Community structure of macrobenthos in Ponnani estuary, South India with reference to occurrence of invasive alien species

Int. J. Aquat. Biol. (2016) 4(4): 269-276; DOI: ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2016 Iranian Society of Ichthyology Original Article Community structure of macrobenthos in Ponnani estuary, South India with reference to occurrence of invasive alien species Ranjeet Kutty*1, Muhsina Chakkayil2, Shahul Hameed Pentam Veli Pura3 1 Department of Fishery Hydrography, Kerala University of Fisheries and Ocean Studies, Panangad P.O., 682 506, Kerala, India. Department of Aquaculture and Fishery Microbiology MES Ponnani College, Ponnani South P.O., 679 586 Malappuram Dist., Kerala, India 3 Department of Aquaculture and Fishery Microbiology MES Ponnani College, Ponnani South P.O., 679 586, Malappuram Dist., Kerala, India. 2 Abstract: Benthic organisms have been studied in past to assess the health of an aquatic ecosystem. Moreover, being sedentary forms they have been used as indicator organisms. In the present study, an attempt has been made to study the distribution and assemblage of major macrobenthic forms occurring in Ponnani estuary. A total of 23 genera of benthic invertebrate fauna belonging to 6 groups viz., Polychaetes, Bivalve, Gastropod, Amphipod, Isopod and Tanaidacian were recorded during the study. Faunistic study revealed that in high saline regions of the estuary (Veliyancode), a very good macrobenthic biodiversity was present. Bivalves were the major group enumerated from Veliyancode and Ponnani (39% and 35%, respectively), while in Biyyam predominance of gastropods (37%) were observed. Among the bivalve groups, presence of Maculista senhousia and Pholas candida, both considered as invasive species was noteworthy. Another interesting observation was the presence of Amphipod Melita zeylanica, another alien species evenly represented in all the three stations, indicating that the species had well established in Ponnani estuary. The present study is the first description of benthic organism assemblages inhabiting in the region. Results indicate that salinity is a major parameter that governs the diversity, occurrence, abundance and distribution of macrobenthos in Ponnani estuary. It also elucidates that any perturbance in the physico-chemical nature of the estuary favours the invasiveness of alien macrobenthic species in Ponnani backwaters. Introduction Estuary is one of the most important coastal life supporting system and an ideal tryst of various economically important marine and fresh water organisms. However, owing to the high primary productivity, suitable physic-chemical conditions and less hydrographical perturbations, they also are favourable grounds for establishment of new alien species. Usually the establishment of a new group in estuary is facilitated with sharp fluctuation in the physico-chemical parameters as part of climate change in the region (Occhipinti-Ambrogi, 2007). Climate change could alter the structure and composition of native communities and, as a consequence, the way an ecosystem functions, increasing the risk of biological invasion. As * Corresponding author: Ranjeet Kutty E-mail address: Article history: Received 28 March 2016 Accepted 9 August 2016 Available online 2 5 August 2016 Keywords: Amphipod Melita zeylanica Benthic community Open estuary Climatic variability invasive species and climate change are considered two of the three main threats to biodiversity, the two operating together could be expected to produce extreme outcomes (Masters and Norgrove, 2010). It is also likely to increase the potential distribution and abundance of invasive species, further enlarging areas at risk of invasion, and threatening even the survival of less prolific groups such as the benthic forms. Temperature is a major factor influencing the settlement of tropical alien species (Ben Rais Lasram et al., 2008). Warming of seawater influences the spatial and temporal distribution of many marine organisms, ranging from phytoplankton and zoobenthos to higher trophic levels (Beaugrand et al., 2008). This warming not only stresses the native 270 Kutty et al./ Macrobenthic fauna of Ponnani Estuary dwellers, but also facilitates the arrival of alien ones, adding extra pressure on the ecosystem (Harris and Tyrell, 2001). Macrobenthos are an important component of estuarine ecosystem and play an important role in the system dynamics (Herman et al., 1999). They are a central element of estuarine food webs, being an important food resource for large crustaceans, fish and birds (Day et al., 1989). Macroinvertebrates cycle nutrients throughout the water column and provide a food source for many economically important fish species (Silva et al., 2006). The spatial heterogeneity of macrobenthos along the estuarine gradient is traditionally described in relation to salinity and sediment composition (Ysebaert et al., 1993). Studies have shown a complex interaction between hydrodynamics, sediment dynamics, and benthic biology in structuring distribution patterns of benthos (Herman et al., 2001). Benthic communities are sensitive to many environmental stresses. Benthic invertebrates are extremely important indicators of environmental changes. The study of the alien species is necessary to understand the long term consequences of marine ecosystems, their goods and services. Since estuarine environments are continuously dominated by species that can thrive well under harsh physico-chemical conditions, the possibility of invasive species establishing in the new environment cannot be ruled out. The impact of these species on native communities has been evaluated in many localities all over the world leading to the concept of biotic pollution. Once invasive alien species become established in large numbers, their consequences are often irreversible. Although there has been fairly good research on the ichthyofaunal diversity of Ponnani estuary, an open estuary of South India, very little works pertaining to the diversity of macrobenthic community in the region has been published. Moreover, the influence of hydrographical parameters on the resident community and occurrence of any invasive alien species in the region has yet to be reported. Under the above pretext, a study was conducted to understand the distribution of macrobenthic community in Ponnani backwaters with a view to develop an in depth knowledge on the environmental dynamics prevailing in the region and also to investigate the establishment of any alien/invasive groups in the region. The major objectives included to make community structure analysis of benthic fauna in Ponnani estuary, analyze spatial distribution of benthos based on salinity regime prevailing in the region and to identify the presence of any alien/invasive macrobenthic group in the region. Materials and Methods Study Area: The Ponnani estuarine system is located between 10°46' and 10°48' N and 75°54' to 75°56' E. It is an open estuary drained by a tributary of the Bharathappuzha River, (...truncated)