盐度正相关(P < 0.01).此外,调查水域小型水母丰度与其饵料——小型桡足类亦存在显著正相关关系(P < 0.01). Abstract:Small jellyfish (here including medusae, siphonophores, and ctenophores) are widespread in the marine pelagic realm. They usually constitute one of the most important assemblages of predators in pelagic food webs by serving as a direct link between zooplankton and higher trophic levels. They can at times be the most abundant non-crustacean invertebrate predators due to their great voracity and their rapid population growth, resulting in extensive seasonal blooms. Thus, studies on small jellyfish have become popular in marine ecology. Studies concerning zooplankton distribution at large spatial scales, particularly for weak swimmers like small jellyfish, emphasize the importance of the physical characteristics of water masses, including salinity and temperature. In our study, the seasonal abundance and horizontal distribution of small jellyfish were assessed in the Changjiang Estuary (Yangtze River) and the adjacent East China Sea (29°00'-32°00'N, 122°00'-123°30'E) in 2002-2003. The Changjiang Estuary and the adjacent East China Sea are one of the most productive aquatic ecosystems. High primary production supports high fishery production in adjacent coastal waters, including the Changjiang and Zhoushan fishery grounds. A total of 41 species of small jellyfish (11 siphonophores, 28 medusae, 2 ctenophores) were collected. Numerically, siphonophores were most abundant (58.56%-91.05% of the total collection by number). The dominant species were the siphonophores Diphyes chamissonis, Muggiaea atlantica, and Physophora hydrostatica and medusae Liriope tetraphylla, Solmundella bitentaculata, and Eirene brevistylus. Muggiaea atlantica was dominant all year round, particularly in spring (76.19% of the total collection by number) and winter (39.12%). D. chamissonis was dominant in summer and autumn, with abundances of 249.03 ind./m2 (73.82% of the total collection by number), and 98.04 ind./m2 (73.80%), respectively. The numerical abundance of small jellyfish was highest in summer ((337.33±55.68) ind./m2), lowest in winter ((113.69±32.72) ind./m2), and intermediate in spring and autumn ((142.09±67.71) ind./m2 and (132.84±35.17) ind./m2). Seasonal variations in the abundance of small jellyfish were closely associated with the surface water temperature. The average surface water temperature peaked in summer ((27.26±0.02) ℃). Then, both the temperature and salinity in the studied area were suitable for the development and reproduction of D. chamissonis. In addition, the summer upwelling and its associated high productivity might also benefit the jellyfish because large numbers of carnivores ultimately require an elevated level of primary production. There were strong correlations between temperature, 10-m water salinity, and small jellyfish abundances (P < 0.01), suggesting that they are important in determining the spatial distribution of small jellyfish. The bottom salinity in spring was positively related with the abundance (P < 0.05), and the 10-m water salinity in summer was also positively correlated with abundance (P < 0.01). In winter, the abundance was obviously increased from inshore to offshore. In addition, small jellyfish abundance was also strongly correlated with their food, small copepods (P < 0.01), which proved the importance of food availability for carnivores. This study provides basic knowledge on the distribution patterns of small jellyfish, which is essential to further understand the ecological roles played by small jellyfish and their responses to the hydrological conditions in the Changjiang Estuary and the adjacent East China Sea. 参考文献 相似文献 引证文献

Hydraulic forces impact larval fish drift in the free flowing section of a large European river

ABSTRACTDispersal of fluvial freshwater fish larvae occurs commonly in heavily regulated rivers. Studies increasingly indicate that drifting young fish have an active component to their movement and so are capable of coping with the dynamic hydraulic forces typical of rivers. We investigated hydraulic–drift relationships of the young stages of fish over one breeding season along a gravel shore of the Austrian Danube using stationary drift nets from the first occurrence until the end of the seasonal peak (April–June 2008). Observed densities of families and developmental stages were related to the hydraulic parameters flow velocity (in three spatial directions), turbulent kinetic energy and water depth, derived from a three‐dimensional hydrodynamic model of the sampling site. We detected distinct responses of drifting young fish to several hydro‐physical factors under conditions (low light level, over‐critical currents), which were considered to cause washouts and passive drift. In general, drift densities decreased with water depth and flow velocity. Weak swimmers (e.g. bull head Cottus gobio and early‐stage cyprinid larvae) avoided turbulent flows, as their abilities to orientate and hold position may be limited. Early larval as well as early juvenile stages of cyprinids used lateral currents directing to the bank, potentially to drop out of the flow and reach inshore areas. Our study indicates that there are family‐specific and stage‐specific responses to hydraulic variables and that fish actively disperse, probably to minimize mortality and maximize successful dispersal. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Facilitation of upstream passage for juveniles of a weakly swimming migratory galaxiid

The mitigating effects of fish passes to aid fish dispersal are well recognised; however, non-sports fish species, juveniles and weak swimmers have mostly been neglected when developing solutions to fish passage issues. We studied the juvenile (fork length, FL <60 mm) swimming ability of a weakly swimming fish species, īnanga (Galaxias maculatus), up an artificial ramp to evaluate the effects of fish size, ramp slope (5°, 15°, 25°), water velocity and the potential need for resting opportunities (pools) for a successful ascent. Water velocity significantly increased and fish passage success significantly decreased with ramp angle, with only one fish passing the 25° ramp. On average, fish had to be 10 mm larger to ascend a 15° ramp angle than at 5°. Pools did not enhance passage success in this study. To facilitate fish passage at barriers for weakly swimming fish species like juvenile īnanga, ramps should provide a rough surface substrate and have an optimal angle of 5° for a 3-m ramp.

An opinion paper: emphasis on white muscle development and growth to improve farmed fish flesh quality

Due to rapid depletion of wild stocks, the necessity to cultivate fish is eminent. Current fish farming practices seek to improve flesh quality. The notion that white muscles are the main target of the fishing industry is emphasized. A novel approach is suggested based on the development of white muscles in wild fish from eggs to adults. A compilation of facts about white muscle structure, function and ontogeny is followed by an account of the changes in swimming behaviour and performance related to the use of white muscle during growth from larva to adult. Ecological data narrate early swimming performance with white muscle development and growth, unveiling some of the important natural selection factors eliminating weak swimmers and poor growers from the breeding stock. A comparison between fish culture practise and natural conditions reveals fundamental differences. New approaches following wild breeding processes promise several important advantages regarding the quality of white muscle.

A simple approximation for larval retention around reefs

Estimating larval retention at individual reefs by local scale three-dimensional flows is a significant problem for understanding, and predicting, larval dispersal. Determining larval dispersal commonly involves the use of computationally demanding and expensively calibrated/validated hydrodynamic models that resolve reef wake eddies. This study models variation in larval retention times for a range of reef shapes and circulation regimes, using a reef-scale three-dimensional hydrodynamic model. It also explores how well larval retention time can be estimated based on the “Island Wake Parameter”, a measure of the degree of flow turbulence in the wake of reefs that is a simple function of flow speed, reef dimension, and vertical diffusion. The mean residence times found in the present study (0.48–5.64 days) indicate substantial potential for self-recruitment of species whose larvae are passive, or weak swimmers, for the first several days after release. Results also reveal strong and significant relationships between the Island Wake Parameter and mean residence time, explaining 81–92% of the variability in retention among reefs across a range of unidirectional flow speeds and tidal regimes. These findings suggest that good estimates of larval retention may be obtained from relatively coarse-scale characteristics of the flow, and basic features of reef geomorphology. Such approximations may be a valuable tool for modeling connectivity and meta-population dynamics over large spatial scales, where explicitly characterizing fine-scale flows around reef requires a prohibitive amount of computation and extensive model calibration.

The effect of flow on larval vertical distribution of the sea urchin, Strongylocentrotus droebachiensis

Most meroplanktonic larvae have been considered to behave as passive particles in the water column, and their dispersal determined by advection. However, larvae may influence their horizontal transport by sinking or swimming between overlying water masses. The flow conditions under which larvae influence their vertical distribution through depth regulation are presently unclear. Using an annular flume, we examined the effect of increasing flow, repeated exposure to flow, and acceleration and deceleration on the vertical distribution of 4-arm stage echinoplutei of Strongylocentrotus droebachiensis. Specifically, we generated different levels of vertical velocity and shear strengths by manipulating horizontal velocity ( u). We increased and decreased flow speed incrementally from no flow ( u = 0 cm s − 1 ) to intermediate flow ( u = 0.48 cm s − 1 ) to high flow ( u = 1.02 cm s − 1 ) for each of 3 cycles within each of 2 independent trials. We used a high resolution digital camera to record, and image-analysis to quantify, larval distribution. In the absence of flow, larvae swam upwards and aggregated near the surface of the flume. With increasing flow, increasing numbers of larvae were observed in the mid to low water column indicating a negative influence on larval ability to aggregate near the surface. No differences were observed between distributions in acceleration and deceleration phases of the cycles; however, results suggest that increased exposure can decrease the ability of larvae to regulate their vertical position over time. Vertical shear can result in the re-orientation of swimming larvae and likely compromised larval ability for directed swimming in our study. The threshold shear level beyond which larvae cannot regulate their vertical position is > 2 s − 1 , suggesting that echinoid larvae may be more vulnerable to shear than other weak swimmers, most likely because of their shape. However, echinoid larvae can likely influence their vertical distribution within many areas in the ocean, since shears > 2 s − 1 are present only in highly turbulent regions such as fronts.

Variations in the dietary compositions of morphologically diverse syngnathid fishes

We examined the diets of 12 morphologically diverse syngnathid species in shallow seagrass-dominated marine waters of south-western Australia to determine whether they differed among species that varied in body form, size and snout morphology, and in particular whether species with long snouts ingested more mobile prey. Although all species consume mainly small crustaceans, the dietary compositions of these species often vary markedly. We suggest that these differences are related to factors that influence both their foraging capabilities and/or locations. Those species with long snouts (e.g. the common seadragon Phyllopteryx taeniolatus and long-snouted pipefish Vanacampus poecilolaemus) consume far more relatively mobile prey than species with short snouts. Species with short snouts (e.g. the pug-nosed pipefish Pugnaso curtirostris and Macleay’s crested pipefish Histiogamphelus cristatus) mainly consume slow moving prey. Spotted pipefish, Stigmatopora argus, and wide-bodied pipefish, Stigmatopora nigra, restrict their diets to planktonic copepods, probably because their small gape size limits their ability to feed on alternative larger prey. Both the short-snouted seahorse, Hippocampus breviceps, and West Australian seahorse, Hippocampus subelongatus, ingest mainly slow-moving prey, even though the latter species possesses a moderately long snout. This may reflect the fact that seahorses are weak swimmers that anchor themselves to vegetation or the substrate with a strongly prehensile tail and rarely venture into open water to pursue mobile prey. In contrast, the relatively large P. taeniolatus, which resides above, rather than within, the macrophyte canopy, consumes mysids, which aggregate in open water above the seabed. Those pipefishes with characters that imply relatively enhanced mobility, such as well developed caudal fins and non-prehensile tails, are trophically diverse, suggesting that they are able to feed either on the sediment or phytal surfaces or in the water column.