Niche and interspecies association of shrimps in spring and 

autumn in the east area of Zhoushan Islands

JIANG Xinqin, NIU Weizhen, ZHENG Ji, XU Yongjiu, 

ZHANG Peiyi, LIU Kun, YU Nanjing, YU Cungen

（College of Fisheries, Zhejiang Ocean University, Zhoushan Zhejiang316022, China）

Abstract: In order to understand the competitiveness and utilization status of major shrimps for habitat resources in Zhoushan sea area, this study analyzed shrimp data obtained from the bottom trawl survey of fishery resources conducted in April (spring) and October (autumn) 2018 in waters east of Zhoushan Islands. Niche width, niche overlap, cluster analysis, Pearson correlation test, Spearman rank correlation test, Ochiai index, Dice index and other measures were used to analyze the niche and interspecies relationship among major shrimp species. In this survey, shrimp species occurring in both two voyages were defined as major shrimp species. Pinkas index relative importance(IRI) was used to determine dominant species of major shrimps. Shrimps with IRI≥1 000 were defined as dominant species, and IRI<100<1000 were defined as important species. The results showed that: A total of 32 shrimp species were captured and identified, belonging to 21 genera and 10 families. The dominant species were Metapenaeopsis Barbata, Metapenaeopsis Dalei, Parapenaeopsis hardwickii and Solenocera crassicornis and their IRI were 2 547.26, 2 835.16, 4 507.25 and 1 753.93, respectively. A total of 19 shrimp species were found in both voyages. The top 3 shrimp species were Penaeus chinensis, Parapenaeopsis tenella and Penaeus harteni, with niche widths of 2.41, 2.38 and 2.25, respectively. Aegaeon rathbuni had the lowest niche width, which was 0.53.

According to niche width cluster analysis, the main shrimp species could be divided into 3 groups: wide niche species (niche width value was between 2.00 and 2.50), middle niche species (niche width value between 1.00 and 2.00) and narrow niche species (niche width value less than 1.00). The similarity test was carried out by results of the cluster analysis. The results showed that R=0.943,P=0.001<1%, indicating that the grouping results were reasonable. Main shrimp species niche overlap value ranged from 0 to 0.99, 11 shrimps with overlap value of 0, 6 higher than 0.90, The highest overlap value was 0.99, and the niche overlap value between Aegaeon rathbuni and Processa japonica was significantly different, indicating that there were differences in similarity degree of species in resource utilization.

VR (variance ratio) method was used to calculate the overall correlation between the main shrimp species. VR value was 2.23>1, indicating that there was a positive correlation between the main shrimp species. After analysis by Pearson correlation test and Spearman rank correlation test, the results of the two correlation tests were not completely equal, but both showed significant positive correlation among populations of main shrimps, which was consistent with the results of the overall correlation test.Ochiai index and Dice index were used to measure the degree of interspecific association of major shrimp species. 115 pairs with OI correlation index greater than 0.5, accounting for 67.3% of species logarithms, and 95 pairs with DI correlation index greater than 0.5, accounting for 55.6% of species logarithms. The species logarithms with both indices greater than 0.5 were far more than 50%. The overall results tended to be positively correlated, indicating strong interspecific association.

The niche width of shrimp in the study area was segmented obviously. The high niche width was typical in Solenocera crassicornis and Parapenaeopsis tenella. Both Solenocera crassicornis and Parapenaeopsis tenella were dominant species, indicating that they were evenly distributed and had a large range of activities, and had strong ability to use resources and adapt to environment. The low niche width values might be related to the location of survey stations, the abundance and occurrence of species, and might also be closely related to marine environmental degradation.

The results of this survey showed that there were great differences in the overlap value and degree among main shrimps. The niche width values of Solenocera crassicornis (2.41) and Parapenaeopsis tenella (2.38) were large and had a high degree of overlap with each other, indicating that these species pairs were similar in their ability to utilize habitat resources and occupied similar resource sites.In general, species with smaller niche width values also had smaller niche overlap values with other species, which might be due to their low utilization ability of habitat resources and relatively weak competition between species pairs. Meanwhile, among shrimps obtained in this survey, shrimps with narrow niche width did not necessarily have low overlap value with shrimps. For example, shrimps with the smallest niche width had high overlap value with other species, especially shrimps with Aegaeon rathbuni, which reached 0.99, it might be caused by the high station overlap rate between them.There was a significant positive correlation between the overall association(VR) of major shrimp species, which indicated that there was a phenomenon of interdependence among shrimp species and they had the same or similar needs for habitat resources. Meanwhile, the community structure in this area was stable and showed a positive succession trend. This might be due to the similarity of adaptation or utilization of nonrestrictive factors in the habitat (water temperature, salinity, ocean current, etc.), or to the strong association between the dominant species.Spearman rank correlation test was relatively higher than Pearson correlation test in significant and extremely significant logarithms of shrimp species. The reason may be that Pearson correlation test is a parameter test method, which requires that species must follow a continuous normal distribution, while shrimps in the sea area are distributed in clusters. Spearman rank correlation coefficient test is a nonparametric test method, and there is no requirement for the distribution form of penaeus. Therefore, Spearman rank correlation coefficient test has higher reliability and sensitivity.

The results of this study showed that shrimp species pairs with significant and extremely significant positive correlation in correlation test also had larger niche width overlap value and stronger interspecies association. However, niche overlap and linkage analysis could not fully reveal the internal mechanism of the association between species in a community. In order to fully reflect the relationship between niche overlap and interspecific linkage, it is necessary to select appropriate measurement methods in subsequent investigations and comprehensively consider the changes of niche overlap in multiple dimensions.

Keywords: shrimps; niche breadth; niche overlap; interspecific association; sea area to the east of Zhoushan Islands