UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 Effects of ocean tides, tidepool shorelines, their biota are generally less well-stud- ied compared to that of broader intertidal areas or nearby shallow-water marine environments in assemblages at Lalakea and which they are generally nested (Almada & Faria Lehia Beach Parks, Hilo, 2005; Cox et al. 2013; Wiegner et al. 2016). Little - Lisa L. K. Mason, Nikola Rodriguez, Sebastian and fewer studies have examined factors affecting Abraham Waiola Wells community structure and dynamics of tidepools Conservation Biology Environmental Science 601 at either the regional or local scale (Cox et al. 2011). The high variability of tidepool structure Abstract and functionality from one locale to another poses Marine tidepools are unique ecosystems that unique challenges for comparing tidepool char- provide critical habitat and refugia to many near- acteristics between locations (Arakaki & Tokeshi shore species. The abundance and diversity of spe- 2019). Nonetheless, tidepools are important eco- cies within tidepool communities are highly vari- logical zones that are deserving of more focused pool size, water quality, and their proximity to the ocean and outlying reefs. In this study, we exam- Tidepools are distinct rocky marine or estua- ined the effects of three physical characteristics rine habitats that are daily connected to the ocean - Fish assemblages were assessed in terms of abun- pletely isolated from surrounding water bodies dance, species richness, and species composition. during low tides. Tidepools are known to harbor a We tested the effects of ocean tides (high vs low), diverse collection of marine species. Some species tidepool location (Lehia vs Lalakea), and tidepool may live their entire lives in tidepool areas, while others are only temporary residents that eventually - disperse to outer ocean areas as they outgrow the - - cies richness at high tides and lower at low tides. semblages and may disperse far beyond local We found that changes in ocean tides did not affect coastlines (Stamoulis et al. 2018; Friedlander et al. - 2019). Tidepools vary widely in their abiotic char- acteristics (Nakamura 1976; Todgham et al. the larger tidepools at each location, and higher 2006; Cox et al. 2011), community compositions (Metaxas & Lewis 1992; Shelton 2010), and en- a difference in species composition between loca- ergy dynamics (Trussell et al. 2004), and serve as tions and between pool sizes. We found that ma- unique ecotones between terrestrial and marine nini (Acanthurus triostegus), aholehole (Kuhlia ecosystems (Ray & Hayden 1992). Many taxa uti- sandvicensis), and mamo (Abudefduf adbomina- lize tidepools as breeding areas (Moring 1986), lis refugia (Underwood & Chapman 1996) from predators (Dethier 1980), and as integral parts of assemblages across sites similar to the ones in this study may serve as a critical strategy for sustain- Tidepools comprise rocky substrata (Arakaki et al. 2014) that provide ample shelter and resources Introduction One of the most prominent and diverse features 1990; Bezerra et al. 2017). Fishes in tidepool sys- of Hawaiian intertidal areas are tidepool systems. - Although tidepools are common along Hawaiian dents or transients (Machado et al. 2015) whose 108 UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 movements across tidepool systems can strongly of the calendar and provided inspiration for this - research. nity structure (Metaxas & Scheibling 1993) and - trophic dynamics (Castellanos-Galindo & Giraldo - 2008) across the system. Little is known about the degree to which phys- - - semblages at high and low tide at Lalakea Beach tion of biological communities in tidepool sys- abundance and species richness would be greater at high tide than low tide across locations because (i.e., abundance, species richness, and diversity) deeper pools and wider ocean connections at high in tidepool systems across the world are related to - factors such as geographical location and latitude (Arakaki et al. 2014), temperature (Cox et al. 2011; would differ based on location and pool size, with Shelton 2010), pool areas and depths (Mahon & no effect based on high or low tides. At each site, Mahon 1994; Cox et al. 2011), microhabitat fea- tidepools were situated at varying distances from tures (Willis & Roberts 1996), and the physical makeup of the benthos (Metaxas et al. 1994; Cox could be found at each of the pools at the different et al. 2011; Bezerra et al. 2017). Additionally, locations. Additionally, we predicted that larger shoreline topography (Archambault & Bourget pools would contain a larger number and higher & Scheibling 1993) may affect the biota of marine of resources in larger areas and deeper water. We coastal areas including tidepools. These types of interactions are well-studied for many other tropi- Beach and Lehia Beach parks, where we counted cal and temperate locations but not necessarily in - - pool at different tides during November 2019. line topography, their degree of connectedness to Methods the open ocean, and proximity to the waterline are Study sites considerably variable across Hawaiian coastlines. It is not known to what effect diel changes such as two sets of rocky intertidal tidepools along the - Beach (LALA), is situated near residential prop- A major source of traditional ecological knowl- erties and is exposed to moderately high levels (Friedlander et al. 2002). This tool was constructed Lehia (LEHI), is located away from residential by Hawaiians of old to reinforce understandings properties, yet, still experiences some level of of the interconnectedness between terrestrial and marine systems. Additionally, it describes many of sites due to the presence of the set of comparable the natural rhythms of physical and ecological pro- tidepool pairs (i.e., relatively similar sizes, depths, cesses that guide harvesting and replenishment of and structures) at two different locations along the coastline. Additionally, these sites were easily ac- spawning, aggregation and feeding behaviors over cessible for surveys. the course of a moon cycle can be gleaned from The presence of apparent natural features the calendar making it a practical guide for many around each tidepool helped distinguish them as ecologically unique features within the landscape. al. 2007). The inherent connection between tides Each set of adjacent tidepools was made up of one larger (Pool 1) and one smaller (Pool 2) tidepool 109 UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 connected at some parts of their borders to a more extensive pool system. Approximate measure- surveys in two phases. During phase 1, our team ments for pool areas were taken using Google Earth Pro (2019). Large pools areas ranged from species presence. During phase 2, we counted the 106 m2 to 211 m2, and small pool areas ranged 38 to 54 m2 minutes. To prevent double counting, we did not of the pools were measured using a meter stick and - ranged from 0.48 m (small) to 1.91 m (large) at their deepest points during high tide. At each lo- for each species in all tidepools for each location, cation, these sets of tidepools directly connect to day, and tide. We also recorded the total number of species present in all tidepools for each location, day. However, natural lava rock boundaries gener- day, and tide. ally protect them from swell surges. Lehia’s pools Data analyses were consistently connected during high and low tides, while Lalakea pools were isolated from each other during low tides. The water at both sites was tidepool survey per day. We determined species brackish in some places because of underground richness as the total number of different species freshwater springs. Several natural features were observed per pool per day. For each site, we ana- similar between the two locations, including benthic substrates, pool sizes, and pool depths. for abundance and species richness. Checks for Benthic substrates at both sites were relatively het- normality revealed our data to be nonnormal. We erogeneous with sections of sandy bottom, small analyzed the effects of tides, locations, and pool boulders, and rocky rubble, and minimal vegeta- tion, or human-made debris. tests. We analyzed the effects of tides, locations, Field days and pool sizes on species richness and composi- tion using the chi-squared test for independence. (NOAA) to ensure surveys occurred within a one Results to a two-hour margin of time, encompassing the Fish abundance peak tide of the day. We surveyed all pools at each site for either the high tide or low tide within a during high tides and low tides (W = 79874, p- single day. We collected data at each site location value = 0.4401). We also found no differences in tides and low tides at Lehia (W = 14246, p-value before sunrise or after sunset. The duration of the = 0.8616) and at Lalakea (W = 27136, p-value = study lasted during one lunar cycle. We also refer- enced the Hawaiian moon calendar for supplemen- in Lalakea tidepools than in Lehia tidepools (W = - - cultural practices during this time (i.e., Makahiki) dances between the large and small tidepools were that may have impacted our surveys. similar (W = 79489, p-value = 0.7695). Fish surveys Species richness counts for all forty surveys. Completion of a total both sites during this study. There were thirty spe- for all four tidepools occurred during November 2019. We completed our underwater surveys by 1). We found that tides did not affect overall spe- snorkeling in the tidepools. In some cases, sur- 2 = 19.937, df = 35, p-value = face observations and counts were possible at low 2 tide and during calm conditions. We divided each 2 = tidepool into three equally sized stations labeled 11.25, df = 9, p-value = 0.259, Figure 4). We also 110 UNIVERSITY OF HAWAI‘I AT HILO ◆ HOHONU 2020 ◆ VOL. 18 found that overall species richness was similar be- assemblage dynamics in these particular Keaukaha 2 = 10.533, df = 8, p-value = tidepool areas.