Composition Of Algal Assemblages Research Articles

Modification of benthic communities by territorial damselfish: a multi-species comparison

The effects of territorial damselfish on coral reef benthos have been well-studied for a few relatively large-bodied species with visually distinct territories. Despite a growing body of research demonstrating their abundance, and their effects on algae, corals and other grazers, there has been little research on the effects of the territorial damselfish community as a whole. This study investigated the space occupation, territory composition, and diet of ten damselfish species at three locations: Magnetic and Orpheus Islands (Great Barrier Reef), and Kimbe Bay (Papua New Guinea). Territories were measured, and the composition of benthic communities inside and outside territories was assessed both in situ and from algal collections. The stomach contents of territorial damselfishes were also quantified. Although the larger, previously well-studied species had the most visible effect on the benthic community in their territories, all the smaller species also significantly affected the algal composition, normally with an increase of palatable algae. However, the composition of algal assemblages inside the territories of different species varied considerably. Damselfish territories were highly individual, not just among species, but also among locations. Diets were diverse and indicated a greater degree of omnivory and detritivory than previously thought. At all locations, territories occupied a substantial proportion of the substratum: >25% on Magnetic Island, >50% at Orpheus Island, and ∼50% in Kimbe Bay. Within individual zones, this figure was as high as 70%. The contribution of territorial damselfishes to a range of benthic patterns and processes is considerable, and future benthic studies may need to distinguish more closely between territory and non-territory areas.

Spectral fingerprinting' for specific algal groups on sediments in situ: a new sensordoi:10.1127/0003-9136/2006/0167-0575

Currently it is still extremely difficult to adequately sample populations of microalgae on sediments for large-scale biomass determination. We have now devised a prototype of a new benthic sensor (BenthoFluor) for the quantitative and qualitative assessment of microphytobenthos populations in situ. This sensor enables a high spatial and temporal resolution and a rapid evaluation of the community structure and distribution. These determinations are based on the concept that five spectral excitation ranges can be used to differentiate groups of microalgae, in situ, within a few seconds. In addition, because sediments contain a lot of yellow substances, which can affect the fluorescence and optical differentiation of the algae, the device was equipped with a UV-LED for yellow substances correction. The device was calibrated against HPLC with cultures and tested in the field. Our real-time approach can be used to monitor algal assemblage composition on sediments and is an ideal tool for investigations on the large-scale spatial and temporal variation of algal populations in sediments. Apart from the differentiation of algal populations, the BenthoFluor allows instantaneous monitoring of the chlorophyll concentrations and determination of which algae are responsible for this on the uppermost surface of sediments in the field and in experimental set-ups.

Spatial variation in groundwater-related resource supply influences freshwater benthic algal assemblage composition

The landscape position of a lake relative to local and regional groundwater flow patterns has important ecosystem consequences. The local hydraulic gradient sets up seepage regimes, influences hydrologic and nutrient budgets, and alters site stoichiometry (molar N:P). However, little is known about the biotic (ecological) consequences of groundwater–lake coupling. We investigated the relationship between groundwater flux (resource supply rates), resource supply ratios, and species patterns of benthic algae in Sparkling Lake, Wisconsin, USA, a north-temperate flow-through seepage lake. Nutrient fluxes of seepage waters influenced both local benthic algal biomass and species composition. Sites of high groundwater discharge (HGD) were characterized by low N:P flux, high algal biovolume, and low species richness and diversity. In contrast, low groundwater discharge (LGD) and low groundwater recharge (LGR) sites had high N:P, low algal biovolume, and high richness and diversity. HGD sites were dominated by diatoms and cyanobacteria characteristic of high P, whereas LGD and LGR sites were characterized by taxa associated with low P. Many species were unique to the local flow regimes, increasing overall benthic algal species richness in Sparkling Lake.

Choice of substrate in algae-based water-quality assessment

Our study investigated whether algae-based water-quality assessments are affected by differences between algal assemblages on hard substrates (rocks, wood) and soft substrates (fine- grained sediments). We analyzed a US Geological Survey National Water-Quality Assessment (NA- WQA) program data set that consisted of 1048 pairs of samples collected from hard and soft sub- strates at 551 river sampling locations throughout the US. Biovolume and diversity of algal assem- blages, biovolume of major taxonomic groups, and abundance of motile diatoms differed significantly between samples collected from hard and soft substrates at the same sites. Ordinations of assemblages from hard and soft substrates were highly concordant and provided similar information on environ- mental gradients underlying species patterns. The strengths of relationships between composition of algal assemblages and water chemistry parameters (conductivity, pH, total P, and total N) did not differ consistently between substrate types. Performance of weighted averaging (WA) inference mod- els did not differ between models based on assemblages from hard and soft substrates. Moreover, the predictive power of inference models developed from single-substrate data sets was not reduced when these models were applied to samples collected from other substrates. We concluded that the choice of substrate to sample should depend on the assessment indicators to be used. If indicators based on the autecologies of many algal taxa (e.g., inference models or autecological indices) are used, restricting samples to a single type of substrate is unnecessary. If algal diversity, total algal biovolume, or abundance of specific algal taxa is used, samples should be collected from a single type of sub- strate.

Algal community composition within territories of the damselfish Stegastes nigricans (Pomacentridae, Labroidei) in Fiji and the Cook Islands

The species composition of algal assemblages inside territories of the damselfish Stegastes nigricans was examined from Nananu-i-ra Island, Fiji and Rarotonga, Cook Islands. A total of 32 algal species were identified, the majority of them Rhodophytes (24 species). Seven species were unique to Rarotonga, six were unique to Fiji, with the remaining 19 species recorded at both locations. The biodiversity of territories was similar at both locations. The red alga, Herposiphonia secunda, was the most abundant species found, comprising 40.33% � 3.51SE and 33.94% � 3.58SE from Rarotonga and Fiji respectively. Gelidiopsis intricata, Polysiphonia sp., Aglaothamnion cordatum, and various Cyanophytes were also abundant at both locations. As a group, filamentous algae accounted for 70.35% of the algae found within the territories at all sites. We suggest that if S. nigricans are actively weeding their territories, they are selecting filamentous algae, and particularly Herposiphonia sp. and Polysiphonia sp.

Effects of freshwater shrimp assemblages on benthic communities along an altitudinal gradient of a tropical island stream

1. In tropical island stream ecosystems freshwater shrimps are often the dominant macroconsumers and can play an important role in determining benthic community composition. However, most studies of the ecological role of shrimps are limited to high‐altitude shrimp‐dominated sites where other biota (fishes and snails) are absent or significantly less abundant than at lower altitudes.2. We examined how effects of different shrimp assemblages on benthic communities changed along an altitudinal gradient in a tropical island stream in Puerto Rico. We used electroshocking and observations to quantify abundance and taxonomic composition of shrimp assemblages at three sites (300, 90 and 10 m a. s. l) along the Río Espíritu Santo. We also experimentally manipulated access of shrimps to the benthic environment simultaneously at each site using electric fences over a 35‐day period.3. At the high‐altitude site, exclusion of shrimps (predominantlyAtyaspp. andXiphocariselongata) resulted in significantly greater accrual of organic and inorganic material, chlorophyllaand algal biovolume. In the absence of shrimps, the algal community was dominated by filamentous green algae (Chlorophyta:OedogoniumandRhizoclonium). Excluding shrimps did not affect total insect biomass but significantly increased sessile chironomids (Diptera: Chironomidae). We observed similar treatment effects at the mid‐altitude site where shrimps (primarilyMacrobrachiumspp. andX. elongata) occurred at lower densities. In contrast, at the low‐altitude site there were no treatment differences in organic and inorganic material, chlorophylla, algal biovolume, algal assemblage composition and insects.4. The lack of treatment differences at the low‐altitude site was probably because of very high densities of grazing snails (ThiaragraniferaandNeritinaspp.) which reduced organic and inorganic resources and obscured potential shrimp effects.5. This study demonstrates that freshwater shrimps can play an important role in determining benthic community composition; however, their effects vary and appear to depend on the presence of other biota. This study suggests that loss of shrimps as a result of anthropogenic disturbances will have different effects on the stream community depending upon location along the altitude gradient.

Ecoregions and benthic diatom assemblages in Mid-Atlantic Highlands streams, USA

AbstractEcoregional differences in geology and hydrology may affect physical and chemical conditions in streams and, consequently, the species composition of algal assemblages. Stresses resulting from human disturbance, however, may constrain species membership in algal assemblages and reduce regional diversity. We expected that ecoregional differences in diatom assemblages, if they were present, would be more evident in relatively undisturbed sites than in randomly selected sites. Benthic diatom and water chemistry samples were collected from streams in 7 ecoregions of the Mid-Atlantic Highlands to evaluate correspondence between ecoregional classification and diatom assemblages. Ecoregional differences were assessed using 196 randomly selected stream sites (probability sites) and 60 sites with less disturbance by humans (reference sites). Multivariate analyses showed that significant ecoregional differences in diatom assemblages were observed only in probability sites and not in reference sites. Water c...

Induced metal tolerance in microbenthic communities from three lowland rivers with different metal loads

The response of microbenthic communities to sustained metal stress was studied in three lowland rivers with different levels of pollution. Tolerance against zinc and cadmium was determined in short-term toxicity tests with microbenthic assemblages colonizing glass discs. Photosynthetic activity served as an endpoint in tests for algae, whereas for bacteria thymidine incorporation was determined. For bacterial assemblages from unpolluted locations, EC50 values in short-term tests ranged between 6.7 and 56.2 &mgr;M zinc, and 8.7 and 25.5 &mgr;M cadmium, respectively. Bacterial assemblages from the two most polluted sites were significantly more tolerant for zinc (EC50: 994 &mgr;M and >1,000 &mgr;M) and cadmium (EC50: 218 &mgr;M and 154 &mgr;M). Results indicated a shift in community composition toward pollution-adapted organisms when a threshold concentration of 1 &mgr;M zinc is exceeded. Although an increasing community tolerance was also indicated for algae, EC50 values for microbenthic algae from all sites exceeded in most cases the highest metal concentrations tested (Zn: 1,000 &mgr;M; Cd: 320 &mgr;M). Since species composition of algal assemblages was found to change at much lower metal levels, it is concluded that short-term toxicity tests measuring photosynthesis inhibition do not reflect well the long-term effects of these metals. Toxic effects of metals on both algal and bacterial assemblages are attenuated by precipitation and complexing capacities of the biofilm.

Freshwater stream ecosystems of James Ross Island, Antarctica

The freshwater streams of James Ross Island share many of the features common to other Antarctic streams. There is a diel variation in temperature and discharge, which follows the daily insolation cycle; catchments are barren; stream vegetation is predominantly algal, comprising mat-forming cyanobacteria and filamentous chlorophytes; and physical factors, particularly turbidity and bed stability are important in determining biomass and composition of algal assemblages. Nutrient concentrations vary from stream to stream and over a diel cycle, with minimum dissolved N in late afternoon. Biomass attained and photosynthetic and respiratory rates are also comparable to those recorded in other Antarctic streams, with low productivity/biomass ratios in perennial assemblages.

Effects of Herbivore Type and Density on Chemical Composition of Algal Assemblages in Laboratory Streams

The chemical composition of algal assemblages in laboratory streams was determined 3 and 27 d after adding snail (Juga silicula) and larval caddisfly (Dicosmoecus gilvipes) grazers. Three days after the herbivores were introduced (day 8 of algal growth), the fatty acid and amino acid profiles among algal assemblages were similar. Substantial differences were noted after 4 wk (day 32 of algal growth), however, especially with respect to the 16:0, 16:1, 16:3, 18:3, and 20:5 fatty acids. On day 32, algal assemblages subjected to zero or 125 snails/stream (66/m²) had higher levels of glycine, leucine, isoleucine, tyrosine, and the 16:3 and 18:3 fatty acids than assemblages exposed to 500 snails/stream (250/m²), 50 caddis/stream (25/m²), or 200 caddis/stream (100/m²). On the other hand, assemblages subjected to high grazing pressure (i.e., 500 snails/stream, 50 and 200 caddis/stream) had higher levels of alanine, glutamic acid/glutamine, and the 16:0, 16:1, and 20:5 fatty acids than algae exposed to zero or 125 snails/stream. These data provide detailed information on the food quality of lotic algae and may serve as a starting point for future research in this field.