Alan R. Emery

The basis of fish community structure: marine and freshwater comparisons

SynopsisFreshwater and marine fish communities are described and compared for arctic, boreal and tropical latitudes. Details of habitat characteristics, species numbers, and diel and seasonal differences in distribution are given for each community type. The order of increasing richness of fish species in these environments is (1) arctic lakes, (2) arctic marine, (3) boreal lakes, (4) tropical lakes, (5) boreal marine and (6) tropical marine. The richness of numbers of species can be related to a series of factors, each of which may function at some threshold value. These factors include climatic perturbation, solar radiation, spatial heterogeneity, available nutrient supply, availability of cover, and geological time. Discontinuities in the availability of some factors can be partially compensated for by torpor or aestivation; this effectively removes the fish from the community for a period of time. Increased diversity may also be effected through the diurnal/nocturnal shift in activity in some fish communities.The development of an organic matrix, notably macrophyte beds or coral reefs, may contribute significantly to an increase in diversity within fish communities. This matrix operates by an increase in spatial heterogeneity and in biological interactions. The apparent lack of resilience of high diversity fish communities can be related to the characteristics of the underlying organic matrix. A change in the matrix will cause a change in the level of fish diversity that can be maintained in the system.

A new genus and two new species of gobiid fishes (Perciformes) from the Chagos Archipelago, Central Indian Ocean

SynopsisA recent (1979) expedition to the Chagos Archipelago resulted in the collection of about 40 new taxa of fishes. A new genus,Trimmatom, and two new species,T. nanus andT. offucius, are described here. The new genus is characterized by having all pelvic-fin rays simple (unbranched), a scaleless body, no head pores, a wide gill opening extending anteroventrally to below the eye, and hypurals 1 and 2 fused to the complex formed by the fusion of the ural centrum and hypurals 3 and 4.T. nanuss andT. offucius are differentiated on the basis of fin ray counts and colour pattern.T. nanus is the smallest vertebrate yet to be described. Mature females with ovaries full of eggs are 8–10 mm in standard length.

Sediments of Deep Canadian Shield Lakes: Observations of Gross Structure and Biological Significance

Sediments of deep Canadian shield lakes have a firm mud-water interface and an intricately structured, oxygenated surface. Surface relief is not uniform, but is broken by small ridges and upright chironomid tubes. The sedimentary material behaves like a weak jelly and becomes flocculent only when violently disturbed. Sculpins were observed to rest on and, when started, to hide in the oxygenated layers. Sequestering of nutrients in the bottom sediments is enhanced by the structuring of the substrate surface below 10 meters, and may inhibit nutrient recycling at overturn.