Wave-exposed Areas Research Articles

Geographical parthenogenesis in the brown alga Scytosiphon lomentaria (Scytosiphonaceae): Sexuals in warm waters and parthenogens in cold waters.

Geographical parthenogenesis, a phenomenon where parthenogens and their close sexual relatives inhabit distinct geographical areas, has been considered an interesting topic in evolutionary biology. Reports of geographical parthenogenesis from land and freshwater are numerous, but this occurrence has been rarely reported from the sea. Brown algae are mostly marine and are thought to include numerous obligate parthenogens; still, little is known about the distribution, origin and evolution of parthenogens in this group. Here we report a novel pattern of geographical parthenogenesis in the isogamous brown alga Scytosiphon lomentaria. Sex ratio investigation demonstrated that, in Japan, sexual populations grew in the coast along warm ocean currents, whereas female-dominant parthenogenetic populations grew mainly in the coast along a cold ocean current. In the two localities where sexual and parthenogenetic populations were parapatric, parthenogens grew in more wave-exposed areas than sexuals. Population genetic and phylogenetic analyses, including those based on genome-wide single nucleotide polymorphism data, indicated that parthenogens have initially evolved at least twice and subsequent hybridizations between the parthenogens and sexuals have generated multiple new parthenogenetic lineages. The origin of the initial parthenogens is not clear, except that it would not be interspecies hybridization. Interestingly, we found that the production of sex pheromones, which attract male gametes, has been independently lost in the initial two parthenogenetic lineages. This parallel loss of the sexual trait may represent the direct origin of parthenogens, or the regressive evolution of a useless trait under asexuality.

Recent dynamics on turbid-water corals reefs following the 2010 mass bleaching event in Tobago

We detail the benthic compositon of the turbid-water coral reefs of Tobago in 2016 and examine the influence of mass coral bleaching and hydro-geomorphic setting (sheltereted vs. wave-exposed) on benthic community dynamics against the 2007 baseline. In the current assessment mean hard coral cover was 14.83% ± 0.85, which ranged from 2% to 37% with few sites exceeding 20%. Mean macroalgal cover was low (6.04% ± 0.61) with most sites experiencing less than 8% macroalgal cover. Differences in benthic cover between sheltered and wave-exposed settings were mainly driven by contrasts in proportions of sponge, macroalgae and Orbicella faveolata corals. Linear mixed-effects modelling suggests stability in hard coral cover and decline in macroalgal cover across sites against the 2007 baseline. Significant spatio-temporal interactions were observed for soft coral and CTB (crustose coralline algae, turf algae and bare substrate). Overall, hard coral cover appears to have declined at some sites and macroalgal cover to have increased at other, but there is no evidence of widespread regime shift. While the hydro-geomorphic setting had a significant but weak effect (R > 0.3) on observed spatial and temporal patterns, our findings suggest that sheltered settings were less predisposed to macroalgal overgrowth compared to wave-exposed areas. In the era of climate change, targeted management should focus on strategies that mitigate macroalgal overgrowth, promote hard coral stability (or resilience) while preventing further loss.

Recruitment of the limpetPatella ulyssiponensisand its relationship with crustose coralline algae: patterns of juvenile distribution and larval settlement

AbstractRecruitment of the limpetPatella ulyssiponensiswas investigated in relation to the presence of living crustose coralline algae (CCA) in rocky-shore habitats. Juvenile limpets (≤10 mm maximum shell length) were counted in CCA-present and CCA-absent habitats, on three shores in SW Portugal during summer 2007 and winter 2009. Furthermore, the settling response of laboratory-reared larvae ofP. ulyssiponensisto CCA-covered substratum, and bare-rock, was examined. Across the intertidal zone, we found a clear association between the distribution and abundance of juveniles and the presence of CCA. Although the presence of CCA was not an absolute requisite for juvenile occurrence, null juvenile densities were mostly recorded in CCA-absent areas. The highest juvenile densities (maximum of 64 individuals in 15 × 15 cm) were consistently found in CCA-dominated habitats, namely steep wave-exposed areas at low-shore and rock-pools. The hypothesis of CCA-enhanced settlement was not supported, as settlement intensities of laboratory-reared larvae were similar between chips of rock encrusted by CCA and chips of bare-rock. From the overall number of settlers onto CCA-encrusted rock chips, 51% were found in tiny pits lacking CCA. This was the first study of the settlement patterns of larvae of the genusPatellausing naturally occurring rocky substrata. These results are preliminary and should be confirmed with choice-experiments and improved monitoring of the position of settlers. We suggest that CCA plays a role in the recruitment ofP. ulyssiponensis, potentially promoting survivorship of early benthic stages, but possibly not enhancing settlement.

Cryptic species in sympatry: nonrandom small-scale distribution patterns in Bostrychia intricata (Ceramiales, Rhodophyta)

:Sympatric coexistence of cryptic species, indistinguishable morphological taxa, has increasingly been detected on the basis of molecular data. This discovery raises the interesting question of how cryptic species can coexist, as hypothetically they would need identical ecological resources. The red alga Bostrychia intricata is commonly found along New Zealand shores. Previous studies indicated several cryptic species within this morphospecies, and that some populations have multiple species. This study aimed to determine how coexisting cryptic B. intricata distribute at a small scale. Along the shore of Moa Point, Wellington, we conducted intensive sampling of B. intricata in different habitats with respect to tidal position, wave and sun exposure levels. Our genetic data clearly documented the coexistence of three cryptic species of B. intricata: N2, N4 and N5. Multiple samples from individual algal patches indicated that each patch was made of the same ramet. Our analyses revealed a habitat-related pattern in small-scale distribution of different cryptic B. intricata, suggesting that the distribution of these cryptic species was not random. Cryptic species N4 was found at a higher tidal position than species N2 and N5, whereas cryptic species N2 occurred in more wave-exposed areas than the other species. Discriminant analysis indicated that tidal height strongly influenced the distribution pattern among these cryptic species. Our observations demonstrated that the co-occurrence of three cryptic B. intricata can partly be explained by their occupation of different intertidal habitats, highlighting the nonrandom distribution of coexisting cryptic algal species.

DISTRIBUSI LOGAM BERAT PADA AIR DAN SEDIMEN LAUT DI WILAYAH PESISISR KABUPATEN SUMBAWA BARAT

Most of coastal waters of West Sumbawa are wave-exposed areas. As part of Alas Strait this region is located between Lombok and Sumbawa Island. On the land and coastal areas, mineral mining (i.e. gold) activities are operated massively by large private company (i.e. PT. Newmont Nusa Tenggara) and traditional mining by local communities. These activities (especially for traditional mining) are expected to increase the content of heavy metals in the marine and coastal waters surrounding. A residual of mining processing will produce heavy metals disposal. In this study, the distributions of heavy metals (i.e. Hg, Cr6+, Cu, As, Ni, Zn, Pb, and Cd) were measured in the water column and bed sediments of coastal waters of West Sumbawa. This study was conducted during dry season in July 2011. The results show the heavy metal concentrations in water column were mainly within the permissible limits (based on Keputusan Menteri Lingkungan Hidup No. 51, 2004). Except for Cu, the concentration was highest found on most of the stations. The heavy metal contents in bed sediment were low, but varied among sampling points. Furthermore, Cu content in bed sediment also found remarkably high (101,7 mg/Kg) with additionally Zn content was closed (10,6–105,5 mg/Kg) within the permissible limits (based on criteria by Australian and New Zealand Environment and Conservation Council – ANZECC, 2000).

Trying to fit in: are patterns of orientation of a keystone grazer set by behavioural responses to ecosystem engineers or wave action?

The distribution of animals varies at different temporal and spatial scales. At the smallest scale, distribution may be orientated in regard to particular environmental variables or habitat features. For animals on the rocky intertidal, the processes which set and maintain patterns of distribution and abundance in wave-exposed areas are well studied, with explanatory models focused on wave action and, more recently, the role of biogenic habitats. In contrast, patterns of orientation by intertidal animals have received less attention, although having ecological and fitness consequences. Here, we report tests of competing models to explain the observation that limpets on steeply sloped surfaces orientate downwards. A greater proportion of downwards-facing limpets was found in sheltered sites and areas without barnacles and this pattern was consistent across many shores and sampling occasions. Additionally, the frequency at which limpets were dislodged after a storm was independent of orientation. To test whether orientation is a behavioural response to habitat-forming barnacles, barnacles were removed and/or killed from patches of substrata and the change in proportion of downwards-facing limpets measured. The proportion increased with barnacle removal and this behaviour was a response to the structure of the barnacles, not a biotic effect associated with the living organism. Our study suggests that biogenic habitat not wave action sets patterns of limpet orientation and barnacle shells, regardless of whether the barnacle is alive or not, limit the ability of limpets to adopt a downward orientation.

Biomechanical consequences of epiphytism in intertidal macroalgae.

Epiphytic algae grow on other algae rather than hard substrata, perhaps circumventing competition for space in marine ecosystems. Aquatic epiphytes are widely thought to negatively affect host fitness; it is also possible that epiphytes benefit from associating with hosts. This study explored the biomechanical costs and benefits of the epiphytic association between the intertidal brown algal epiphyte Soranthera ulvoidea and its red algal host Odonthalia floccosa. Drag on epiphytized and unepiphytized hosts was measured in a recirculating water flume. A typical epiphyte load increased drag on hosts by ~50%, increasing dislodgment risk of epiphytized hosts compared with hosts that did not have epiphytes. However, epiphytes were more likely to dislodge from hosts than hosts were to dislodge from the substratum, suggesting that drag added by epiphytes may not be mechanically harmful to hosts if epiphytes break first. Concomitantly, epiphytes experienced reduced flow when attached to hosts, perhaps allowing them to grow larger or live in more wave-exposed areas. Biomechanical interactions between algal epiphytes and hosts are complex and not necessarily negative, which may partially explain the evolution and persistence of epiphytic relationships.

The Influence of Wave Energy and Sediment Transport on Seagrass Distribution

A coupled hydrodynamic and sediment transport model (Delft3D) was used to simulate the water levels, waves, and currents associated with a seagrass (Zostera marina) landscape along a 4-km stretch of coast in Puget Sound, WA, USA. A hydroacoustic survey of seagrass percent cover and nearshore bathymetry was conducted, and sediment grain size was sampled at 53 locations. Wave energy is a primary factor controlling seagrass distribution at the site, accounting for 73% of the variability in seagrass minimum depth and 86% of the variability in percent cover along the shallow, sandy portions of the coast. A combination of numerical simulations and a conceptual model of the effect of sea-level rise on the cross-shore distribution of seagrass indicates that the area of seagrass habitat may initially increase and that wave dynamics are an important factor to consider in predicting the effect of sea-level rise on seagrass distributions in wave-exposed areas.

Macrofaunal recolonisation following the intertidal placement of fine-grained dredged material

Dredged material is increasingly being regarded as a potential resource, and one of its many uses is to create and/or improve intertidal habitats (i.e. beneficial use). However, uncertainties over the longer-term environmental consequences of such schemes have, to date, limited the practice to small-scale applications in UK waters. This paper studies the macrofaunal recolonisation of fine-grained dredged material recharged concurrently at four adjacent recharge areas along the south-east coast of the UK in order to facilitate predictions regarding the recolonisation of comparable schemes and, thereby, to promote effective environmental management. During the 2-year study period, the four recharge areas were distinctly different in terms of their environmental characteristics, primarily wave exposure and bed level. These conditions resulted in different macrofaunal recolonisation rates and community structures. While the low-level, wave-sheltered area experienced rapid recolonisation, the process was delayed until 12 months post-recharge at the relatively wave-exposed areas. Bed level differences resulted in distinctly different communities in wave-sheltered areas but not under wave-exposed conditions. While we are unable to separate the effects of individual environmental variables on recolonisation, these results provide general conclusions as to the importance of environmental conditions on resulting macrofaunal communities.

Egg release and settlement patterns of dioecious and hermaphroditic fucoid algae during the tidal cycle

The timing of gamete release by fucoid algae, although known to be restricted to calm days is not clearly understood within a circadian time scale. The need for externally fertilizing species to avoid gamete dilution suggests that in wave-exposed areas spawning may occur during particular tidal phases. However, this may differ between mating systems, as selfing species may be less affected by gamete dilution. In this study, two different approaches were used to determine when egg release occurs during the tidal cycle in two sister species with different mating systems. First, egg settlement of Fucus vesiculosus (dioecious) and Fucus spiralis (selfing hermaphrodite) was quantified on removable substrates (egg settlement disks) every day for 2 months and settlement patterns were used to statistically estimate the radius of a circle that would encompass 99% of each patch of settled eggs (the egg dispersal radius). Also, egg release was quantified every 2 h during the tidal cycle. A significantly larger egg dispersal radius (P < 0.02) was found for F. spiralis than F. vesiculosus, and this difference was somewhat site dependent with a greater difference between species in exposed sites. The egg dispersal radius was negatively correlated with significant wave height and positively correlated with sea surface temperature for both the species (P < 0.05), with a greater effect of both the factors for F. spiralis than for F. vesiculosus. Egg release during the tidal cycle was variable between species and experiments, with F. vesiculosus releasing more eggs, later in the day, and at a lower tide, than F. spiralis, which released fewer eggs, throughout the day and at all tides. The dioecious species, F. vesiculosus, may have developed a specific adaptation for timing the egg release to periods when emersed in exposed habitats to avoid rapid dilution of gametes that require outcrossing for fertilization. On the other hand, egg release for F. spiralis, which can self-fertilize, occurred both when emersed and immersed, suggesting this species has developed less synchrony with specific environmental factors. Site dependence also suggests local wave conditions can modulate timing of release. The data are consistent with the relaxation of the selective constraints of water motion on fertilization success in a selfing hermaphrodite, relative to an obligate outcrossing species. Results support the idea that species with different mating systems evolve different sensitivities to environmental cues for gamete release with specific implications for inbreeding and successful external fertilization in the ocean.

The expanding range of Undaria pinnatifida in southern New Zealand: distribution, dispersal mechanisms and the invasion of wave-exposed environments

Very few studies have addressed how the invasive kelp Undaria pinnatifida (Harvey) Suringar spreads beyond initial founding populations in harbours. Surveys of the harbours and accessible areas of open coast throughout southern New Zealand were conducted to determine how far U. pinnatifida populations had extended since initial incursions. Our findings clearly demonstrate that U. pinnatifida is capable of invading native communities and can establish reproductive populations in locations subjected to significant and consistent wave action. The extent of spread from source populations differs between harbours in which it has established. Dispersal is greatest in harbours with long established populations, those where populations have not been strategically managed, harbours with high water exchange with surrounding coastal waters, and where prevailing currents allow establishment of U. pinnatifida on suitable substrata close to harbour entrances. Dispersal along the open coast is primarily achieved by drifting adult sporophytes that are washed up in the rocky intertidal zone. Founding populations are most often found in the intertidal zone, primarily within rockpools. Subtidal transects and observations indicate that U. pinnatifida is well adapted to invade exposed coastlines and can establish within a broad range of niches in wave-exposed areas including rockpools, the low intertidal, shallow subtidal, Macrocystis pyrifera kelp forests, and in low light areas beyond the vertical extent of large native macroalgae. The current range of U. pinnatifida is much greater than expected and appears to be expanding. Due to its ability to grow in a broad range of environments and to form dense monospecific stands, U. pinnatifida has the potential to strongly modify almost all rocky subtidal and intertidal communities in temperate locations.

Overgrazing of Kelp Beds Along the Coast of Norway

The aim of this study was to better understand the down-grazing of kelp beds by sea urchins (Strongylocentrotus droebachiensis) along the coast of Norway. Barren grounds were first observed in sheltered areas along the coast of the counties of Trondelag, Nordland and Troms in 1974. In the 1980s, the barren grounds spread to areas more heavily exposed to waves. In the 1990s, the kelp beds were re-established in some localities in southern Trondelag, initially in wave-exposed areas. In the northernmost parts of Norway, i.e. the counties of Troms and Finnmark, the barren ground areas may still be increasing. Crabs (Cancer pagurus) and common eiders are the most common predators on urchins. Predation on sea urchins in kelp beds is probably not among the factors that limit the sea urchin populations. Along the coast of Nordland and further north, sea urchins are infected by nematodes, resulting in a low, but significant increase in their mortality. No re-growth of kelp beds has been found in the most infected areas. In the late 1960s and the early 1970s, a high occurrence of echinoderm larvae was observed in deeper waters. This was a period with cold water, which may have caused high recruitment of sea urchins. The bet-hedging life strategy of sea urchins may account for the sudden increase in the size of the populations. In the present paper I propose the hypothesis that higher individual growth rates and higher mortality rates in the south than in the north may explain the decrease in the populations, which may in turn account for the re-growth of kelp in the southern areas.

Life on the edge: do biomechanical and behavioral adaptations to wave-exposure correlate with habitat partitioning in predatory whelks?

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 282:193-204 (2004) - doi:10.3354/meps282193 Life on the edge: do biomechanical and behavioral adaptations to wave-exposure correlate with habitat partitioning in predatory whelks? Gil Rilov1,3,*, Yehuda Benayahu2, Avital Gasith1 1Institute for Nature Conservation Research, 2Department of Zoology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel 3Present address: Marine Ecology Research Group, School of Biological Sciences, University of Canterbury,Private Bag 4800, Christchurch, New Zealand *Email: gil.rilov@canterbury.ac.nz ABSTRACT: The rocky littoral is a highly stressed but species rich environment in which adaptive trade-offs underlie the specialization that permits habitat partitioning by closely-related species. Habitat partitioning by prey species is generally attributed to differential tolerances to physiological stresses and competition for resources. Partitioning by predators is, however, less understood and also mainly related to thermal tolerance. We test the hypothesis that differential biomechanical and behavioral adaptations to wave action can result in habitat partitioning of mobile predators using 2 Mediterranean whelks. Stramonita haemastoma is found mainly at wave-exposed habitats on lower midlittoral or shallow (1 to 3 m) subtidal rocks. By contrast, Hexaplex trunculus is found only subtidally in more quiescent littoral environments (shallow bays and lagoons or deeper in wave-exposed sites). Morphologically, S. haemastoma is squatter than H. trunculus and the ratio of its foot surface area to the maximum projected surface area of its shell is 35% higher, making S. haemastoma less prone to dislodgment by waves. Mechanically, at least a 2-fold higher force (12 N) is required to dislodge S. haemastoma from the substrate, probably due to its larger foot, because tenacity per foot area was similar between species. The feeding technique and foraging behavior of S. haemastoma is also adapted to life in high-energy environments. Higher feeding rates and much shorter prey handling time compared to H. trunculus allow this species shorter foraging bouts that reduce the risk of dislodgment and increase predation success in wave-exposed areas. H. trunculus thrives in low-flow habitats where food density is low compared to shallow subtidal rocks. This is compensated for by a broader diet than S. haemastoma, feeding on any available food item, including conspecifics, and by reducing adhesion when not feeding, thus saving energy. S. haemastoma is more adapted to survive desiccation conditions than H. trunculus, which may exclude the latter from intertidal habitats. Our findings suggest that habitat partitioning between the whelks is maintained mainly by a ‘distinct preferences’ mechanism that might be relevant for other benthic predatory species. KEY WORDS: Species distribution · Adaptation · Distinct preferences · Rocky shore · Wave action · Morphology Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 282. Online publication date: November 16, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

The effects of exposure to wave action on the distribution and morphology of the epiphytic hydrozoans &lt;i&gt;Clava multicornis&lt;/i&gt; and &lt;i&gt;Dynamena pumila&lt;/i&gt;

The spatial distribution patterns of two species of epiphytic hydrozoans, Clava multicornis and Dynamena pumila, on the intertidal alga Ascophyllum nodosum were studied in adjacent wave-sheltered and wave-exposed areas. Clava were more abundant on the wave-sheltered algae than on the wave-exposed fronds, and in both areas occupied the basal and middle sections of the algae. There was no difference in the abundance of Dynamena between the wave-sheltered and wave-exposed areas, but in both areas Dynamena were most abundant on the basal and apical sections of the algae than on the central sections. The number of hydranths per colony of Clava was higher in the sheltered area than in the exposed area. The hydrocauli of Dynamena on the wave-exposed algae bore fewer hydrothecae than those on the sheltered algae. The proportion of Dynamena hydrothecae that contained hydranths was close to 100% in the sheltered area, but only 70% in the exposed area. It was concluded that variations in distribution and morphology could be caused by the direct or indirect effects of one or more variables, including wave action, feeding rates, and exposure to solar radiation. Experiments are required to elucidate the specific effects of these variables.

Variations in holdfast attachment mechanics with developmental stage, substratum-type, season, and wave-exposure for the intertidal kelp species Hedophyllum sessile (C. Agardh) Setchell.

Biomechanical models that describe physical and biological interactions on wave-exposed shores typically assume that a species' attachment properties are similar between seasons and sites. We tested this assumption using Hedophyllum sessile to investigate how macroalgal biomechanical attachment properties vary with developmental stage, substratum-type, season, and wave-exposure. Hedophyllum sessile is an intertidal kelp species that is able to survive in wave-exposed areas in the Northeast Pacific. For both juveniles and adults, holdfast attachment force and strength were measured at a wave-exposed and wave-protected site in Barkley Sound, British Columbia, Canada. Substratum and wave-exposure effects on attachment properties were tested in juvenile populations. Adult populations were sampled prior to (in July 1996) and after (in November 1996) a series of storms. Site and seasonal wave-exposure effects on attachment properties were tested in these adult populations. Comparisons to known attachment properties of other temperate macroalgal species were also made. Causes for these patterns are discussed but were not isolated in these studies. Juveniles' attachment properties differed on different substrata types and between wave-exposures, with the highest attachment forces and the most attached juveniles in articulated coralline algal turfs. Adult attachment is firm ( approximately 100 N), but relatively weak ( approximately 0.07 MNm(-2)). Adult attachment did not vary with site wave-exposure, but there was a shift within each site to more resistant holdfasts after a series of early winter storms. Seasonal increases in storm swells correlated to more thallus tattering and selected against large, loose holdfasts. The data presented here suggest that results from holdfast attachment field studies in one season cannot be extrapolated to another due to a complex set of dynamics. This is the first documentation of seasonal patterns in macroalgal attachment properties.

Spatial variability in prey preferences of the intertidal whelks Nucella canaliculata and Nucella emarginata

Feeding preferences of predatory intertidal whelks from three sites with marked differences in the availability of sessile prey were studied on the Oregon coast. Mussels ( Mytilus trossulus) and barnacles ( Balanus glandula) were simultaneously offered in replicated experimental arenas to individual Nucella emarginata in relatively wave-protected and N. canaliculata in wave-exposed areas at two sites, Strawberry Hill (SH) and Boiler Bay (BB). Each experimental arena in the two sites received either no whelks (controls for change in prey unrelated to whelks) or whelks collected from areas with (a) no mussels (Eagle Point, EP, San Juan Island, WA), (b) consistently low mussel cover (BB), and (c) seasonally high cover of small mussels (SH). Whelks from the site with no mussel cover (EP) largely ignored mussels and overwhelmingly preferred barnacles. Whelks from SH and BB did not significantly differ from one another in prey selectivity nor did they differ from the controls, suggesting no clear preferences for either prey. These results suggest that natural differences in relative abundance of prey among sites can affect whelk preferences for sessile prey and possibly influence their per capita effect on communities.

Geographic and environmental factors affecting the distribution of kelp beds and barren grounds and changes in biota associated with kelp reduction at sites along the Norwegian coast

Sites at 244 locations along the west and north Norwegian coasts were investigated to evaluate whether kelp (Laminaria hyperborea) beds had been overgrazed by the sea urchins Strongylocentrotus droebachiensis and Echinus esculentus in the years 1981-1992. Barren ground communities were found in sheltered and moderately wave-exposed areas mainly in the inner and middle archipelago from Nordmøre (63°N) northwards. Densities of large-sized (adult and intermediate) L. hyperborea were 20.7 individuals ·m-2 in kelp beds and 9.7 individuals ·m-2 in transition areas. Juvenile Laminaria spp. were present at densities of 23.9 individuals ·m-2 in kelp beds, 3.6 individuals ·m-2 in transition areas, 0.0 individuals ·m-2 in barren grounds, and 59.1 individuals ·m-2 in kelp-harvested locations. Both the densities and the mean size of S. droebachiensis in barren grounds decreased northwards. The mean densities were 52.2 and 26.1 individuals ·m-2 for the areas south and north of the Arctic Circle, respectively. Multivariate analysis (CANOCO) showed that seven ``environmental'' factors (i.e., kelp depth gradient, distance (latitude), time of sampling, nematode infection in S. droebachiensis, wave exposure, coastal gradient, and substratum) contributed significantly to variability in the distribution of kelp beds and barren grounds. Species in hard-bottom communities in shallow waters could be divided into three distinct BIOTA.

Use of Habitat, Size of Prey, and Food-Niche Relationships of Two Sympatric Otters in Southernmost Chile

In Magallanes (southernmost Chile), the marine otter Lutra felina tends to use more open and wave-exposed coastal areas, whereas L. provocax is found in more protected habitats. To investigate the hypothesis that the two species segregate habitats to avoid competition for food, we surveyed the available literature on food habits and analyzed food-niche relationships of both species of otters in Magallanes. Overlap of diet between species of otters was relatively high, and L. provocax tended to have a narrower diet than L. felina . Both species consumed prey of similar size. These findings are consistent with the use of different habitats to avoid competition for food resources. However, alternate models, including habitat segregation resulting from differential abilities of the two species at catching prey in more wave-exposed habitats, deserve some attention. Our analysis also revealed that niche breadth and size of prey taken by L. felina at three sites along the Chilean coast were relatively similar. At Chiloe, however, L. felina exhibited the narrowest diet and consumed the largest prey. Although such a difference might be related to variation in abundance of prey among localities, it may also have resulted from the relatively small sample available for Chiloe.

Influence of phytoplankton concentration and wave exposure on the ecophysiology of Mytilus californianus

The relationship between nearshore food availability and physiological state of the suspension-feeding mussel Mytilus californianus was examined along a wave-exposure gradient at 2 rocky intert~dal sites on the Oregon coast, USA. differing in nearshore concentrations of phytoplankton. The RNA:DNA ratio (an indirect measure of protein synthetic capacity) of adductor muscle was used as an indicator of dietary status and growth. The activities of 2 metabolic enzymes, citrate synthase (CS) and malate dehydrogenase (MDH), were measured for gill (CS) and adductor (MDH) as indicators of metabolic activity. Mussels were sampled at wave-exposed and wave-protected areas at Strawberry Hill (SH), a site with relatively high phytoplankton concentrations, and Boiler Bay (BB), a site with relatively low phytoplankton concentrations. Individuals at wave-exposed areas at both SH and BB had higher RNA:DNA ratios in spring and summer than those at wave-protected areas. RNA:DNA ratios in spring and summer were higher at SH than at BB, and these differences were especially pronounced following coastal upwelling events Increases in RNA:DNA ratio dunng phytoplankton blooms after upwelling suggest that mussels respond rapldly to short-term changes in nearshore oceanographic conditions. Both CS and MDH activities were higher at SH than at BB many times throughout the year. suggesting metabolic activity was higher overall for SH mussels. Reciprocal transplant experiments were performed to evaluate the degree of physiological plasticity in relation to siteand exposurerelated factors (e.g. phytoplankton concentration, heat and/or desiccation stress, wave forces). Between-site transplants were done between wave-exposed areas at SH and BB; within-site transplants were done between areas of different wave-exposure at each of the 2 sites. RNA:DNA ratios of transplanted mussels converged on those of the site or area to which they were transplanted, suggesting that mussel physiology is h~ghly plastic in response to site and area-related variations in environmental factors. The strong apparent response of mussels to variations in phytoplankton concentration suggests that physiological indices may be useful tools in assessing the magnitude of 'bottom-up' effects in rocky intertidal communities.

Predation, physical disturbance, and sublethal arm damage in ophiuroids: a Jurassic-Recent comparison

proportion of ophiuroids with sublethal arm damage (regenerating arms) was censused over 4 yr (1987 to 1990) in a lagoonal population of Ophioderma brevispinum (Say) (Ophiodermatidae) at Belize, and over 3 yr (1988 to 1990) in back-reef populations of 0. appressum (Say) at Belize and Jamaica. The Jamaican population was sampled in sheltered and wave-exposed areas. Over the study period, the frequency of injuries within populations did not differ significantly, nor did the 2 0 . appressum populations show consistent differences. Arm injuries were more common in the 3 living populations (30 to 74 O/O injured) than in a Lower Jurassic population composed of 2 ophiodermatid species (0 O/O injured) from a similar warm-water habitat. The incidence of sublethal disk damage was negligible in all cases. Hurricane-generated rubble movement did not cause any detectable damage to either the protected or exposed Jamaican 0. appressum subpopulations. Predation is the primary source of arm injuries in living Ophjoderma spp. This study supports the hypothesis that predation on ophiuroids increased when durophagous teleostean fishes and decapod crustaceans diversified in the late Mesozoic.