The effects of salinity on the density, shell size and survival of a mangrove gastropod: laboratory and field evidence

The macro-detritivore gastropod Melampus coffeus plays an important role in energy transfer in neotropical mangroves and, because it consumes tree leaves, it may be a potential ecological indicator of degraded mangrove areas. The objective of this study was to analyse the spatial-temporal distribution and population dynamics parameters of M. coffeus in mangroves and correlate environmental variables with population density, shell morphology and survival. Samples were collected monthly in two mangrove forests with different salinities, located on the north-eastern coast of Brazil. Height, width and aperture height of the animals’ shell were measured. The effects of salinity on population density and size distribution in M. coffeus were evaluated in field and laboratory experiments. The results showed that populations of M. coffeus present low density and are composed of large individuals during the dry season in both mangrove forests. These populations are denser and show predominance of small individuals during the rainy season when salinity decreases. The results obtained in the experiments confirm the observations in the field. Animals at extreme sizes (small and large) subjected to different salinity treatments over a moderate period showed higher mortality rates than individuals of intermediate size.

Ecological relations between mangrove leaf litter and the spatial distribution of the gastropod Melampus coffeus in a fringe mangrove forest

Leaf litter represents a food source to many organisms that may directly contribute to organic matter decomposition. In addition, the physical presence of these vegetal detritus contributes for the modification of some environmental areas and produce microhabitats that may act as a refuge against predators and desiccation for many animals. The pulmonate gastropod Melampus coffeus (Linnaeus, 1758) (Ellobiidae) is a very common specie in Atlantic Coast mangrove forests and feeds on fallen mangrove leaves. It was hypothesized that the spatial distribution of Melampus coffeus is directly affected by mangrove leaf litter biomass deposition. Thus, this research aimed at evaluating the spatial distribution of these gastropods in relation to the biomass of mangrove leaf litter through a twelve-month period. The study area was established in the middle estuary of Pacoti River, state of Ceará, Brazil where two adjacent zones with different topographic profiles were determined. Samples of Melampus coffeus and leaf litter were collected monthly, throughout a year, from the mangrove ground surface. The results indicated that the presence of twigs in mangrove litter favor the occupation by smaller individuals of M. coffeus, probably because smaller individuals are more susceptible to predator attacks and desiccation than larger ones, and twigs and branches may provide a safe microhabitat.

DISTRIBUSI DAN KELIMPAHAN GASTROPODA PADA HUTAN MANGROVE TELUK AWUR JEPARA

Teluk Awur Jepara merupakan pesisir yang memiliki hutan mangrove yang dijadikan permodelan untuk program rehabilitasi mangrove. Untuk pengelolaan kawasan hutan mangrove secara terpadu perlu diketahui keberadaan biota yang ada di dalamnya. Gastropoda merupakan penghuni tetap hutan mangrove dengan informasi yang masih kurang sehingga perlu dilakukan penelitian tentang kelimpahan dan distribusi gastropoda di dalam hutan mangrove tersebut. Pengambilan sampel menggunakan 3 buah Line Transect sepanjang 100 m dengan jarak 30 m. Line ditempatkan tegak lurus dengan garis pantai. Pengamatan vegetasi mangrove menggunakan metode transek yang berukuran 10x10 m2 yaitu untuk pengamatan tingkat pohon, 5x5 m2 sebanyak dua buah dan 1x1 m2 sebanyak lima buah untuk pengamatan vegetasi mangrove tingkat pancang dan semai. Pengambilan data sampel gastropoda menggunakan kuadran 1x1 m2 sebanyak lima buah yang ditempatkan secara acak pada kuadran 10x10m2. Jenis gastropoda yang ditemukan di hutan mangrove Teluk Awur Jepara didapat 16 jenis yaitu Cerithidea cingulata, Cerithidea cingulata cingulata, Cerithidea quadrata, Cerithidea obtusa, Litorina carinifera, Littorina angulifera, Littorina scabra, Casidula nucleus, Casidula aurisfelis, Casidula multiflicata, Melampus nuxcastaneus, Melampus coffeus, Telescopium telescopium, Sphaerassiminea miniata, Neritina violacea dan Pythia plicata. Vegetasi mangrove yang paling mendominasi adalah Rhizophora mucronata baik pada tingkat pohon, pancang, dan semai. Jenis gastropoda yang paling melimpah dan mendominasi adalah Cerithidea cingulata dan Casidula nucleus. Cerithidea cingulata lebih mendominasi pada daerah mangrove terbuka sedangkan Casidula nucleus mendominasi pada daerah mangrove tertutup yaitu pada daerah mangrove yang lebih rapat. Distribusi gastropoda pada umumnya mengelompok. Keberadaan gastropoda pada hutan mangrove dipengaruhi oleh vegetasi hutan mangrove.

Reproductive cycle and embryonic development of the gastropod Melampus coffeus (Linnaeus, 1758) (Ellobiidae) in the Brazilian Northeast

Melampus coffeus belongs to a primitive group of pulmonate mollusks found mainly in the upper levels of the marine intertidal zone. They are common in the neotropical mangroves. Little is known about the biology of this species, particularly about its reproduction. The aim of this study was to 1) characterize the morphology and histology of M. coffeus' gonad; 2) describe the main gametogenesis events and link them to a range of maturity stages; 3) chronologically evaluate the frequency of the different maturity stages and their relation to environmental factors such as water, air and sediment temperatures, relative humidity, salinity and rainfall; and 4) characterize M. coffeus' spawning, eggs and newly hatched veliger larvae. Samples were collected monthly between February, 2007 and January, 2009 from the mangroves of Praia de Arpoeiras, Acaraú County, State of Ceará, northeastern Brazil. The characterization of the gonad development stages was carried out using routine histological techniques. The results of this study show that Melampus coffeus is a simultaneous hermaphrodite. The follicles have masculine and feminine elements, interleaved within the gonad. M. coffeus presents a well-defined synchronous reproductive cycle, showing successive maturation, release and resting periods. The average diameter of the oocytes was negatively correlated with salinity and positively correlated with rainfall. The results show that no reproductive activity occurs during periods of drought. After the dry season, the increasing rainfall levels and reduced salinity lead to the appearance of very dense populations, predominantly composed of small individuals.

Contribuição de Melampus coffeus (Gastropoda, Ellobiidae) na degradação da serapilheira do médio estuário do rio Pacoti, Ceará, Brasil

A degradação da serapilheira no médio estuário do rio Pacoti foi estudada na presença e na ausência do gastrópode Melampus coffeus (Linnaeus, 1758), visando verificar a possível contribuição desse invertebrado na ciclagem da matéria orgânica dos manguezais. A densidade populacional de M. coffeus e a distribuição das folhas, em termos de biomassa úmida, biomassa seca e abundância, presentes na serapilheira do local, foram estimadas a partir de uma amostragem. Um experimento em campo foi realizado com amostras de coloração e biomassas similares de folhas de Rhizophora mangle (Rhizophoraceae) sem sinais de herbivoria, distribuídas igualmente entre 64 gaiolas. Em 32 destas foram colocados também exemplares de M. coffeus. Essas gaiolas foram distribuídas entre quatro pontos, sendo oito pares de gaiolas (controle e experimento) por ponto. Durante oito semanas, quatro pares de gaiolas foram coletados semanalmente. Após coletadas, os sinais de pastagem nas folhas causados por M. coffeus foram contados e as biomassas úmida e seca das amostras foram determinadas. Comparando controle e experimento, verificou-se que M. coffeus é capaz de contribuir na degradação da serapilheira na área estudada, porém, não foi verificada uma participação significativa desse gastrópode na degradação das folhas quando comparados experimento e controle ao longo do experimento.

Avaliação de efeitos de espécies de mangue na distribuição de Melampus coffeus (Gastropoda, Ellobiidae) no Ceará, nordeste do Brasil

Melampus coffeus (Linnaeus, 1758) é um gastrópode pulmonado, macrodetritívoro, importante na transferência de energia em manguezais neotropicais, mas sua distribuição em diferentes escalas espaciais ainda é pouco conhecida nas regiões brasileiras. Assim, o objetivo deste trabalho foi verificar a distribuição de M. coffeus com relação: 1) às espécies Rhizophora mangle Rhizophoraceae e Laguncularia racemosa Combretaceae; 2) à posição dos rizóforos de R. mangle e 3) à altura das árvores em diferentes manguezais. O seu comportamento ao longo do ciclo de marés também foi descrito. A densidade de M. coffeus foi similar entre R. mangle e L. racemosa, porém os maiores caramujos foram encontrados nas árvores de R. mangle. A distribuição dos caramujos encontrados no sedimento diferiu em relação aos rizóforos, com maior densidade no centro e o maior tamanho na borda da área amostral. Entretanto, não houve relação com a disponibilidade de recursos alimentares formados por folhas. A densidade também foi maior nos manguezais baixo e médio quando comparados ao alto, porém não foram encontradas diferenças de tamanho dos caramujos em mangues de alturas distintas. Observamos também que, durante a maré alta, M. coffeus sobe nas árvores mais próximas. Estes resultados podem estar relacionados principalmente com a disponibilidade de recursos e abrigos fornecidos por R. mangle. Desta forma, novos estudos sobre a distribuição de M. coffeus sob diversas condições são recomendáveis, já que as regiões de manguezais estão cada vez mais sujeitas a perturbações.