Activity and feeding of Dotilla fenestrata (Brachyura: Ocypodidae) in a warm,temperate South African estuary

The activity of and consumption of organic material by the sand-bubbler crab Dotilla fenestrata was studied over neap and spring tides on a sheltered sand bank close to the mouth of the warm, temperate Kowie Estuary, South Africa. Crabs emerged from their burrows only after the tide receded, and it was light. Time to emergence therefore varied from about 30 minutes to three hours after exposure, depending on the time of low water in the early morning vs at midday. General activity of the crab population was longer on a spring tide (about five hours) than on a neap tide (about three hours). Maximum densities of active crabs were 140 m^–2 and 41 m^–2 on spring and neap tides, respectively. After emergence, crabs spent 60% to 80% of their time feeding. In the Kowie Estuary, D. fenestrata produced between 7 and 12 pseudofaecal pellets, average weight 0.0358 g per pellet, per minute. These pellets had a significantly lower organic and chlorophyll a content than the substratum, and it was estimated that crabs removed about 25% of the organic content from the sediment.     

DISTRIBUTION AND POPULATION DYNAMICS OF THREE POPULATIONS OF SIPHONARIA ON ROCKY INTERTIDAL SHORES IN HONG KONG

The pulmonate limpets Siphonaria japonica and Siphonana siriusoccur over a wide range of local habitat types in terms of exposureto wave action and salinity. This is a study of these two specieson three different shore types in Hong Kong, ranging from anextremely exposed, high salinity (32–35) shore at Caped'Aguilar to a sheltered, low salinity (16–33) shore atTai Lam Chung. Both species are restricted to the low shore,year round. S. japonica is a winter breeder and recruitmentoccurred between October and January. The recruitment of S.sirius could not be recognised from the size-frequency histograms.The algal standing crop at Tai Lam Chung was higher than atWu Kwai Sha during the winter period, i.e., between Octoberand April. Seasonal fluctuations in growth rate were recordedfor both Siphonaria species with the time of fastest growthoccurring in winter. S. japonica grew faster at Tai Lam Chungthan at Wu Kwai Sha. Food availability is thought to be an importantfactor affecting growth. (Received 17 September 1993; accepted 16 June 1994)     

FORAGING ACTIVITY OF HELCION PRUINOSUS (PATELLOGASTROPODA) ON A SOUTH AFRICAN BOULDER SHORE

Foraging activity of the mid-shore limpet Helcion pruinosuswas monitored on an exposed boulder beach in the Eastern Capeof South Africa. Numbers of limpets active in 10 fixed quadratswere monitored and compared in different seasons and during springand neap tides. Foraging excursions were mainly associated with nocturnallow tides, limpets only emerging from beneath rocks when theywere completely uncovered by the receding tide, and they hadall retreated to beneath rocks before being splashed by theadvancing tide. The number of animals active was greater onfull moon spring tides. Significantly more limpets were activeon an autumn spring tide than on similar tides in other seasons. ^* To whom correspondence should be addressed. (Received 27 March 2000; accepted 5 July 2000)     

Interspecific variation in spawning time and male mating tactics of the parrotfishes on a fringing coral reef at Iriomote Island,Okinawa

Spawning time and male mating tactics of parrotfishes (family Scaridae) were investigated on a fringing coral reef at Iriomote Island, Okinawa. Spawning was observed in 14 species, and more frequently in more abundant species such as Chlorurus sordidus, Scarus rivulatus and Chlorurus bowersi. At the reef-edge spawning site, C. bowersi spawned at high tide, C. sordidus spawned both at high tide and in the early morning, whereas Calotomus carolinus and most of the Scarus species such as S. rivulatus spawned only in the early morning, mostly 0630–0830 h. Spawning only in the early morning irrespective of tide phase and moon age has seldom been reported from the scarid species of other localities. It is suggested that spawning in the early morning would be adaptive in species such as S. rivulatus, which migrated considerable distances (ca. 500 m) to the inshore feeding sites, in order to minimize feeding losses due to migration. For male mating tactics, pair spawning by territorial TP (terminal phase) males occurred in all 14 species, and streaking and group spawning by nonterritorial small IP (initial phase) males were seen more frequently in more abundant species. Moreover, group spawning by nonterritorial TP males, which were larger than the IP males but smaller than the territorial TP males, frequently occurred in S. rivulatus. Such mating tactics of TP males have not been reported from Scaridae.     

TEMPORAL VARIATION IN FORAGING BEHAVIOUR OF PATELLA GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA CONCINNA (BASOMMATOPHORA) ON A SOUTH AFRICAN SHORE

Foraging activity of two mid- to low- shore species of limpet,Patella granulans (Prosobranchia) and Siphonaria concinna (Pulmonata)from an exposed shore on the Eastern Cape coast of South Africawas monitored. In both species, activity was compared duringspring and neap tides and, in P. granularis between summer andwinter. Rhythms of activity of the two species were similar,with foraging excursions being mainly associated with nocturnallow tide times, although some P. granularis foraged during daytimelow tides. It is suggested that foraging excursions in P. granularisare triggered by wave action. Both species foraged further onspring tides than on neap tides and this is suggested to bea result of the limited time limpets have to forage. P. granulariswas also found to forage further during summer when comparedto winter and the possibility that seasonal micro-algal productivityinfluences foraging distances in limpets is discussed. The foraging activity of both species could be divided into3 distinct phases, a relatively rapid outward phase, a muchslower foraging phase and a rapid homeward phase. Whether ornot these limpets graze throughout an excursion is not known.S. concinna was found to home to a fixed scar, although duringthe experiment some scar-swapping occurred. P. granularis didnot home to a fixed scar but possessed a ‘home range’(approx. 5 cm²) to which it returned after each excursion. Patella granularis was found to move randomly during foraging,whilst S. concinna foraged in a non-random direction -whichtook individuals upshore. No tidal-influence is thought to bepresent in this case and the possibility of a learning componentin the foraging behaviour of certain limpet species in relationto the return to optimal feeding patches is discussed. (Received 18 May 1996; accepted 2 September 1996)     

A study of the endogenous activity rhythms of the marine isopod Exosphaeroma truncatitelson

The endogenous activity rhythms of the South African endemic isopod Exosphaeroma truncatitelson were explored. Isopods were collected on days coinciding with either a neap or spring tide. High- and low-energy beaches, which vary in the intensity of wave action, were selected as study sites. Isopods, in groups of 10–30, were placed in glass tanks with different experimental conditions: darkness + no sand, darkness with sand and natural ambient light (no sand). Activity of the isopods was measured for 50 h by recording the number of isopods swimming actively during a 30-s period. These isopods exhibited an endogenous activity rhythm which coincided with the tidal cycle even though removed from their natural habitat. Cosine curves were fitted to the observed activity data and statistical differences across variables were investigated. Peak activity was shown to occur shortly after high tide. Similar activity cycles were observed for both neap and spring tides and for different times of the year. Results also indicated that the activity cycles at both low- and high-energy beaches were similar. Two survival advantages of this rhythm are proposed: prevention of stranding on high shores and competitive avoidance with other local isopod species.     

Primary production and photoadaptation of phytoplankton in relation with tidal mixing in coastal waters

In the eastern English Channel (a coastal and shallow system),photosynthetic parameters of the pbytoplankton population weremeasured during 36 h at four depths, in a neap tide period.The vertical distilbutions of chlorophyll a (chl a), nutrients,and hydrodynamic properties were monitored during the cruise.Despite vertical homogeneity in salinity, chlorophyll a andnutrient profiles,a vertical gradient in both photosyntheticparameters (     

Semilunar spawning cycle of the humbug damselfish Dascyllus aruanus

A very distinct semilunar spawning cycle was found in a population of the damselfish Dascyllus aruanus on the coral reefs of Sesoko Island, Okinawa. Spawning occurred from June to September, only in the early morning, during a period of 2–4 days immediately before or around the time of the new and full moon. Males cared for the eggs deposited on the substrate for 2.5 days until hatching. Hatching occurred just after sunset, i.e., at the high tide of spring tide; the strong ebb current then would rapidly disperse the newly hatched larvae offshore. Females tended to synchronize spawning in a male's nest, also because multiple clutches in a nest would be more likely to survive until hatching. Thus, the distinct semilunar spawning cycle may favor females in reducing mortality of both eggs and larvae. Received: July 9, 1999 / Accepted: January 29, 2000     

Maturation, Spawning and Development in Siphonaria Pectinata Linnaeus (Gastropoda: Pulmonata) at Gibraltar

A comparative study of some aspects of the reproductive biologyof Siphonaria pectinata was carried out at Gibraltar. Maturationoccurred at 5-6 mm shell length corresponding to an age of 6-12months. At the more sheltered Atlantic site spawning was evidentfrom March to June 1992 with peak spawning occurring in May-June1992. The patterns of spawning activity for the following twoyears were very similar. Egg ribbons were very scarce at themore exposed Mediterranean site and were found in considerablyless quantities than at the Atlantic site. Individuals at bothsites contained mature eggs in their gonads at the onset, andthen throughout the duration of the spawning season, but exhibitedspent gonads by October. The spawn of S. pectinata consistedof small oval ribbons filled with numerous egg-shaped capsulesspaced irregularly in a jelly-like matrix. Spawn was depositedmainly away from the home scar in shallow depressions, cracksand crevices and between barnacles and mussels. S. pectinataexhibited planktonic development. The fertilised eggs took between14 and 21 days to develop at ambient temperature (14-19°),and hatched as free-swimming planktotrophic veligers. The timingof spawning activity and the placement of egg masses in protectivemicrohabitats on the shore are discussed in terms of adaptationsto reduce desiccation stress, predation and possible food shortages.The mode of development in S. pectinata is placed in contextwith current theories regarding siphonariid ancestry and evolution. (Received 6 January 1998; accepted 25 June 1998)     

REPRODUCTIVE CYCLES OF CERASTODERMA GLAUCUM(BRUGUIERE) AND C. EDULE (L.) WITH SPECIAL REFERENCE TO THE EFFECTS OF THE 1981-82 SEVERE WINTER

Gonadal changes in two species of Cerastoderma occurring indiscrete populations in South Wales were monitored by stereologicalanalysis during the breeding seasons of 1981 and 1982. Fecundityand spawning efficiencies were determined quantitatively. Therelationship between reproductive activity and changes in meatcondition are discussed. Both species are opportunistic breeders. Their normal patternsof reproduction are similar, consisting of minimum activityin winter and peak activity during spring/early summer. Thetwo species were affected differently by the severe winter of1981–82—C. glau-cum exhibited a single, ‘epidemic’spawning and resumed gametogenesis after a 4-month resting period.C. edule adopted a ‘polycyclic’ pattern withouta resting period. Both of these unusual reproductive strategies,augmented by reduced predation resulted in heavy spatfalls. (Received 20 March 1985; revised 20 March 1985;     

Diel and tidal changes in the distribution and feeding habits of Japanese temperate bass Lateolabrax japonicus juveniles in the surf zone of Ariake Bay

Japanese temperate bass Lateolabrax japonicus juveniles recruit to the surf zone and grow by feeding on commonly occurring coastal copepods. However, little is known about diel and tidal patterns in their migration and feeding habits. We sampled wild juveniles during the neap and spring tides, over periods of 24 h, with small seine nets in the sand flat of the eastern part of Ariake Bay, Kyushu, western Japan. In both the neap and spring tides, abundance of juveniles significantly increased during the daytime, being highest around the time of high tide. The relative gut fullness indices of juveniles drastically increased in the morning (0700–0900) and during the flood tide in the daytime, while major prey copepod (Paracalanus spp.) density in the ambient water was relatively constant. We summarized that L. japonicus juveniles would migrate to the surf zone after sunrise to feed on copepods, and then emigrate from the surf zone after sunset. The migratory behavior of L. japonicus juveniles would be influenced by light (daytime) and feeding activity influenced by both light (morning) and tidal condition (flood tide). The intertidal region of the tidal flat was recognized to be one of the important habitats for L. japonicus during their early life history.     

Diel and lunar spawning periodicity of the hawkfish Paracirrhites forsteri (Cirrhitidae) on the reefs of Kuchierabu-jima Island, southern Japan

We observed spawning behavior of the hawkfish Paracirrhites forsteri on reefs of southern Japan. Spawning generally occurred after sunset, prior to the full and new moon with semi-lunar spawning peak periodicity. No egg predation was observed in spawning after sunset, and high tide often occurred at dusk in the lunar phases. Thus, diel timing and lunar synchronicity may increase larval survival. We found that the mating activity tended to start earlier in the day during early mating season than during mid-to-late mating season. The advantages of the earlier start of mating activity were also examined in relation to adult biology contexts.     

Circadian and circatidal rhythms of oxygen consumption in the sandy-beach isopod Tylos granulatus Krauss

The sandy-beach isopod Tylos granulatus Krauss burrows at the high tide mark, and has rhythms of nocturnal emergence coincident with the low tide period. Measurements of the respiration rate show that a low rate of oxygen consumption is maintained throughout the day but there is a circatidal rhythmic increase of between 300 and 700% during the nocturnal low tide. The height of this peak and the percentage of animals displaying a peak both increase from spring tide to neap tide suggesting a semi-lunar rhythm. The respiratory peaks have a 24.8 h periodicity, being later each night until low tide falls in the dawn, when there is a ‘switch-back’ so that peaks are then during the subsequent evening low tide. These respiratory rhythms are persistent under constant light and coincide with previously described activity rhythms. The respiratory rhythms considerably reduce metabolic energy losses, particularly as the activity rhythms ensure avoidance of high diurnal temperatures and activity during the cooler nocturnal period.     

The Role of Temperature and Embryo Development Time in the Diel Timing of Spawning in a Coral-reef Damselfish with High-frequency Spawning Synchrony

We studied the diel timing of spawning in the demersally spawning Hawaiian damselfish, Dascyllus albisella, from mid-June to late-September 1997 at two small patch reefs in Hawaii. Our objectives were to elucidate daily timing of spawning in relation to water temperature, diel timing of hatching, and short-period spawning synchrony. Spawning occurred every 5–7 days at both reefs, with all spawning on a reef concluded either within a single day (1-day spawning) or within two successive days (2-day spawning). Spawning began in early morning and continued for most of the day. There was a significant, positive linear relationship between mean daily average water temperature (= daily average temperature averaged over the period starting from the day following the last spawning day of the preceding nest cycle till the day before the first spawning day of the current cycle) and peak spawning hour of day, for 1-day spawning, and the first and second days of 2-day spawning at both reefs. The relationship between mean daily average water temperature and peak spawning hour of day was comparable among all spawning-day classes and reefs. Hatching occurred on the fourth day of development throughout the study despite the 26.5–29.1°C change in water temperature during the study period, and hatching was restricted to within two hours after sunset. We propose that D. albisella's peak spawning time is positively correlated with increased water temperature because it maintains the benefits of synchronous spawning within two constraints: the narrow daily period of hatching, and the inverse relationship between water temperature and embryo developmental time.     

Tidally driven distribution of phytoplankton blooms in a shallow, macrotidal estuary

The influence of the ebb tide on the abundance and distributionof bloom-forming species, as well as the mechanisms for theselection of those species which remain, were investigated inthe shallow, tidal-flushed Urdaibai estuary, north Spain. Phytoplanktonwas collected monthly from May to September 1998 during differenttidal conditions (neap-spring) at five stations along the salinitygradient of the estuary. During the neap tides of May, Leptocylindrusdanicus dominated in the lower estuary, together with Thalassiosiraguillardii and Peridinium foliaceum in the upper segment; T.guillardiiexperienced the broadest displacement along the estuary. Duringthe June and July cruises, coinciding with mid-tidal amplitudesand high temperatures, Peridinium quinquecorne densely aggregatedin the upper estuary at the slack high tide, whereas Chaetocerossalsugineum bloomed at the intermediate stations. Cyclotellaatomus and Protoperidinium achromaticum reached high concentrationsin the upper zone only during the late stages of the ebb. Duringthe spring tides of September, Prorocentrum minimum, Heterocapsapygmaea and Heterocapsa rotundata appeared in the lower marineestuary, being washed out at low tide. By contrast, the diatomsSkeletonema costatum, Thalassiosira guillardii and Cyclotellaatomus were the most abundant species in the upper reaches,peaking during the ebb. Physical trapping and high water residencetimes served to retain blooming species in the upper estuary.The intense growth of the estuarine diatoms may compensate forthe advective seaward losses of cells during the ebb, thus allowingthe development of stable populations in the estuary. Only Peridiniumquinquecorne seems to combine an endogenous tidal rhythm witha photic response to remain in the tidal area of the estuary.     

Embryonic and larval development of Ensis arcuatus (Jeffreys, 1865) (Bivalvia: Pharidae)

The razor clam Ensis arcuatus (Jeffreys, 1865) is distributedfrom Norway to Spain and along the British coast, where it livesburied in sand in low intertidal and subtidal areas. This workis the first study to research the embryology and larval developmentof this species of razor clam, using light and scanning electronmicroscopy. A new method, consisting of changing water levelsusing tide simulations with brief dry periods, was developedto induce spawning in this species. The blastula was the firstmotile stage and in the gastrula stage the vitelline coat waslost. The shell field appeared in the late gastrula. The trochophoredeveloped by about 19 h post-fertilization (hpf) (19°C).At 30 hpf the D-shaped larva showed a developed digestive systemconsisting of a mouth, a foregut, a digestive gland followedby an intestine and an anus. Larvae spontaneously settled after20 days at a length of 378 µm. (Received 5 December 2006; accepted 19 November 2007)     

Tidal influence upon appendicularian abundance in North Inlet estuary, South Carolina

Tidal influences on appendicularian densities were observedat North Inlet, South Carolina, by sampling along a transectwhich ran from a tidal creek to a station 5 km offshore. Oikopleuradioica was the dominant species in North Inlet, while Oikopleuralongicauda and Appendicularia sicula contributed marginallyto appendicularian numbers during midsummer and fall. A strongtide-dependent density pattern was clear for inshore waters.Low-tide densities of all three species showed a dramatic increasein an offshore direction. At high tide, densities were similarbetween all stations for O. dioica, while O. longicauda andA. sicula showed a less pronounced density gradient than atlow tide. Population densities within the inlet were greateron spring tides than neap tides and tidal influences were generallyconsistent between seasons. Appendicularians enter the estuaryin densities as high as 20 072 animals m^–3, indicatingthat tidal currents may be an important mechanism for exchangeof appendicularian biomass between coastal and estuarine waters. ¹Present address: Allan Hancock Foundation, University of SouthernCalifornia, Los Angeles, CA 90007, USA.     

Aggregation and spawning of the humphead wrasse Cheilinus undulatus (Pisces: Labridae): general aspects of spawning behaviour

The humphead wrasse Cheilinus undulatus formed resident spawning aggregations daily after high tide at specific locations along the seaward edge of the Palau barrier reef. The location and extent of one aggregation site remained consistent for 6 years with no physical features distinguishing it from adjacent areas. Spawning was documented most months and probably occurred year round with possible seasonal and lunar variation. Spawning males arrived first at the site, followed by females and potentially small primary males. The aggregation female to male sex ratio was estimated to be between 6:1 and 10:1. A maximum of 15 males and 100–150 females were observed at the site. A male courtship posture with the anal fin pointed, the caudal fin folded down and the dorsal fin folded against the body was maintained while swimming a few metres off the bottom in view of females. When ready to spawn females rose up as the posturing male passed and the pair released gametes in a relatively sedate fashion near the surface along the shelf break. No attempted predation on spawning adults was seen. Egg predation after spawning was uncommon. On days with early to mid‐day high tides the spawning period started 2·0–2·5 h after high tide when the speed of lagoon–ocean tidal currents peaked and lasted c. 1 h. On days with later afternoon high tides, spawning occurred sooner after high tide and before current speeds peaked. Other fishes with planktonic eggs spawned at the site as pairs or small groups in a rough succession after high tide with C. undulatus, the last species to spawn.     

Role of the tidal cycle in the gonadal development and spawning of the tropical wrasse Halichoeres trimaculatus

Many wrasses on coral reefs exhibit daily spawning that peaks around daytime high tides. In this study, we examined tidal-related ovarian development in the threespot wrasse, Halichoeres trimaculatus, a species common on coral reefs in the Indo-Pacific Ocean. When the fish were collected in the morning at different tidal phases, the gonadosomatic index (GSI) and ovarian histology changed; concomitant with increases in GSI towards high tide, a clutch of the most advanced oocytes developed from vitellogenic to maturation stages. Ovulated eggs and post-ovulated follicles (POF) existed in most ovaries around high tide, but only POF remained around ebb tide, suggesting that spawning occurred during or after high tide. We noticed that tidal-related spawning was considerable in the morning and that most ovaries collected on the afternoon high tide exhibited post-spawning features. This suggests that certain labrid species possess plasticity with regard to their spawning time and utilize potent environmental cues to ensure their reproductive success. When pieces of ovary were incubated with precursor steroids, high conversion of testosterone to 17beta-estradiol occurred during high and ebb tides, while that of 17alpha-hydroxyprogesterone to 17alpha,20beta-dihydroxy-4-pregnen-3-one and 17alpha,20beta,21-trihydroxy-4-pregnen-3-one was observed during low and flood tides. Incubation of pieces of ovary with human chorionic gonadotropin resulted in similar fluctuations in the steroid hormones with tidal phase. Production of these steroid hormones correlated with oocyte development in the ovaries and was probably regulated by gonadotropin. These results demonstrate that the daily cycle is fundamental for oocyte development, and that the tidal cycle is superimposed on this process.     

Notes on a Mesodinium rubrum red tide in San Francisco Bay (California, USA)

Discrete red patches of water were observed in South San FranciscoBay (USA) on 30 April 1993, and examination of live samplesshowed that this red tide was caused by surface accumulationsof the pigmented ciliate Mesodinium rubrum. Vertical profilesshowed strong salinity and temperature stratification in theupper 5 m, peak chlorophyll fluorescence in the upper meter,and differences in the small-scale density structure and fluorescencedistribution among red patches. Events preceding this Mesodiniumred tide included: (i) heavy precipitation and run-off, allowingfor strong salinity stratification; (ii) a spring diatom bloomwhere the chlorophyll a concentration reached 50 mg m^–3;(ii) depletions of dissolved inorganic N and Si in the photiczone; and (iv) several days of rapid warming and stabilizationof the upper surface layer. These conditions may be generalprerequisites for M.rubrum blooms in temperate estuaries. ¹Present address: Station Marine d'Endoume, Centre d'Oceanologiede Marseille, rue Batterie des Lions, 13007 Marseille, France