Lunar influenced community structure among Seagrass associated Epifaunal

Introduction

Generally, lunar behaviors result from established rhythmicity through evolutionary success as an outcome of favorable mechanisms such as mating, fertilization, nursery retention, and; predation (Omori, 1995). These favorable adaptive mechanisms influence reproductive rate, population density, and community structure. Literature has documented the reproductive cycles of planktons, corals, fishes, and mollusks as influenced by lunar phases but rarely in a community structure viewpoint. Reproductive success of organisms became an adaptive significance, establishing; the "rule of the game," and organisms exhibited community assemblages patterned upon this rhythm.

The lunar cycle refers to the 29.5 days- lunar month, required for the moon to orbit around the Earth, and; the 24.8 hours -lunar day, required for the moon to travel by the same spot around the Earth (Stolov, 1965; Bell & Defouw, 1966). These two lunar cycles give rise to several environmental patterns, such as illumination levels, tides, and geomagnetic fields (Kronfeld-Schor et al., 2013; Naylor, 2001). Like all organisms, moonlight affects macroinvertebrates' behavior and survival, as moon phases directly affect the lunar intensity and tidal pattern. Shore crab (Carcinus maenas) molts habitually during spring tides than neap tides with fortnightly periodicity. Molting during neap tides, when the crab's habitat is exposed, is maladaptive for juveniles' lack of cover, making them susceptible to damaging wave action and predation (Naylor, 2001). Peak molting after the new or full moon is advantageous for the crabs since they are covered by seawater at high spring tides.

Species in diverse phyla exhibit lunar rhythms, mostly in their reproductive behavior. Many examples of varying complexity are known among annelids and all marine polychaetes. Their periodicities and causation are variable and often poorly understood. Sponges that release larvae (spawn) based on their perception of environmental light calculate the time of the day, establishing a lunar rhythm, either an endogenous circalunar clock or an exogenous rhythm driven directly by moonlight (Tessmar‐Raible et al., 2011). Other invertebrate phyla, such as Mollusca, Echinodermata and Arthropoda have also exhibited lunar rhythms, but most are poorly documented (McDowall, 1970).

Light changes during the lunar cycle influence rhythms among organisms in several non-mutually exclusive ways. Light intensities from the moon's phases change the ability of animals to use visual cues and senses like communication, navigation, and prey or predator location (Kronfeld-Schor et al., 2013). Ecosystem functions affect the activity levels of predators, competitors, and prey, attributed to visual acuity and prey activity fluctuations (Kronfeld-Schor et al., 2013). Prey visualization resulted in successful detection, capture, and even avoidance. Prey and predators are in a constant disposition of eating and being eaten; both are exposed to probabilities and risks of foraging. Predation with the influence of moonlight enables the organism to be successful in nocturnal foraging. As moonlight intensity changes, predation activities will also change, generating a pattern of a lunar rhythm.

Nighttime is an integral part of the diel cycle, and several macroinvertebrates have demonstrated nocturnal activity in different aquatic ecosystems (Florencio et al., 2011). These rhythms, patterned into a lunar cycle, establish an assemblage of organisms accustomed to predictive behavior based upon adaptive significance at night time. Community structures depict distinct assemblages shifting from diurnal-nocturnal patterns, giving a complex dynamic in seagrass-associated epifaunal macroinvertebrates. Seagrass communities should be regarded in a parallel outlook and should be studied based on this temporal frame. In a study by Matillano and Rosada, 2022, diel collections manifested increased species richness compared to a diurnal collection showing that there were more active species at night compared to day time. As lunar phases influence population assemblages, community structure is also patterned within these rhythms. This paper seeks to (1) identify species of seagrass-associated macrofaunal invertebrates and; (2) depict the community structure patterned upon the lunar phases employing the same sites used by Matillano and Rosada, 2022.

Seagrasses provided complex and critical habitats for macroinvertebrates and had been confronted with continuous threats (Matillano, 2017) from both natural and human influence. In the Philippines, there are 16 seagrass species out of the 47 species worldwide (Fortes, 2012), harboring macroinvertebrates communities that are primarily active at night (Hessing et al., 2018). Diverse phyla such as Cnidaria, Annelida, Mollusca, Echinodermata, and Arthropoda were reported to exhibit lunar rhythms; however, it is poorly documented (Campbell et al., 2015).