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Impact of artificial coastal protection structures on Ascidians settlement along the Tamil Nadu coast, India

Jebarathanam Prince Prakash Jebakumar, Nandhagopal Ganesan, Rajan Babu Bose, Ragumaran Shunmugavel, Ramakritinan Chokalingam Muthiah, Ali Abdul Jaffar, Arshan Mohammed Kaleem, Ravichandran Vijaya

Oceanologia

2019

No. 61 (1)

60--67

Ascidians are one of the dominant marine sedentary filter feeders recorded more frequently as introduced species than other taxa. It is renowned that artificial structures offer novel niches to the non-native species. A yearlong investigation was carried out to understand the role of ascidian colonization on various artificial structures located along 84 stations stretched on the 1076 km long Tamil Nadu coast of South India. It revealed the occurrence of 26 ascidian species, among these18 specimens were identified to species level, 8 were identified to genus level based on morphological characters. As on origin and nativity, out of the total 26,3 species were classified as introduced, 8 specieswere classifiedas native and 15 as cryptogenic species. Interestingly, Polyclinum isipingense and Diplosoma variostigmatumwere reported first time inIndianwaters.Thecryptogenic and colonial forms of ascidians are dominant in the artificial structures. There were significant differences observed between artificial structure type, geographic locations ( p = 0.0071) and between ascidians forms as well as geographic areas ( p = 0.00375). This study also confirms the artificial structures offer new niches for non-native ascidian colonization. The influence of the substrate (structure type) aswell as geographic locations on the biotic assemblage was also observed.

Impact of Chinese mitten crab Eriocheir sinensis on blue mussel Mytilus edulis trossulus – laboratory studies of claw strength, handling behavior, consumption rate, and size selective predation

Wójcik D., Normant M., Dmochowska B., Fowler A.

Oceanologia

2015

No. 57 (3)

263--270

We examined the claw strength, handling behavior, consumption rate, and size selective predation of the invasive Chinese mitten crab Eriocheir sinensis feeding on native Baltic Sea blue mussels Mytilus edulis trossulus during 24 h laboratory experiments. Single starved crabs were offered 15 mussels (five mussels in three length classes) at a time. The total number of mussels consumed by a single crab increased significantly (P < 0.05) with the experimental time from 1.7 ± 0.7 # mussels crab−1 h−1 after 4 h to 0.2 ± 0.7 # mussels crab−1 h−1 after 24 h. The highest consumption rate was observed within the first 4 h, and it decreased significantly (P < 0.05) during the experiment. This was most likely due to the crabs being starved before the start of the experiment. E. sinensis can also harm blue mussel shells by crushing them without further consumption. The mean daily damage, and not consumption, by a single crab was 0.9 ± 1.4 of 11–40 mm mussels. The claw strength of E. sinensis ranged from 1.50 to 20.43 N (mean 8.51 ± 5.93 N) and was significantly correlated (P < 0.05) with sex and both claw size and carapace size. The study showed that E. sinensis may be able to impact the native M. edulis trossulus population abundance in the coastal Baltic waters either through direct predation or indirect mortality by damaging (crushing) the shell.

Population structure, morphometry and individual condition of the non-native crab Rhithropanopeus harrisii (Gould, 1841), a recent coloniser of the Gulf of Gdańsk (southern Baltic Sea)

Hegele-Drywa J., Normant M., Szwarc B., Podłuska A.

Oceanologia

2014

No. 56 (4)

805--824

The aim of this study was to characterise the introduced North American Harris mud crab Rhithropanopeus harrisii, which occurs in the Gulf of Gdańsk, Poland (southern Baltic Sea). Of the 920 specimens caught between 2006 and 2010, males and females made up 44 and 40% respectively, whereas juveniles (<4.4 mm carapace width) comprised 16%. Overall carapace widths ranged from 1.96 mm to 21.40 mm (mean 9.03±4.11 mm). Ovigerous females (mean 11.12±2.76 mm) were present in the population from June to October. Most of the adult specimens collected (n = 158) had carapace widths between 10.1 and 12.0 mm. The wet weight of R. harrisii varied from 0.005 to 4.446 g (mean 0.410±0.569 g). Females exhibited a negative allometric increase in weight (b = 2.77), males an isometric increase in weight (b = 3.02). The condition factor (K) in R. harrisii varied from 0.02 to 0.08 (mean 0.05±0.01).