Ichthyofaunas of a temperate estuary and adjacent marine embayment. Implications regarding choice of nursery area and influence of environmental changes

A fine-mesh seine net was used at regular intervals to collect fishes from the entrance channel and basin of the Blackwood River Estuary (south-western Australia), from Deadwater Lagoon, which is joined to the entrance channel by a narrow and shallow water-course and thus constitutes part of this estuary, and from Flinders Bay into which the estuary discharges. Sampling was at six-weekly intervals between February and December 1994. The juveniles of some marine species, such as Pelates sexlineatus, Rhabdosargus sarba and Aldrichetta forsteri, were either found only in the estuary or were in far higher densities in the estuary than in Flinders Bay. In contrast, the juveniles of some other marine species, such as Sillago schomburgkii, were relatively abundant in both environments, while others such as S. bassensis, Pelsartia humeralis, Lesueurina platycephala and Spratelloides robustus were either far more abundant in Flinders Bay or entirely restricted to this marine embayment. The various marine species found in inshore waters thus apparently vary considerably in their “preference” for estuaries as nursery areas. Although some marine species were abundant in the shallows of the estuary, the fish fauna of these waters was dominated by the estuarine-spawning species Leptatherina wallacei, Favonigobius lateralis, L. presbyteroides and Atherinosoma elongata. The above regional differences help account␣for the very marked difference that was found between the compositions of the shallow-water␣ichthyofaunas of Flinders Bay and each of the three estuarine regions. The ichthyofaunal compositions of the basin and channel underwent pronounced changes during winter, when freshwater discharge increased markedly and salinities in the estuary thus declined precipitously. This faunal change was mainly attributable to the emigration of marine stragglers, a reduction in the densities of marine estuarine-opportunist species such as Pelates sexlineatus and R. sarba, and the immigration of large numbers of both young 0+ Aldrichetti forsteri from the sea and of L. wallacei from the river. Although most of the above species were also abundant in Deadwater Lagoon, the ichthyofaunal composition of this region did not undergo the same seasonal changes, presumably due to the lack of riverine input and thus the maintenance of relatively high salinities throughout the year. The number of marine straggler species was much lower in Deadwater Lagoon than in the estuary basin, reflecting a far more restricted tidal exchange with the entrance channel. However, the overall density of fishes was far higher in Deadwater Lagoon than in the estuary basin or entrance channel, due mainly to the far higher densities of the estuarine species Atherinosoma elongata and L. wallacei and of the 0+ age class of the marine species R. sarba. The high densities of certain species in Deadwater Lagoon are assumed to be related, at least in part, to the high level of productivity and protection that is provided by the presence of patches of Ruppia megacarpa, an aquatic angiosperm that was not present in the estuary basin or entrance channel. Received: 3 December 1996 / Accepted: 19 December 1996     

Reproductive biology of the red alga Polysiphonia lanosa (Ceramiales) in the Bay of Fundy, Canada

The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum. During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus. Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life cycle was common at the studied location. Received: 10 December 1996 / Accepted: 16 January 1997     

Do protandric pandalid shrimp have environmental sex determination?

Based on demographic analysis of four different temporally enclosed demes of Pandalus borealis in Gullmarsfjorden on the Swedish west coast and published information, I discuss the notion of environmental sex determination in protandric pandalid shrimps as suggested by sex allocation theory. Demographic results showed that age structure and mortality rates varied substantially between four studied periods without noticeable effects on the age of sex change in the fjord populations. The majority of shrimps changed sex at an approximate age of 3 years and became females at an age of 3 to 4 years, however, low proportions (4 to 7%) of 2nd year females (transitional at ca. 1 year) and 3rd year females (5 to 12%) (transitional at ca. 2 years) were present each year. Low proportions of primary females were also found in two of the temporally enclosed demes, in 1985 (9%) and in 1987 (5%). These results do not indicate that yearly variations in age structure, mortality, or frequency of older breeders in the breeding population affect the age of sex change in temporally enclosed fjord demes of this protandric species. An alternative to assuming that the protandric mode of reproduction in pandalid shrimp is combined with environmental sex determination is suggested. Received: 24 September 1996 / Accepted: 6 November 1996     

Larval fish assemblages in Independencia Bay,Pisco, Peru: temporal and spatial relationships

The structure of the larval fish assemblages in Independencia Bay on the coast of Peru was examined using a combination of univariate and multivariate techniques. The plankton of Independencia Bay was sampled during 2000, to ascertain ichthyoplankton composition, abundance, and seasonality. These data were used to assess the function of the bay as spawning and nursery grounds and were related to the regional oceanography. In total, 16,156 fish larvae, representing 34 families, 48 genera, and 48 species were collected. Engraulidae, Normanichthyidae, Blenniidae, Gobiesocidae, Haemulidae, Labrisomidae, Pinguipedidae, and Atherinidae comprised 96.8% of the larvae captured; the remaining 3.2% included 26 families. Greatest mean larval fish densities, 319–1,381 per 100 m³, were recorded between September and November, suggesting a major spring spawning period. The most abundant fish larvae during this period were preflexion stage mote sculpins (Normanichthyidae) and newly hatched and preflexion stage anchovies (Engraulidae). A second, smaller summer peak was dominated by preflexion stage anchovies, followed by preflexion stage mote sculpins. The occurrence of high larval fish densities and the wide range of larval stages suggest that Independencia Bay is a regionally important spawning and nursery ground for marine fish. The principal component analysis showed that temperature and salinity were the dominant variables within the first two principal components, which accounted for 74.4% of the variation in environmental conditions. These conditions varied over time, station, and depth; however, interaction terms could not clearly be identified. Fitting a multinomial logistic model showed that larval fish assemblages and environmental conditions were associated in a complex way. The spring and summer ichthyoplankton abundance peaks in Independencia Bay coincided with high zooplankton standing stock and also coincided approximately with the periods of increased upwelling in the area.Communicated by O. Kinne, Oldendorf/Luhe     

Population structure and genetic diversity in green turtles nesting at Tortuguero,Costa Rica,based on mitochondrial DNA control region sequences

The green turtle (Chelonia mydas) nesting population at Tortuguero, Costa Rica, is the largest nesting aggregation in the Atlantic, by at least an order of magnitude. Previous mitochondrial DNA (mtDNA) surveys based on limited sampling (n = 41) indicated low genetic diversity and low gene flow with other Caribbean nesting colonies. Furthermore, a survey of nuclear DNA diversity invoked the possibility of substructure within the Tortuguero rookery. To evaluate these characteristics, mtDNA control region sequences were determined for green turtles nesting at Tortuguero in 2001 (n = 157) and 2002 (n = 235). The increased sample revealed three additional haplotypes; five haplotypes are now known for Tortuguero female green turtles. Analyses of molecular variance indicated that there was no significant spatial population structure along the 30-km nesting beach. In addition, no temporal population structure was detected either between the two nesting seasons or within the nesting season. As a result of the larger sample size and additional haplotypes, estimates of genetic separation among Caribbean nesting colonies have changed and the concordance of phylogenetic and phylogeographic patterns reported in the past for green turtles in the Greater Caribbean has weakened. The five haplotypes from Tortuguero represent 36% of the haplotypes identified in green turtle nesting aggregations in the Greater Caribbean and 17% of the haplotypes known to occur in nesting or foraging aggregations in the Greater Caribbean. Haplotype diversity (0.16) and nucleotide diversity (0.0034) for the Tortuguero population are substantially lower than those for the combined rookeries in the Greater Caribbean (0.44 and 0.0078, respectively). Although comprehensive evaluation of regional genetic diversity requires nuclear DNA data, our study indicates that conserving genetic diversity in Caribbean green turtles will require careful management of the smaller rookeries in addition to the Tortuguero rookery.     

A morphological approach for relating decapod crustacean cephalothorax shape with distribution in the water column

Cephalothorax profiles for individuals of 18 decapod crustacean species were obtained from pictures of specimens captured using various experimental bottom trawls in the Mediterranean basin, at depths ranging from 200 to 4000 m in 2000 and 2002. Profiles were compared using the shape (outline) of the entire cephalothorax (including and excluding the rostrum). Principal component analysis (PCA) of the profiles, rostrum included, yielded two large species groupings related to rostrum size, species having a long rostrum being clustered on the positive portion of the first axis and species having a short rostrum being clustered on the negative portion of this same axis (the F1 axis explained 72.17% of the total variance). The PCA separated pelagic and endobenthic animals (with short rostrums) from nektobenthic animals (with long rostrums). Only the two deepest-dwelling species (dwelling at depths below 2000 m) were distanced from their respective groups. The pelagic shrimp Acanthephyra pelagica was clearly grouped with the nektobenthic species despite being reported to have a pelagic habitat. The nektobenthic deep-sea species Nematocarcinus exilis has a relatively medium-size rostrum and was placed among the pelagic–endobenthic species. The endobenthic and pelagic groups remained stable even when rostral morphometrics were excluded from the PCA analysis. The hypothesis that predation and diet are the fundamental determining factors for all habitats throughout most of the lifetimes of individuals and hence that species will evolve specialised phenotypes to adapt to local environmental conditions is considered in the discussion.Communicated by O. Kinne, Oldendorf/Luhe     

Changes in morphology and physiology of an East Mediterranean sponge in different habitats

The sponge Tetilla sp. (Tetractinomorpha: Tetillidae) is a common species in the eastern Mediterranean. This sponge inhabits four different habitat types differing in wave impact and irradiance levels. Two of these habitats (a shallow cave and deep water) are characterized by relatively calm water, whereas the other two (shallow exposed site and tide pools) are in turbulent water with high energy flow. The present study examined the influence of physical (depth, illumination and water motion) and biotic factors on morphology, skeletal plasticity and reproductive traits among the four spatially separated populations. Sponges from tidal pools had significantly larger body volume than sponges from deep water and from shallow caves (ANOVA: tidal-deep P<0.0001; tidal-shallow caves P<0.05). Sponges from exposed habitats were significantly larger than deep-water sponges (ANOVA: P=0.01). In addition, individuals from tide pools and from the exposed habitat had a significantly higher proportion of structural silica than sponges from the calmer deep water and from the cave sites. Oxea spicules in sponges from the calm habitats were significantly shorter than in those from the tidal pools and the exposed habitats. The percentage of spicules out of a sponges dry weight in individuals transplanted from deep (calm) to shallow (turbulent) water significantly increased by 21.9±12.9%. The new spicule percentage did not differ significantly from that of sponges originally from shallow water. Oocyte diameter differed significantly between habitats. The maximal size of mature eggs was found in deep-water sponges in June (97±5 m). In the shallow habitats, a smaller maximal oocyte diameter was found in the cave, in May (56.5±3 m). Furthermore, oocyte density in shallow-water sponges was highest in May and decreased in June (with 88.2±9 and 19.3±9 oocytes mm^–2, respectively). At the same time (June), oocyte density of deep-water sponges had just reached its maximum (155±33.7 oocytes mm^–2). The difference in oocyte size and density between deep- and shallow-water individuals indicates an earlier gamete release in the shallow sponge population. The results suggest that plasticity in skeletal design of this sponge indicates a trade off between spicule production and investment in reproduction.Communicated by O. Kinne, Oldendorf/Luhe     

Nematocyst complements of nudibranchs in the genus <Emphasis Type="Italic">Flabellina</Emphasis> in the Gulf of Maine and the effect of diet manipulations on the cnidom of <Emphasis Type="Italic">Flabellina verrucosa</Emphasis>

Aeolid nudibranchs maintain functional nematocysts, which are sequestered from the nudibranchs’ cnidarian prey and provide protection against predators. Some species exhibit extensive variation in incorporated nematocysts, while others maintain a limited number of types. This study examines the apparent diversity in uptake and patterns of nematocyst incorporation among related species. Nematocyst complements were described for four Gulf of Maine nudibranch species in the genus Flabellina exhibiting a variety of feeding strategies and prey specificities. Diet manipulations were performed to examine the response to changing nematocyst availability using a generalist consumer, Flabellina verrucosa, to assess nematocyst uptake based on diet. The flabellinid species examined exhibited significant differences in nematocyst incorporation, reflecting differences in their specificity as predators and nematocyst types available in their natural prey. The nematocyst complement of F. verrucosa was the most variable and differed among collection regions. When diet was manipulated, nematocyst uptake depended on the prey the nudibranchs consumed, but when offered a variety of prey, F. verrucosa selectively preferred nematocysts from scyphistomae. The observed variation in nematocyst uptake among species and regions probably relates to environmental disparities among populations.     

Divorce in common murres (Uria aalge): relationship to parental quality

Behavioral precursors of 12 divorces were examined in 30 color-banded pairs of common murres (Uria aalge) over six breeding seasons. Common murres are long-lived seabirds that typically return each year to the same mate and nest site in dense colonies. At least one parent is present continuously from egg lay to chick fledging. Murres, therefore, have considerable opportunities to compare their mates parental behavior with that of several familiar neighbors. Previous reproductive success was lower for divorcing birds than for reuniting pairs. As predicted by the better option hypothesis, there were clear choosers (seven females and five males) that initiated divorce by moving to a new birds site or by courting a new partner at their current site. Choosers improved their reproductive success after the divorce, whereas their previous partners, the victims did not. Yearly divorce rates (average 8.2% per year) were significantly correlated with yearly mortality rates. Divorces appear to be opportunistic: pairs divorced after varying numbers of reproductive failures with the immediate precursor usually being the disappearance (death) of a murre from a successful neighboring site. In contrast to the delays experienced by victims, choosers formed new pairs quickly and laid their eggs no later than reuniting pairs. Prior to the divorce, victims fed their chicks less often than choosers, and some engaged in other behaviors that compromised egg or chick survival. These observations suggest that deficiencies in parental behavior were precursors to the divorce. This report is one of the first cases where reproductive failure of divorcing pairs has been linked to deficits in the parental behavior of the subsequent divorce victim.Communicated by C. Brown