Does the composition of the demersal fish assemblages in temperate coastal waters change with depth and undergo consistent seasonal changes?

The aim of this study was to determine whether the composition of the demersal fish fauna in coastal marine waters in temperate Australia changes markedly with increasing water depth and distance from the shore and whether the composition of the fish fauna in water depths of 5 to 35 m undergoes cyclic, seasonal changes. Samples of demersal fishes were therefore collected by trawling over the predominantly sandy substrate at nine sites located in water depths of 5 to 15 m or 20 to 35 m and within 20 km of the shore in four regions along ∼200 km on the lower west coast of Australia. The sampling regime involved trawling for fishes at each site at night in seven consecutive seasons between the summer of 1990/1991 and winter of 1992. A total of 72 435 fishes, representing 77 families, 143 genera and 172 species was caught. The compositions of the fish faunas in offshore waters with depths of 5 to 35 m were shown to differ markedly from those previously recorded for nearshore marine waters in the same regions. However, as some species, such as Sillago burrus, S. vittata, S. bassensis and Rhabdosargus sarba, increase in size, they move out from their nursery areas in nearshore waters into deeper and more offshore waters, where spawning occurs. Ordination showed that, in each of the four regions, the composition of the fish fauna in depths of 5 to 15 m differs from that in depths of 20 to 35 m. This difference is attributable to the fact that some species, such as  S. burrus, S. vittata and Upeneichthys lineatus, are far more abundant in depths of 5 to 15 m, whereas other species, such as S. robusta, U. stotti and Lepidotrigla modesta, occur predominantly in depths of 20 to 35 m. However, the samples collected from the single site that was inshore but in deeper water demonstrate that the composition of the fish fauna is influenced by distance from shore as well as by water depth. The compositions of the fish faunas differed with latitude, largely due to the fact that some subtropical species, such as Polyspina piosae, S. burrus and  S. robusta, did not extend down into the more southern regions. Ordination also showed that the composition of the fish faunas at all but one of the nine sites underwent pronounced and consistent cyclic, seasonal changes. This seasonal cyclicity at the different sites was attributable to sequential patterns of immigrations and emigrations by a number of fish species during the course of the year. These seasonal migrations involved, inter alia (1) movements of certain species from their nursery areas into these deeper waters, e.g.  S. bassensis and Scobinichthys granulatus; (2) migrations into and off the sandy areas of the inner continental shelf, e.g. Arnoglossus muelleri; (3) migrations to spawning areas, e.g. Sillago robusta; and (4) movements into areas where detached macrophytes accumulate in winter, e.g. Cnidoglanis macrocephalus and Apogon rueppellii. Received: 21 August 1998 / Accepted: 9 February 1999     

Relationships between the movements,growth, age structures,and reproductive biology of the teleosts Sillago burrus and S. vittata in temperate marine waters

Sillago burrus and S. vittata both use sheltered, nearshore shallow waters ( 1.5 m) as nursery areas. However, the juveniles of the former species remain there for only a few months, before migrating into deeper waters (5 to 15 m) as they increase in size, whereas some juvenile S. vittata do not undergo a similar migration until considerably later. S. burrus rarely exceeded 2 yr of age and was never found beyond 4 yr of age. Although only a small number of S. vittata exceeded 2 yr of age, a few individuals of this species were caught between 4 and 7 yr old. The maximum and asymptotic lengths of S. burrus (251 and 180 mm, respectively) were far lower than those of S. vittata (325 and 320 mm, respectively), whereas the growth coefficients (K) were much higher for the former species, i.e. 2.4 vs 0.4. Virtually all S. burrus, and also those S. vittata that moved into deeper waters early in life, spawned at the end of their first year of life. Since relatively few S. burrus reached 2 yr of age, the attainment of almost full size by the end of their first year of life enables a relatively large number of eggs to be produced by fish at the end of their first year-for many, their only spawning period. Those individuals of S. vittata that remained in their shallow nursery areas until the end of their first year of life, did not reach maturity until the end of their second year of life. The proportions of mature gonads and the numbers of yolk-vesicle and yolk-granule oocytes and post-ovulatory follicles in ovaries were far higher in both S. burrus and S. vittata during December to February than in any other month, demonstrating that these two species spawn largely in these summer months. During this period, the ovaries of individual S. burrus and S. vittata often contained post-ovulatory follicles, as well as yolkvesicle and yolk-granule oocytes that ranged widely in size, strongly suggesting that both species are multiple spawners. During the spawning period of S. burrus, the ovaries possessed large numbers of hydrated oocytes and no post-ovulatory follicles or the reverse situation, and the oocytes tended to form several relatively discrete size groups. This indicates that S. burrus produces eggs in batches and that the spawning of the members of this species is synchronised. The presence of large numbers of yolk-granule oocytes with migrating nuclei in the ovaries of many S. vittata at certain times suggests that this species is also a batch- and synchronised spawner. Comparisons between the results of the present study and past work emphasise that the relationships between the timing of offshore movements and the sizes and ages at first maturity vary considerably amongst whiting species.     

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     

Spatial and seasonal differences in the fish fauna in the shallows of a large Australian estuary

Samples of fish were collected by beach seine throughout the shallow waters of the large Peel-Harvey estuarine system (south-western Australia) in the wet (June to November) and dry periods (December to May) between August 1979 and July 1981. The number of species, density and biomass declined with distance from the estuary mouth and rose with increasing temperature and salinity. Both classification and ordination distinguished the faunal composition of the saline reaches of the rivers from that of the narrow Entrance Channel and two large basins (Peel Inlet and Harvey Estuary). Classification also separated the fauna of the riverine group into wet- and dry-period components, and divided samples taken in the Entrance Channel from those in the basins. Differences between the faunal composition of the Peel Inlet and its tributary rivers were related to differences in salinity regime. The riverine fauna was subjected to much more variable and lower minimum salinities. Species characteristic of the rivers included teleosts such as Atherinosoma wallacei and Amniataba caudavittatus, which are estuarine sensu stricto in southwestern Australia, the semi-anadromous Nematalosa vlaminghi and juveniles of the marine Mugil cephalus. The species diagnostic of the wet periods in the rivers were the estuarine species A. wallacei and Favonigobius suppositus, while the dry periods were characterised by the marine species Atherinomorus ogilbyi and Sillago schomburgkii. Marine species also characterised the Entrance Channel (Favonigobius lateralis, Sillago bassensis), whereas the indicators in Peel Inlet and Harvey Estuary were Hyporhamphus regularis and Apogon rueppellii, both of which can pass through the whole of their life cycle in estuarine as well as marine environments.     

Feeding and predation impact of two chaetognath species, Eukrohnia hamata and Sagitta gazellae, in the vicinity of Marion Island (southern ocean)

The predation impact of the two chaetognaths Eukrohnia hamata and Sagitta gazellae on mesozooplankton standing stock were investigated in three depth layers during two 24 h stations occupied in the vicinity of Marion Island in late austral summer (April/May) 1986. The zooplankton community at both stations was dominated by small copepods (Oithona spp., Microcalanus spp.), which accounted for >95% of total zooplankton abundance. Chaetognaths comprised <2% of total zooplankton abundance. E. hamata constituted >95% of the total chaetognath stock. The general trend in both species was decreasing abundance with increasing depth, which appeared to be correlated to the distribution of copepods (r ² = 0.45; P <0.05). Gut-content analysis showed that copepods (mainly Oithona spp., Calanus spp. and Rhincalanus gigas) and ostracods were the main prey of both species, accounting for 87 and 61% of the total number of prey in E. hamata and S.␣gazellae stomachs, respectively. In the guts of S.␣gazellae, pteropods (Limacina spp.) and chaetognaths were also well represented. The mean number of prey items (NPC) for E. hamata ranged from 0.02 to 0.06 prey individual⁻¹ which corresponds to an individual feeding rate (Fr) of between 0.05 and 0.12 prey d⁻¹. For S.␣gazellae, the NPC values were higher, varying between 0.04␣and 0.20 prey individual⁻¹, or between 0.15 and 0.76 prey d⁻¹. The daily predation impact of the two chaetognaths was estimated at between 0.3 and 1.2% of the copepod standing stock or between 7 and 16% of the daily copepod production. Predation by S. gazellae on chaetognaths accounted for up to 1.6% of the chaetognath standing stock per day. Received: 26 November 1996 / Accepted: 31 October 1997     

Spatial and temporal distributions of copepods to leeward and windward of Oahu, Hawaiian Archipelago

The spatial and temporal distributions of two island-associated copepod species, Undinula vulgaris Dana and Labidocera madurae Scott, were compared to the distributions of two open ocean species, Cosmocalanus darwinii Lubbock and Scolecithrix danae Lubbock, along 28-km windward and leeward transects off the island of Oahu, Hawaii. Samples were taken in September and December 1985 and April and June 1986. A warm, low salinity pool on the leeward side was a prominent feature during all transects except December. The abundances of the two oceanic species did not change significantly between leeward and windward stations, with distance from shore, or between September 1985 and April 1986 samples. As expected, very high abundances of U. vulgaris occurred at some nearshore stations, up to 3 g dry wt m⁻² for adults alone. Calculations of respiratory loss at these densities (0.7 g C m⁻² d⁻¹) suggest a high local productivity would be required to meet these demands. L. madurae, a surface-dwelling species normally restricted to within 1 km of shore, was an effective indicator species of nearshore water movement. It was more common in offshore samples on the leeward transects, rarely being found offshore on the windward side, consistent with prevailing currents and the presence of the leeward warm, low salinity pool. The occurrence of a strong mixing event in April 1986 resulted in L. madurae being distributed throughout the upper 100 m of the water column. The presence of oceanic species close to shore on the windward side also coincided with this wind-driven event. The primary environmental influence on vertical distributions was daytime cloud cover, with U. vulgaris tending to be found shallower on cloudy days. Of the two oceanic species, S. danae exhibited the most pronounced vertical migration, however, vertical distributions were not significantly correlated with environmental factors for either species. The abundant nearshore U. vulgaris population cannot be explained by differences in vertical distribution between it and the two oceanic species that might allow a physical mechanism to concentrate U. vulgaris. A high population growth rate is likely necessary to explain U. vulgaris' dominance. Received: 26 June 1998 / Accepted: 31 March 1999     

Zooplankton responses to hypoxia: behavioral patterns and survival of three species of calanoid copepods

Seasonally recurrent and persistent hypoxic events in semi-enclosed coastal waters are characterized by bottom-water dissolved oxygen (d.o.) concentrations of < 2.0 ml l⁻¹. Shifts in the distribution patterns of zooplankters in association with these events have been documented, but the mechanisms responsible for these shifts have not been investigated. This study assessed interspecific differences in responses to hypoxia by several species of calanoid copepods common off Turkey Point, Florida, USA: Labidocera aestiva (Wheeler) (a summer/fall species), Acartia tonsa (Dana) (a ubiquitous year-round species), and Centropages hamatus (Lilljeborg) (a winter/spring species). Under conditions of moderate to severe hypoxia 24-h survival experiments were conducted for adults and nauplii of these species from August 1994 to October 1995. Experiments on adults used a flow-through system to maintain constant d.o. concentrations. Adults of A. tonsa showed no decline in survival with d.o. as low as 1.0 ml l⁻¹, sharp declines in survival at d.o. = 0.9 to 0.6 ml l⁻¹, and 100% mortality with d.o. = 0.5 ml l⁻¹. Adults of L. aestiva and C. hamatus were more sensitive to oxygen depletion: both species experienced significant decreases in survival for d.o. = 1.0 ml l⁻¹. Nauplii of L. aestiva and A. tonsa showed no significant mortality with d.o. = 1.1 to 1.5 ml␣l⁻¹ and d.o. = 0.24 to 0.5 ml l⁻¹, respectively. In addition, experiments investigating behavioral avoidance of moderate to severe hypoxia were carried out for adults of all three species. None of the three species effectively avoided either severely hypoxic (d.o. < 0.5 ml l⁻¹) or moderately hypoxic (d.o. ≈ 1.0 ml l⁻¹) bottom layers in stratified columns. These results suggest that in␣nearshore areas where development of zones of d.o. < 1.0 ml l⁻¹ may be sudden, widespread, or unpredictable, patterns of reduced copepod abundance in bottom waters may be due primarily to mortality rather than avoidance. Received: 31 August 1996 / Accepted: 24 September 1996     

Prey, feeding rates, and asexual reproduction rates of the introduced oligohaline hydrozoan Moerisia lyonsi

Moerisia lyonsi Boulenger (Hydrozoa) medusae and benthic polyps were found at 0 to 5‰ salinity in the Choptank River subestuary of Chesapeake Bay, USA. This species was introduced to the bay at least 30 years before 1996. Medusae and polyps of M. lyonsi are very small and inconspicuous, and may occur widely, but unnoticed, in oligohaline waters of the Chesapeake Bay system and in other estuaries. Medusae consumed copepod nauplii and adults, but not barnacle nauplii, polychaete and ctenophore larvae or tintinnids, in laboratory experiments. Predation rates on copepods by medusae increased with increasing medusa diameter and prey densities. Feeding rates on copepod nauplii were higher than on adults and showed no saturation over the range of prey densities tested (1 to 64 prey l⁻¹). By contrast, predation on copepod adults was maximum (1 copepod medusa⁻¹ h⁻¹) at 32 and 64 copepods l⁻¹. Unexpectedly, M. lyonsi colonized mesocosms at the Horn Point Laboratory during the spring and summer in 4 years (1994 to 1997), and reached extremely high densities (up to 13.6 medusae l⁻¹). Densities of copepod adults and nauplii were low when medusa densities were high, and estimated predation effects suggested that M. lyonsi predation limited copepod populations in the mesocosms. Polyps of M. lyonsi asexually produced both polyp buds and medusae. Rates of asexual reproduction increased with increasing prey availability, from an average total during a 38 d experiment of 9.5 buds polyp⁻¹ when each polyp was fed 1 copepod d⁻¹, to an average total of 146.7 buds polyp⁻¹ when fed 8 copepods d⁻¹. The maximum daily production measured was 8 polyp buds and 22 medusae polyp⁻¹. The colonizing potential of this hydrozoan is great, given the high rates of asexual reproduction, fairly wide salinity tolerance, and existence of a cyst stage. Received: 29 October 1998 / Accepted: 3 March 1999     

A novel symbiosis between a cyanobacterium, Synechococcus sp., an aplastidic protist, Solenicola setigera, and a diatom, Leptocylindrus mediterraneus, in the open ocean

The abundance, biomass and distribution of Solenicola setigera, a colonial heterotrophic protist found only with the centric chain-forming diatom Leptocylindusmediterraneus, are reported for four major ocean basins. The distribution is cosmopolitan, and abundances and biomass are usually low (<500 colonies l⁻¹); however, in the summer of 1993, we observed a major biomass component (range = 5 to 31 μg C l⁻¹) in the surface waters of the North Atlantic attributable to S. setigera. These colonies of S. setigera were exceptionally large, and unusual in possessing high abundances of Synechococcus sp., a normally solitary cyanobacterium, embedded in the matrix covering the cells. We hypothesize that this relationship was mutually beneficial for both Solenicola setigera and Synechococcus sp. Received: 5 January 1998 / Accepted: 22 May 1998     

Determining prey availability for rock lobsters, Jasus lalandii : diver-sampling versus monochrome video photography

Accurate determination of diet is important in ecological studies. Many macrobenthic predators fragment their prey so finely that identification of component organisms is difficult. Knowledge of the food available to masticatory predators such as lobsters can help in determining potential prey and enhance the accuracy of dietary assessments. With SCUBA divers limited by depth and submersion time, benthic analyses are becoming increasingly reliant on camera systems. Here, based on paired samples, we assess the relative merits of using removal-sampling by divers versus monochrome video photography to determine the prey spectrum available to macrobenthic predators. We also relate the results to the gut contents of rock lobsters (Jasus lalandii) that were collected simultaneously. Diver samples took on average four times longer to collect and process than video-image samples. No significant differences were evident between the number of species identified in diver samples and video-image samples (n = 21 paired samples, Student's t = 0.233, P > 0.1), although an analysis of similarity (ANOSIM) test revealed that the results obtained from the two sampling methods were significantly different in terms of species composition (global R = 0.203, P < 0.01). Cluster analysis based on Bray–Curtis similarity to compare diver and video-image samples revealed four clusters of samples with <35% similarity, confirming that the two techniques do sample different assemblages of species. Video images detected and allowed identification of all species of prey recorded in the rock lobsters' stomach contents, probably because rock lobsters prey mainly on relatively large prey which are readily detected by video. Diver-sampling underestimated or failed to detect two important prey types, namely small barnacles and encrusting coralline algae. We concluded that the camera system employed was adequate for assessing the prey assemblages available to macrobenthic predators such as lobsters, and that it was considerably more economical than using divers. Received: 10 September 1998 / Accepted: 6 May 1999     

Reproduction and distribution of the invasive European fanworm Sabella spallanzanii (Polychaeta: Sabellidae) in Port Phillip Bay, Victoria, Australia

 The European fanworm Sabella spallanzanii (Gmelin, 1791) was recently introduced to Port Phillip Bay and is now a conspicuous component of most benthic communities. Reproduction of the worm was investigated in a population at Queenscliff over a 2 yr period (October 1995 to October 1997) using gonadal histology. The worms are dioecious (sex ratio 1:1, n=250), and attained sexual maturity at ∼50 mm body length. Reproductive periodicity followed a distinct annual cycle, and spawning proceeded through an extended autumn/winter period. Spawning was broadly synchronous between sexes, and coincided with falling seawater temperatures and shorter day-lengths. The females were highly fecund, and >50 000 eggs were probably shed from large females (>300 mm body length) during the annual spawning period. Breeding cycles of S. spallanzanii in Port Phillip Bay are ∼6 mo out of phase with endemic populations located at similar latitudes in the northern hemisphere. The spread of S. spallanzanii within Port Phillip Bay has been monitored by divers on an annual basis since 1994. The most recent dive survey (1998) indicates that S. spallanzanii has extended its range through out the entire 2000 km² embayment, and has invaded most subtidal habitats. Quantitative estimates of S. spallanzanii abundances were highest on pier pylons (12.5 individuals m⁻², 0.5 to 7 m depths). On sediments, estimates were highest at shallow sites (0.3 m⁻², 7 m depth), but numbers declined significantly with depth (0.1 m⁻², 17 to 22 m depth). Mean worm lengths and biomass were, by contrast, significantly higher at intermediate depths (12 to 17 m) than in shallower (7 m) or deeper (22 m) locations. S. spallanzanii demonstrates a clear preference for growth in sheltered, nutrient-enriched waters, so it may not spread from Port Phillip Bay into the adjacent oceanic waters of Bass Strait; however, in view of S. spallanzanii's current high abundance, fecundity and extended spawning periodicity, there is a high risk of future range expansions, mediated by shipping, into other temperate-water ports. Received: 17 November 1998 / Accepted: 6 January 2000     

Zooplankton growth rates: the influence of size in nauplii of tropical marine copepods

Growth rates and development times were determined for nauplii of the genera: Acartia, Centropages, Corycaeus, Oithona, Paracalanus, Parvocalanus and Temora in nearshore waters of Jamaica from in situ microcosm incubations. At these high local temperatures (∼28 °C), total naupliar development time was short: 3 to 4 d inshore and 4 to 5 d offshore. Mean instantaneous growth rates (g) ranged from as high as 0.90 d⁻¹ for Parvocalanuscrassirostris to as low as 0.41 d⁻¹ for Corycaeus spp. In general, nauplii of cyclopoid copepods appeared to grow more slowly than those of calanoids of the same size. Naupliar growth rates were significantly related to body size (r ²= 0.43 to 0.50), but were unrelated to chlorophyll concentration in any measured size-fraction. This suggests that nauplii are generally not limited by resources, but are growing at their maximum temperature and size-dependent rates. Received: 30 May 1997 / Accepted: 13 May 1998     

Zooplankton growth rates: the influence of size and resources in tropical marine copepodites

Growth rates were determined for copepodites of the genera: Acartia, Centropages, Corycaeus, Oithona, Paracalanus, Parvocalanus and Temora in nearshore waters of Jamaica from in situ microcosm incubations. At these high local temperatures (∼28 °C), total copepodite development time was as short as 4 to 5 d. Mean instantaneous growth rates (g) ranged from as high as 1.2 d⁻¹ to as low as 0.1 d⁻¹. In general, cyclopoid copepods appeared to grow more slowly than calanoids of the same size. Enhancement of resources by nutrient addition caused a 32% increase in growth rates in experiments from a mesotrophic site, but only a 17% increase at a more eutrophic site. Additionally, copepodites at both sites showed faster development and generally larger size at stage in response to nutrient addition. Growth rates were positively related to chlorophyll concentration in the >2 μm size-fraction. A significant relationship of growth rate to body size (r ² = 0.45) emerged across a wide range of trophic status, but it was confounded with resource availability. It appears that growth in tropical copepod copepodites may be frequently limited by resources in a size-dependent manner. Received: 30 May 1997 / Accepted: 13 May 1998     

Spatial and temporal pattern in seagrass community composition and productivity in south Florida

We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites, delimiting 12,800 km² of seagrass beds in the 17,000-km² survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km². The range of T. testudinum was almost as extensive (6,400 km²), followed by Syringodium filiforme (4,400 km²), Halodule wrightii (3,000 km²) and Halophila engelmanni (50 km²). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m⁻²day⁻¹, with a range of 0.05–3.29 g m⁻² day⁻¹. Specific productivity ranged between 3.2 and 34.2 mg g⁻¹ day⁻¹, with a mean of 18.3 mg g⁻¹ day⁻¹. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 10¹⁰ g S. filiforme, which translate to a yearly production of 9.4 × 10¹¹ g T. testudinum leaves and 2.4 × 10¹¹ g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as a benchmark against which future change in the system can be quantified. Received: 30 January 2000 / Accepted: 24 July 2000     

Carbon and nitrogen exchange between sandy beach clams (Donax serra) and kelp beds in the Benguela coastal upwelling region

Carbon consumption and nitrogen requirements were estimated for populations of the sandy beach bivalve Donax serra on nine beaches of the west coast of South Africa. Subtidal populations composed mainly of adult clams were responsible for the bulk of standing stock (3538 g C m⁻¹), annual carbon consumption (13 444 g C m⁻¹ yr⁻¹), faeces production (6478 g C m⁻¹ yr⁻¹ ) and nitrogen regeneration (2525 g N m⁻¹ yr⁻¹). Kelp detritus, bacteria and kelp consumers' faeces available in the water column surpass several times the carbon and nitrogen requirements of intertidal and subtidal clam populations. Individual Donax serra pop ulations, in turn, may regenerate up to 3.2% of the total nitrogen requirements of all primary producers from kelp beds and 14% of the requirements of phytoplankton. These high standing stocks of clams are presumably supported mainly by organic matter originating from kelp which, in contrast to phytoplankton, is in constant supply and comprises the largest proportion of the annual production of particulate organic matter on this coast. Wide and shallow continental shelves with gentle slopes probably limit the penetration of upwelled waters to the nearshore waters, decreasing the influence of external inputs and increasing the importance of internal flows of nutrients and carbon within the nearshore zone. In this context, sandy beaches, rocky shores and kelp beds may be more closely interlinked compartments of a larger ecosystem encompassing the whole nearshore than traditionally thought. Received: 28 August 1996 / Accepted: 7 October 1996     

Nuclear ITS region of the alga Heterosigma akashiwo (Chromophyta: Raphidophyceae) is identical in isolates from Atlantic and Pacific basins

The internal transcribed spacer (ITS) region from 19 isolates of the algal genus Heterosigma (Chromophyta: Raphidophyceae) was amplified by polymerase chain-reaction (PCR) and sequenced. Isolates were obtained from both the Atlantic and Pacific basins, including Europe, eastern North America, western North America, Japan and New Zealand. This study presents evidence that all Heterosigma isolates in this study are representatives of one species (H. akashiwo). All 19 isolates, except one (LB 2005) had identical ITS sequence (98.31% similar by pairwise comparison); Isolate LB 2005 may represent a separate subspecies. Such high degree of ITS sequence identity implies that the organism has spread between oceanic regions in geologically recent times, possibly by human means. In addition to those from Heterosigma spp., the ITS regions from other marine Raphidophyceae (Chattonella antiqua, C. marina, C. subsalsa, Fibrocapsa japonica, and Olisthodiscus luteus) were amplified and sequenced using PCR. Total ITS lengths differed among the Raphidophyceae (C. antiqua, 577 base pairs (bp); C. marina, 577 bp;. C. subsalsa, 579 bp; F. japonica, 830 bp; H. akashiwo, 561 and 563 bp; O. luteus, 829 bp), but 5.8S rDNA sequences were similar in size (13 to 142 bp). The high ITS sequence identity between C. antiqua and C. marina (>99.9% by pairwise comparison) suggests the need for a taxonomic review of these species encompassing all morphological, genetic, physiological and biochemical information. Additionally, a number of cultures of Raphidophyceae were positively identified. In general, ITS comparisons among the Raphidophyceae may be most useful at the level of species determination rather than at the population level. Received: 12 July 1999 / Accepted: 16 March 2000     

Allozyme variation in global populations of striped mullet, Mugil cephalus (Pisces: Mugilidae)

The striped mullet, Mugil cephalus Linnaeus, 1758, is one of the few species of marine shore fish with a worldwide circumtropical distribution. Because of this distribution and the dependency of M. cephalus on coastal waters during various phases of its life cycle, as well as nearshore living habits, questions have been raised regarding levels of genetic divergence and gene flow among transoceanic populations. To cast more light on this, allozyme variation at 27 presumptive gene loci was investigated in ten globally diverse populations. The observed heterozygosity ranged from 0.018 (Hawaii) to 0.081 (Florida), averaging 0.050. The proportion of polymorphic loci showed a similar trend. Several populations were characterised by fixed allelic differences. Estimated gene diversities were very high, the allele frequency variation among populations was found to be 68%; genetic distances reached 0.242, with an average of 0.117. Estimated rates of gene flow were high among Mediterranean populations (Nm = 7.26), and between Mediterranean and East Atlantic populations (Nm= 2.86), but extremely low between non-contiguous populations within the Indian, Pacific and Atlantic Oceans, where Nm ranged from 0.03 to 0.05. Received: 7 April 1997 / Accepted: 4 February 1998     

RAPD-PCR investigations of systematic relationships among four species of eels (Teleostei: Anguillidae), particularly Anguilla anguilla and A. rostrata

 We examined the genetic identities of 49 individuals of four species of eels in the genus Anguilla Shaw, A. anguilla, A. japonica, A. reinhardti and A. rostrata, using the random(ly) amplified polymorphic DNA (RAPD)-PCR technique. We used 15 random decamer primers. Out of the 22 148 amplification products detected, 454 markers were evaluated using Nei's distance coefficient, two numerical methods (neighbor-joining, UPGMA), and phylogenetic analysis using parsimony (PAUP). Both numerical and parsimony methods were congruent and confirmed the specific status of all four examined Anguilla species. In all dendrograms, all individuals of each of the species clustered together within four closed groups with highly significant bootstrap values (between 97 and 100%). Additionally 1 to 18 species-specific monomorphic diagnostic fragments were detected in three of the species; none were detected in A. anguilla. Mean interspecific genetic distances ranged from 0.384 to 0.559, with the minimum between A. anguilla and A. rostrata and the maximum between A. anguilla and A. reinhardti. Individuals collected at one locality and belonging to a single species did not cluster together, and neither were any diagnostic monomorphic fragments found for individuals of single localities. This probably reflects a random dispersal of larvae in ocean currents before they reach coastal waters. Among all possible species pairs, only the two Atlantic species were consistently clustered in all dendrograms, with highly significant bootstrap values (100%). Additionally, we detected ten diagnostic markers for this pair of eel species. From RAPD data, we suggest a phylogram which was routed by the descending analysis method: A. reinhardti appears to have been the first species to diverge from a putative common ancestor of the four eel species. Later, A. japonica separated from the hypothetical ancestor of the Atlantic species, which then split recently into A. anguilla and A. rostrata. The close relationship of A. anguilla and A. rostrata is indicated by their low genetic distance (GD = 0.384) and a high degree of shared RAPD fragments (SF = 71.2%); this compares with the following means for all other species pairs: ( = 0.531,  = 44.2%). The prerequisites for using RAPD data for the reconstruction of phylogenies are discussed. Received: 2 September 1999 / Accepted: 8 May 2000     

Sequence divergence of mitochondrial DNA indicates cryptic biodiversity in Octopus vulgaris and supports the taxonomic distinctiveness of Octopus mimus (Cephalopoda: Octopodidae)

DNA sequence diversity of octopods was investigated using the mitochondrial cytochrome oxidase III gene (mtCOIII). DNA was obtained from ethanol- or formalin-fixed tissue of 15 specimens belonging to Octopus mimus Gould, 1852, Octopus vulgaris Cuvier, 1797 and Scaeurgus unicirrhus d'Orbigny, 1840, from coastal waters of the Mediterranean (France), the southwestern Atlantic (Brazil), the Caribbean (Costa Rica) and the southeastern/tropical Pacific (north Chile/Costa Rica). A 612 bp fragment of the mtCOIII gene was sequenced and aligned to the orthologous sequences available from northeastern Pacific Octopus species. Possible phylogenetic relationships were reconstructed. The mtCOIII gene tree revealed two main clusters, one comprised O. rubescens, O. dofleini and O. californicus, while the other included all O. vulgaris specimens, O. bimaculatus, O. bimaculoides and O. mimus. With one exception all South American haplotypes including O. bimaculatus and O. bimaculoides appeared as the sister group of the Mediterranean haplotype of O. vulgaris, indicating that most of the South American O. vulgaris specimens investigated would not belong to the recently redescribed species O. vulgaris restricted to the Mediterranean and eastern Atlantic. The treatment of O. mimus as a species distinct from Mediterranean O. vulgaris is supported by a high nucleotide divergence of 12.7%. Based on the mtCOIII gene tree the existence of cryptic species among O. vulgaris-like octopods is suggested. Received: 15 January 1999 / Accepted: 15 October 1999     

Evidence of limited gene flow in three species of coral reef fishes in the lagoon of New Caledonia

Allozyme variation was used to investigate the genetic structure of the coral reef fishes Stegastes nigricans, Epinephelus merra and Acanthurus triostegus around New Caledonia. Each species was sampled from each of three sites in the ≃1000 km circumference of the lagoon of New Caledonia. Allelic variation was recorded for each species at 14, 13 and 17 loci, respectively, and heterozygosity diversity (H s) was 0.082, 0.065 and 0.116, respectively. Analysis of genetic differentiation between sites produced inconsistent results between species, with spatial heterogeneity in two species (S. nigricans, F st  = 0.038; A. triostegus, F st = 0.049) and homogeneity in one species (E. merra, F st = 0.000). Hydrological and climatic data from the lagoon suggest that the eastern and western sides of the lagoon are isolated, since they lie in water masses of different origin. This may explain the genetic differentiation and restricted gene flow found at a local scale for S. nigricans and A. triostegus. Homogeneity in populations of E. merra is discussed in relation to its low genetic diversity and its reproductive behaviour. Received: 23 April 1997 / Accepted: 25 September 1997