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Species Diversity In Space And Time

The pollution of rivers and lakes is of concern because of the threat to public water supplied and because of the damage caused to natural ecosystems. Waterborne diseases remain rife in the Third World, while in developed countries there has been a decline in the quality of water. It has also become apparent that pollutants may destroy ecosystems hundreds of miles from their source. Some of these toxic materials such as lead and PCBs also pose threats to public health. This text describes the sources of various types of pollutants, their effects on aquatic organisms, ecosystems and man, using case histories where appropriate. Ways of mitigating the effects of pollutants by control and ecosystem manipulation are described. Techniques for assessing the effects of pollution, both in field and laboratory, are introduced. The role of the biologist in pollution assessment and control and in the wider sphere of mangement of acquatic resources is also examined.

Biology of Freshwater Pollution.

There is a long-standing debate whether mangrove and seagrass habitats in the Indo- Pacific region function as nurseries for coral reef fishes. We studied the use of all major shallow-water habitat types by juvenile coral reef fish using visual census surveys at 4 islands along the Tanzanian coast (East Africa) and at the island of Grande Comoros (Comoros archipelago). We investigated the value of mangroves, seagrass beds, coral reefs, macroalgae and intertidal flats as a juvenile habitat for fish by studying density distribution patterns of juveniles and adults of 76 reef fish species in these habitats. We assessed (1) which part of the reef fish community used mangrove-seagrass habitats as juvenile or adult habitats, (2) whether adult fish densities and diversity on adjacent reefs were related to the presence of these shallow habitats, and (3) whether adults of species that use these habitats when juvenile were less abundant on coral reefs situated far away from these juvenile habitats. Sea- grass beds and coral reefs were the most important juvenile fish habitats. Ontogenetic migrations between seagrass beds and reef habitats possibly occur, since several species showed their highest juvenile densities on seagrass beds, whereas adults showed their highest densities on reefs adjacent to these seagrass beds. The presence of areas with seagrass beds positively influenced adult densi- ties of many reef fish species on adjacent coral reefs. Of the 36 fish species whose juveniles were observed in seagrass beds along the Tanzanian coast, 32 species were absent from or showed low densities on coral reefs of the island of Grande Comoros (lacking seagrass beds or mangroves). On reefs far from seagrass beds and mangroves along the Tanzanian coast, 25 of these 36 species were absent or showed low densities in comparison with reefs adjacent to these habitats.

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Indo-Pacific seagrass beds and mangroves contribute to fish density and diversity on adjacent coral reefs

Each year millions of larval and 0+ juvenile fishes are recruited into estuarine fish populations around the world For several decades the roles of littoral aquatic and emergent macrophyte habitats as nursery areas for many of these species have been studied and debated at length This review attempts to collate the published literature and provide a synopsis of the varying, and sometimes conflicting, views on this topic A large number of studies have shown that a range of species and an abundance of juvenile fishes are associated with littoral macrophytes in estuaries, some of which are found almost exclusively within particular plant habitats Other studies have shown the movement of certain juvenile fishes from one type of littoral plant habitat to another as they grow and develop new feeding strategies and dietary requirements Overall, it would appear that seagrass beds and mangrove forests are particularly favoured by fishes as nursery areas in both estuaries and the nearshore marine environment, and that the loss of these habitats leads to a decline in juvenile fish diversity and abundance Salt marshes and reed beds generally have a lower diversity of fishes than seagrass and mangrove habitats, possibly due to the more temperate location of salt marshes and the dense structure of some reed beds Stable isotope studies in particular are providing increasing evidence that carbon assimilated by juvenile fishes in mangrove, marsh and reed habitats is not primarily derived from these macrophytes but comprises a mixture of these sources and a diverse range of macro- and microalgae, particularly epiphytic, epipsammic, epipelic and epilithic diatoms and algae found in these areas The closest trophic link between the macrophyte food chain and associated fishes occurs in seagrass habitats where a significant portion of the overall macrophyte leaf biomass often consists of epiphytic algae and diatoms Structurally, mangrove forests, salt marshes and reed beds provide more substantial and complex habitats for juvenile fish refuge, but some of these habitats are constrained with regard to nursery provision by being fully exposed at low tide Under such circumstances the small fish are sometimes forced into creeks and channels where larger piscivorous fishes are often present Overall, in terms of a broad ranking of the four habitats as potential fish nursery areas, seagrass meadows are ranked first, followed by mangrove forests, salt marshes and then reed beds This ranking does not imply that the lower ranked habitats are unimportant, since these plants perform a myriad of ecosystem services that are not related to the provision of fish nursery areas, eg bank stabilization It is also emphasized that the protection of specific plant species should not be encouraged because it is important to have an ecosystem approach to conservation so that the diversity of habitats and their connectivity for fishes is maintained

The role of seagrass meadows, mangrove forests, salt marshes and reed beds as nursery areas and food sources for fishes in estuaries

highlights is very real and is a major stumbling block to those who have to teach the biology of these groups which probably demands of a biology student a greater vocablary of latinised words than your average classics student. None the less, knowledge advances and the structure that Margulis and Schwartz support here panders to that prejudice. I can see no rational reason to lump the Archaea and the Bacteria into one unit and it impedes comprehension to say that they are one unit on a par, in diversity terms, with the plants. Phylogenetically, the 5-Kingdom system is under active debate as a result of the rapidly accumulating molecular data which have allowed for the first time rational intra-phylum comparison. It is not a stable field yet and we are still trying to identify the largest scale of grouping which is both sensible and convenient. Some of this debate comes over in the introduction, but being pitched at student level is inevitably somewhat oversimplified. The new edition lays down definitions of the Kingdoms themselves and the introduction sections are also greatly expanded. This is a very useful addition which should, I would like to think, stimulate debate about where the demarkation lines should be drawn.

Biodiversity: An Introduction

The fish communities of mangrove and cleared sites were investigated in Gazi Bay, Kenya. Five forested sites were compared with paired sites that had been cleared of mangroves by human activity. Forested sites included plantations and natural stands of Sonneratia alba and natural Rhizophora mucronata stands. Two methods of stake netting were used to take quantitative samples; method one used a single 100-m-long, 18-mm mesh net, method two used paired 24-m-long, 1-mm mesh nets—samples were taken during seven different months in 2002. Mean abundances of fish found in mangrove and cleared sites, respectively, were 0.004 m−2 and 0.014 m−2 (method 1) and 0.21 m−2 and 0.25 m−2 (method 2). Thirty species were sampled, 12 of which were found exclusively in mangrove habitats and 10 of which were limited to cleared sites. The most abundant species in mangrove plots was Atherina afra (although it was only found in two, large catches); the most abundant in cleared plots was Gerres oyena (found frequently). Mean abundance (using data pooled for all sites) was significantly higher in cleared, compared with forested, sites, and multivariate analysis showed significantly different community structures in the two habitat types. There was large variation in catch rates between dates and sites, with one forested site recording no catches at all. These results do not support the predator refuge hypothesis (which predicts higher abundance of juvenile fish inside mangroves). The low abundance of fish recorded in the mangrove sites may have been due to site-specific factors determining fish abundance within mangrove forests, to the sampling techniques used or to relatively high turbidities at these sites.

Mangrove fish: a comparison of community structure between forested and cleared habitats

Fishery trends, resource-use and management system in the Ungwana Bay fishery Kenya

The Malindi–Ungwana Bay fishery Kenya is one of the most important marine fisheries of the Western Indian Ocean. There are two fishing grounds: Formosa and Malindi, with a designated 5-nM no-trawl zone offshore. However, the fishery was faced with numerous resource use conflicts and a decline in catches, culminating in a trawl ban in 2006. This study analyses catches and fishery dynamics before and after the 2006 trawl ban. Results show that artisanal landings declined before the ban, but rapidly recovered within 2 years after the ban was imposed. However, shrimp landings in the artisanal fishery remain low. Commercial shrimp landings gradually declined before the ban: ~550 t in 2001 to 250 t in 2006, and the shrimp: fish bycatch ratio was 1:1.5 compared to early reports of 1:7 in 1999. SIMPER analyses shows that 6 and 16 families (groups) accounted for 91.0 and 90.2% of the similarity in catch within the Formosa and Malindi fishing grounds, respectively. Formosa was important for Claridae, Cichlidae and Protopteridae, while Malindi recorded Carangidae, Siganidae, Carcharhinidae and Lethrinidae as the main families. Future studies should therefore embark on analyses of the factors driving the spatio-temporal distributions of the species and assess the impacts of bottom trawling on fishery dynamics before the trawl ban can be lifted.

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Bottom shrimp trawling impacts on species distribution and fishery dynamics; Ungwana Bay fishery Kenya before and after the 2006 trawl ban

The ratios of stable isotopes 18O:16O and 13C:12C were measured in otolith carbon taken from nine species of fishes caught within mangroves and on the reef at Gazi Bay, Kenya Before analysis, otoliths were divided into `larval'`post-larval' and `adult' sections using a drill Fishes were putatively classified as `mangrove residents'`offshore residents' or `migrants' on the basis of information from the literature, and depending on where they were caught (mangroves only, offshore only or both mangroves and offshore) in the present study Eight of the species exhibited an increase in otolith 13C:12C with age, but this was significant only in the two migrant species Lethrinus harak and Lutjanus fulviflammus There were no consistent patterns in 18O:16O with age, or between migrants and non-migrants These results suggest that comparing absolute values of otolith oxygen and carbon isotope signatures between fish species is not a useful way of determining migration patterns at this site, because of species-specific differences in carbon metabolism and insufficiently steep gradients in temperature and salinity Changes in carbon isotope signatures between life stages within a species, however, do hold promise as migration tracers

Edward Kimani

Papers

Mangrove fish: a comparison of community structure between forested and cleared habitats

Fishery trends, resource-use and management system in the Ungwana Bay fishery Kenya

Bottom shrimp trawling impacts on species distribution and fishery dynamics; Ungwana Bay fishery Kenya before and after the 2006 trawl ban

Stable isotope records from otoliths as tracers of fish migration in a mangrove system

Catch composition and sustainability of the marine aquarium fishery in Kenya