Introduced and cryptogenic species in Port Phillip Bay, Victoria, Australia

Port Phillip Bay (PPB) is a large (1,930 km²), temperate embayment in southern Victoria, Australia. Extensive bay-wide surveys of PPB have occurred since 1840. In 1995/1996 the Commonwealth Scientific and Industrial Research Organization (CSIRO) Centre for Research on Introduced Marine Pests (CRIMP) undertook an intensive evaluation of the region with the aims of developing a comprehensive species list of native and introduced biota and contrasting previous bay-wide assessments with a current field survey in order to detect new incursions and discern alterations to native communities. Two methods were used to meet these aims: a re-evaluation of regional museum collections and published research in PPB to identify and determine the timing of introductions; and field surveys for benthic (infauna, epifauna and encrusting) organisms between September 1995 to March 1996. One hundred and sixty introduced (99) and cryptogenic (61) species were identified representing over 13% of the recorded species of PPB. As expected, the majority of these are concentrated around the shipping ports of Geelong and Melbourne. Invasions within PPB appear to be increasing, possibly due to an increase in modern shipping traffic and an increase in aquaculture (historically associated with incidental introductions); however the records of extensive biological surveys suggest that this may, in part, be an artefact of sampling effort. In contrast to Northern Hemisphere studies, PPB (and Southern Hemisphere introductions in general) have significantly different suites of successfully invading taxa. PPB is presented as one of the most invaded marine ecosystems in the Southern Hemisphere.Communicated by M.S. Johnson, Crawley     

Morphological divergence of Eastern Pacific and Caribbean isopods: effects of a land barrier and the Panama Canal

The Isthmus of Panama rose approximately 3 million years before the present (mybp) and isolated biotas in the tropical eastern Pacific from those in the Caribbean Sea. Populations that were split by the Isthmus and have evolved in allopatry since that time are known as geminates. The surf zone/beach isopod Excirolana braziliensis Richardson was examined between 1984 and 1989 to test the hypothesis that divergence in geminate isopod morphology has occurred, and that geminate divergence is greater than divergence between local populations from the same coastline. Three morphs of Excirolana braziliensis, one in the Caribbean and two in the eastern Pacific, were discovered using numerical taxonomic methods that adjust for body size. The two Pacific morphs have overlapping large-scale distributions, but those morphs are segregated on a smaller scale by beach. We inferred that one Pacific morph and one Caribbean morph were geminates, based on their relative similarity in shape, their geographical ranges, and natural history information about the organism's dispersal capabilities. The origin of the third morph probably predates the Isthmus of Panama, given its relative dissimilarity from the geminate morphs. The presumed geminates differ primarily with respect to the rostrum, antennae and one male reproductive structure. Divergence between geminates is greater than divergence between local populations of any morph along a coastline. Because only one morph occurs in the Caribbean, that region contains less morphological variation than the eastern Pacific, which contains two morphs. There was weak evidence that some introductions may have taken place in the last century from the Caribbean to the Pacific; however, introductions have not masked the pattern of divergence that has developed over millions of years.     

Introduction and spread of Philine auriformis (Gastropoda: Opisthobranchia) from New Zealand to San Francisco Bay and Bodega Harbor

Specimens of Philine auriformis have been observed in the southern portion of San Francisco Bay, California, since summer 1992. Specimens from Bodega Harbor were first discovered from intertidal mudflats in April 1994 and probably represent the spread of the San Francisco Bay population to a neighboring estuary. Their numbers have increased steadily and the species is now well established in both estuaries. Examination of the anatomy of specimens collected from California was compared with that described from New Zealand. No significant differences in anatomy were detected in animals from these different localities. It is suggested that the species was introduced into California waters by release of ballast water from international shipping.     

Group-specific dialects and geographical variation in coda repertoire in South Pacific sperm whales

Codas, which are patterned series of clicks, were recorded from female and immature sperm whales (Physeter macrocephalus) in a number of locations around the South Pacific Ocean and in the Caribbean Sea. Using K-means cluster analysis, 3,644 codas were categorized based on the number of clicks and their patterning. There were 30 resulting types of coda. The numbers of codas of the different types recorded were used to construct repertoires for each recording session, day, group of whales, place, area, and ocean. Strong group-specific dialects, which seem to persist over periods of years, were apparent, overlaid on weaker geographical variation. Significant differences in repertoire were found between the Caribbean and the Pacific Ocean. Sperm whales now join killer whales (Orcinus orca) as the only cetacean species in which dialects (differences in vocal repertoire among neighboring, potentially interacting groups) have been found. Received: 13 June 1996 / Accepted after revision: 19 January 1997     

Variability of epipelagic macrozooplankton/micronekton community structure in the NW Weddell Sea,Antarctica (1995–1996)

Macrozooplankton/micronekton in the epipelagic zone (0–100 m) of the NW Weddell Sea were sampled with a 10 m² multiple opening-closing net environmental sampling system (MOCNESS) trawl during three cruises in 1995 and 1996. A total of 40 species were collected during all cruises. Community composition, as measured using Bray-Curtis analysis and multi-dimensional scaling, permitted separation into two groups: group 1 included samples collected during September–October 1995 and group 2 contained samples collected during April-May 1996 and November–December 1996. Zooplankton collections were dominated by Thysanoessa macrura in September–October 1995 (high pack-ice cover) and by both Euphausia superba and Salpa thompsoni in April–May 1996 (intermediate pack-ice cover) and November–December 1996 (open water). Copepods were not sampled quantitatively by the MOCNESS trawl and were not included in this analysis. Trends in measured parameters of community structure are discussed with respect to environmental characteristics during each sampling period.Communicated by P.W. Sammarco, Chauvin     

Non-indigenous ascidians in southern California harbors and marinas

Southern California's many large harbors form an important coastal ecosystem, yet they are also a␣major destination for thousands of pleasure craft and cargo vessels that have often traveled great distances. Many groups of marine organisms, including ascidians, have now been documented as undergoing range extensions as a consequence of rapid ship-transport between distant harbors phenomenon. This has resulted in a rapid increase in the rate of introductions of non-indigenous species worldwide, yet these effects of boat traffic remain largely unstudied in southern California. Ascidians are sessile marine filter-feeders, hermaphroditic, and often self-fertilizing; many species are tolerant of a wide range of environmental conditions, can reach sexual maturity in just a few weeks, and have a long breeding season. This paper documents the arrival of 14␣non-indigenous species in southern California harbors␣during this century, 13 of which have persisted:␣four prior to the 1960s (Cionaintestinalis, Styelaclava, S.␣plicata, Botryllusschlosseri), another by 1972 (S.␣canopus, formerly S. partita), and 8 since 1983 [C.␣savignyi, Ascidia zara, Ascidia sp., Polyandrocarpa zorritensis, Symplegma brakenhielmi (formerly S. oceania, and S. reptans, Microcosmus squamiger, and Molgula␣manhattensis)]. We estimate the relative abundance and seasonal fluctuations of both non-indigenous and native ascidians in all harbors in southern California from San Diego to Santa Barbara based upon the historical record, our 35 yr of field notes, and our recent surveys carried out during fall 1994, spring and fall 1995, fall 1996 and spring 1997. Possible points of origin of the exotics and predictions on further U.S. Pacific coast range-extensions are included. The concomitant decline in numbers and species of native ascidians in the harbors of southern California during this century is also reviewed. Received: 4 March 1997 / Accepted: 26 September 1997     

Mesopelagic fishes and thermal fronts in the western Sargasso Sea

Analysis of 25 midwater trawl collections, disposed along the meridian 70°20′W from off Hispaniola to the Gulf Stream, showed a change in the mesopelagic fish fauna at about 27°N. The point of faunal change corresponded to a change in the temperature structure of the upper part of the water column, i.e., at a (the?) so-called “thermal front”, perhaps identical to the so-called “North Atlantic subtropical convergence”. Of 44 species occurring in four or more collections, 13 species were collected only to the north of the front and 1 species only to the south. By most criteria, north-of-the-front collections were larger than southern ones. This is in accord with the north-south difference in primary production noted by other workers which, in turn, seems atributable to the north-south difference in temperature structure. To the north the upper part of the water column is well stratified in summer only, while to the south it is well stratified at all seasons. Taken altogether, what is now known suggests that the thermal front logically divides the upper Sargasso Sea into northern and southern portions that differ in many ways.     

The potential of marine live-bait introductions into oceanic islands

The likely introduction of non-indigenous species into the coastal ecosystems of oceanic islands through live-bait utilizations was studied. A store survey identified the species that are traded as live fishing-bait. Only Polychaeta species were identified as imported live-bait on São Miguel Island and all specimens were identified as Perinereis linea. Reponses to surveys of 77 anglers showed that: 44 % harvest from native sources, 44 % buy live-bait and 12 % do both; 56 % of the anglers’ fish on a weekly basis; 31 % dispose of the bait into the sea. A field survey at five sites where fishing rods are routinely utilized was developed to investigate if the non-indigenous polychaetes sold as fishing-bait are already established in the natural environment of the Azores archipelago. Three species of Nereididae were identified: the native Neanthes nubila and P. oliveirae and the cryptogenic P. cultrifera. The escalating utilization of live-bait argues for a change in the habits of fishermen with respect to the discarding of leftover bait, as the higher the volume of discards the higher becomes the probability of non-indigenous species establishment successes, especially on oceanic islands characterized by vulnerable ecosystems with simpler trophic webs.     

Vertical distribution, population structure and life cycle of Neocalanus cristatus (Crustacea: Copepoda) in the Oyashio region, with notes on its regional variations

Vertical distribution and population structure of Neocalanus cristatus were investigated at Site H in the Oyashio region from September 1996 through October 1997 to evaluate their life cycle mode. Additional temporary samplings were also made at several stations covering the entire subarctic Pacific, Okhotsk Sea and Japan Sea, as a basis for regional comparison of life cycles of this species. At Site H, N. cristatus spawned throughout the year below 500 m depth, with a peak from October to December. The resulting eggs and nauplii floated/migrated upward, and formed an abundance peak of Copepodite Stage 1 (C1) in the surface layer in February. In the surface layer, the C1 developed and reached C5 by early June through a phytoplankton bloom which occurred in mid-March to end of June. The C5 migrated to deeper layers in July and August, where they molted to adults. Apparently, the developmental time from C5 to adults was highly variable (>1 month), and some might overwinter. The life cycle of N. cristatus appeared to be annual for the major portion of the population. Taking into account sampling season, temporal changes in vertical distribution and population structure data collected from regions other than Site H, there was a close correlation in the timing of the life cycle over the entire subarctic Pacific, but the reproduction season (April to June) was observed to be different in the Okhotsk and Japan Sea populations. Regional comparison of prosome length of C5 individuals, including those in the Bering Sea, indicated significantly larger sizes of specimens from the Japan Sea and Okhotsk Sea, as compared with those from the entire subarctic Pacific. Possible causes for regional variability in life cycle patterns and body sizes are discussed. Received: 18 December 1998 / Accepted: 19 April 1999     

Distribution of euphausiid assemblages in the Mediterranean Sea

Eleven species of euphausiids from 24 Isaac-Kidd Midwater Trawl (IKMT) night collections taken at stations throughout the Mediterranean Sea were counted. The frequency of occurrence and dominance of individual species and percent similarity faunal analysis of the euphausiid community were used to describe changes in faunal composition between geographical areas and differences in vertical distribution. Although most species were widespread, three distinct patterns of abundance were apparent: Euphausia krohnii, Nematoscelis megalops, Meganyctiphanes norvegica, and Stylocheiron abbreviatum predominated in western basin areas west of the Tyrrhenian Sea; Euphausia hemigibba, Thysanopoda aequalis, and Stylocheiron longicorne predominated in the Tyrrhenian Sea and eastern Mediterranean Sea; Euphausia brevis and Stylocheiron suhmii predominated in the eastern Mediterranean Sea. Percent similarity analysis of data from the IKMT samples and data from Ruud (1936) indicates the Tyrrhenian Sea fauna at the time of the collections was more similar to eastern Mediterranean areas than to most other areas in the western basin, although the degree of similarity was dependent, to some extent, on the depth at which the samples were collected. The composition of euphausiids living above 150 m at night in this area was more similar to eastern basin areas, while the composition of deeper living forms was more similar to those of the rest of the western basin. Comparison of euphausiids collected at three points over a 60 year time-span in the Balearic Sea shows the similarity in composition to be greater within the area over time than between adjacent areas in the western Mediterranean Sea.Contribution No. 2732 from the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA. This research was supported by the Atomic Energy Commission Contract AT (30-1)-3862, ref. NYO-3862-49, National Science Foundation Grant GA 29303 and Office of Naval Research Contract N00014-71-C-0284.     

Population structure of yellowfin tuna (Thunnus albacares) in the western Pacific Ocean, inferred from microsatellite loci

Five polymorphic microsatellite loci were examined in 1391 yellowfin tuna (Thunnus albacares) from eight regions of the western (Coral Sea, eastern Australia, Fiji, Indonesia, Philippines and Solomon Islands) and eastern (California and Mexico ) Pacific Ocean. Across all samples, numbers of alleles per locus ranged from 7 to 30 (mean: 17.0), and observed heterozygosities per locus ranged from 0.223 to 0.955 (mean: 0.593). Temporal collections were available for three areas: no significant temporal heterogeneity was observed for the Coral Sea (1991/1992 and 1995/1996 collections) or eastern Australia (1994/1995, 1995/1996, 1996/1997 and 1997/1998), but there was slight but significant heterogeneity at one locus (cmrTa-161) between the two Philippines collections (1994/1995 and 1996/1997). Genotypes generally showed a good fit to Hardy-Weinberg expectations within populations; only cmrTa-208 in the pooled Coral Sea population gave a significant deviation after Bonferroni correction for 40 tests, with a small but significant excess of homozygotes. Four loci showed no evidence of population differentiation following contingency Chi-squared and F_ST analyses. The fifth locus, cmrTa-161, showed small but significant differentiation (F_ST=0.002, P<0.001). This heterogeneity was largely a result of the Philippines 1994/1995 and Fiji collections; there was no correlation with geographic distance. The average F_ST across all five loci was very low (F_ST=0.002), but it was significant (P<0.001). It is unclear whether this low but significant differentiation reflects noise in the dataset, perhaps arising from experimental error, or real population differentiation. The finding of very limited population heterogeneity accords with most of the earlier allozyme and mitochondrial DNA studies of yellowfin tuna in the Pacific Ocean.     

Differences in stress tolerance and brood size between a non-indigenous and an indigenous gammarid in the northern Baltic Sea

Differences in stress tolerance and reproductive traits may drive the competitive hierarchy between non-indigenous and indigenous species and turn the former ones into successful invaders. In the northern Baltic Sea, the non-indigenous Gammarus tigrinus is a recent invader of littoral ecosystems and now occupies comparable ecological niches as the indigenous G. zaddachi. In laboratory experiments on specimens collected between June and August 2009 around Tvärminne in southern Finland (59°50′N/23°15′E), the tolerances towards heat stress and hypoxia were determined for the two species using lethal time, LT₅₀, as response variable. The brood size of the two species was also studied and some observations were made on maturation of juveniles. Gammarus tigrinus was more resistant to hypoxia and survived at higher temperatures than G. zaddachi. Brood size was also greater in G. tigrinus than in G. zaddachi and G. tigrinus matured at a smaller size and earlier than G. zaddachi. Hence, there are clear competitive advantages for the non-indigenous G. tigrinus compared to the indigenous G. zaddachi, and these may be further strengthened through ongoing environmental changes related to increased eutrophication and a warming climate in the Baltic Sea region.     

Shifting Baselines and The Extinction of The Caribbean Monk Seal

The recent extnction of the Caribbean monk seal Monachus tropicalis has been considered an example of a human‐caused extinction in the marine environment, and this species was considered a driver of the changes that have occurred in the structure of Caribbean coral reef ecosystems since colonial times. I searched archaeological records, historical data, and geographic names (used as a proxy of the presence of seals) and evaluated the use and quality of these data to conclude that since prehistoric times the Caribbean monk seal was always rare and vulnerable to human predation. This finding supports the hypothesis that in AD 1500, the Caribbean monk seal persisted as a small fragmented population in which individuals were confined to small keys, banks, or isolated islands in the Gulf of Mexico and the Caribbean Sea. This hypothesis is contrary to the assumption that the species was widespread and abundant historically. The theory that the main driver of monk seal extinction was harvesting for its oil for use in the sugar cane industry of Jamaica during the 18th century is based primarily on anecdotal information and is overemphasized in the literature. An analysis of reported human encounters with this species indicates monk seal harvest was an occasional activity, rather than an ongoing enterprise. Nevertheless, given the rarity of this species and its restricted distribution, even small levels of hunting or specimen collecting must have contributed to its extinction, which was confirmed in the mid‐20th century. Some sources had been overlooked or only partially reviewed, others misinterpreted, and a considerable amount of anecdotal information had been uncritically used. Critical examination of archaeological and historical records is required to infer accurate estimations of the historical abundance of a species. In reconstructing the past to address the shifting baseline syndrome, it is important to avoid selecting evidence to confirm modern prejudices. Puntos de Referencia Cambiantes y la Extinción de la Foca Monje Caribeña     

Vertical distribution,population structure and lifecycle of<Emphasis Type="Italic"> Eucalanus bungii</Emphasis> (Copepoda: Calanoida) in the Oyashio region,with notes on its regional variations

Vertical distribution and population structure of Eucalanus bungii were investigated at site H in the Oyashio region (western subarctic Pacific) from September 1996 through October 1997 to evaluate the species lifecycle pattern and associated ontogenetic vertical migration. Additional temporary samplings were also made at several stations covering the entire subarctic Pacific, Okhotsk Sea and Japan Sea, as a basis for regional comparison of lifecycle features of this species. At site H, a marked phytoplankton bloom occurred from mid-March to June, and E. bungii spawned in April/May in the surface layer. Resulting nauplii and copepodite stage 1 (C1) formed a prominent abundance peak in early June. The C1 developed and reached C5 by August. The development of nauplii through C4 occurred in the surface layer. From August onwards, C5 and a small fraction of C3–C4 sank gradually deeper, and entered diapause to overwinter at >500 m depth. The C5 molted to C6 males and females in February and March, respectively. The C6 males and females mated at 250–500 m depth, and only mated C6 females ascended to the surface layer in April for spawning. Judging from the size of lipid droplets in the body, the C3–C5 specimens deposited lipids in the body through the phytoplankton bloom period, and the lipids were consumed gradually during overwintering. Taking account of sampling season, temporal changes in population structure, and vertical distribution, the data collected from the western subarctic Pacific and Okhotsk Sea are consistent with a 1-year lifecycle for the site H population, while the data from the central and eastern subarctic Pacific were consistent with a 2-year lifecycle. The populations from the southern and southeastern Japan Sea did not fit the features of either lifecycle scenario, and because of their very small population size it is suggested that they originated from the northern Japan Sea. Regional comparison of the prosome length of C6 females, including those in the Bering Sea, indicated significantly larger specimens from the Japan Sea and Okhotsk Sea, and smaller specimens in the eastern subarctic Pacific, as compared with those in the western subarctic Pacific (including site H) and Bering Sea. A possible overwintering mechanism of E. bungii is discussed.Communicated by O. Kinne, Oldendorf/Luhe     

Metabolic diversity in oceanic animals

Relatively little overlap exists in faunal assemblages in the oceanic waters found north of, and over the reef-like structure south of, Cape Hatteras, North Carolina, USA. To better understand the mechanisms influencing the zoogeography of these animals, metabolic-temperature patterns have been characterized for both larvae and adults of animals collected in waters north and south of Cape Hatteras and from the Caribbean Sea. Southern affinity species from north of Cape Hatteras are the most metabolically labile of the groups, based on seasonal and laboratory-acclimated studies. Adults having a northern affinity found north of Cape Hatteras are metabolically depressed at high temperatures, whereas species from the reef area and the Caribbean are metabolically depressed at low temperatures. Metabolic rates of first stage zoea of crabs from the reef area are depressed at lower temperatures than larvae of the same stage of other species of crabs from the Cape Hatteras region or the Caribbean Sea.Supported by Grant NSF GB 7435 from the National Science Foundation. The authors thank Duke University Marine Laboratory and the Cooperative Program of Biological Oceanography for the use of the R.V. Eastward. The Co-operative Program is supported through the National Science Foundation Grant GB-8189.     

Cryptic species within the commercially most important lobster in the tropical Atlantic, the spiny lobster Panulirus argus

Panulirus argus (Latreille in Ann Mus Hist Nat Paris 3:388–395, 1804) is the lobster of greatest economic importance throughout its distribution. In this study, mitochondrial (Cytochrome Oxidase I and 16S ribosomal genes) and nuclear (Adenine Nucleotide Transporter gene) sequences were used to evaluate the taxonomic status of P. argus sampled from five sites in the Caribbean Sea and nine sites in the Southwest Atlantic. Phylogenetic analyses indicate that lobsters from the two regions form two monophyletic groups with a molecular divergence similar to that observed between distinct congeneric lobster species and much larger than that found between conspecific lobster populations. Therefore, the Caribbean and the Southwest Atlantic lobster populations originally attributed to P. argus belong to different species, with an estimated time of isolation of around 16 Million years. An important consequence of these findings is that the fisheries of spiny lobsters from the Caribbean and the Southwest Atlantic species must be managed separately.     

Heterotrophic flagellates from the water column in Shark Bay, Western Australia

The diversity of heterotrophic flagellates in the water column at Denham, in Shark Bay, Western Australia, was examined in April 1995 by observations of living cells in freshly collected samples, and in enrichment cultures. Observations were also made of cells on whole-mount preparations, using light and electron microscopy. A total of 41 species are described, drawn from the apusomonads, cercomonads, choanoflagellates, cryptomonads, euglenids, heteroloboseids, stramenopiles and groups of uncertain taxonomic affinities (Protista incertae sedis). A new species, Percolomonas denhami, is described and assigned to the Heterolobosea. Three-quarters of the species seen have not previously been reported from southern sub-tropical regions. The biogeography of the species seen in Western Australia is discussed with reference to studies in other localities. It appears that many heterotrophic flagellates have a cosmopolitan distribution. Received: 11 June 1996 / Accepted: 13 December 1996     

Dietary composition and diel feeding patterns of epipelagic siphonophores

Prey consumption patterns are described for 24 species of epipelagic siphonophores studied during 1977–1980 in the Gulf of California, off Southern California, in the Sargasso Sea, and in Friday Harbor, Washington. Of the species, 7 were studied by day and at night, 15 were studied only by day, and 2 were studied only at night. Each of the 3 suborders of siphonophores had a characteristic diet. Siphonophores in the suborder Cystonectae, which had large gastrozooids, fed primarily on fish larvae. Species in the suborder Physonectae, which generally had few, large gastrozooids, consumed some small copepods, but consumed mainly large copepods and a variety of large, noncopepod prey. Species in the suborder Calycophorae, which generally had many small gastrozooids, fed mainly on small copepods, and also on other small prey organisms. The maximum size of prey tended to be correlated with gastrozooid length for all the siphonophores studied. For a given siphonophore species, the number of ingested prey was greatest at localities where prey organisms were most abundant in the surrounding seawater. For siphonophore species collected both day and night, there was a tendency for more prey to be consumed at night. Behavioral observations in the laboratory indicated that of 7 siphonophore species tested, 2 fed only in the light, and another fed only in the dark.     

Sexual reproduction of the reef coral Montastreacavernosa (Scleractinia: Faviidae) in the Santa Marta area, Caribbean coast of Colombia

Sexual reproduction of the reef-building coral Montastreacavernosa was studied in the Santa Marta area, Caribbean coast of Colombia, from October 1990 to October 1991. The area is subjected to a seasonal upwelling–outwelling regime. From microscopical analysis of tissue sections sampled each lunar month around the full moon, it was confirmed that this is a gonochoric, broadcasting species, with a single gametogenic cycle per year, and a 1:1 sex ratio. Oogenesis began a few weeks after spawning, and extended for 11 mo. The onset of spermatogenesis occurred just before the full moon of June, later than at other localities where sea-water temperatures during the first half of the year are not as low. The amount of reproductive tissue strongly increased in both sexes after July, in association with an increase in sea-water temperature and a decrease in photoperiod. The gonad index of fully mature female colonies was about four times lower than at other localities, perhaps due to the stressful seasonal regime. The male gonad index was lower than that of the female, indicating sex-related differences in the rates of biomass allocation to reproduction. As in other Caribbean localities, spawning occurred after the full moons of August and September. However, there was some evidence of a third spawning episode after the full moon of October, possibly associated with a delay in the occurrence of maximum sea-water temperatures in near-equatorial localities compared to higher latitudes. The probability of cross-fertilization in this species with a gonochoric breeding system and a broadcasting mode of reproduction is favored by its balanced sex ratio, its usually high within-reef zone abundance, and by localized and repeated spawning episodes, synchronized by lunar phase. Received: 19 April 1996 / Accepted: 24 September 1996     

A retrospective analysis of pollen host plant use by stable and declining bumble bee species

Understanding population declines has been the objective of a wide range of ecological studies. When species have become rare such studies are complicated because particular behavior or life history traits may be the cause but also the result of the decline of a species. We approached this problem by studying species' characteristics on specimens that were collected before the onset of their decline and preserved in natural history museums. In northwestern Europe, some bumble bee species declined dramatically during the 20th century whereas other, ecologically similar, species maintained stable populations. A long-standing debate focuses on whether this is caused by declining species having stricter host plant preferences. We compared the composition of pollen loads of five bumble bee species with stable populations and five with declining populations using museum specimens collected before 1950 in Belgium, England, and The Netherlands. Prior to 1950, the number of plant taxa in pollen loads of declining species was almost one-third lower than that in stable species even though individuals of stable and declining species generally originated from the same areas. There were no systematic differences in the composition of pollen loads between stable and declining species, but the plant taxa preferred by declining species before 1950 had experienced a stronger decline in the 20th century than those preferred by stable species. In 2004 and 2005, we surveyed the areas where bumble bees had been caught in the past and compared the composition of past and present pollen loads of the stable, but not of the by now locally extinct declining species. The number of collected pollen taxa was similar, but the composition differed significantly between the two periods. Differences in composition reflected the major changes in land use in northwestern Europe but also the spread of the invasive plant species Impatiens glandulifera. The main question now is why declining species apparently were not able to switch to less preferred food plants when stable species were. This study shows that natural history collections can play an important role in improving our understanding of the ecological mechanisms driving species population change.