Hydrobiologia

Loaches of the genus Lepidocephalichthys are ubiquitous in Peninsular India and the nearby continental-shelf island of Sri Lanka. Four valid species are reported from this region: L. thermalis, a species reported from across this region; L. jonklaasi, confined to rainforests in southern Sri Lanka; L. coromandelensis, from the Eastern Ghats and L. guntea, from the northern Western Ghats of the Indian peninsula. Here, based on collections from 25 locations in 13 river basins in Sri Lanka and 20 locations across India, including a dataset downloaded from GenBank, we present a molecular phylogeny constructed from the mitochondrial cytochrome b (cytb) and cytochrome c oxidase subunit 1 (cox1) sequences. We show that ancestral Lepidocephalichthys colonized Sri Lanka in the late Miocene. Multiple back-migrations to India, as well as colonizations from the mainland, took place in the Plio-Pleistocene. The persistence on the island of L. jonklaasi, an obligatory rainforest associate, suggests that perhumid refugia existed in Sri Lanka throughout this time. Lepidocephalichthys thermalis appears to have colonized the Sri Lankan highlands as recently as the Pleistocene. The data suggest that Lepidocephalichthys thermalis is a species complex in which multiple species remain to be investigated and described, both in India and Sri Lanka.

Two species of the calanoid copepod Pseudocalanus, P. acuspes and P. elongatus, have been reported from the Baltic and North Seas. Morphometric analysis based on Frost (Can J Zool 67:525–551, 1989) did not identify the species in samples collected during the German GLOBEC program; the majority of measurements fell outside reported ranges for Baltic and North Sea specimens. A multiplexed species-specific PCR (SS-PCR) protocol was designed from a ~700 bp sequence of mitochondrial cytochrome oxidase I (mtCOI), with primers designed to amplify regions of different sizes for the two species to allow detection by gel electrophoresis. The accuracy and reliability of the multiplexed SS-PCR reaction was confirmed by sequencing the mtCOI region. Preliminary SS-PCR analysis of geographic distributions of the two species indicated that P. acuspes occurred exclusively at sampling sites in the Baltic Sea, whereas P. elongatus was found in the southern North Sea and at one site in the Baltic. The SS-PCR protocol can be used for routine identification of the two species for studies of population, community and ecosystem dynamics.

It is important to view eutrophication as an increase in the supply of organic matter to an ecosystem rather than as a simple problem of nutrient pollution. This emphasizes that eutrophication is a fundamental change in the energetic base that may propagate through the system in various ways and produce a variety of changes. Some of these changes may be desirable (e.g., increased secondary production) and some may not (e.g., hypoxia). Defining eutrophication in terms of changing nutrient concentrations or chlorophyll levels or species composition confuses symptoms with the underlying phenomenon. While nutrient enrichment is the most common cause of eutrophication, it is not the only one. As recent and ongoing nutrient reductions make an impact in the coastal waters of the wealthier nations, we will see an increasing number of systems in which primary production is decreasing. This reduction in the supply of organic matter is here defined as oligotrophication, a phenomenon now well documented in lakes. So far, there has been little appreciation of this limnological study by coastal marine ecologists or managers, but there is much we can learn from it. The great ecologist H.T. Odum long argued that we need ‘macroscopes’ to help ecologists see the problems they study as they are embedded in the larger scales of nature and society. Marine eutrophication (and oligotrophication) is a perfect example of a problem that must be studied with a view toward the larger scales as well as toward the microscopic details. While much of the hardware (e.g., satellite imagery) for the mythical macroscope has been developed in the last 30 years, many ecologists and managers still look at eutrophication as a local problem linked to local sources of nutrient enrichment. Such a parochial view isolates eutrophication from its long intellectual history—a history that is linked to the development of our understanding of production in coastal waters. It also neglects the intellectual richness and complexity of eutrophication. One example of the importance of the macroscopic view is the emerging importance of climate-induced changes in phenology and the consequences of changing phenology on productivity. These changes may lead to eutrophication or oligotrophication. Climate changes may also exacerbate or alleviate conditions such as hypoxia that are associated with eutrophication. Seeing eutrophication in the macroscopic view is important for understanding and managing the phenomenon.

Two rotifers, Polyarthra vulgaris and P. dolichoptera may have different temperature and oxygen optima. In addition, they consume similar foods including Chryptomonadales and Crysomonadales. P. dolichoptera disappeared from the plankton after experimental elimination of fish from a small lake. The disappearance may have been caused by a change in temporal availability of suitable food species (e.g. crysomonads) during early spring. A lack of food during this period, when the water was still cold, may have influenced the competitive balance between the two Polyarthra species.

Gut contents and feeding activity of five dominant Antarctic copepods (Calanus propinquus, Calanoides acutus, Rhincalanus gigas, Metridia gerlachei and Microcalanus pygmaeus) were studied from samples collected during several cruises of the RV Polarstern to the eastern Weddell Sea. In summer, feeding activity, estimated as percentage of copepods with food in the guts, was high in all the species, and diatoms dominated all gut contents. In winter, C. acutus was trophically inactive, and C. propinquus and R. gigas considerably decreased their feeding activity, while a decrease in feeding of M. gerlachei and M. pygmaeus was less pronounced. Unidentified mass dominated gut contents in winter, supplemented by phytoplankton and protozoans. Prior to the spring bloom, feeding activity of C. acutus was low, with unidentified food predominating, while carnivory was important in actively feeding C. propinquus. Rhincalanus gigas tended to be more carnivorous than C. acutus, however with less feeding activity than C. propinquus. Seasonal changes in feeding patterns are discussed.