Nearshore distributional gradients of larval fish (15 taxa) and planktonic crustaceans (6 Taxa) in Hawaii

Fifteen taxa of fish larvae (most identified to species) and 6 taxa of crustaceans (most identified to species) were studied in zooplankton samples collected 0.2, 0.5, 1.0 and 3.0 km off the leeward coast of Oahu, Hawaii in May and July 1975. The following distributional patterns were elucidated: inshore (2 spp); inshore-neritic (2 spp); neritic (7 spp); and offshore-neritic (7 spp). Three of these 18 species had age-related differences in behaviour that led to age-dependent distributional patterns, and 4 further species had a random distribution. All abundant types of fish larvae were either oceanic as adults or were hatches from the demersal or brooded eggs of reef species. The larvae of reef fishes with pelagic eggs were not abundant in the nearshore region sampled and were probably to be found more than 3 km offshore. The offshore-neritic distributional pattern evidently resulted from relatively passive movement with currents. In contrast, maintenance of inshore and neritic patterns probably required relatively active swimming by the animals. The current regime, including a tidal eddy and possible nearshore upwelling, probably helped maintain the inshore and neritic patterns of such animals. The limited area occupied by these inshore coastal plankton communities could make them particularly vulnerable to environmental changes, including anthrogenic ones.     

Comparative persistence of marine fish larvae from pelagic versus demersal eggs off southwestern Nova Scotia,Canada

Two groupings of larval fish were repeatedly identified by principal component analyses of larval densities from four broad-scale surveys during the spring and summer of 1985–1987 off southwestern Nova Scotia, Canada. Larvae originating from pelagic eggs (four species within Gadidae and Pleuronectidae) constituted one group, which were uniformly distributed over the sampling area with densities not correlated with bathymetry, although nearly all spawning occurs on the shallow western cap of Browns Bank, 100 km offshore. Larvae from demersal eggs (five species within Pholidae, Stichaeidae, Cottidae, Agonidae) constituted the second group, which dominated the shallow-water environments both inshore and on Browns Bank. Lower patchiness indices were evident amongst larvae from pelagic eggs in small and large sampling-gear collections (average 3.4 and 3.1, respectively) compared to fish hatching from demersal eggs (average 5.1 and 4.6). Fine-scale nearshore surveys over a 5 wk period in 1987 also showed that larvae of demersal eggs had a less variable distribution along an inshoreoffshore transect. Larvae from demersal eggs appear spatially persistent through the release of well-developed larvae from non-drifting eggs. These conclusions are consistent with other studies over a range of spatial scales in temperate and tropical environments, demonstrating that single-species models of larval dispersal are inadequate to account for the distributional patterns of larval fish in general.     

Horizontal distribution patterns of presettlement reef fish: are they influenced by the proximity of reefs?

The distribution patterns of presettlement reef fish and how they were influenced by the proximity of reefs were investigated off the coast of Northland, New Zealand, from 1981–1986. We used ichthyoplankton tows and visual counts of fish. Distributions of presettlement fish of some species were influenced by the proximity of reefs, regardless of whether reefs were on the coast of the mainland or islands across the shelf. Presettlement fish of families that lay demersal eggs were most abundant near reefs: Gobiescocidae, Acanthoclinidae, Tripterygiidae, Eleotridae, and Gobiidae. The distribution of presettlement sparids, mullids (pelagic eggs), and blenniids and monacanthids (demersal eggs) was not determined in a predictable way by the proximity of reefs. High-frequency sampling over three days suggested that patches of presettlement sparids of 1 to 2 km in dimension may move quickly through a study area. High abundance of presettlement gobiescocids and tripterygiids were found in 0 to 2 m of water over rocky reefs at high and low tides. Presettlement eleotrids were associated with reefs in deeper water (3 to 20 m) and in some habitats with aggregations of mysids. The lack of general patterns of distribution for presettlement reef fish suggests that modelling patterns of drift of these fish as a single group is inappropriate; this concurs with evidence from tropical waters.     

Spatial patterns of ichthyoplankton distribution in relation to hydrographic features in the Northern Benguela region

The spatial distribution of the most abundant eggs and larvae of teleost fish species on the continental shelf and slope off the northern Benguela region was studied in April 1986. The horizontal and vertical distribution of eggs and larvae were analysed together with environmental data, in order to determine patterns of ichthyoplankton distribution. Both species composition and relative egg and larval abundance levels exhibited important latitudinal differences during a period of quiescent upwelling with an intense intrusion of Angolan water into the system. Larval diversity was higher in the northern part of the study area, where, because of the intrusion of the warmer Angolan water, the water column was more stratified than in the southern part, where the affect of upwelling of South Atlantic Central Water was continuous and only a few species spawned. The frontal zone appeared to be a nursery ground for the most important pelagic species of the region:Trachurus trachurus capensis, Engraulis capensis, andSardinops ocellatus. Vertical egg and larval distributions showed evidence of stratification, with highest concentrations located in the uppermost 50 m. In comparison, during periods of intense upwelling, longitudinal gradients were responsible for the horizontal distribution of ichthyoplankton, and the vertical distribution of eggs and larvae were much more extensive because of the greater mixing of the water column.     

FADs influence on settlement and dispersal of the young-of-the-year greater amberjack (<Emphasis Type="Italic">Seriola dumerili</Emphasis>)

FADs are fish aggregating devices applied worldwide over the centuries to increase fish catch. However, the utilisation of such floating devices can influence dispersion patterns of some fish species. At present it is still not clear if FADs play a role in the shoreward migrations of juvenile fish of reef associated species, such as the greater amberjack Seriola dumerili. In this study, we hypothesised that FADs located along a distance gradient from the shore might lead the greater amberjack inshore. In such case, mean abundance of S. dumerili should decrease over time in offshore FADs and increase in inshore FADs. To test the hypothesis three FAD systems were positioned in the Gulf of Castellammare (Sicily, Italy), between July and September 2001, at increasing distances from the coast. During the study period, five visual censuses were carried out within FADs fields. During the first sampling period, no significant difference in abundance and size of juvenile S. dumerili was found between the three FAD systems. All the other sampling periods reported higher abundances and sizes in the offshore FADs than in the two inshore FADs. The findings suggest that FAD systems might be exerting two different effects on young of the year (YOY) S. dumerili distribution: (a) offshore FADs tend to retain associated fish for longer periods of time, (b) coastal FADs favour the transition of YOY S. dumerili from the pelagic to the benthic domain.     

Fine-scale distribution of larval fishes: patterns and processes adjacent to coral reefs in Kaneohe Bay,Hawaii

Plankton samples were taken from January to June 1987 in Kaneohe Bay, Oahu, Hawaiian Islands, with a free-fall plankton net, to investigate the fine-scale distribution of larval fishes around coral reefs. Daytime samples indicated that the postflexion larvae of two gobiids (Psilogobius mainlandi and an unidentified species) were significantly more abundant at stations immediately adjacent to reefs (near-reef) than at stations in open water off the reef (off-reef). These postflexion gobiid larvae appeared to be capable of resisting advection and dispersal while remaining in the water column near suitable adult habitats. The larvae of Foa brachygramma (Apogonidae) and Encrasicholina purpurea (Engraulidae) were significantly more abundant at off-reef stations than at near-reef stations. Nighttime samples indicated that the gobiid larvae depend on visual cues to remain near the reef. The horizontal distributions of F. brachygramma and E. purpurea larvae appeared to be related to their vertical positioning. These data suggest that typical ichthyoplankton surveys which do not sample close to adult fish habitats would greatly underestimate the abundances of larvae such as the gobiids.     

Vertical structure of very nearshore larval fish assemblages in a temperate rocky coast

Small-scale vertical patterns of larval distribution were studied at a very nearshore larval fish assemblage, during the spring–summer period of several years, at two depth strata (surface and bottom) using sub-surface and bottom trawls. A total of 4,589 larvae (2,016 from surface samples and 2,573 from bottom samples) belonging to 62 taxa included in 22 families were collected. Most larvae belonged to coastal species. Although inter-annual variations in larval density and diversity could be found, total larval abundance was always higher near the bottom whereas diversity was higher at the surface. A marked distinction between the structure of surface and bottom assemblages was found. Sixteen taxa explained 95% of the similarity among surface samples. Larvae which contributed most to this similarity included species like clupeiformes, sparids and serranids, and also blenniids, tripterygiids and some labrids. In the bottom samples, fewer species were present, with only six taxa, almost exclusively from species which lay demersal eggs, contributing to 95% of the similarity between samples. Larvae present at the surface were significantly smaller than at the bottom. For some of the most abundant species found at the bottom, only small larvae occurred at the surface while the whole range of sizes was present at the bottom, indicating that larvae may be completing the entire pelagic phase near the adults’ habitat. These results indicate that larval retention near the reefs probably occurs for these species, although for others dispersal seems to be the prevailing mechanism.     

Temporal and spatial settlement patterns of sympatric hermit crabs and the influence of shell resource availability

Larvae of marine organisms often need specific resources or environments at settlement, and their success at settlement might be strongly influenced by the abundance and distribution of such specific resources. The larvae of hermit crabs need small shells to settle, so it is thought that the distribution and abundance of small shells influence the settlement pattern of hermit crabs. To investigate the influence of small shell distribution on the settlement of pagurid hermit crab larvae, we conducted a field experiment at an intertidal rocky shore in Hakodate Bay, Japan. From the line-transect sampling in the field, we found that Pagurus middendorffii settled extensively in the offshore side of the intertidal zone while P. nigrofascia settled in the uppermost area of the intertidal zone. Small shells were most abundant in a narrow shallow trough, slightly offshore from the uppermost area of the intertidal zone. For both species, settler abundance was high where adults were abundant, but settler abundance did not appear to be related to shells abundance. An experiment to clarify settlement patterns showed that larval recruits tended to be similar to those in the line-transect sampling of settlers. Thus shells may not be a primary factor affecting settlement patterns at relatively large scale within the intertidal flat. However, when we analyzed the relationship of settlers and shells separately within each transect, the distribution of settlers was well explained by shell resource availability. Therefore on a smaller scale, shell availability may influence the number of settlers. Settlement periods of P. middendorffii and P. nigrofascia fully overlapped, so their larvae probably were affected by similar transport factors, such as current and tidal movement. Nevertheless they showed different spatial patterns of settlement.Communicated by T. Ikeda, Hakodate     

Unexpected reproductive strategy of Sardinella aurita off the coast of Venezuela

Biological sampling of Spanish sardine (Sardinella aurita Valenciennes, 1847) off the coast of Venezuela from 1956 to 1989 was used to study the reproductive strategy and migration pattern of the population. Whereas in many pelagic fishes the energy re-allocation necessary for reproduction usually occurs optimally at the end of the upwelling season when planktonic production reaches a maximum, in the present study a 5 mo delay was observed. This suggests that energy was stored as lipids early in the season and released later via metabolism for gamete production. Major reproduction did not occur in an area and at a time when offshore transport and turbulence were low, which is also unusual for a pelagic fish species. These results are discussed in terms of the life cycle of the Spanish sardine and its possible migratory patterns. The reproductive strategy of this population apparently gives priority to optimising food availability for the offspring and not to preventing eggs and larvae being transported offshore. The presence of “retention” areas could explain this unexpected strategy. Received: 4 November 1996 / Accepted: 20 December 1996     

The distribution of herbivorous fishes on the Great Barrier Reef

The composition and functionality of ecologically important herbivorous fish assemblages were examined throughout much of Australia’s Great Barrier Reef (GBR). Diversity and abundance of surgeonfishes (Acanthuridae), parrotfishes (Labridae) and rabbitfishes (Siganidae) were strongly associated with position on the continental shelf, whilst effects of latitude were weaker and inconsistent. Species distributions varied considerably amongst taxonomic groups; parrotfishes were mostly widespread whilst distributions of surgeonfishes were often restricted. Most inshore environments supported depauperate herbivore assemblages dominated by different taxa and functional groups compared with assemblages in offshore environments. There were also strong cross-shelf transitions in the main taxa performing each functional role. Overall, this study show that the functional contributions of herbivorous fish assemblages to important ecosystem processes and the contributing taxa vary considerably amongst different GBR environments. Additionally, the two most numerically dominant herbivores actively select detritus, not algae, supporting increasing evidence for the importance of detritus in coral reef ecology.     

Dynamics of parrotfish grazing scars

Parrotfishes exhibit a range of feeding modes. These species vary in both feeding morphology and behaviour, but the vast majority of species leave distinctive scars on the substratum when feeding. Although the role of parrotfishes in reef resilience is well documented, the basis of this role and the effect of their grazing scars on the benthic community structure remain unclear. This study evaluated the dynamics of grazing scars of large adult Scarus rivulatus and Chlorurus microrhinos on an inshore reef in the Great Barrier Reef (GBR). These species represent the most abundant scraping and excavating parrotfish species on inshore reefs. Grazing scars of each species were marked, measured and observed for seven consecutive days. S. rivulatus grazing scars were smaller in area and volume and more rapidly reoccupied by algae than those of C. microrhinos. However, because of the higher abundance and feeding frequency of S. rivulatus at the study site, this species had higher algal removal rates than C. microrhinos. These species appear to play distinctly different functional roles in shaping the benthic community of inshore GBRs. S. rivulatus is primarily responsible for algal dynamics dominated by vegetative regrowth. In contrast, C. microrhinos opens relatively large areas which remain clear for several days. These scars may represent settlement sites which are relatively free from algae and sediment. This study provides new information on the differences between scraping and excavating parrotfishes and, in a system with just one abundant large excavating species, emphasizes the potential for low functional redundancy in high diversity coral reef systems.     

Larval fishes in the zooplankton community of the North Pacific Central Gyre

Patterns of species structure are described for the larval fish assemblage in the North Pacific Central Gyre. About 30,000 larvae, primarily of mesopelagic fish species, were identified for 7 cruises. Samples were collected using Isaacs-Kidd plankton trawls on 6 cruises over a 4 1/2 year period; stratified samples were taken with an opening/closing bongo net on one late-summer cruise. Data on absolute and relative abundances, size ranges and summertime depth distributions of over 150 species of larvae are presented. The depth distribution and abundance of the ichthyoplankton are compared to those of the total zooplankton community. The larval assemblage is also examined with respect to the known adult mesopelagic fish assemblage. Seasonal changes in ichthyoplankton species structure occur but, within seasons, species structure is remarkably constant from year to year. Despite seasonal changes in species abundance and rank order of abundance, a constant cumulative frequency structure was found to exist in the ichthyoplankton, both between seasons and between years. The implications of this result are discussed in light of similar findings in a terrestrial community and with respect to possible mechanisms of regulation.     

Larvae of benthic invertebrates in hydrothermal vent plumes over Juan de Fuca Ridge

Larvae of benthic invertebrates collected in the water column above Juan de Fuca Ridge show distinct variations in abundance and composition in, and away from, the neutrally-buoyant hydrothermal plume emanating from underlying vents. Larvae of vent gastropods (Lepetodrilus sp. and two peltospirid species) occur in significantly higher abundances in the plume than away from it (mean abundance=21.0 individuals 1000 m^?3 vs 1.4 individuals 1000 m^?3), and larvae of vent bivalves (Calyptogena? sp.) occur exclusively in the plume (mean abundance=0.5 individuals 1000 m^?3). Larvae from other benthic taxa known not to be endemic to Juan de Fuca vent communities, such as anthozoans, pholad clams, bryozoans and echinoderms, are less abundant in the plume than away (mean abundance=47.5 vs 16.9 individuals 1000 m^?3) at comparable depths and heights above the bottom. These results support the hypothesis that larvae of vent species are entrained into buoyant hydrothermal plumes and transported at the level of lateral spreading several hundred meters above the seafloor. The discovery of vent-associated larvae in the plume suggests that models used to predict hydrodynamic processes in the plume will also be useful for modeling larval dispersal. Advanced imaging and new molecular-based approaches will be required to resolve taxonomic uncertainties in some larval groups (e.g. certain polychaete families) in order to distinguish vent species and make comprehensive flux estimates of all vent larvae in the neutrally-buoyant plume.     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Age and growth rate determinations for the Atlantic surf clam Spisula solidissima (Bivalvia: Mactracea), based on internal growth lines in shell cross-sections

Marked and recovered surf clams, Spisula solidissima Dillwyn, from Virginia (USA) deposited one internal growth line during a period of 11/2 years, probably in response to spawning during late summer. We have used these annual growth lines to make growth curves for two samples of New Jersey (USA) clams, one from inshore (1.8 km from shore, 15 m deep), the other from offshore (17.5 km from shore, 28 m deep) waters. The offshore and inshore clams grow at approximately the same rate until Age 3 years, after which time the growth rates differ, as does the ultimate lifespan; the offshore clams grow more rapidly and attain a greater age — up to 31 years. Comparison of our growth curves with other published curves revealed a close correspondence to a curve which was based on a study of growth over a 5-year period. Curves based on external growth lines probably underestimate growth rate in early life and overestimate it in later years.     

Small-scale genetic structure in a marine population in relation to water circulation and egg characteristics

Until the last decade it was assumed that most marine species have pronounced gene flow over vast areas, largely because of their potential for dispersal during early life stages. However, recent genetic, modeling, and field studies have shown that marine populations may be structured at scales that are inconsistent with extensive dispersal of eggs and larvae. Such findings have stimulated the birth of new studies explaining the mechanisms that promote population structure and isolation in the oceans, in the face of high potential for dispersal. Here we study the vertical and horizontal distribution of cod (Gadus morhua) eggs in relation to small-scale circulation and water column hydrography in a coastal location of southern Norway. Previous studies conducted in this region have shown that cod populations inhabiting fjord locations, which are on average 30 km apart, are genetically differentiated, a remarkable outcome considering that Atlantic cod have pelagic egg stages and long pelagic larval duration. We document that cod eggs are found in greater abundance in shallow water layers, which on average are flowing up the fjord (away from the open ocean), and in the inner portion of the fjord, which is subject to lower current speeds compared to the outer or mouth of the fjord. Eggs were found to be neutrally buoyant at shallow depths, a trait that also favors local retention, given the local circulation. The same patterns held during two environmentally contrasting years. These results strongly suggest that population structure of Atlantic cod is favored and maintained by a balance between water circulation and egg characteristics.     

Offshore marine cheilostome Bryozoa from Fort Lauderdale,Florida

Cheilostome Bryozoa were collected upon marine fouling test panels exposed offshore from Fort Lauderdale, Florida, USA between 1961 and 1967. Panels were exposed at certain depths, ranging from the surface to the bottom, in several arrays extending to a distance of 4 miles offshore. Twenty-three species were identified from the 114 panels recovered and examined. Most species were found on panels in shallow water, or on panels near the bottom in deeper, offshore water. A notable exception was a large, arborescent colony of Biflustra savartii which engulfed a panel 50 feet (15 m) deep, 4 miles from shore, in the Florida current. The lack of cheilostome Bryozoa on shallow and mid-water panels at the offshore, deepwater stations was apparently due to the low number of larvae reaching them from the distant inshore colonies.     

Regional differences in duration of the planktonic larval stage of reef fishes in the eastern Pacific Ocean

Regional variation in the duration of the planktonic larval phase of three species of reef fishes, Thalassoma lucasanum (Labridae), Stegastes flavilatus, and Microspathodon dorsalis (Pomacentridae) was investigated between 1982 and 1991 at several sites in the tropical eastern Pacific over a distance of 3500 km, encompassing virtually their entire range of distribution. Durations of the larval phase, determined from counts of daily otolith increments, were significantly different (1.3 to 1.6 x) between sites. Populations of all three species had a consistently shorter larval life at the most northern site, Cabo San Lucas (Mexico) compared to Panamá and the offshore islands of Galápagos and Cocos. Analyses of otolith increment width over the precompetent period revealed that this disparity in larval duration primarily reflected differences in larval growth rates: faster growing fish spent less time in the plankton. In T. lucasanum, some of the variation in larval duration between Panamá and offshore sites (Galápagos Islands and Cocos Island) may be accounted for by a higher frequency of individuals delaying metamorphosis at the offshore sites. These data indicate that conditions in the planktonic environment are not homogeneous throughout the tropical eastern Pacific and may have a profound effect on aspects of the larval ecology of reef fishes in this region.     

Distribution of squid paralarvae, <Emphasis Type="Italic">Loligo opalescens</Emphasis> (Cephalopoda: Myopsida), in the Southern California Bight in the three years following the 1997–1998 El Niño

Large numbers of paralarvae of the California market squid, Loligo opalescens (10,560 paralarvae from 422 plankton samples), were collected in the Southern California Bight in 1999, 2000, and 2001 during the spawning season. Paralarval abundance increased dramatically (P<0.0041) from 1.5 squid/1,000m³ in 1999 to 77.9 squid/1,000m³ in 2000, and 73.6 squid/1,000m³ in 2001, following the El Niño of 1997-1998. The effects on the squid fishery of the 1997-1998 El Niño were thus extended for two years, with larval abundance reduced until the 1999-2000 spawning season. Paralarvae were abundant close to shore for up to a month after hatching in 2000 (P<0.003), with tidal surface currents adjacent to shore in the Channel Islands strongly affecting paralarval abundance. Tidally reversing currents within 1-3 km of shore created a boundary layer of "sticky water" within which paralarvae remained entrained inshore immediately after hatching. Neritic currents farther from shore dispersed older paralarvae within the Southern California Bight. The greatest change in paralarval abundance, for all transects, was observed within 1 km of the transition between these two flow regimes. Age of paralarvae (from statolith increments) entrained within the Catalina Island boundary layer averaged 13-16 days, but some individuals remained nearshore for up to a month. Paralarvae in the boundary layer occurred above 80 m depth both day and night, and exhibited a statistically significant pattern of vertical diel migration (P<0.01). Paralarvae at sea were disproportionately abundant adjacent to fronts associated with uplifted isotherms.     

The “pelagic larvaton” and its role in the biology of the World Ocean,with special reference to pelagic larvae of marine bottom invertebrates

Ecological subdivision of marine organisms is often based on two characteristics: presence in a defined environment, and types of locomotion (degree of free active movement) in such an environment. The use of these characteristics results in a simple scheme: (1) Inhabitants of the boundary surface “ocean-atmosphere” (a zone including not only the surface film but also the thin subsurface water layer below it and the air layer just above it, i.e., pleuston and neuston). (2) Inhabitants of the deeper water layers of the ocean i.e., excluding the zone mentioned under (1): (a) passively drifting forms with very limited locomotory capacity, moving practically in the vertical plane only (plankton); (b) actively moving forms which migrate both vertically and horizontally (nekton). (3) Inhabitants of the “bottom”-benthos (level-bottom of oceans and coastal waters, tidal zones up to the upper supralittoral, different types of drifting and floating substrata, e.g. ship bottoms, harbour structures, buoys, driftwood, sargassum, whales, etc.). This simple scheme is essentially based on characteristics of adults. If developmental stages are considered, pelagic larvae of bottom invertebrates, eggs and larvae of fishes and other forms, usually present only temporarily in the plankton, neuston, and pleuston, can be distinguished as “mero-plankton”, “mero-neuston” and “mero-pleuston”, from the permanent “holo”-components of these groups. Division into “mero”-subgroups opposes all these larvae to those of planktonic, neustonic and pleustonic forms developing within the “parental” groups and their environments. However, the last category of larvae in the light of world-wide distribution of the seasonal reproductive pattern of marine invertebrates and some other organisms — especially in temperate and high latitudes — can also be rated to some degree as “mero”-(not “holo”-) components. The present paper proposes to unite all larvae of marine invertebrates (and of other organisms) undergoing pelagic development into one biological group, the “pelagic larvaton”. The main characteristic for all forms of this group is the presence of one and the same life-cycle stage in one and the same environment. All forms of the “pelagic larvaton” are, to various degrees, biologically different from their respective adult forms. Even the pelagic larvae of the holoplanktonic species exhibit some differences. Within the “pelagic larvaton”, 3 subgroups can be distinguished on the basis of their ecological peculiarities;

1. Larvae undergoing their whole development in an environment different from that inhabited by their parents and belonging to a group different from that of their parental forms; e.g. the pelagic larvae of bottom invertebrates which develop in the plankton, neuston or pleuston.
2. Larvae undergoing development in the same general pelagic environment, but in “non-parental” ecological groups; e.g. larvae of nektonic species developing in the plankton, neuston or pleuston; larvae of planktonic species in the neuston or pleuston; larvae of neustonic and pleustonic species in the plankton.
3. Larvae undergoing development in the “parental” groups; e.g. larvae of planktonic species in the plankton, of neustonic species in the neuston, or of pleustonic species in the pleuston.

In contrast to the 5 ecological groups: benthos, plankton, nekton, neuston and pleuston, the “pelagic larvaton” represents rather a biological than an ecological group. The “pelagic larvaton” comprises the 5 ecological groups and maintains the permanent turnover of organic substances between water and bottom. This group short-circuits the interrelations between the 5 ecological groups in all possible combinations. The existence of the “pelagic larvaton” presents another illustration of the unity of the biological nature of the oceans. The present paper also discusses the specific distributional patterns of the pelagic larvae of bottom invertebrates and their biological role in the seas.