Ontogenetic and sex‐based differences in habitat preferences and site fidelity of White's seahorse Hippocampus whitei

The aim of this study was to determine and compare habitat preferences for male and female adult and juvenile White's seahorse Hippocampus whitei and assess their movements and site fidelity over 4 years. Data were collected from three sites along 1·5 km of estuarine shoreline in Port Stephens, New South Wales, Australia, from 2006 to 2009 using H. whitei that had been tagged with visible implant fluorescent elastomer. Relative availability of 12 habitats and habitat preferences of H. whitei was determined, based on the habitat that H. whitei used as a holdfast. Hippocampus whitei occurred in nine different habitats; adults preferred sponge and soft coral Dendronephthya australis habitats with no difference between male and female habitat preferences whilst juveniles preferred gorgonian Euplexaura sp. habitat. There was a significant preference by adults for D. australis colonies with height >40 cm and avoidance of colonies <20 cm. Neither adults nor juveniles used sand or the seagrasses Zostera muelleri subsp. capricorni and Halophila ovalis. Hippocampus whitei showed cryptic behaviour with c. 50% of adult sightings cryptic and c. 75% for juveniles with crypsis occurring predominantly in Sargassum sp. for adults and Euplexaura sp. habitat for juveniles. Within sites, females moved significantly longer distances (maximum of 70 m) than males (maximum of 38 m) over 20 months. Strong site fidelity was displayed by H. whitei with males persisting at the same site for up to 56 months and females for 49 months and no H. whitei moved between sites. The longest period that an H. whitei was recorded on the same holdfast was 17 months for a male and 10 months for a female. As this species displays strong site fidelity, specific habitat preferences and has a limited distribution, future management needs to minimize the risk of habitat disturbance as loss of key habitats could have a negative effect on species abundance and distribution.     

Field studies of seahorse population density,structure and habitat use in a semi-closed north-eastern Mediterranean marine area (Stratoni,North Aegean Sea)

The present study was carried out in the marine area of Stratoni, Greece, where two seahorse species are present (Hippocampus hippocampus and Hippocampus guttulatus). Two surveys were conducted (September 2016 and May 2019) to gather information regarding seahorse species' abundance, distribution and habitat characteristics. Four different seahorse natural and artificial habitat types were identified. The results revealed that the presence of H. hippocampus was relatively high, especially at sites with artificial structures, whereas the presence of H. guttulatus was rare. Data collected can provide baseline information for future population assessments.     

Monthly population density and structure patterns of an endangered seahorse Hippocampus capensis: a comparison between natural and artificial habitats

This study investigated aspects of the population ecology of the endangered Knysna seahorse Hippocampus capensis within different habitat types. High densities of H. capensis were found within artificial Reno mattress habitat, within the Knysna Estuary, South Africa. Monthly surveys at three sites were conducted from October 2015 to August 2016 to compare population densities of H. capensis in this artificial habitat with natural eel grass Zostera capensis habitat. Hippocampus capensis densities varied significantly across all sites and highest population densities were consistently observed within the Reno mattress habitat. Hippocampus capensis were also found to be significantly larger within the Reno mattress habitat and pooled data showed that males were significantly larger than females. The overall sex ratio for all three sites was female biased, although this varied across seasons at two sites. The findings suggest that artificial Reno mattresses provide novel habitat for this endangered species and consideration should be given to the usefulness of these structures in future conservation actions.     

Does a No-Take Marine Protected Area Benefit Seahorses?

Seahorses are iconic charismatic species that are often used to ‘champion’ marine conservation causes around the world. As they are threatened in many countries by over-exploitation and habitat loss, marine protected areas (MPAs) could help with their protection and recovery. MPAs may conserve seahorses through protecting essential habitats and removing fishing pressures. Populations of White''s seahorse, Hippocampus whitei, a species endemic to New South Wales, Australia, were monitored monthly from 2006 to 2009 using diver surveys at two sites within a no-take marine protected areas established in 1983, and at two control sites outside the no-take MPA sites. Predators of H. whitei were also identified and monitored. Hippocampus whitei were more abundant at the control sites. Seahorse predators (3 species of fish and 2 species of octopus) were more abundant within the no-take MPA sites. Seahorse and predator abundances were negatively correlated. Substantial variability in the seahorse population at one of the control sites reinforced the importance of long-term monitoring and use of multiple control sites to assess the outcomes of MPAs for seahorses. MPAs should be used cautiously to conserve seahorse populations as there is the risk of a negative impact through increased predator abundance.     

An endangered seahorse selectively chooses an artificial structure

The development of a residential marina estate within the Knysna estuary, South Africa, introduced Reno mattresses (horizontal wire cages filled with rocks) as a novel habitat for the endangered Knysna seahorse Hippocampus capensis. Consistently high seahorse densities on these artificial structures, despite the availability of seagrass habitat, begged the question of whether this habitat was chosen by the seahorse in preference to natural vegetation. An in situ habitat choice experiment was conducted which focused on the choice made by adult H. capensis between natural vegetation (Zostera capensis) and artificial (Reno mattress) habitat within a choice chamber. Seahorses were significantly more likely to move away from Z. capensis onto a Reno mattress structure or remain on this structure. This study concludes that higher H. capensis densities on Reno mattresses within Thesen Islands Marina are owing to some positive feature of this habitat and the underlying processes responsible for the choice made by this species (additional food, holdfasts, protection) can now be investigated.     

Home range behaviour of the monogamous Australian seahorse, <Emphasis Type="Italic">Hippocampus whitei</Emphasis>

We provide a quantitative account of local movements in the monogamous Australian species Hippocampus whitei, as a rare report of home range size in fishes living in seagrass habitats. Our study took place in shallow Posidonia seagrass beds in Port Jackson (Sydney Harbour), principally during January to March. Daily monitoring of individual seahorses during underwater observations revealed that both sexes maintained small and apparently undefended home ranges for several breeding cycles at least. Female home ranges were significantly larger than males, when analysed by both the minimum convex polygon and grid cell methods. Home range size was not correlated with either body size or seahorse density. Presumably, home ranges were small in H. whitei because camouflage (to avoid predation and to capture prey), mate fidelity and parental brooding meant they accrued little benefit (and potentially considerable cost) from moving more extensively. Sex differences in home range size may arise from constraints associated with male pregnancy. These fish are among the most sedentary of vertebrates, with relatively small home ranges equalled only by coral reef species. In terms of their conservation, relatively small protected areas may be sufficient to support breeding populations of H. whitei although that limited movement may result in considerable delays in the recolonisation of depleted areas.     

Does underwater flash photography affect the behaviour,movement and site persistence of seahorses?

The effect of flash photography on seahorse species has never been tested. An experiment was established to test the effect of flash photography and the handling of Hippocampus whitei, a medium‐sized seahorse species endemic to Australia, on their behavioural responses, movements and site persistence. A total of 24 H. whitei were utilized in the experiment with eight in each of the three treatments (flash photography, handling and control). The effect of underwater flash photography on H. whitei movements was not significant; however, the effect of handling H. whitei to take a photograph had a significant effect on their short‐term behavioural responses to the photographer. Kaplan–Meier log‐rank test revealed that there was no significant difference in site persistence of H. whitei from each of the three treatments and that flash photography had no long‐term effects on their site persistence. It is concluded that the use of flash photography by divers is a safe and viable technique with H. whitei, particularly if photographs can be used for individual identification purposes.     

Benthic assemblages,biodiversity and invasiveness in marinas and commercial harbours: an investigation using a bioindicator group

Fouling communities on artificial marine structures are generally different from benthic communities in natural rocky habitats. However, they may also differ among different types of artificial structures. Two artificial structures in direct contact with arriving vessels were compared: floating pontoons within recreational marinas, and sea-walls within commercial harbours. Natural rocky habitats were used as a reference, and the genus Eudendrium (Cnidaria, Hydrozoa) was chosen as a bioindicator. The assemblages were different among the three types of habitat studied, with different species characterising each habitat. The probability of finding an invasive Eudendrium species was significantly higher on pontoons. Diversity was the lowest on pontoons, but it was not significantly different between sea-walls and natural rocks. In general, a barrier to the spread of exotic species exists between harbours and natural rocky habitats. Floating pontoons seem to be a less suitable habitat for native fauna and a key element in marine biological invasions.     

Settlement and Density of Juvenile Fish Assemblages in Natural, Zostera Capricorni (Zosteraceae) and Artificial Seagrass Beds

Few studies have validated the use of artificial seagrass to study processes structuring faunal assemblages by comparison with natural seagrass. One metric (fish recruitment) for evaluating the use of artificial seagrass was used in the present study. Settlement and recruitment of juvenile fish was estimated in natural, Zostera capricorni Aschers, and artificial seagrass in Botany Bay, NSW, over 6 consecutive days. Tarwhine, Rhabdosargus sarba, dominated the catch from both habitats, and there was no significant difference in abundance of recruits among the habitats. This was at least partly caused by large spatial and temporal variation in abundance. Daily abundances of R. sarba recruits suggested movement between seagrass beds, but could not be confirmed without tagging individual fish. Rhabdosargus sarba settlers were less abundant than recruits, but were also patchily distributed amongst natural and artificial seagrass beds. Most other species were also found in similar abundance in the two habitats, except stripey, Microcanthus strigatus, which was more abundant in artificial seagrass. Overall, fish assemblages in natural and artificial seagrass were similar. Artificial seagrass may therefore be useful for monitoring settlement and recruitment of juvenile fishes to disturbed habitats, to predict the success of habitat remediation. However, if artificial seagrass is used to model processes occurring in natural seagrass, it is necessary to consider species-specific responses to the artificial habitat.     

Juvenile sparids (Rhabdosargus holubi) consistently select structurally dense vegetated habitat in nursery seascapes

Seagrass habitats provide structural complexity in coastal estuarine and marine environments, which offer fish optimal foraging grounds and refuge from predation. However, seagrasses are some of the most threatened ecosystems globally, with anthropogenic activities such as population growth and environmental degradation leading to the fragmentation, thinning, and loss of these habitats. Rhabdosargus holubi is one of only a few vegetation-associated marine fish species in South African estuaries. Although field studies have shown a strong association with seagrass over other aquatic vegetation for the juveniles of this species, habitat choice has never been empirically tested. Here, we used artificial vegetation units to test habitat choice (different structural complexities) for this species. We also tested whether habitat choice is influenced by a predatory threat, with fish preferentially selecting dense habitat in the presence of a predator and whether this effect may be more apparent in smaller individuals. We found that R. holubi significantly prefer greater structural complexity over less complex habitats, in both the absence and presence of a predator and for both small and large juveniles, showing that R. holubi actively choose more complex structures and are attracted to the structure per se irrespective of the threat of predation. This study highlights the importance of dense seagrass as nursery areas for this species and demonstrates how the loss of these habitats could impact the nursery function of estuaries.     

Artificial Spawning Habitats Improve Egg Production of a Declining Diadromous Fish,Galaxias maculatus (Jenyns, 1842)

Anthropogenic impacts from urbanization, deforestation, and agriculture have degraded the riparian margins of waterways worldwide. In New Zealand, such impacts have caused changes in native vegetation, enhanced invasion by exotic grasses, and altered river bank morphology. One consequence has been a great reduction in obligate spawning habitat of a diadromous fish, Galaxias maculatus. Juvenile G. maculatus comprise a culturally important fishery that has been considerably reduced over recent decades. Rehabilitation of riparian vegetation needed for spawning is relatively straightforward, but slow. We hypothesized that artificial spawning habitats could accelerate restoration of fish egg production by creating an environment that would support at least the same density and survival of eggs as non‐impacted vegetation. We tested three artificial devices (straw bales, straw tubes, and moss tubes) in degraded and intact sites. Eggs were laid in all of these with numbers and survival usually exceeding that in riparian grasses. Where habitat was degraded, artificial spawning habitats yielded up to 10,000 eggs compared to none in nearby natural spawning habitat. The ground‐level environment of artificial habitat was similar to that of intact vegetation in buffering ambient temperature and humidity fluctuations. Crucial properties of the artificial habitats were (1) shelter to provide shade and hold moisture; (2) accessibility to allow adult fish to deposit and fertilize eggs; and (3) robustness to provide reliable surfaces and protection for the eggs during their development. We show that artificial spawning habitats are a viable short‐term alternative to rehabilitating spawning habitat while legacy effects abate and riparian vegetation recovers.     

Spawning habitat enhancement in the European bullhead (Cottus gobio), an endangered freshwater fish in degraded lowland rivers

Due to river regulation, the natural habitat of the European bullhead (Cottus gobio) has been degraded and often there is an apparent lack of suitable spawning substrates (hard objects like stones). Addition of artificial structures to degraded habitats may be a very promising tool for habitat enhancement. In this study, we evaluated the use of ceramic tiles as artificial spawning substrates in canalised and (remaining) meandering parts of anthropogenically perturbated lowland rivers in Flanders (northern part of Belgium). Furthermore, we examined whether water depth and velocity were important determinants for the choice of tiles in these different river trajectories. Tiles were successfully used by the bullhead as spawning substrates. In the meandering parts of the river, the number of egg deposits was significantly positively correlated with water depth, while in canalised river parts, water depth and velocity were of no importance for tile usage. In general, supplementation of rivers with artificial substrates like tiles may be a promising, inexpensive and easy-to-use enhancement technique for degraded bullhead spawning habitat.     

Size,relative abundance,and catch‐per‐unit‐effort of round goby,Neogobius melanostomus,in anthropogenically modified and natural habitats in the western basin of Lake Erie

To determine if anthropogenically modified habitats possess greater numbers of round goby and serve as dispersal vectors, we used angling to compare catch‐per‐unit of effort for 64 natural and modified habitat areas. In addition, a gravel natural habitat was seined to compare length frequency distribution with anthropogenically modified habitats. Natural habitats included gravel beaches and natural rubble and cliff wall, while modified habitats included artificial riprap, concrete sea wall, and metal sheet piling. No significant difference in relative abundance was observed in round goby preference among modified habitats (P = 0.52), but natural gravel habitats were significantly different from modified habitats that included artificial riprap (P = 0.002), concrete sea wall (P < 0.001), and metal sheet piling (P = 0.003). When habitat subcategories were compared using anova , the natural gravel beach habitat was significantly different from the three artificial substrates and from natural rubble and cliff wall substrates (P < 0.004). No round goby were caught from gravel beach habitats; thus, this habitat was removed from further analysis. A Student t‐test indicated no significant difference between habitats was found between the natural rubble and cliff wall habitat and the three other artificial habitats (concrete sea wall, P = 0.33; riprap, P = 0.53; metal sheet piling, P = 0.11). We further evaluated gravel beach habitats to determine the reason for the lack of goby capture. We seined gravel beach habitat and collected 328 individuals, with which we evaluated the length‐frequency distribution and calculated length–weight relationships by sex. Our results indicated that only 5.2% of the goby population was available for capture by angling on the gravel beach habitat. A t‐test comparing the demographic attributes between seining and angling indicated a significant difference between goby length (P < 0.001) and weight (P < 0.001). The regression slope indicated an ontogenetic habitat shift occurred near 62 mm standard length. Smaller round goby individuals were found in less structurally complex gravel beach habitat, while larger individuals were associated with complex habitat.     

The relative importance of food and shelter for seagrass-associated invertebrates: a latitudinal comparison of habitat choice by isopod grazers

The generality of mechanisms affecting habitat choice and grazing in seagrass meadows was evaluated in a latitudinal comparison of seagrass grazers from the temperate (60°N) Baltic Sea and the subtropical (30°N) Gulf of Mexico. Using similar habitat choice experiment set-ups in Finland and the USA, the role of food type, habitat complexity and predation hazard on habitat choice of the isopods Idotea baltica (Pallas) and Erichsonella attenuata Harger were tested. When shelter was provided by both living and artificial seagrass, epiphytic food resources on artificial vegetation were clearly preferred by both species, although Idotea was attracted to epiphyte-free seagrass when no alternative food was present. When choosing between food and shelter, both species preferred epiphytic food over shelter. However, under predation hazard of fish, Erichsonella clearly switched to the habitat offering shelter, while the presence of a predatory fish produced no preference for shelter by Idotea. Food type may be considered as an universal mechanism that partly determines the presence of grazers in seagrass habitats and is, in the absence of a predator, more important than shelter. Predation risk affected the behaviour of the grazers, but the response varied between species possibly due to varying importance of fish predation in the areas studied. Received: 16 November 1998 / Accepted: 13 February 1999     

GENETIC,ACCLIMATIZATION, AND ONTOGENETIC EFFECTS ON HABITAT SELECTION BEHAVIOR IN DAPHNIA PULICARIA

Daphnia pulicaria from three different populations were observed to express within-population variation in habitat-choice behavior in field assays. Individuals from different habitats (i.e., lake depths) were isolated and cultured as clonal lines under standard conditions. Habitat choices by clonal descendants were then estimated in the field, using replicate experimental columns. There was significant heritable and ontogenetic variation in habitat choice, but the heritable effect was small relative to the phenotypic variation of the original isolates. In a second set of experiments, D. pulicaria that were acclimatized to different habitats showed a strong tendency to choose the habitat to which they had been acclimatized. These data suggest that a given genotype can use a wide range of habitats, given appropriate acclimatization. Although genetic variation is significant, we hypothesize that natural selection on correlated ecological traits is more likely to maintain patterns of genotypic segregation among habitats in Daphnia.     

Habitat constraints on carotenoid‐based coloration in a small euryhaline teleost

Display of bright and striking color patterns is a widespread way of communication in many animal species. Carotenoid‐based coloration accounts for most of the bright yellow, orange, and red displays in invertebrates, fish, amphibians, reptiles, and birds, being widely considered a signal of individual health. This type of coloration is under the influence of several factors, such as sexual selection, predator pressure, pigment availability, and light transmission. Fish offer numerous examples of visual communication by means of color patterns. We used a small cyprinodontid fish, Aphanius fasciatus (Valenciennes, 1821), as a model species to assess habitat constraints on the color display in male caudal fin. Populations from natural and open/closed artificial habitats were tested for differences in the pigmentation of caudal fins. The most important factors explaining the intensity of coloration were the habitat type and the chlorophyll concentration in the sediment, followed by water turbidity; yellow fins were observed in natural habitats with low chlorophyll concentration and high water turbidity, while orange fins occurred in artificial habitats with high chlorophyll concentration and low turbidity. Furthermore, A. fasciatus in artificial habitats showed a higher somatic and a lower reproductive allotment with respect to natural habitats, according to the existing literature on the species. Furthermore, in closed artificial habitats, where the most intense reddish coloration of caudal fins was observed, a trade‐off between somatic growth and the coloration intensity of a carotenoid‐based sexual ornament has been observed; in these populations, intensity of caudal fin coloration was negatively related to the somatic allotment. Results of this study suggested how both the pigmentation of male's caudal fin and the life history strategies of the species are constrained by habitat characteristics.     

Preferences of juveniles and adults of the invasive Ponto-Caspian amphipod <Emphasis Type="Italic">Pontogammarus robustoides</Emphasis> for various species of macrophytes and artificial substrata

We studied preferences of invasive Ponto-Caspian amphipod P. robustoides for various macrophyte species (Myriophyllum spicatum, Ceratophyllum demersum, Potamogeton perfoliatus, Elodea canadensis) and artificial plant-like objects (artificial Christmas tree branches) in laboratory pairwise-choice tests. Juvenile (<7 mm) and adult gammarids exhibited different habitat preferences. Adults did not discriminate between artificial and natural substrata, or among most of the tested species of plants. In contrast, juveniles clearly preferred all tested macrophytes over artificial substrata. Moreover, they particularly preferred plants with the finest leaf elements: M. spicatum and C. demersum over the others and E. canadensis over P. perfoliatus. We found no influence of chironomid larvae, a potential food source for adult gammarids, on their distribution, nor any effect of adults on the habitat choice by juveniles. The habitat partitioning between juvenile and adult P. robustoides may help them survive in a new environment and increase their invasive potential by reducing the intraspecific competition and cannibalism.     

Studies on ticks of veterinary importance in Nigeria XII. Oviposition and eclosion in five species of IXODID ticks in contrasting habitats

The preoviposition and oviposition periods, the eclosion periods and numbers of eggs laid by adult ticks of five species, namelyAmblyomma variegatum, Boophilus decoloratus, B. geigyi, Hyalomma rufipes andH. truncatum, maintained in a natural habitat were compared with those maintained in semi-natural and artificial habitats. Within the natural habitats, open and shady sites were distinguished.Maximum oviposition occurred during the peak of the rains in engorgedA. variegatum andB. decoloratus, and the numbers of eggs laid by those kept in the natural and semi-natural habitats were significantly lower in the dry season than in the rainy season. Maximum oviposition in engorgedH. rufipes kept in the natural habitat occurred during the early rains while minimum oviposition took place during the peak of the rains.Oviposition in engorgedH. truncatum was poor among those kept in the natural habitat during the peak and end of the rains. EngorgedA. variegatum andB. decoloratus kept in shady sites of the natural habitat laid significantly more eggs than in all other habitats at all seasons, while forH. truncatum andH. rufipes, numbers of eggs laid in the open site were significantly higher than those laid in other habitats at all seasons.In all species investigated, success in oviposition was aided by moisture provided by light to moderate rainfall, while excessive moisture in terms of heavy rainfall adversely affected oviposition.     

Habitat choice by juvenile cod (Gadus morhua L.) on sandy soft bottoms with different vegetation types

Habitat choice by juvenile cod (Gadus morhua L.) on sandy bottoms with different vegetation types was studied in laboratory. The experiment was conducted day and night in flow-through tanks on two different size-classes of cod (7–13 and 17–28 cm TL). Four habitats, typical of shallow soft bottoms on the Swedish west coast:Fucus vesiculosus, Zostera marina, Cladophora sp. and bare sand, were set up pair-wise in six combinations. The main difference between habitats in this study was vegetation structure, since all parameters except vegetation type was considered equal for both sides of the experimental tanks and natural prey was eliminated. The results showed a difference in habitat utilization by juvenile cod between day (light) and night (dark). During day time the fishes showed a significant preference for vegetation, while nocturnally no significant choice of habitat was made. Both size-classes preferredFucus, considered the most complex habitat in this study, when this was available. The smaller size-class seemed to be able to utilize the other vegetation types as well, always preferring vegetation over sand. Larger juvenile cod, on the other hand, appeared to be restricted toFucus. This difference in habitat choice by the two size-classes might be due to a greater dependence on shelter from predation by the smaller juveniles, causing them to associate more strongly with vegetation. The larger juveniles avoidedCladophora, since they might have difficulties in entering the compact structure of this filamentous algae. Availability of vegetation at day time, as a predation refuge, as well as of open sandy areas for feeding during night, thus seems to be important for juvenile cod. It is concluded that eutrophication-induced changes in habitat structure, such as increased dominance by filamentous algae, could alter the availability of predation refuges and foraging habitats for juvenile cod.     

Modeling foraging behavior of piping plovers to evaluate habitat restoration success

Habitat restoration projects are often deemed successful based on the presence of the target species within the habitat; however, in some cases the restored habitat acts as an ecological trap and does not help to improve the reproductive success of the target species. Understanding wildlife–habitat relationships through precise measurements of animal behavior can identify critical resources that contribute to high quality habitat and improve habitat restoration practice. We evaluated the success of a restored piping plover (Charadrius melodus) breeding habitat in New Jersey, USA. We identified the major factors influencing foraging rates, compared foraging activity budgets over 3 yr at restored and natural habitats, and explored the potential of artificial tidal ponds as a viable restoration alternative. Adult foraging rates were higher in artificial pond and ephemeral pool habitats, during low tide, and after breeding activity ended. Adult foraging rates were impeded by the presence of people and vehicles within 50 m. Chick foraging rates were highest at artificial ponds and bay shores and lowest in dunes and on sand flats. Chick foraging rates were strongly hindered by the presence of corvids and the number of people within 50 m. In addition, at artificial tidal ponds, piping plovers spent more time foraging and less time engaged in defensive behaviors (vigilance, crouching, and fleeing) compared to other potential habitats. Our findings support the hypothesis that artificial tidal ponds are a valuable, perhaps superior, foraging habitat. Future beach restoration projects should include this feature to maximize habitat quality and restoration success. © 2011 The Wildlife Society.