Botanica Marina 2018; 61(6): 547–557 Nina Ann Jin Ho, Jillian Lean Sim Ooi*, Yang Amri Affendi and Ving Ching Chong Influence of habitat complexity on fish density and species richness in structurally simple forereef seagrass meadows https://doi.org/10.1515/bot-2017-0115 Received 1 December, 2017; accepted 12 October, 2018; online first 14 November, 2018 Abstract: Seagrass meadows are highly productive habi- tats that support commercially and ecologically impor- tant fishes and invertebrates. However, evidence of fish-habitat relationships are seldom drawn from forereef seagrass meadows that are structurally simple in terms of species richness and relative size and, consequently, their role as habitats is unclear. In this study, fish-habitat relationships were examined in such meadows in the for- ereef seagrasses of Tinggi Island and Babi Besar Island, Malaysia, by documenting habitat complexity attrib- utes (canopy height, shoot density and percent cover), distance to adjacent coral reefs, and water depth within 2 × 2 m quadrats. Fish assemblages were recorded using the Remote Underwater Video Station method. A total of 1166 individuals from 86 taxa were found and enumer- ated. This study showed that (1) fish density and species richness were significantly associated with seagrass per- cent cover alone; (2) commercially important carnivores formed the majority of the fish populations in the mead- ows, and (3) fish density and species richness were posi- tively correlated with distance to the nearest adjacent coral reef, indicating the need to account for the effects of neighboring habitats in studies of this nature. Thus, structurally simple seagrass meadows are still important fish habitats, especially as feeding grounds for commer- cially significant carnivores. Keywords: fish-habitat relationships; forereef seagrass; marine park area; remote underwater video station. Introduction Seagrass meadows are well recognized as high-produc- tivity marine habitats that function as nursery and for- aging grounds for many commercially and ecologically important invertebrates, fishes, and other large verte- brates including sea turtles and dugongs (Nagelkerken et al. 2000, Duarte 2002, Larkum et al. 2006). Despite this, most marine protected areas (MPA) are declared for the general protection and conservation of coral reefs and mangrove habitats, whilst seagrass habitats receive incidental and thus, indirect protection. This may partly be due to a lack of knowledge about the significance of this habitat in maintaining fish popula- tions (Unsworth and Cullen 2010). Meanwhile, seagrass meadows are declining worldwide at an alarming rate due to numerous factors, including climate change and anthropogenic effects on coastal ecosystems (Duarte 2002, Orth et al. 2006, Waycott et al. 2009). The loss of seagrass habitat also marks a loss of habitat complex- ity in soft-sediment substrate, causing disruption to ecosystem services that include nursery function and food provision (Duarte 2000, Worm et al. 2006). Con- sequently, fisheries productivity will be greatly affected by the loss of seagrass, particularly for commercially important fishes that utilize seagrass habitats as nursery and foraging grounds (Hemminga and Duarte 2000, Nagelkerken et al. 2000). The loss of habitat is not the only concern. The structural quality of a habitat is also an important con- sideration because habitats can occur as a range of structurally “simple” to “complex” entities in an abso- lute sense, or can undergo natural or induced changes from one to the other. Ecologists have long acknowl- edged the importance of habitat structural complexity and its relationship with species richness and abun- dance, although the mechanisms behind this effect are still unclear (Kovalenko et al. 2012). Habitat complexity has been defined and measured in many different ways (Bartholomew et al. 2000) but, in the popular defini- tion by McCoy and Bell (1991), “complexity” refers to the absolute abundance of habitat structural components. *Corresponding author: Jillian Lean Sim Ooi, Department of Geography, Faculty of Arts and Social Sciences, University of Malaya, 50603, Kuala Lumpur, Malaysia, e-mail: jillian_03@um.edu.my Nina Ann Jin Ho and Ving Ching Chong: Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia Yang Amri Affendi: Institute of Ocean and Earth Sciences, University of Malaya, 50603, Kuala Lumpur, Malaysia Brought to you by | Lancaster University Authenticated Download Date | 4/12/19 3:44 PM