Transitional ecological requirements for early juveniles of two sympatric stichaeid fishes,Cebidichthys violaceus andXiphister mucosus

Synopsis The distribution patterns, diets, and substratum (refuge) requirements of early juveniles of two sympatric stichaeid fishesCebidichthys violaceus andXiphister mucosus, were investigated in a rocky intertidal habitat at Diablo Canyon, California. Monthly investigations were conducted at low tide for four consecutive months, to assess ontogenetic differences in distribution, diet, and refuge requirements within and between the two species. Distinct differences in vertical zonation were exhibited by both stichaeids throughout the study. Interspecific zonation patterns were similar to those recorded for adults of both species. Diet analyses showed that early juveniles of both stichaeids were zooplanktivorous, differing markedly from the primarily herbivorous diets of adults. Changes in diet were largely due to the selection of larger prey taxa as both fishes, and their mouth size, grew over the study period. Predation by both fishes on water-column planktors (calanoid copepods, zoea and polychaete larvae) was greatest following initial intertidal settlement and habitat establishment by early juvenile fishes. Greater dependence on substrate-oriented and/or benthic prey (harpacticoid copepods, gammarid amphipods and mysid shrimp) was exhibited by both fishes as they grew in size. Affinities for sand, gravel, and pebbles during monthly field surveys were similar for both species throughout the study. As the fishes grew, their substratum preferences changed in relation to the substrata which provided the best refuge. Results from laboratory experiments indicated that young stichaeids select very specific substrata based on fish age (size) and substratum suitability (i.e. adequate refuge). Similarities in diet and substratum preferences, and changes in those preferences over time, appear to be the result of morphological similarities (body size and shape and mouth gape) for both species at a given age.     

Experimental analyses of patch selection by foraging black surfperch (Embiotoca jacksoni Agazzi)

The dynamics of microhabitat use by foraging adult and juvenile black surfperch (Embiotocajacksoni Agazzi) were explored. Detailed observations of black surfperch feeding at Santa Catalina Island, California, revealed that adults and young-of-year juveniles co-occurred in the same habitat but used different algal substrata as foraging sites. Juveniles selected invertebrate prey almost exclusively from the surface of foliose algae. The occurrence of young E. jacksoni was highly correlated with that of foliose algae. Adults tended to bite most frequently from turf, a low-growing matrix of plants, colonial animals, and debris covering the rocky substratum. The abundance of adults was negatively correlated with the occurrence of foliose algae. Adults and juveniles showed marked, but different, preferences in their utilization of taxa of algae as foraging substrata. Certain algae (e.g., Zonaria farlowii Setchell & Gardner) were preferred while other taxa (e.g., Sargassum palmeri Grun) were avoided by both age groups. However, most types of algae were preferred by one group but not the other. To test the hypothesis that knowledge of algal substratum composition allows prediction of fish occurrence and foraging behavior in a patch, algal cover on 2 × 2 m² areas of bottom was manipulated creating plots dominated by turf, Zonaria farlowii, or Sargassum palmeri. Fish occurrence could be accurately predicted on the basis of abundance of foliose algae, but foraging activity of fish was highly dependent on the algal taxon that dominated the patch. Differential prey availabilities among foraging substrata provided some insight into the patterns of foraging patch preferences displayed by adult and juvenile Embiotoca jacksoni.     

Thermal tolerance,evaporative water loss,air-water oxygen consumption and zonation of intertidal prosobranchs: a new synthesis

Duration of emergence increases with tidal height on rocky shores therefore, emergence adaptations in intertidal species such as littorine and other prosobranch gastropods have been considered correlated with zonation patterns; temperature tolerance, desiccation resistance and aerial respiration rate all commonly assumed to increase progressively with increasing zonation level. Such direct correlations are rarely observed in nature. Maximal aerial gas exchange occurs in mid-shore, not high shore species. Temperature tolerance and desiccation resistance do not increase directly with shore height. Thus, hypotheses regarding physiological correlates of zonation require revaluation. A new hypothesis is presented that the high tide mark presents a single major physiological barrier on rocky shores. Above it, snails experience prolonged emergence and extensive desiccation; below it, predictable submergence and rehydration with each tidal cycle. Thus, desiccation stress is minimal below the high tide mark and maximal above it. Therefore, species restricted below high tide (the eulittoral zone) should display markedly different adaptive strategies to emergence than those above it (the eulittoral fringe). A review of the literature indicated that adaptations in eulittoral species are dominated by those allowing maintenance of activity and foraging in air including: evaporative cooling; low thermal tolerance; elevated aerial O₂ uptake rates; and high capacity for radiant heat absorption. Such adaptations exacerbate evaporative water loss. In contrast, species restricted to the eulittoral fringe display adaptive strategies that minimize desiccation and prolong survival of emergence including: foot withdrawal, preventing heat conduction from the substratum; aestivation in air; elevated thermal tolerance reducing necessity for evaporative cooling; position maintenance by cementation to the substratum and increased capacity for heat dissipation. In order to test of this hypothesis the upper thermal limits, tissue and substratum temperatures on emergence in direct sunlight and evaporative water loss and tissue temperatures on emergence in 40 °C were evaluated for specimens of six species of eulittoral and eulittoral fringe gastropods from a granite shore on Princess Royal Harbour near Albany, Western Australia. The results were consistant with adaptation to the proposed desiccation barrier at high tide. The eulittoral species, Austrocochlea constricta, Austrocochlea concamerata, Nerita atramentosa and Lepsiella vinosa, displayed adaptations dominated by maintenance of activity and foraging during emergence while the eulittoral fringe littorine species, Bembicium vittatum and Nodilittorina unifasciata displayed adaptations dominated by minization of activity and evaporative water loss during emergence. The evolution of adaptations allowing tolerance of prolonged desiccation have allowed littorine species to dominate high intertidal rocky shore gastropod faunas throughout the world's oceans.     

Tidal activity rhythms and depth distribution of rocky shore fish in an altered intertidal environment

In this note we report on changes of activity level of littoral fish and their use of different microhabitats in an altered intertidal environment, where intertidal fish are never emersed and turbulence is confined to high tides. Despite these atypical conditions, the structure of the assemblage is basically the same found in a typical rocky-shore situation. Two intertidal fish known to possess internal tidal rhythms, Lipophrys pholis and Coryphoblennius galerita, retain those rhythms in these altered conditions, and the associated social changes in L. pholis are also retained. These observations support the studies of Gibson (1971), who showed that changes in hydrostatic pressure were of prime importance in keeping the tidal rhythm entrained. The subtidal Parablennius pilicornis, on the contrary, is more active during low tide than at high tide. The hypothesis that some subtidal species are excluded from the intertidal by a turbulence-avoiding mechanism is discussed.     

210Pb dating by low background gamma counting

An intertidal fish community in Trinidad Bay, Humboldt County, California, was studied between November 1968 and May 1970. The nursery function of rocky tidal pools for juveniles of subtidal fishes was indicated by peaks in indices of seasonally abundant fish species in summer. The proportion of juveniles of seasonal species in the intertidal fish community rose significantly in collections of late spring and summer, to a maximum of 35% of the individuals collected in July. Annual dominance was relatively high due to abundant populations of the tidepool sculpin, Oligocottus maculosus, but two other fish species were also encountered in tidepools every month of the year.     

Analysis of patterns of dispersion of intertidal prosobranch gastropods in relation to macroalgae and rock-pools

Summary The patterns of dispersion of Nerita atramentosa, Austrocochlea constricta, Bembicium nanum and Cellana tramoserica are analysed from quadrat samples taken between June 1972 and June 1973. In each quadrat, the proportion of animals in each of two substrata, the encrusting alga Peyssonelia gunniana and small pools, was recorded, with the proportional area of cover of each substratum, height on the shore, density of the species and the time of sampling. Multiple regression and covariance analysis showed that, in all cases, there was a linear relationship between proportion in a substratum and proportional area of substratum. No other variables were significant.Juvenile Nerita and Austrocochlea showed preferences for both substrata. Adult Nerita and all Bembicium were dispersed at random with respect to both substrata. Adult Austrocochlea were randomly dispersed with respect to Peyssonelia, but showed a preference for water. Cellana showed a preference for water and against Peyssonelia. These microhabitat preferences are discussed in relation to previously described effects of substrata on the densities of these four species.     

Substratum preferences of settling larvae of marine fishes reared in the laboratory

Various species of marine fish larvae were reared in the laboratory to allow observation of the substratum preferences of newly settling fish. The range of preferences for settling larvae of intertidal species corresponded to the adult niche breadth. The preferred substratum was always an element of the adult habitat, although not necessarily the same substratum preferred by the adults. Experiments with artificial substrata indicated that settlement preferences are based on tactile cues and light transmission. Depending upon the species, other factors such as current speed or salinity can also influence settlement.     

Effect of the substratum in the recruitment and survival of the introduced barnacle Balanus glandula (Darwin 1854) in Patagonia, Argentina

The barnacle Balanus glandula was introduced in Argentina in the 1970s, and today it dominates the high intertidal level in most Argentinean rocky shores. The aim of this work was to evaluate the effect of the type of substrata and intertidal height on a population of Balanus glandula by conducting field surveys and one-year field experiments in which we combined different substrata (hardness: hard and soft, and texture: smooth and rough) at two intertidal heights (mid and high). In natural populations, the highest density of adults and recruits occurred on soft-rough substratum and in the high intertidal. The different textures were important only on the soft substrata and high intertidal, and the density of barnacles of the soft-rough substrata was higher than soft and smooth ones. The most suitable experimental substratum was the soft-rough of the high intertidal, which had the highest recruitment, survival and final density of barnacles at the end of the experiment. In contrast, the hard and smooth of the high and middle intertidal were the least suitable in all cases. Although the recruitment of B. glandula occurred throughout the year, it was higher in the high intertidal, and it showed a recruitment peak in the winter and a second in the summer. While most studies on this barnacle investigated the effects of granite or other volcanic hard substrata, our study also focused on soft substrata. The effects of soft substrata are particularly important because soft sedimentary rocks characterise the southern Atlantic coast of South America and the presence of soft rocks appears to optimize the success of Balanus glandula.     

The effects of grazing by gastropods and physical factors on the upper limits of distribution of intertidal macroalgae

Summary The cover of foliose algae is sparse to non-existent above a low-level algal zone on many shores in N.S.W., except in rock-pools. Above this algal zone, encrusting algae, mostly Hildenbrandia prototypus, occupy most of the primary substratum on sheltered shores. Experimental manipulations at midtidal levels were used to test hypotheses about the effects of grazing by molluses and of physical factors during low tide on this pattern of algal community structure.Fences and cages were used to exclude grazers: molluscs grazed under roofs and in open areas. Cages and roofs provided shade, and decreased the harshness of the environment during low tide: fences and open areas had the normal environmental regime.In the absence of grazers, rapid colonization of Ulva and slower colonization by other foliose algae occurred in all experimental areas. The rate of colonization by Ulva sporelings was initially retarded on existing encrusting algae, but after a few months, cover of Ulva equalled that on cleared rock.Most species of algae only grew to maturity inside cages, and remained as a turf of sporelings inside fences. No foliose algae grew to a visible size in open, grazed areas. Grazing thus prevents the establishment of foliose algae above their normal upper limit on the shore, but the effects of physical factors during low tide prevent the growth of algae which become established when grazers are removed. Physical factors thus limit the abundance of foliose algae at mid-tidal levels.The recolonization of cleared areas by Hildenbrandia was not affected by the presence of a turf of sporelings, nor by the shade cast by roofs, but was retarded in cages where mature algae formed a canopy. Even under such a canopy, Hildenbrandia eventually covered as much primary substratum as in open, grazed areas. This encrusting alga is able to escape from the effects of grazing by having a tough thallus, and by its vegetative growth which allows individual plants to cover a lot of substratum, and by the tendency for new individuals to start growing from small cracks and pits in the rock, which are apparently inaccessible to the grazers.Mature foliose algae are removed from the substratum by waves, and many individual plants died during periods of hot weather. Sporelings in a turf were eliminated, after experimental fences were removed, by the combined effects of macroalgal grazers, which invaded the areas, and microalgal grarers which ate the turt from the edges inwards.The results obtained here are discussed with respect to other studies on limits to distribution of intertidal macroalgae, and the role of grazing in the diversity and structure of intertidal algal communities. Some problems of these experimental treatments are also discussed.     

Substratum preferences and planulae settling of two red sea alcyonaceans: Xenia macrospiculata Gohar and Parerythropodium fulvum fulvum (Forskl)

The settling behaviour and substratum preferences of the planulae of the Red Sea soft corals Xenia macrospiculata Gohar and Parerythropodium fulvum fulvum (Forskl) were examined in the laboratory. The planulae of the two species have a short pelagic phase and they tend to settle immediately upon leaving the parent colonies. Mucous secretion is used by the larvae for crawling and adhering to the substratum. They exhibit an aggregated pattern of settlement. The developing polyps are found in depressions or pits of the substratum. The planulae preferentially settle on rough substrata and avoid smooth surfaces. They search for substrata covered with an organic coating, composed of turf or crustose coralline algae. Such substrata create better conditions for larval settlement and metamorphosis. The planulae of P. f. fulvum exhibit a striking preference for upside-down attachment on undersides of the substrata, while Xenia macrospiculata utilizes both substratum faces for settlement. Light intensity seems insignificant in determining attachment sites. The findings of the experiments correspond well with the distributional patterns of juveniles of the two species as found in the natural environment. The specific requirements for settling of both species increase their chances of successful development and thus enhance their survival.     

Differences in the activity rhythms of juvenile gobiid fish,Chasmichthys gulosus,from different tidal localities

Activity patterns of intertidal gobiid fish,Chasmichthys gulosus, collected from different tidal localities, were recorded in a constant environment. Gobies collected from a rocky shore with a large tidal range and a regular tidal regime displayed a ca. 12 hour rhythm in their activity pattern. Gobies from a rocky shore with a small tidal range and an irregular tidal regime, however, did not clearly display any such rhythm. The ecological implications of such activity rhythms are discussed from the viewpoints of feeding and avoidance of predators.     

Colonization and substratum preference of an introduced burrowing crustacean in a temperate estuary

Habitat use in marine invertebrates is often influenced by multiple abiotic and biotic factors. Substratum composition is one factor known to have a dramatic effect on habitat selection. The Australasian burrowing isopod (Sphaeroma quoianum, H. Milne Edwards 1840) is a common introduced species in many estuaries on the Pacific coast of North America. S. quoianum burrows into a variety of firm substrata including marsh banks (composed of peat, clay, and/or mud), wood, friable rock, and Styrofoam floats. In some areas, isopods achieve high densities and may accelerate the rate of shoreline erosion and damage marine structures; thus, understanding the substratum preference of this species may be important for conservation and management efforts. Field experiments were conducted in Coos Bay, Oregon to examine substratum preference, burrowing rates, and the life stage of colonizers. In three experimental trials (Fall 2005, Spring 2006, Fall 2006), replicates of four intertidal substrata (marsh banks, decayed wood, sandstone, Styrofoam) were deployed near intertidal populations of S. quoianum. The numbers of burrows created in each substratum were enumerated weekly or daily (depending on trial). After the trials were completed, the total numbers of isopods inhabiting each substratum were counted. In weeks, S. quoianum extensively burrowed the substrata but exhibited a distinct preference for decayed wood. Significantly more isopods were present in wood than the other substrata at the end of the experiments and rates of burrowing were greatest in wood, although significance varied across time in one trial. Nearly 90% of colonizing isopods were under 5 mm in length suggesting that juvenile isopods primarily colonize intertidal substrata. Differences between burrow densities measured in the field and the results from these preference trials may indicate other factors, such as relative availability of substrata, recruitment and dispersal limitations, and possible gregarious behavior also influence local isopod densities.     

HABITAT DIFFERENCES IN THE TIMING OF REPRODUCTION OF THE INVASIVE ALGA SARGASSUM MUTICUM (PHAEOPHYTA,SARGASSACEAE) OVER TIDAL AND LUNAR CYCLES1

Sargassum muticum (Yendo) Fensholt is an invasive species that is firmly established on intertidal and subtidal rocky shores of Europe and the Pacific coast of North America. Local success and spread of S. muticum is thought to rely on its reproductive potential that seems dependent on exogenous factors like tidal and lunar cycles. This study is the first to compare the reproductive patterns (periodicity of egg expulsion and embryo settlement) of this invader in two different habitats: the middle and low intertidal. The combination of monthly, daily, and tidal samples at triplicate sites within each habitat showed a semilunar periodicity of egg expulsion and embryo settlement coincident with increasing tidal amplitude just before full and new moons. In both habitats, duration of each egg expulsion event was ～1 week, and embryo settlement occurred during the first daily low tide and with the incoming high tide during spring tides. However, both expulsion and settlement started 1–2 d earlier, expulsion saturation was faster, and settlement was higher in the mid‐ compared to the low intertidal. Our results suggest that the exact timing of gamete expulsion and embryo release of S. muticum responds to local factors, including tidal cues, which result in differences between mid‐ and low‐intertidal habitats.     

New ecological information onScytalina cerdale (Pisces: Scytalinidae) from a central California rocky intertidal zone

Synopsis New information regarding the ecology ofScytalina cerdale was obtained over a four year period as a consequence of a long-term marine ecological study at the Diablo Canyon Power Plant (DCPP), San Luis Obispo County, California. Twenty intertidal fish surveys were conducted at approximately quarterly intervals, between March 1979 and June 1983, at three separate rocky shore locations (stations). During each survey, a total of 108 square meters (36 m² per station) was searched for fish during periods of low tide. A total of 280S. cerdale were collected, identified, measured, and released back into the same 4 m² area, from the same intertidal station (Diablo Cove), throughout the study period. This limited intertidal occurrence most likely reflectsS. cerdale microhabitat requirements; a combination of intertidal elevation (mean = +0.3 MLLW), substratum specificity (loose gravel, 5–10mm size range, overlying a base of sand and shell fragments), and degree of wave exposure (semi-protected). Throughout the study,S. cerdale was seasonally more abundant during summer months (June through August) and less abundant during winter months (November through February). The only exception to this abundance trend followed the 1982 winter storms, which coincided with an El Niño event, whenS. cerdale abundance uncharacteristically dropped during the subsequent 1983 spring and summer surveys. Mean total lengths did not vary greatly, reflecting the absence of early juvenile fishes, and relatively high mean fish densities (3.5 fish per m² for 20 surveys) were recorded. Qualitative comparisons betweenS. cerdale abundance and seasonal changes in water temperature indicated an inverse relationship. Gravid females, demersal egg masses, and early juvenile individuals were never observed during the four years of the study. This suggests that unlike most other intertidal fishes, particularly other blennioids,S. cerdale may not utilize the intertidal zone for reproductive and recruitment purposes; Diablo Canyon is the most southerly reported distribution for this intertidal species, and therefore, may not entirely represent the species' biology as a whole.     

Juvenile Chinese mitten crabs (<Emphasis Type="Italic">Eriocheir sinensis</Emphasis>) in the Thames estuary: distribution,movement and possible interactions with the native crab <Emphasis Type="Italic">Carcinus maenas</Emphasis>

The Chinese mitten crab, Eriocheir sinensis is a successful invader. Whilst non-breeding adult E. sinensis have been associated with the destruction of riverbanks, little is known about the ecology of this species in its invaded areas. This is especially true of the juveniles which are a key migratory stage. Intertidal surveys along the Thames estuary indicated an increase in the population since the 1990s. Juvenile E. sinensis were abundant in the sampled upper tidal region of the Thames, refuging under boulders in the intertidal at low tide. Seasonal differences in sampled populations were observed, with a significantly lower abundance of crabs found during winter compared to summer. Mark-recaptures indicated movement in the intertidal occurring during high tide, with an influx of new crabs evident after a single tidal cycle. Endogenous rhythms were also apparent, with peaks in activity occurring corresponding with night-time high tide conditions. E. sinensis juveniles can successfully exclude similar sized native Carcinus maenas from shelters in the laboratory, regardless of which species originally inhabited the shelter. This may have implications for native estuarine Carcinus populations, which can rely on such intertidal shelters for refuges.     

Tidal activity pattern and feeding behaviour of the ophiuroid Ophiocoma scolopendrina on a Kenyan reef flat

Ophiocoma scolopendrina exhibits a distinctive pattern of feeding activity on intertidal reef platforms off Kenya. With the first wave of the flooding tide, dense aggregations of these ophiuroids (up to 320 m⁻²) engage in a 1–2 min burst of surface-film feeding, vigorously sweeping the air-water interface and associated sea foam with the ventral surface of 2–4 arms. Suspension feeding (with arms extended in the water column) is the primary feeding mode throughout the rest of the tidal cycle (involving 25–65% of the population at a time), while bottom feeding (with arms extended along the substratum) is infrequent (<10%). Field experiments showed that surface-film feeding is regulated by water depth and can be triggered by suspended particles. This feeding mode appears to be an adaptation to the intertidal habitat, enabling the ophiuroids to exploit a nutrient-rich surface film during a temporal refuge (low tide) from fish predation. Dense populations of O. scolopendrina may represent an important trophic link between producers of particulate organic material and higher-level consumers in coral reef environments.Tara Oak and Robert E. Scheibling contributed equally to this paper. The order of authorship is alphabetical     

Feeding and territorial behaviour in juveniles of three co-existing triggerfishes

Of three coexisting triggerfishes, in the intertidal and immediate subtidal zones of a coral reef within the Kenting National Park, southern Taiwan, Balistoides viridescens was observed only in the subtidal zone and foraged preferentially by nipping directly at small invertebrates among algal covered substrata. They fed also, although at a lower frequency, by using a water-jet technique to uncover prey on sandy substrata. Territory size ranged from 61·05 to 161·57 m² but was not related to rates of feeding or defence. Feeding frequency was, however, positively related to the area of algae present in the territory, and inversely related to the frequency of defence. In contrast to B. viridescens, Rhinecanthus verrucosus and R. aculeatus foraged mainly in the intertidal zone when the tide was high. They fed preferentially off rocky substrata and used only nipping (not water-jetting) to secure prey.     

Barnacle larval supply to sheltered rocky shores: a limiting factor?

In northwest Europe, sheltered rocky shores are dominated by fucoid canopy algae and barnacles are rare, although the latter are extremely abundant on exposed shores. The supply of the intertidal barnacle Semibalanus balanoides (L.) to sheltered, fucoid dominated rocky shores was investigated to determine the importance of larval supply in limiting the abundance of adults in shelter. Larval supply was measured at two spatial scales, at the scale of shore (100s of metres), by comparing larval concentrations at exposed and sheltered sites, and at a smaller spatial scale (m), by examining the role of fucoid canopies in limiting supply to the substratum. Replicate plankton trawls were carried out above the intertidal zone at high water at two sheltered sites and nearby exposed headlands. The concentration of S. balanoides cyprid larvae was significantly higher at the sheltered sites on two out of three sampling occasions with up to 14 times greater larvae on one occasion than the nearby exposed site. The effect of the macroalgal canopy on supply to the substratum was assessed in two ways: directly, by pumping water from the substratum in areas with and without Ascophyllum nodosum (L.) Le Jolis, and indirectly by measuring cyprid settlement in a canopy-manipulation experiment. Pumped plankton samples from mid tide level showed that the A. nodosum canopy did not form a barrier to larval supply and may have had a positive effect on larval concentrations at the substratum. Cyprid settlement was assessed in the mid shore A. nodosum and low shore Fucus serratus L. zones to areas with canopy algae (but protected from the sweeping effects of macroalgal fronds) and without canopy. Settlement over three consecutive 24-h periods showed a consistent pattern; settlement was consistently lower beneath the F. serratus canopy than in cleared areas, suggesting that this algal species forms a barrier, limiting supply of cyprid larvae to the substratum.