Littoral Distribution Research Articles

Habitat distribution of fish in late summer: changes along a nutrient gradient in Danish lakes

Abstract – The horizontal distribution of fish in lakes varies with species, age, predation risk, vegetation coverage and water clarity. Although sporadic data are available for specific lakes, little is known about how habitat distribution generally changes along a gradient in nutrients and clarity. Here we analyse littoral and pelagic fish catch data for 34 Danish lakes (covering 94 lake years) with contrasting total phosphorus (TP) concentrations and mean depth levels (but mainly eutrophic and shallow). Electrofishing was conducted during day along the shore or along the edge of the reed belt if such existed. Gill nets were set overnight for 18 h in open water. We calculated a littoral proportion as: LITPRO = (100 × number caught by electrofishing in the near‐shore area)/(number caught by electrofishing in the near‐shore area and nets in the open water). At all summer TP concentrations LITPRO was high for several ‘littoral’ species such as gudgeon (Gobio gobio), rudd (Scardinius erythrophtalmus) and pike (Esox lucius) and low for more typical pelagic species like pikeperch (Sander lucioperca), ruffe (Gymnocephalus cernuus) and smelt (Osmerus eperlanus). However, for many of these species including the dominant roach (Rutilus rutilus) and perch (Perca fluviatilis) LITPRO increased with TP or lake water chlorophyll a (CHLA) for fish >10 cm, suggesting a more littoral distribution with increasing turbidity. Exceptions are pikeperch and bream (Abramis brama). For bream, LITPRO increased significantly with mean lake depth only. For fish ≤10 cm LITPRO showed only a weak relationship to TP, CHLA or depth. In accordance with the TP‐dependent distribution, major changes occurred in the fish community structure during the monitoring period following nutrient loading reduction. A comparison of LITPRO from the first part of the monitoring period (1989–1993) with a subsequent period (1997–2003) for four abundant species showed a significant decline in LITPRO over time for large‐ and small‐sized roach and perch and large rudd. This suggests a fast response in fish distribution to improved water quality. It further demonstrates that fish monitoring in lakes should cover both littoral and pelagic habitats to describe the recovery process.

Distribution of Age-0 Largemouth Bass in Relation to Shoreline Landscape Features

Relations between landscape features and the littoral distribution of young largemouth bass Micropterus salmoides were determined for 43 contiguous sections along the entire 8-km shoreline of an unvegetated embayment in B. E. Jordan Lake, North Carolina. Night shoreline electrofishing was conducted in July and October 1991–1992 and individual capture points of age-0 largemouth bass were recorded. Significant correlations among and between years in catch rate per section of shoreline indicated consistency in distribution. Habitat was characterized in 35 sections in July–August and 22 sections in October to quantify the relation between abundance and landscape components. Stepwise multiple regression indicated that distribution was strongly and positively related to landscape features, specifically bottom slope and gravel substrata. Correlations of catch rates with cover components were negative for July but positive for October. These data indicate that cover may be limiting late in the year, coincident with declines in water level. Habitat–catch relations were stronger in October of both years despite lower mean abundance, indicating that reduced habitat at low water levels limits carrying capacity for young largemouth bass. The multiple regression model precisely predicted relative abundance along five sections of shoreline in another embayment for which habitat variables were assessed. Age-0 largemouth bass exhibited patchy distributions that were linked to spatially and temporally heterogeneous landscape parameters on the embayment-level scale. Because relative densities of age-0 largemouth bass were related to availability of specific shoreline landscape features, habitat management may enhance carrying capacity for young largemouth bass.

Some Aspects of the Specific Habitat Requirements of Ophelia Bicornis (Polychaeta)

The discrete habitat requirements of Ophelia bicornis from the Exe estuary are reported in relation to: the influence of tidal activity; the nature of the sandy substratum; the associated meiofauna; the interstitial bacteria; the interstitial water, organic matter and calcareous material; and the interstitial and sand-adsorbed free amino acids. The interrelationships of these features as potential limiting factors in the highly specific littoral distribution of O. bicornis is speculated upon.

Tolerances to high temperature of infaunal bivalves and the effect of geographical distribution, position on the shore and season

There are four important influences on the temperature tolerance displayed by infaunal bivalves, namely their position on the shore, the depth to which they burrow, their geographical distribution and the seasonal cycle.The temperature tolerance of a species is closely related to shore position and burrowing depth, since these both modify the actual range of temperatures to which the organism is exposed and the tidal variation in temperature. As one might expect, southern populations of a species tend to be lower on the shore than equivalents in northern Europe, but at any one location it is difficult to detect a difference in tolerance between individuals from the top of the shore and those from the bottom. Southern populations do have a higher tolerance to high temperatures than northern, despite the shift in littoral distribution. A similar pattern of response and shift in tolerance is shown between summer- and winter-acclimated specimens.However, the seasonal shift in response to temperature is not entirely as might be expected, as oxygen consumption measurements show reverse acclimation (i.e. winter respiration rates lower than summer). Reverse acclimation has been demonstrated in a number of bivalve species, and the degree of reverse acclimation is here suggested to be related to the degree of deposit- or filter-feeding habit.There is evidence that bivalves are capable of regulating to some extent their metabolic rate, independent of temperature. Six groups of Macoma balthica were investigated, of which the four from relatively high temperature environments regulated from 20°C, while the other two did not, suggesting that this capability can be acquired.

Population structure, growth and distribution of Lingula anatina (Brachiopoda) in Queensland, Australia

Size‐frequency data collected in large samples from five populations of Lingula anatina from North Queensland intertidal sandflats conformed to previously known brachiopod size‐frequency distributions. Probability paper analysis of the samples and constituent sub‐samples confirmed that all the distributions had a hidden poly‐modality resulting from a long but defined breeding season. Two patterns of annual recruitment were revealed; the first is the periodic failure of the populations to gain recruits and the second is one of patchy distribution of settlement cohorts. These patterns introduce sampling bias into the derivation of lingulid size frequency curves unless compensated by more extensive sampling methods than have previously been considered adequate. The interpretation of year classes has enabled a growth curve to be derived. The populations inhabited predominantly sandy sub‐strates and displayed aggregated distributions. Littoral distribution of the species is regarded as optimal rather than marginal.

Littoral Distribution of Lumbricillus reynoldsoni Backlund and Other Enchytraeidae (Oligochaeta) in Relation to Salinity and Other Factors

The distribution of littoral Enchytraeidae was determined on an Anglesey beach by means of baited bags. L. reynoldsoni was found chiefly above the Pelvetia zone, while L. lineatus was more widely distributed. The salinity preferenda of these two species were determined by means of multiple-choice chambers, in which different salinity regimes were maintained on moist blotting paper balls. L. reynoldsoni was found to prefer salinities less than half that of the seawater, while L. lineatus displayed no preference over a range from distilled water to a salinity 1.5 x that of the sea-water. Both species showed marked tolerance for sea-water. L. reynoldsoni was apparently unable to prevent water loss when transferred from a weaker to a stronger strength of sea-water. Fluids collected from the upper shore on absorbent cotton pads were found to have generally low osmotic pressures, depending upon rainfall. L. reynoldsoni was found to be attracted to both fresh and decayed seaweed. It is concluded that the distribution of this species is governed by low salinities and the presence of a drift-line of sea-weed. Pe3ioMe

Activity and heart rate of bivalve molluscs in their natural habitat.

KNOWLEDGE of the ecophysiology of intertidal molluscs is largely derived from observations of their littoral distribution and experiments carried out under laboratory conditions1. The results of a preliminary investigation of the activity and heart rate of the bivalves Cardium edule and Donax vittatus in situ in their natural habitat are presented here.