Ontogenetic Habitat Shifts Research Articles

Growth and Habitat Use of Guadalupe Bass in the South Llano River, Texas

Abstract Predicting how stream fishes may respond to habitat restoration efforts is difficult, in part because of an incomplete understanding of how basic biological parameters such as growth and ontogenetic habitat shifts interact with flow regime and riverscape ecology. We assessed age-specific Guadalupe Bass Micropterus treculii habitat associations at three different spatial scales in the South Llano River, a spring-fed stream on the Edwards Plateau of central Texas, and the influence of habitat and flow regime on growth. We classified substrates using a low-cost side-scan sonar system. We used scale microstructure to determine age and to back-calculate size at age. Over 65% of captured Guadalupe Bass were age 2 or age 3, but individuals ranged from 0 to 7 y of age. Habitat associations overlapped considerably among age classes 1–3+, but age-0 Guadalupe Bass tended to associate with greater proportions of pool and run mesohabitats with submerged aquatic vegetation. Although habitat metrics across multiple scales did not have a large effect on growth, river discharge was negatively correlated with growth rates. Understanding age-specific Guadalupe Bass habitat associations at multiple scales will increase the effectiveness of restoration efforts directed at the species by assisting in determining appropriate ecological requirements of each life-history stage and spatial scales for conservation actions.

Mangroves reduce the vulnerability of coral reef fisheries to habitat degradation.

Despite general and wide-ranging negative effects of coral reef degradation on reef communities, hope might exist for reef-associated predators that use nursery habitats. When reef structural complexity is lost, refuge density declines and prey vulnerability increases. Here, we explore whether the presence of nursery habitats can promote high predator productivity on degraded reefs by mitigating the costs of increased vulnerability in early life, whilst allowing for the benefits of increased food availability in adulthood. We apply size-based ecosystem models of coral reefs with high and low structural complexity to predict fish biomass and productivity in the presence and absence of mangrove nurseries. Our scenarios allow us to elucidate the interacting effects of refuge availability and ontogenetic habitat shifts for fisheries productivity. We find that low complexity, degraded reefs with nurseries can support fisheries productivity that is equal to or greater than that in complex reefs that lack nurseries. We compare and validate model predictions with field data from Belize. Our results should inform reef fisheries management strategies and protected areas now and into the future.

Comparative analysis of habitat use and ontogenetic habitat-shifts among coral reef damselfishes

Habitat characteristics play an important role in determining the structure of fish communities. The decline in fish diversity and abundance with the decline in coral diversity and cover may be explained by habitat specialisation and partitioning among reef fishes and/or preferences for particular corals that are susceptible to disturbance. These preferences may develop at different life history stages. Here, we investigated patterns of habitat specialisation and ontogenetic shifts in habitat preference among 14 co-existing damselfish species at Lizard Island lagoon on the Great Barrier Reef. Although live coral cover contributed only 26% of the substratum, 28% of adults and 57% of new settlers were mostly found on live coral, indicating a strong preference for live coral habitat by new settlers. Only a few species exhibited a high degree of habitat specialisation and low overlap in habitat use with other species. Specialisation differed among species and life stages. New settlers were more commonly associated with finely branched corymbose corals and using those habitats with higher frequency than expected based on habitat availability alone. Adults were more commonly linked to more open branching morphologies or non-coral substrata. Our results suggest that habitat loss may not uniformly impact on all life stages. While adult individuals may not be as reliant as juveniles on corals, detrimental effects of habitat loss on juvenile survival may have longer-term impacts on adult populations. As juveniles show preferential associations with particular coral species, such as corymbose corals, the loss of these growth forms is likely to have the most significant negative impacts on this critical life history stage.

Ontogenetic habitat shift of age-0 Japanese flounder Paralichthys olivaceus on the Pacific coast of northeastern Japan: differences in timing of the shift among areas and potential effects on recruitment success

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30–80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June–August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success.

Atlantic Tarpon (Megalops atlanticus) exhibit upper estuarine habitat dependence followed by foraging system fidelity after ontogenetic habitat shifts

Fish can have complex life histories and use multiple habitats and resources during different life stages. Consequently, their complete life histories are often poorly understood. Atlantic Tarpon (Megalops atlanticus) is an ecologically and economically important sport fish, yet little is known about its lifelong habitat and resource use. We used stable isotope analysis of eye lens δ13C and δ15N to explore patterns in trophic history and habitat use of 16 Atlantic Tarpon from west-central Florida and Louisiana. The stable isotope chronologies indicated dependence on upper estuarine habitats during the early life history, and an ontogenetic shift to coastal waters at approximately 10 years of age and 140 cm total length. During the coastal phase, Atlantic Tarpon displayed among-individual variability and within-individual consistency in basal-resource dependence. Our study highlights the importance of upper estuarine habitats to the early life stages of Atlantic Tarpon, as well as the possibility that adults show fidelity to coastal systems for feeding and growth.

Regional climate, primary productivity and fish biomass drive growth variation and population resilience in a small pelagic fish

Abstract Environmental change often combined with selective harvesting has profound and diverse impacts on marine fish populations. Unlocking the biological consequences of these effects on wild fish is notoriously challenging, especially in highly productive but naturally variable systems with uncertain futures such as Eastern Boundary current systems. Here, we developed otolith increment-based growth chronologies covering half a century (53 years) for a small pelagic fish (Atlantic horse mackerel, Trachurus trachurus) in the northern limb of the Canary current upwelling system. We used increasingly complex mixed-effects models to partition individually resolved growth variation among intrinsic (Age and Age-at-capture) and extrinsic (biotic and abiotic factors) sources in four complementary data sets: a general population chronology, and three chronologies derived from age groups that reflect ontogenetic habitat shifts. First, we investigated the timing and scale of growth phase shifts and assessed the effects of extrinsic factors on inter-annual growth variation. Second, we quantified among and within cohort growth variability over time. Our results provided strong evidence for inter-annual SST and primary productivity variation impacting on Atlantic horse mackerel growth. We also identified phase shifts in growth that point to larger ecosystem-wide changes (regime shifts), potentially driven by large-scale climatic indices, such as North Atlantic Oscillation and East Atlantic pattern. Cohort-dependent growth effects likely reflect persistent environmental influences and density dependence. Further, we found evidence for carryover effects in growth whereby a poor start in life tended to persist despite compensatory growth being observed in some individuals. We show how population productivity can be impacted by multiple, interacting environmental and biotic factors leading to potential ecosystem regime shifts. Such information is key to understand recruitment dynamics and population persistence, and will have important implications for fisheries management and to those seeking to understand the effects of large-scale climate change on marine productivity.

Evidence of local adaptation in a waterfall-climbing Hawaiian goby fish derived from coupled biophysical modeling of larval dispersal and post-settlement selection

BackgroundLocal adaptation of marine and diadromous species is thought to be a product of larval dispersal, settlement mortality, and differential reproductive success, particularly in heterogeneous post-settlement habitats. We evaluated this premise with an oceanographic passive larval dispersal model coupled with individual-based models of post-settlement selection and reproduction to infer conditions that underlie local adaptation in Sicyopterus stimpsoni, an amphidromous Hawaiian goby known for its ability to climb waterfalls.ResultsOur model results demonstrated that larval dispersal is spatio-temporally asymmetric, with more larvae dispersed from the southeast (the Big Island) to northwest (Kaua‘i) along the archipelago, reflecting prevailing conditions such as El Niño/La Niña oscillations. Yet connectivity is nonetheless sufficient to result in homogenous populations across the archipelago. We also found, however, that ontogenetic shifts in habitat can give rise to adaptive morphological divergence when the strength of predation-driven post-settlement selection crosses a critical threshold. Notably, our simulations showed that larval dispersal is not the only factor determining the likelihood of morphological divergence. We found adaptive potential and evolutionary trajectories of S. stimpsoni were greater on islands with stronger environmental gradients and greater variance in larval cohort morphology due to fluctuating immigration.ConclusionsContrary to expectation, these findings indicate that immigration can act in concert with selection to favor local adaptation and divergence in species with marine larval dispersal. Further development of model simulations, parameterized to reflect additional empirical estimates of abiotic and biotic factors, will help advance our understanding of the proximate and ultimate mechanisms driving adaptive evolution, population resilience, and speciation in marine-associated species.

Questioning assumptions of trophic behavior in a broadly ranging marine predator guild

We evaluated whether existing assumptions regarding the trophic ecology of a poorly‐studied predator guild, northwest (NW) Atlantic skates (family: Rajidae), were supported across broad geographic scales. Four hypotheses were tested using carbon (δ13C) and nitrogen (δ15N) stable isotope values as a proxy for foraging behavior: 1) species exhibit ontogenetic shifts in habitat and thus display a shift in 13C with differential use of the continental shelf; 2) species exhibit ontogenetic prey shifts (i.e. from smaller to larger prey items) and become enriched in 15N; 3) individuals acquire energy from spatially confined local resource pools and exhibit limited displacement; and 4) species exhibit similarly sized and highly overlapping trophic niches. We found some evidence for ontogenetic shifts in habitat‐use (δ13C) for thorny and little skate and diet (δ15N) of thorny and winter skate and hypothesize that individuals exhibit gradual trophic niche transition, especially in δ15N space, rather than a clear and distinct shift in diet throughout ontogeny. Spatial isoscapes generated for little, thorny, and winter skate highlighted distinct spatial patterns in isotopic composition across the coastal shelf. For little and thorny skate, patterns mimicked expected spatial variability in the isotopic composition of phytoplankton/POM, suggesting limited displacement and utilization of spatially confined resource pools. Winter skate, however, exhibited a much narrower range of δ13C and δ15N values, suggesting individuals may use resources from a more confined latitudinal range. Although high total trophic niche overlap was observed between some species (e.g. little and thorny skate), sympatric species (e.g. little and winter skate) exhibited a degree of trophic niche separation. These findings offer new insight into the trophic dynamics of a poorly‐studied, vulnerable group of predators, and highlight a need to re‐examine assumptions pertaining to aspects of their ecology.

Competition during early ontogeny: Effects of native and invasive planktivores on the growth, survival, and habitat use of bluegill

Abstract Early life stages of fishes are sensitive to ecological and environmental disturbances and experience very high mortality rates. During early ontogeny, the growth and survival of larval fish often depends on food availability. Because habitat and diet shifts are strongly tied to individual body size, factors that influence the growth rates of individuals (e.g. resource limitation, competition) also affect other aspects of ontogeny including the timing of habitat or diet shifts. In the context of biological invasions, non‐native species can potentially disrupt the interaction of larval fish with their food via competition for shared prey, reducing growth and survival during a vulnerable period of an organism's life history. We hypothesised that invasive planktivores negatively affect native species through the vulnerable larval life stage via competition for zooplankton resources. To test this hypothesis, we conducted a series of experiments to assess and contrast the effects of invasive (bighead carp, Hypophthalmichthys nobilis) and native (golden shiners, Notemigonus crysoleucas) planktivores on zooplankton densities, and their effects on the growth, survival, abundance, and habitat use of larval bluegill (Lepomis macrochirus). Overall, the effects of the invasive planktivore were consistently greater than the native planktivore in terms of reduced prey densities, reduced bluegill growth rates, and delays to the timing of ontogenetic habitat shifts. Growth rates of bluegill larvae were reduced by 58–87% in the presence of bighead carp and 37% in the presence of golden shiners (relative to controls), but such reductions did not consistently lead to reduced survival (in mesocosm experiment) or relative abundance (in pond experiment). However, we estimated that bighead carp and golden shiners delayed ontogenetic habitat shifts in bluegill by 9–24 and 1–3 days, respectively. Although we did not detect an effect of planktivores on the numbers of larval bluegill, our findings suggest that bighead carp may still affect bluegill ontogeny and freshwater food webs by disrupting the timing of ontogenetic habitat shifts. By affecting the coupling of habitats via organism movements during early ontogeny, bighead carp may indirectly disrupt predator–prey interactions of native taxa.

Reconstructing sea turtle ontogenetic habitat shifts through trace element analysis of bone tissue

Reconstructing sea turtle ontogenetic habitat shifts through trace element analysis of bone tissue

Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 606:151-173 (2018) - DOI: https://doi.org/10.3354/meps12765 Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale Janet A. Ley*, Holly J. Rolls Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Avenue Southeast, St. Petersburg, Florida 33701, USA *Corresponding author: danceswithfish.jal@gmail.com ABSTRACT: Estuarine tributaries are vital links in connectivity for transient coastal fish undergoing ontogenetic habitat shifts, yet these resources are on the frontlines of anthropogenic change. Prioritizing actions to protect valuable fisheries may require fine-scale analyses of the relative value and function of tributaries as nurseries for regional populations. For sectioned otoliths from young-of-the-year (YOY) common snook Centropomus undecimalis; snook), we used laser ablation-inductively coupled plasma-mass spectrometry and stable isotope analysis to obtain microchemical signatures distinguishing 9 tributaries (each <1.0 km2, <5 km apart) along a mangrove-to-saltmarsh gradient in the Little Manatee River (LMR), Florida, USA. Using canonical analysis of principal coordinates and jackknifed leave-one-out classification for 123 fish, 70 (56.9%) were classified correctly based on microchemical signatures, compared with 11.1% that would have been correctly classified by chance alone (χ2, p < 0.0001). Months later, 39 of 40 (98%) yr-1 snook collected from throughout the LMR were assigned to a YOY nursery tributary based on otolith core signatures. The 3 tributaries making the greatest contribution of YOY snook to the yr-1 population were in pristine, low salinity (0.5-1.5 psu) saltmarshes farthest from the estuary mouth. Since other studies have identified completely different spatial patterns in fish nursery use from year to year, this study should be replicated to assess temporal variation in snook contribution from these nurseries. Nevertheless, this fine-scale application of otolith microchemistry is encouraging for future efforts seeking to protect locations having the greatest likelihood of contributing to survival of fishes that make ontogenetic habitat shifts within coastal ecosystems. KEY WORDS: Otolith microchemistry · Mangrove · Salt marsh · Ecology · Estuary · Centropomus undecimalis · Nursery · Tampa Bay · Connectivity · Contribution analysis Full text in pdf format Supplementary material PreviousNextCite this article as: Ley JA, Rolls HJ (2018) Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale. Mar Ecol Prog Ser 606:151-173. https://doi.org/10.3354/meps12765 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 606. Online publication date: November 15, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Long‐term ecological studies in northern lakes—challenges, experiences, and accomplishments

AbstractWe review three long‐term research programs performed over the last four decades on the ecology and management of oligotrophic lake systems with different fish communities at 69° N in Norway. Through whole‐lake perturbation experiments, intensive culling of stunted fish removed 35 tons (1984–1991) of Arctic charr Salvelinus alpinus in Takvatn (15 km2) and 153 tons (1981–1983, 2002–2004) of European whitefish Coregonus lavaretus in Stuorajavri (25 km2). In Takvatn, the overcrowded charr population decreased to 20% of the initial abundance, whereas brown trout Salmo trutta abundance increased. Somatic growth improved strongly in both species. In charr, ontogenetic habitat shifts broke down, the diet changed to more benthos, and plankton‐borne parasites decreased. High abundance of juvenile, littoral charr provided new prey for trout, creating an alternative, predator‐regulated stable state. Similar density reductions, positive effects on growth and reduced parasite loads occurred in whitefish in Stuorajavri. Despite the heavy culling, however, a new stable state did not occur and the fish community returned to the pre‐culling situation. In the Pasvik watercourse, vendace Coregonus albula invaded around 1990 after an upstream introduction. The population of this non‐native, highly specialized planktivore increased rapidly, resulting in steep density declines in zooplankton and the native planktivorous whitefish morph, and large changes in energy flow and structure and dynamics of the lacustrine food web. These programs show that long‐term research is essential for understanding the ecology of manmade disturbances and providing a scientific basis for management efforts.

Utilizing individual fish biomass and relative abundance models to map environmental niche associations of adult and juvenile targeted fishes

Many fishes undergo ontogenetic habitat shifts to meet their energy and resource needs as they grow. Habitat resource partitioning and patterns of habitat connectivity between conspecific fishes at different life-history stages is a significant knowledge gap. Species distribution models were used to examine patterns in the relative abundance, individual biomass estimates and environmental niche associations of different life stages of three iconic West Australian fishes. Continuous predictive maps describing the spatial distribution of abundance and individual biomass of the study species were created as well predictive hotspot maps that identify possible areas for aggregation of individuals of similar life stages of multiple species (i.e. spawning grounds, fisheries refugia or nursery areas). The models and maps indicate that processes driving the abundance patterns could be different from the body size associated demographic processes throughout an individual’s life cycle. Incorporating life-history in the spatially explicit management plans can ensure that critical habitat of the vulnerable stages (e.g. juvenile fish, spawning stock) is included within proposed protected areas and can enhance connectivity between various functional areas (e.g. nursery areas and adult populations) which, in turn, can improve the abundance of targeted species as well as other fish species relying on healthy ecosystem functioning.

Habitat availability and ontogenetic shifts alter bottlenecks in size‐structured fish populations

For species that utilize different habitats throughout their life cycle, the habitat limitation at a given stage can act as a bottleneck on population abundance, impacting density-dependent processes such as individual growth and survival. We explore the influence of habitat limitation on population dynamics by developing a multi-stage population model based on lake-dwelling rainbow trout (Oncorhynchus mykiss) populations where adults occupy the lake habitat but use tributaries for spawning and juvenile rearing. The model details density-dependent ecological processes and ontogenetic habitat shifts, harvest mortality, and the impact of climate on growth. We ran model simulations using a range of early life stage habitat availabilities and climatic conditions representative of the native range of rainbow trout in Canada and compared the results to empirical data. The results suggest that (1) increases in early life stage habitat leads to increases in population abundance but, due to density-dependent processes, also results in slower growing stunted populations; (2) population bottlenecks can occur at any life stage, even at the adult stage if spawning and rearing habitats are abundant; (3) when the level of competition for early life stages is increased, inter-cohort competition can lead to population cycles. The model's conclusions are further reinforced by empirical data showing a similar trend in the relationship between fish density and maximum size and providing evidence that limited early life stage habitat leads to lower fish densities and larger fish size. We provide a model that links environmental conditions to population dynamics and is useful for fisheries management and habitat conservation decisions.

What Makes Nearshore Habitats Nurseries for Nekton? An Emerging View of the Nursery Role Hypothesis

Estuaries and other coastal habitats are considered essential for the survival of early life stages of commercial, recreational, and other ecologically important species. While early designations simply referred to habitats with higher densities of juveniles as nurseries, the definition was improved by arguing that contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, in nursery habitats. However, this and related approaches typically consider critical habitats as individual, homogeneous entities that are static in nature and do not specifically incorporate important dynamics that determine nursery function. The latter include environmental variability, estuarine hydrodynamics, trophic coupling, ontogenetic habitat shifts, and spatially explicit usage of habitat patches and corridors within larger seascapes. Subsequent studies have identified important factors that regulate nursery value, and researchers working independently across the globe have not only supported the advances made in defining the processes underlying nursery function but, as set forth in this narrative, have advanced it while suggesting that much work still needs to be done to improve our understanding of the links between juvenile nekton survival and the estuarine-coastal seascape. We discuss the current nursery role hypothesis and the data supporting (or refuting) it along with the implications for management of estuarine habitats for the conservation or restoration of nursery function.

Ontogeny of turbiditaxis in hatchery-reared Japanese anchovy Engraulis japonicus.

The ontogenetic change in turbiditaxis (i.e. attraction to turbid waters) was examined in the larvae and juveniles of Japanese anchovy Engraulis japonicus by testing three levels of turbidity (0, 20 and 100 ppm of kaolin). Larvae of 12, 20 and 30 mm standard length (LS ) exhibited turbiditaxis to both 20 and 100 ppm of kaolin, whereas 6 mm LS larvae and 45 mm LS juveniles did not exhibit any turbiditaxis. Turbiditaxis might explain the ontogenetic habitat shift from coastal to offshore waters reported for this species.

Ontogenetic habitat shift of age-0 Japanese flounder Paralichthys olivaceus on the Pacific coast of northeastern Japan: differences in timing of the shift among areas and potential effects on recruitment success

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30–80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June–August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success.

Ontogenetic habitat shift in abalone Haliotis discus hannai: a review

Ecological literature on abalone Haliotis discus hannai populations is reviewed to identify processes and factors driving ontogenetic shifts in habitat. Abalone recruitment is related to the algal community type, with abalone shifting with growth from deeper crustose coralline algal (CCA) habitats to shallower kelp bed habitats via algal turfs. Timing of the habitat shifts is linked to ontogenetic changes in diet, from benthic diatoms to a diet dominated by macroalgae. Susceptibility to predation appears to change, concomitant with the shift from cryptic microhabitats during early-life stages to more exposed habitats during latter-life stages. Interstitial spaces between cobbles and boulders in the CCA habitat are considered to be important for reducing predation risk. The loss of CCA nursery habitat through sedimentation and macroalgal overgrowth likely negatively affects abalone recruitment. Preservation of diverse algal communities, including suitable habitats for the different abalone growth stages, is critical for successful abalone recruitment.

Ontogenetic habitat and dietary shifts in Japanese turban snail Turbo cornutus at Nagai, Sagami Bay, Japan

A field survey and a laboratory experiment were conducted to examine ontogenetic shifts in habitat and diet of the turban snail Turbo cornutus. The main habitat of turban snail juveniles smaller than 10 mm shell height (SH) was turfs of articulated coralline algae, and that of adults larger than 50 mm SH was kelp beds of Ecklonia bicyclis and Ecklonia cava. However, the ontogenetic habitat shift during the juvenile stage of 20–50 mm SH was unclear. From the results of a long-term feeding experiment and stable isotope analysis, the gelidiacean alga Gelidium elegans was assumed to be more important as a food source for juvenile turban snail than E. cava in the field. However, the frequency of individuals inhabiting gelidiacean algal turfs was low in both juvenile and adult stages. Thus, the ontogenetic shifts in habitat and diet did not coincide and other factors, i.e., daytime refuge, are important. As the growth rate was higher in the juveniles fed on the two algal species than those fed on single algal species, co-occurrence of various algal habitats in rocky shore ecosystems as a coastal ecosystem complex may enhance growth of turban snail juveniles feeding on a combination of different algal species.

Ontogenetic habitat shift in Pugettia quadridens on the coast of Sagami Bay, Japan

Population dynamics of the kelp crab Pugettia quadridens, a potential predator of juvenile abalone, were investigated on the coast of Nagai, Sagami Bay, to examine its cryptic ontogenetic habitat shift. Monthly quantitative sampling over 2 years, which was carried out in 11 different subtidal habitats (< 0.1–8 m deep), revealed that P. quadridens changes ontogenetically according to its habitat: P. quadridens occurred in shallow lower subtidal (1–4 m) small red algal turfs (mainly Grateoloupia cornea) almost all year around, when the population was dominated by juveniles and stage I (immature) individuals; on the other hand, in the shallow upper subtidal (0.1–1 m) habitat (mainly Sargassum fusiforme beds near the low tidal mark), P. quadridens occurred only during winter to early spring, when the population was dominated by individuals of senior ontogenetic stages. These finding suggest that P. quadridens inhabit subtidal small red algal turfs during their early benthic phase, and then, the majority of larger individuals of stages II and III migrate to Sargassum beds. Our results suggest that the impact of P. quadridens predation on abalone stocks is limited in the present study site, primarily because the habitat of P. quadridens is segregated from that of juvenile abalone.