The influence of climate change on marine organism abundance has rarely been assessed (1) at the functional-group level; (2) simultaneously in major functional groups within the same ecosystem; (3) for >10 years; and (4) at metapopulation/community scales. A study simultaneously addressing these gaps would greatly enhance our understanding of the influence of climate change on marine ecosystems. Here, we analyzed 21 years of abundance data at the functional-group and species levels on a regional scale for four major functional groups (benthic algae, sessile animals, herbivorous benthos, and carnivorous benthos) in a rocky intertidal habitat along the northeastern Pacific coast of Japan. We aimed to examine the 21-year trends in regional abundance at both functional-group and species levels, plus their driving mechanisms and their dependence on species properties (thermal niche, calcification status, and vertical niche). Significant temporal trends in abundance were detected at functional-group levels for benthic algae (increasing) and herbivores and carnivores (both decreasing); they followed the temporal population trends of the dominant species. At species level, the metapopulation size of 12 of 31 species were increasing and 4 of those were decreasing, depending on the thermal niche and species calcification status. At both functional-group and species levels, temporal trends in abundance are caused by the direct or indirect influence of warming and ocean acidification. Comparing these results with community responses to marine heat waves in the same study area offered two implications: (1) long-term ecosystem changes associated with global warming will be unpredictable from the community response to marine heat waves, possibly owing to a lack of knowledge of the influence of calcifying status on species’ responses to climate change; and (2) thermal niches contribute greatly to predictions of the influence of warming on population size, regardless of the time scale.
Indirect interactions among species may be important for understanding community dynamics because species generally interact with more species indirectly than directly. Although various kinds of indirect effects have been documented, estimates of indirect effects are based on estimates of the direct interactions occurring on a short time scale. In the present study, we report that predicted indirect effects may not represent the actual indirect effects in a rocky intertidal habitat. Gulls feed on green foliose algae during winter, and these foliose algae inhibit crows from foraging on chitons. This is because algal mats cover the chitons during spring. By connecting these direct interactions, gulls are expected to indirectly increase crow foraging. However, gulls indirectly decreased crows foraging because gull feeding increased the number of foliose algal mats during spring. This result indicates that the consequence of a direct effect may occasionally change temporally from negative to positive before an indirect effect appears. Therefore, indirect effects should not be estimated merely by connecting direct effects on a short-term basis.
Abstract The impacts of large‐scale disturbance events on the species diversity of rocky intertidal sessile assemblages across multiple spatial scales are not well understood. To evaluate the influence of the 2011 Tohoku Earthquake on alpha and beta diversities of rocky intertidal sessile assemblages, we surveyed sessile assemblages in the mid‐shore zone from 2011 to 2019 and compared the data with those collected from 2003 to 2010 before the earthquake at the same region. The census was conducted across 22 study plots on five rocky shores along 30 km of the Sanriku Coast of Japan, which is located 150–160 km north–northwest of the earthquake epicenter. Alpha diversity was measured with three Hill numbers ( H 0 , H 1 , and H 2 ), which represent the number of equally common species that would exist in a community with the same diversity as the sampled community, with higher values of the subscript indicating more weight placed on abundant species. Beta diversity was measured with two metrics ( BD total at two spatial scales). Values were compared between the post‐earthquake period (2011–2019) and the pre‐earthquake period (2003–2010). The results show that the Tohoku Earthquake significantly altered the species diversity of intertidal sessile assemblages across multiple spatial scales. All diversity metrics obtained at multiple spatial scales (i.e., alpha diversities: H 0 , H 1 , and H 2 ; beta diversities: BD t otal at the shore and regional scales) decreased immediately after the earthquake and then increased in subsequent years. At 2 years after the earthquake, H 0 recovered to within the range of pre‐earthquake values and H 1 and H 2 became significantly higher than pre‐earthquake values. Most metrics of alpha and beta diversities recovered to pre‐earthquake levels after several years, but regional BD total remained low for a longer period.
Piscivorous birds affect terrestrial ecosystems by transporting and introducing organic material and nutrients from aquatic systems. While most of these effects have been evaluated by simple comparisons of the abundance of terrestrial organisms within and outside colonies, little is known about the effects of nest density of piscivorous birds on rates of supply of material inputs within colonies, or on the abundance of terrestrial organisms consuming the materials. To clarify the effects of material inputs by the Grey Heron Ardea cinerea on necrophagous insects and under-story plants in a forest, we evaluated the effects of nest density of herons on the spatial pattern of rates of supply of aquatic materials to the forest floor, and the response of necrophagous insects and understory plants to those supply. The herons transported aquatic secondary production in the form of chick carcasses and feces to the forest floor beneath their breeding colonies, and the supply rates were well explained by the nest density. Carcasses and feces increased the densities of necrophagous insects, but feces decreased the biomass of understory plants as supply rates increased. These findings suggest that to evaluate the effects of allochthonous inputs by piscivorous birds on terrestrial communities, it may be necessary to examine not only the presence or absence of bird colonies, but also to examine the relationship between nest density and terrestrial organisms.
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