Spatial and temporal patterns in Hawai‘i’s intertidal: decadal changes in benthic community composition

Abstract

Spatially broad and long-term monitoring studies are lacking in tropical intertidal systems yet are necessary to test predictions regarding community assembly. To fill this gap, we examined spatial and decadal temporal patterns in benthic community structure at rocky intertidal sites along the main islands of Hawai'i. Quantitative community surveys done in 2017 across nine sites and five islands showed that organismal composition differed by site, substrate type, and island. Secondly, we leveraged an earlier dataset collected using the same methods and analyzed intertidal communities at five sites on three Hawaiian islands for temporal changes in organismal abundance and composition from 2006 and 2007 vs. 2016 and 2017. Overall community structure differed significantly across years and decades. Most decadal differences were site specific, such as the fivefold increase in turf algae at one site. Crustose coralline algae and Turbinaria ornata increased significantly across five sites; both are physically resilient algae and similar increases in their abundances have been observed in tropical systems worldwide. This increase in physically resilient macroalgal species is potentially caused by global drivers, such as rising temperatures and changing land uses. In conclusion, there is evidence that both local and regional factors contribute to structuring tropical intertidal communities.

Spatial variation and antecedent sea surface temperature conditions influence Hawaiian intertidal community structure

“…Many foundational concepts in ecology have been developed in the intertidal environment [13,14], which is also prized for its economic benefits [15][16][17][18], cultural significance [19], and ease of study [20,21]. Intertidal ecological communities can vary significantly across small spatial scales [22][23][24] and in response to the cumulative effects of ecological determinants through time. In addition to nutrient influx [25,26], substrate type [23,27], grazing and predation [22,25], and anthropogenic disturbance [28], there is compelling evidence from around the world that intertidal communities are responding to warming temperatures across multiple temporal scales.…”

“…Temperate continental intertidal systems (particularly in North America and Europe) have had a long history of intensive Western scientific study [13,14]. In comparison, intertidal systems in more geographically isolated locations such as the MHI have received relatively little attention until recently [e.g., 23,24,36,37]. Although Hawai'i's tidal range is limited (~1 m between the highest high and lowest low tides) [36] the intertidal zone has a diverse assemblage of fishes, algae, and invertebrates [23,37].…”

“…Although Hawai'i's tidal range is limited (~1 m between the highest high and lowest low tides) [36] the intertidal zone has a diverse assemblage of fishes, algae, and invertebrates [23,37]. A few notable studies conducted within Hawaiian intertidal zones have investigated both spatial and temporal variation in community structure [23,24,37]. These studies have found high variability in Hawaiian intertidal communities both between sites and across islands [23,24], with site-level differences in substrate type [23], topography [27], and wave/wind exposure [24,38] suggested as factors influencing local community composition.…”

“…A few notable studies conducted within Hawaiian intertidal zones have investigated both spatial and temporal variation in community structure [23,24,37]. These studies have found high variability in Hawaiian intertidal communities both between sites and across islands [23,24], with site-level differences in substrate type [23], topography [27], and wave/wind exposure [24,38] suggested as factors influencing local community composition. One study at 'Ewa Beach on the southwest side of O'ahu identified maximum water temperature as a significant variable for explaining yearly variation in intertidal algal community composition [27].…”

“…If SST in Hawai'i increases according to projected trends [3], there is a need to understand how both the individual taxa and the intertidal communities will respond. Due to the large variability in physical characteristics and community composition between Hawaiian intertidal sites [23,24], analyses limited to a single intertidal site may not be representative of the entire MHI. To effectively capture responses to SST change across the MHI, investigations conducted across multiple spatial and temporal scales with the highest resolution SST data possible are required.…”