Peter J. Hogarth

Breakdown of mangrove leaf litter in a managed mangrove forest in Peninsular Malaysia

Decomposition of Rhizophora apiculata, Rhizophora mucronata, Bruguiera parviflora and Sonneratia alba leaves was studied in situ using litter bags in both Cleared and Virgin Jungle Reserve (VJR) mangrove forests in Peninsular Malaysia. A single exponential model best described the rate of decomposition for each species. All leaf species decomposed faster in the VJR site than in the Cleared site (R. apiculataP <0.05, R. mucronataP <0.01, B. parvifloraP <0.01, S. alba not significant and mixed bags P <0.05). The rate of decomposition was species specific: Sonneratia alba leaves decomposed the fastest (P <0.001) in both sites. The time in days required for the loss of half the initial dry mass (t50) was Cleared site: R. apiculata 76, R. mucronata 122, B. parviflora 122, S. alba 22, mixed 51; VJR: R. apiculata 43, R. mucronata 34, B. parviflora 70, S. alba 15 and mixed 32. Increasing litter diversity, by mixing leaves of different species in bags, had no effect on decomposition rate. The mass of air controls showed an initial decline to 65% in 14 d but then remained fairly constant (t50=108 d). This initial loss may represent the leaching of dissolved organic matter. Water controls (mixed litter bags submerged in seawater) had a t50 of 10 d, a rate significantly different (P < 0.01) from air controls. Our results show that breakdown of leaf litter is site and species dependent. This affects ecological functioning of the mangrove ecosystem and may have implications for management and conservation of mangroves.

A baseline study of the diversity and community ecology of crab and molluscan macrofauna in the Sematan mangrove forest, Sarawak, Malaysia

Baseline ecological studies of pristine mangroves are important for monitoring, management and conservation of mangrove ecosystems. Diversity, density, biomass and community structure of crab and molluscan macrofauna were studied in a near-pristine mangrove forest in Sematan, Sarawak. In each of the nine 100-m 2 plots, six 15-min catching periods were used to collect crabs and three 1-m 2 quadrats were sampled for molluscan epifauna. Environmental variables and vegetation were also recorded in each 100-m 2 plot. Thirty-one crab species and 44 molluscan species were recorded, including a few species not previously reported from Sarawak. Crab community structure was correlated with topographical height and surface water pH and salinity. Gastropod community structure was correlated with redox potential of water at depth, topographical height, surface water pH and leaf litter. Crab community structure and species number were positively correlated with tree and seedling community structure and diversity, suggesting that the mangrove vegetation is important to the crab fauna as a habitat and food supply. Molluscan abundance was positively correlated with sapling diversity and negatively correlated with the numbers of mangrove associates and tree species. The young leaves on mangrove saplings may provide a better food source than those on mature trees or mangrove associates. The data from this study provide a valuable baseline for future use at this site and for comparison with more degraded mangrove habitats elsewhere in South-East Asia.

A Comparison of Brachyuran Crab Community Structure at Four Mangrove Locations under Different Management Systems along the Melaka Straits-Andaman Sea Coast of Malaysia and Thailand

Brachyuran crab community structure was compared between mangrove sites under different management systems from four locations along the Melaka Straits-Andaman Sea Coast. Klong Ngao, a mangrove estuary in Ranong Province of southern Thailand, lies within a Biosphere Reserve designated in 1997. Sites were positioned in plantations at a former charcoal concession forest, a disused tin mine, and an abandoned shrimp pond along this estuary. The Merbok estuary in Kedah, Malaysia, is partially managed: the mangroves are cut for charcoal and poles on a small scale and the forests are left to regenerate naturally. The Matang Mangrove Forest Reserve in Perak, Malaysia, is heavily exploited but well managed, forRhizophora wood to produce charcoal, and has been for 100 years. Sites were positioned in plantations of different ages. Kuala Selangor Nature Park, Selangor, Malaysia, was established as a nature reserve in 1987 and contains mature mangrove forest regenerating naturally from previous selective felling. At Klong Ngao and Matang, mature reserve forest sites were also studied for comparison with plantation sites. The sites included both upstream and downstream locations and were of similar area, minimizing effects from possible species-area relationships. Sites were chosen with similar environmental conditions and with a dominance ofRhizophora spp. At each site per location, the brachyuran crabs were sampled quantitatively in 100 m2 quadrats by three independent 15-min timed crab catches. The crab community recorded was analyzed by univariate and multivariate statistical techniques. Management history plays an important role in moderating the crab community structure. The crab community also changes with the age of the mangrove forest stand. Sesarmid crabs consistently dominated in mature forests, whereas young plantations were colonized mainly by ocypodid crabs. The findings show that heavily effected sites—e.g., disused tin mining areas, former concession forests, and abandoned shrimp ponds—can be rehabilitated by planting mangroves and that the crab community is a useful ecological indicator of habitat status.

Aspects of mangal ecology along the Red Sea coast of Saudi Arabia

Surveys of the mangal along the Red Sea coast of Saudi Arabia form the basis of this study. Both soft-bottomed mangals and the less well known hard-bottomed mangals are represented. The distribution of Avicennia marina, the dominant mangrove species, is discontinuous in the northern part of the Red Sea. Its development increases southwards, and mean height is inversely correlated both with latitude (P<0·05) and salinity (P<0·05). Another species, Rhizophora mucronata, was recorded in only five areas. Molluscs and crabs represent the principal faunal elements within the mangal. The density of Cerithidea cingulata, the dominant mollusc species, shows significant correlation (P<0·01) with the abundance of blue-green algae. Four species of fiddler crab (Uca) are included among the crab fauna of the mangal, one of which (U. urvillei) is here newly recorded for the Red Sea. Evidence is given for suggesting that the mangal biota in the region sampled may not be distinctive. Rather, it consists of many species fo...

The response of predators to varying densities of Gregaria locust nymphs

Abstract The response to varying densities of prey was investigated by presenting predators (four human volunteers and a lizard, Lacerta lepida Daudin), in an arena, with from 5 to 120 fifth instar phase gregaria nymphs of the desert locust (Schistocerca gregaria Forskal). The activity of the nymphs was also varied by varying the feeding and temperature conditions. Above a certain prey density (which differed between predators) human catching efficiency declined, while the lizard became totally incapable of catching any locusts. Efficiency of all predators was reduced by increasing activity of the prey.

Anomuran Crustacea (Paguridea, Porcellanidae, and Hippidea) from Oman, principally from Dhofar province, southern Oman

Anomura (Crustacea, Decapoda) are described from 5 collection sites in Dhofar (southern Oman) and from near Muscat (northern Oman). These consist of the following: Paguridea: Aniculus erythraeus, Calcinus (3 species), Cestopagurus coutieri, Clibanarius (3 species), Dardanus (5 species), Diogenes (2 species), Paguristes (2 species) and Coenobita scaevola; Porcellanidae: Pachycheles (2 species), Petrolisthes (7 species), Pisidia (3 species) and Polyonyx (1 species, probably undescribed); and Hippidea: Emerita holthuisi, Hippa pacifica and Albunea steinitzi. The anomuran fauna of the region is not well known, and that of Dhofar has not previously been investigated. The present records establish a number of significant range extensions. The anomura species composition of Dhofar is discussed in relation to that of other areas of the Indian Ocean. In general, pagurideans appear less cosmopolitan, and more parochial within the region than porcellanids. This is discussed in relation to larval dispersal and other ...

Brachyuran crabs (Xanthoidea: Xanthidae, Pilumnidae, Menippidae and Trapeziidae) of southern Oman

Thirty-eight species of xanthoid crab are recorded for the first time from Dhofar Province, southern Oman. The geographical range of three species [Nanocassiope alcocki (Rathbun 1902), Actumnus digitalis (Rathbun 1907), and Macromedaeus crassimanus (A. Milne Edwards 1867)] is substantially extended. The pattern of xanthoid species diversity is discussed in relation to the effect of the seasonal monsoon-driven upwelling, and compared with that of other parts of the Western Indian Ocean.

Passive Transfer of Immunity

Although mammalian fetuses are generally capable of antibody synthesis well before birth, little antibody is in fact produced. This is doubtless due partly to depression of the immune response by various immuno suppressive measures (p. 134). However, it stems also from the fact that the fetus is protected from exposure to foreign antigens (other than those of the mother herself). After birth, this is no longer the case, and the newborn mammal is suddenly and simultaneously exposed to a wide spectrum of microorganisms, many of them pathogenic. An immunologically naive animal, possibly with some residual depression of its capacity to respond, would be extremely vulnerable to this onslaught.

Pattern Polymorphism and Predation in the Shore Crab, Carcinus Maenas (L.)

consumption of only 0.12 ml Oo/g/hr. compared to the smallest animal (1.84 g) which had a mean oxygen consumption of 0.49 ml 02/g/hr. The unit rate of metabolism, the theoretical metabolic rate when body weight is 1 g, for Coenobita is 0.70 ml 02/g/hr. at 24? C. This is relatively large when compared to a fully aquatic crustacean such as Procambarus alleni which has a unit metabolic rate of only 0.115 ml 02/g/hr. at 25? C. Uca, a littoral crab, has a higher unit oxygen consumption of 0.019-0.217 ml 02/g/hr. at 24? C, while Talitrus, a littoral amphipod, has a unit oxygen consumption of 0.533 ml 02/g/hr. at 25? C (Wolve kamp & Waterman, 1961). The data acquired in the present study for Coenobita, one of the most terrestrial species of Decapoda, support observations by previous workers that terrestrial Crustacea exhibit higher unit oxygen consumption than more aquatic species. Edney (1961) suggests that the ready availability of oxygen and the low density of air permit rapid and prolonged locomotion and subsequent elevated oxygen consumption in terrestrial species. However, higher rates of oxygen consumption in terrestrial species may also be a reflection of the increased energy required to cary the mass of the animal in a less buoyant medium.

Crabs in Labs: The Shore Crab (Carcinus maenas) as Teaching Material.

The Shore Crab (Carcinus maenas) is an excellent subject for school study, both in the field and the laboratory. It is easily collected and maintained and can be used for a wide range of investigations. Some background details are given and possible areas of investigation suggested.