Trophic Models of Seagrass Ecosystems in Maqueda Channel, Caramoan Peninsula, Philippines

Steady-state trophic models were constructed using the Ecopath with Ecosim software to examine the general status, development trends, and functional integrity of three extensive seagrass meadows located in Maqueda Channel of Caramoan Peninsula, Southern Luzon Island, Philippines. The results show that the ecosystems are composed of 23-24 functional groups with effective trophic levels extending from 1.00 to 3.76. Mixed trophic impacts show that decrease in the biomass of grazers Tripneustes gratilla (collector urchin) had a positive impact on the biomass of seagrasses. On the other hand, a positive effect on the benthic groups is expected with an assumed decrease in the biomass of detritus and phytoplankton. Analysis of the flow network of organic matter and trophic efficiencies showed that flows were generally low for higher TLs but high for lower TLs (i.e., from TL 1 to IV. The ecosystems were found to be in mature and stable state based on the system statistics.

Ecological singularity of temperate mesopredatory myliobatoid rays (Chondrichthyes: Myliobatiformes)

Many myliobatoid rays are important mesopredators, having significant effects on coastal benthic communities. In tropical and subtropical high-diversity oligotrophic ecosystems, they partition their trophic resources, which results in high ecological singularity. However, it is unknown whether this is true for temperate low-diversity eutrophic ecosystems. In the present study, we tested, for the first time, the hypothesis that myliobatoid mesopredators are ecologically redundant in a temperate low-diversity eutrophic ecosystem. We quantified diet and measured intra- and interspecific trophic overlap in the three species that regularly occur off Uruguay and northern Argentina, namely Myliobatis goodei, Myliobatis ridens and Dasyatis hypostigma. M. ridens had a typical durophagic diet composed of bivalves and gastropods, M. goodei fed primarily on polychaetes and decapods, diverging from the durophagic diet typical of its genus, and D. hypostigma preyed primarily on amphipods and decapods. There were ontogenetic and seasonal dietary differences in all three species. It is concluded that ecological singularity is present in this temperate myliobatoid assemblage, with each species having a different trophic niche. The practice of pooling together myliobatoid mesopredators in trophic models must be abandoned unless there is evidence of ecological redundancy.

Evaluation of the complexity and performance of marine planktonic trophic models

ABSTRACT Planktonic models represent a powerful tool for creating hypotheses and making predictions about the functioning of marine ecosystems. Their complexity varies according to the number of state variables and the choice of functional forms. We evaluated plankton models during the last 15 years (n =145) with the aims of understanding why they differ in complexity, evaluating model robustness, and describing studies of plankton modelling around the globe. We classified models into four groups: Nutrient-Phytoplankton-Zooplankton (NPZ), Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD), Size-Structured (SS) and Plankton-Functional-Type (PFT). Our results revealed that the number of state variables varied according to the question being addressed: NPZ models were more frequently applied in physical-biological studies, while PFT models were more applied for investigating biogeochemical cycles. Most models were based on simple functional forms which neglect important feedback related to control of plankton dynamics. Modelling studies sometimes failed to describe sensitivity analysis, calibration and validation. The importance of testing different functional forms was commonly overlooked, and the lack of empirical data affected the verification of model robustness. Lastly, we highlight the need to develop modelling studies in the Southern Hemisphere, including Brazil, in order to provide predictions that assist the management of marine ecosystems.