Does the Availability of Various Types and Quantity of Food Limit the Community Structure of the Benthos (Mollusks) Inhabiting in the Hard-bottom Subtidal Area?

먹이생물의 종류와 양이 암반 조하대 저서동물(연체동물) 군집구조 결정요소가 될 수 있는가?

Abstract

Effects of feeding type and food resource availability on community structure of mollusks inhabiting hard-bottom subtidal areas were investigated. By following guidance from several references, mollusks observed in this study were divided into 5 groups according to feeding type - 1) grazing, 2) filter feeding, 3) deposit feeding, 4) omnivorous and 5) predation. The results showed that both grazing and filter feeders were the most numerous, explaining grazing type in the East Sea accounting for 47.9%, 32.6% in the South Sea and 29.6% for filter feeding, and filter feeding as a dominant feeding type in Yellow Sea accounting for 42.3%. Results of this study showed distinctive difference in community structure depending on mechanism of feeding type and geographical areas where sampling took place. With the results, attempts were made to understand whether community structure could be affected by feeding type or feeding availability and found out that community structure depended heavily on food resource availability. In the East Sea where marine algal density was high, the algal community in the forms of thick-leathery and sheet often occurred in water column with high transparency which provides proper environment for growth. In the South Sea where grazing and filter feeding types were predominated similarly, the algal density was high, but had the relative highest phytoplankton density. Whereas in the Yellow Sea showing the lowest algal biomass compared to the one in the East and the South Sea, and phytoplankton density was similar to those. It might be a adequate environment for filter feeders than grazers. This study concluded that community structure of mollusks showing high abundance was present where food resource availability with types and quantity was high.

본 연구에서는 '국가해양생태계종합조사' 결과를 활용하여 "암반 조하대에 서식하는 연체동물의 군집구조가 먹이자원의 종류와 양에 따라 섭식형(feeding type)별로 차이를 보일 수 있는지?"를 확인하였다. 다수의 참고문헌을 바탕으로 연체동물 섭식형을 초식형, 여과섭식형, 퇴적물섭식형, 잡식형, 포식형으로 구분하였을 때, 조사해역에서는 초식형과 여과섭식형이 우점하였다. 해역별로는 동해에서 초식형 비율(47.9%)이 가장 높았고, 남해에서는 초식형(32.6%)과 여과섭식형의 비율(29.6%)이 유사하게 높았으며, 황해에서는 여과섭식형 비율(42.3%)이 우세하여 해역별로 섭식형에 따른 연체동물의 군집구조가 뚜렷한 차이를 보였다. 이 결과를 바탕으로 "연체동물의 해역별 섭식형에 따른 군집구조 차이가 우연한 것인지?" 아니면, 각 "섭식형별 활용 가능한 먹이자원의 종류와 양(조성율, %)적 차이에 의한 것인지?"를 파악한 결과, 섭식형에 따른 군집구조의 차이는 각 섭식형별 활용 가능 먹이자원의 종류와 양적 차이에서 기인됨을 확인하였다. 초식형이 우점한 동해에서는 투명도가 상대적으로 2배 정도 높아 해조류 성장에 유리하였으며, 그 중에서도 엽상형(sheet form)과 다육질형(thick-leathery form)의 해조류 군집이 발달되어 있어 초식형의 먹이자원이 풍부하였다. 한편, 초식형과 여과섭식형의 비율이 유사하게 높았던 남해에서는 해조류 군집이 발달되었을 뿐만 아니라, 식물플랑크톤 밀도가 상대적으로 가장 높았으며, 황해는 타 해역 대비 해조류의 서식량이 가장 낮은 반면 식물플랑크톤의 밀도는 유사하여 여과섭식형의 서식에 유리한 조건이었다. 따라서, 연체동물의 군집구조, 특히 섭식형에 기초한 'Feeding guild'로서의 군집구조는 우연히 결정되는 것이 아니라, 이들의 서식지 내에서 이용 가능한 먹이자원의 종류 및 양이 하나의 주요한 결정 요소로 영향을 미치는 것으로 판단되었다.

Fig. 1. Sampling site of hard-bottom subtidal mollusks and algae in the Korean coasts on May and August from 2015 to 2017 with a specified underwater quadrate and scuba diving.

Fig. 2. Percent composition of feeding type of hard-bottom subtidal mollusks sampled quantitatively from the East Sea of Korea from 2016 to 2017 (in detail see Table 1) with scuba diving and a specified underwater quadrate (a: - 5 m, b: - 15 m).

Fig. 3. Percent composition of feeding type of hard-bottom subtidal mollusks sampled quantitatively from the South Sea of Korea from 2015 (or 2016) to 2017 (in detail see Table 1) with scuba diving and a specified underwater quadrate (a: - 5 m, b: - 15 m).

Fig. 4. Percent composition of feeding type of hard-bottom subtidal mollusks sampled quantitatively from the Yellow Sea of Korea in 2015 and 2017 (in detail see Table 1) with scuba diving and a specified underwater quadrate (a: - 5 m, b: - 15 m).

Fig. 5. Spacial variation of transparency in the Korean coasts on May and August from 2015 to 2017 measured with a Secchi disk in situ. Location in detail see the Table 2.

Fig. 6. Percent composition of feeding type of the hard-bottom subtidal mollusks in the Korean coasts. Annual, stational and vertical data were pooled for analysis (a: East Sea, b: South Sea, c: Yellow Sea).

Table 1. Sampling site, in detail, of hard-bottom subtidal mollusks and algae in the Korean coasts on May and August from 2015 to 2017 with a specified underwater quadrate and scuba diving

Table 2. Survey stations of the transparency in the Korean coasts. Data were collected from MEIS data bank (2015-2017; http://www.meis.go.kr/rest/main)

Table 3. Sampling stations of the phytoplankton in the Korean coasts. Data were collected from MEIS data bank (2015-2017; http://www.meis.go.kr/rest/main)

Table 4. Spacial and vertical variation of percent composition (%) of the mollusk’s feeding type based on the quantitative hard-bottom subtidal samples for 2015-2017 with scuba diving and a specified underwater quadrate in the Korean coasts

Table 5. Spacial and vertical variation of algae biomass with total and two functional forms (sheet (S) and thick-leathery (TL) forms; Litter et al., 1983). Stations represent sum of the number of sampling stations in the each location. Data of the each location were pooled for analysis. Mean represents means of biomass (gDW/m2) of all algae and of the two functional forms at the two vertical positions (- 5 and - 15 m), respectively

Table 6. Spacial variation of the phytoplankton density in the Korean coasts on May and August from 2015 to 2017. Location in detail see the Table 3