Recovery of Subtidal Benthic Macroinvertebrate Communities Following Natural and Experimental Disturbances

<p>The recovery processes of subtidal benthic macroinvertebrate communities following large-scale natural and meso-scale experimental disturbances were studied in Wellington Harbour, New Zealand, a temperate semi-enclosed embayment. This is the first time that long-term effects (>1 year post-disturbance) of a naturally occurring toxic plankton bloom have been investigated in the Southern hemisphere. For 2 years macroinvertebrate communities were studied at three sites of differing hydrodynamic regime. Samples were taken with a Van Veen grab and washed through a 500 [mu]m mesh. Community recovery following the bloom was site-specific. Multivariate analyses revealed that at two sites community recovery was not completed >3 years post-bloom, whereas at the third site the community composition oscillated from year to year, but did not show any signs of a sequential recovery process. The hydrodynamic regime was identified as a major factor influencing the observed recovery processes. Communities exposed to an active hydrodynamic regime were less affected by the bloom and recovered faster, as they were naturally in a perpetual state of recovery as indicated by a dominance of r-selected species. The community at the hydrodynamically less active site was more affected by the bloom. Complete recovery to the pre-disturbance climax community dominated by K-selected species was estimated to take 4-5 years, if not interrupted by other disturbances. For the first time a defaunation experiment was conducted in a hydrodynamically active site to mimic the effects of a plankton bloom on the benthic macroinvertebrate community. Three sediment plots of 25 m2 were covered by plastic tarpaulins, thereby creating a benthic die-off caused by oxygen depletion. This method of defaunation had not been used in the subtidal before. Community recovery was studied for 1 year and compared with community composition in undisturbed control plots. Macroinvertebrate samples were taken by diver-operated cores and washed through a 500 [mu]m mesh. Recovery was slow until after 70 days when abundance and number of species increased synchronously in disturbed and control plots. Multivariate analyses showed that community composition fluctuated strongly in the first 100 days. After 1 year, although disturbed and control communities were converging, differences in community composition were still significant. Time for complete recovery was estimated to be approximately 2 years. Predictions of current succession models were generally fulfilled in both studies. Recovered communities were similar in their composition to either pre-disturbance or surrounding communities. The major deviation from model predictions was that no abundance peak of opportunistic species occurred in either study. Timing of the disturbance, in both studies past the major macroinvertebrate recruitment peak, and the hydrodynamic regime were identified as major factors influencing recovery processes of the communities studied. Such deviation from model predictions indicates that the general models cannot take into account the multiplicity and complexity of factors influencing recovery processes. Thus, their applicability in predicting recovery times and endpoints for specific disturbances at specific locations is limited. Location-specific models might be a useful alternative. Recommendations are made to combine uni- and multivariate techniques to assess recovery processes due to their different sensibilities to changes in community composition.</p>

Recovery of Subtidal Benthic Macroinvertebrate Communities Following Natural and Experimental Disturbances

<p>The recovery processes of subtidal benthic macroinvertebrate communities following large-scale natural and meso-scale experimental disturbances were studied in Wellington Harbour, New Zealand, a temperate semi-enclosed embayment. This is the first time that long-term effects (>1 year post-disturbance) of a naturally occurring toxic plankton bloom have been investigated in the Southern hemisphere. For 2 years macroinvertebrate communities were studied at three sites of differing hydrodynamic regime. Samples were taken with a Van Veen grab and washed through a 500 [mu]m mesh. Community recovery following the bloom was site-specific. Multivariate analyses revealed that at two sites community recovery was not completed >3 years post-bloom, whereas at the third site the community composition oscillated from year to year, but did not show any signs of a sequential recovery process. The hydrodynamic regime was identified as a major factor influencing the observed recovery processes. Communities exposed to an active hydrodynamic regime were less affected by the bloom and recovered faster, as they were naturally in a perpetual state of recovery as indicated by a dominance of r-selected species. The community at the hydrodynamically less active site was more affected by the bloom. Complete recovery to the pre-disturbance climax community dominated by K-selected species was estimated to take 4-5 years, if not interrupted by other disturbances. For the first time a defaunation experiment was conducted in a hydrodynamically active site to mimic the effects of a plankton bloom on the benthic macroinvertebrate community. Three sediment plots of 25 m2 were covered by plastic tarpaulins, thereby creating a benthic die-off caused by oxygen depletion. This method of defaunation had not been used in the subtidal before. Community recovery was studied for 1 year and compared with community composition in undisturbed control plots. Macroinvertebrate samples were taken by diver-operated cores and washed through a 500 [mu]m mesh. Recovery was slow until after 70 days when abundance and number of species increased synchronously in disturbed and control plots. Multivariate analyses showed that community composition fluctuated strongly in the first 100 days. After 1 year, although disturbed and control communities were converging, differences in community composition were still significant. Time for complete recovery was estimated to be approximately 2 years. Predictions of current succession models were generally fulfilled in both studies. Recovered communities were similar in their composition to either pre-disturbance or surrounding communities. The major deviation from model predictions was that no abundance peak of opportunistic species occurred in either study. Timing of the disturbance, in both studies past the major macroinvertebrate recruitment peak, and the hydrodynamic regime were identified as major factors influencing recovery processes of the communities studied. Such deviation from model predictions indicates that the general models cannot take into account the multiplicity and complexity of factors influencing recovery processes. Thus, their applicability in predicting recovery times and endpoints for specific disturbances at specific locations is limited. Location-specific models might be a useful alternative. Recommendations are made to combine uni- and multivariate techniques to assess recovery processes due to their different sensibilities to changes in community composition.</p>

EVALUASIKEBERHASILANPENEBARANIKANBANDENG(Chanos chanos) DIWADUK IR. H. DJUANDA

Waduk Ir. H. Djuanda mempunyai potensi pengembangan budi daya ikan yang tinggi, dan pertumbuhan budi daya tersebut berkembang sangat pesat. Perkembangan yang pesat tersebut sangat berdampak pada penurunan kualitas air dan mendorong peningkatan kelimpahan plankton yang sangat tinggi. Oleh karena itu, pemerintah melakukan penebaran ikan bandeng (Chanos chanos) pada bulan Juli sampai Agustus 2008 sebanyak 2.116.000 ekor benih dalam upaya menanggulangi kelimpahan plankton yang tinggi dan sekaligus meningkatkan produksi ikannya. Tujuan penelitian ini adalah untuk mengevaluasi keberhasilan penebaran ikan bandeng di Waduk Ir. H. Djuanda, Purwakarta, Jawa Barat. Penelitian ini dilakukan setiap bulan pada periode bulan Juli 2008 sampai Januari2009. Pengamatan dilakukan denganmetode teratifikasi dengan enamtitik stasiun pengamatan. Evaluasi keberhasilan penebaran ikan bandeng dievaluasi kemampuan memanfaatkan kelimpahan plankton, pertumbuhannya, dan dapat tertangkap kembali.Hasil analisis kebiasaanmakan, ikan bandeng mempunyai kemampuan yang tinggimemanfaatkan kelimpahan plankton di perairan tersebut, dan ikan ini mempunyai laju pertumbuhan yang sangat cepat (K=3.381 dengan L”=45 cm). Ikan bandeng ini dapat tertangkap kembali oleh nelayan setempat pada bulan September 2008 sampai Pebuari 2009 dan juga secara tidak langsung mampu memperbaiki kualitas perairanWaduk Ir. H. Djuanda. Oleh karena itu, dalam upaya peningkatan dampak penebaran ikan bandeng untuk memperbaiki kualitas perairan dan peningkatan kesejahteraan nelayan, maka perlu dilanjutkan penelitian strategi penebaran ikan bandeng dan penguatan kelembagaan nelayan yang ada. Ir. H. Djuanda Reservoir has high potency in developing of fish culture, that the growth has developed very fast. The fast growth of fish culture affected the degradation of water quality and push increasing of plankton abundance. Therefore, government conduct stocking of bandeng on July until August 2008 as much 2,116,000 individual as on effort of overcoming of plankton bloom and increasing of fish production. The aim of this study is to evaluate the successfulness of fish stocking of bandeng (Chanos chanos) in Ir. H. Djuanda Reservoir, Purwakarta, and West Java. The research was conducted every month at period of July 2008 until January 2009. Observation was done by sampling stratification method at 6 point of observation station. Evaluation of successfulness fish stocking base on the ability using of plankton, the growth and percentage of recaptured. The result should that bandeng have high ability inusing of plankton in waters as a feed (97.8%), and this fish had high growth rate (K=3.381 and L”=45 cm). This fish could be recaptured by local fisherman in September 2008 until February 2009. Beside, this bandeng stocking indirectly have been able to improve waters quality of Ir. H. Djuanda Reservoir. Therefore, the effort of increasing impact of bandeng stocking improved waters quality and improvement of fisherman prosperity, thus require to be continued of bandeng stocking and reinforcement institute of local fisherman.

Constraints and prospects of carp production in Rajshahi and Natore districts, Bangladesh

This study was conducted in Rajshahi and Natore districts of northern area of Bangladesh for a period of three years (2007 to 2009). One hundred carp ponds were selected randomly and fish farmers were interviewed to reveal the existing constraints and prospects. Ten percent farmers reported multiple ownership as a problem and 16% farmers stated that lease value of pond is too high which reducing their profit level. Lack of quality fish seeds was reported by 33% farmers which results in low growth and high mortality of fishes. Nine percent carp farmers reported that inorganic fertilizers were not giving expected performances. Thirty three percent carp farmers failed to apply required inputs in due time due to lack of sufficient credit. Plankton bloom was recorded in 18% ponds. Three percent fish farmers were found to be affected by flood and drought. Eight percent farmers reported non-severe attack of disease. Fish poaching and poisoning were revealed as major constraints. Thirty six percent farmers mentioned lack of technical supports. Due to found constraints, the farmers failed to use inputs and experiences properly resulted in unsatisfactory fish production (3598.72±785.83 kg/ha/yr) to the carp farmers. Further research efforts are recommended to assess the specific impacts of recorded constraints on fish production.DOI: http://dx.doi.org/10.3329/ujzru.v31i0.15435Univ. j. zool. Rajshahi Univ. Vol. 31, 2012 pp. 69-72